Monday, October 16, 2017


For shims I use feeler gauges since they're cheap, precise, come in an assortment of sizes, and have the size written on the shim. I usually use this set from Amazon with starts at 0.0015" (0.038mm) :

If I need longer or thinner shims I'll go with this one which goes down to 0.02mm:

Aluminum foil also makes good shim stock with standard aluminum foil being 0.0006" while heavy duty aluminum foil is 0.0008".

Tuesday, September 19, 2017

Mill: TouchDRO

First off, all credit to Yuriy Krushelnytskiy of

 One of the biggest problems with the X2 is the amount of backlash in all the axis. Instead of trying to lessen the backlash I installed TouchDRO on all three axis. Since they read the table's and head's position directly, you can pretty much ignore the backlash present.

While poking around the internet for information on the X2 mill, I stumbled on Yuriy's blog. What really intrigued me was his DRO application for the Android:

He was using iGaging digital scales, which most X2 owners end up using when installing DROs, connected to an Arduino, which interfaced with an Android via Bluetooth. The DRO app he wrote took the input from the digital scales and displayed it in a nice interface. Just that alone had my attention since the included iGaging remote LCD displays were a little hard to see. However, since all the work is being done in software, it'll be easy to add new features to the DRO in the future. Additionally, since it's open source, you can always add a must have feature yourself. Now that Androids have gotten cheap enough and powerful enough, it makes a lot of sense to do in software what traditional DROs did in hardware. Doing it in software is just much cheaper and much more flexible.

If you have the tilting column, the X scale needs to be offset not to lose travel from the read head hitting the column pivot, the aluminum L channel being used as a chip shield makes a pretty convenient offset mount. With the solid column mill the X scale can be mounted centered.

I used a 2" aluminum angle completely cover the scale, cutting down one side so it fits on top of the chip shield. Without it, tiny chips can get inside the read head and cause reading jumps.

Offset X scale for column pivot clearance.

Centered X scale on solid column mill.
Chip cover in place over the scale.

The Y scale in mounted to the base on the left of the mill. The base's sides have a slight angle to them, but that doesn't matter when mounting the scale so long as it remains parallel to Y axis. I've found the table itself shields the scale sufficiently.

Y scale mounted.

I strongly recommend using two screws to secure the read head to prevent it pivoting on a direction change as the guides wear.

Once I installed the gas spring and removed the old torsion spring, installing the Z axis DRO was super easy. I removed the ruler on the left side of the column a while ago, since it was so course it was pretty much useless. The 12" iGaging digital scale was the perfect length to screw right into the holes left by the ruler. I then quickly fabricated a bracket to connect the scale's reader to the threaded hole on the head which used to hold the ruler's indicator. Perfect.

Z scale mounted using existing threaded holes.

At first I had tried using a prepackaged optical sensor for Arduino (available on Amazon), but switched to a Hall effect magnetic sensor since they're easier to use and for this application tend to be just as accurate. I was able to buy them already mounted on a psb with a LS393 comparator ( The comparator allows you to have an essentially digital signal with it either on or off. 

I already have a belt drive installed, so I drilled two holes at opposite ends of the top pulley and JB Welded in small neodymium magnets. The top of the Hall effect sensor psb was covered with epoxy putty to protect it from swarf. Then it was attached to the pulley cover using foam tape and a mounting screw. The sensor itself hangs over the back of the cover and directly over the path of the magnets.

Magnets on the pulley. The black sections were for the optical sensor.

The Hall effect sensor covered with epoxy putty and mounted on the pulley cover.

For the Arduino I bought the Leonardo model which comes without headers, since I like soldered connections. However, I learned the hard way the app does NOT like the Leonardo. The app would connect, and then immediately lose connection. Once I switched from the Leonardo to the Uno R3 everything started working beautifully. The Uno R3 comes with headers, so I needed to cut them off and de-solder the pins so I could solder the leads in place.

Uno R3 with the headers and pins removed.

The iGaging scales connect to the remote readouts via mini B USB connectors. I couldn't for the life of me find a cable with a female mini B USB connection on it, so I settled for adapters instead. I opened up the end opposite from the mini USB and soldered my leads directly to the pins. Once everything was soldered and tested I covered all the connections with epoxy.

Mini B USB adapters.

Adapters wired to the Arduino.

I used a 3.5mm stereo headphone jack for the tachometer interface. If I get around to repackaging the Arduino I'll change it to another interface since the 3.5mm jack will short power to ground as the connector is inserted or removed, so you need to power down the Arduino before doing so. It's not a show stopper, but it is annoying. I've hot glued the connector so it can't accidentally pull out while in use. A 10K pull down resistor needed to be added to the tach sensor input.

I bought a small project box from Radio Shack, and aside from the very annoying issue with the Leonardo, the hardest part was installing everything inside the box. I machined slots in for the USB adapters to stick out through. I wedged them in there and glued them in place with epoxy. I also cut a hole for the USB cable which will provide power. To mount the Arduino I secured a thin piece of wood in the bottom of the project box, which the Arduino screwed to.

All packaged up.

I then used Sugru to make the USB connectors look pretty, enclose the USB power cable, and provide it with strain relief. If you haven't used it before, Sugru is a really useful thing to have in your tool box. It comes in little packets and it's silicone rubber which sticks to most things and is moldable for 30 minutes after opening, and cures in 24-48 hours.


The project box with Sugru added.

After that the USB cable was hot glued into the USB jack on the Arduino, the unit was tested again, and then the top was screwed in place. Magnets were glued to the box and the box mounted on the back of the column. It draws its power form a Motorola cell phone charge.

All packed up and ready to go.

There were issues with TouchDRO reading 20-40 times too low on the tachometer. After some time spent on the TouchDRO Google+ development forum I changed the Arduino sketch to one being developed by Ryszhard ( and the tach immediately started working. I checked its readings against my laser tachometer and they match to within 20 RPM.

For my readout I'm using a 10" non-widescreen tablet, as I find the non-widescreen format works better for a DRO. This has been one of the best upgrades I could have possibly done and made the mill so much easier and nicer to use. I cannot recommend it enough, and I would never go back to not having one.

Mill: X Axis DRO Cover

Please read the complete article:

I'm using the iGaging linear scales for my DRO, and noticed my X axis would sometimes jump wildly before going back to normal. It turns out I'd gotten some tiny swarf inside the scale's body. After carefully cleaning it out, I used a 2" aluminum angle completely cover the scale. I needed to cut one side shorter so it would fit on top of the existing cover.

DRO cover in place on X axis.

Wednesday, August 9, 2017

Lathe: TouchDRO

I've wanted a DRO on my lathe for a while to deal with the back lash and confusing dial markings. TouchDRO is the best way to go (for many reasons), but first I needed to attach digital scales to the carriage and cross slide.

When I do threading on the lathe I'll just back out my bit and run the lathe in reverse to rest the carriage, so I have no need for a threading dial and had removed it a while ago. That left a great threaded hole to mount the scale bracket to. I suppose if you still have the threading deal there you could always just sandwich the bracket between the apron and dial. The bracket was easily made from 1/8" 1" aluminum angle. It's a bit overkill and I'll probably trim it down a little more later, but it's not really in the way as is.The screws holding the read head in place use crazy glue as a thread locker, since Loctite will attack plastics.

The design I ended up with places the scale below the lead screw, so it's fairly well protected from swarf. The mounting for it is quite stiff, so I only have the scale attached at one end. That was particularly helpful since I didn't want to try drilling into the lathe' body at the head since it houses the motor right there.The end of the scale was wrapped in electrical tape to electrically isolate the scale from the lathe.

Carriage scale in place with stock readout connected.
Carriage travel at the extreme right of the bed is limited slightly.
 The cross slide digital scale sits to the right of the cross slide. The read head is screwed directly to the carriage and the scale's bracket is connected  slide itself. The bracket was made from a non-conducting composite to electrically isolate the scale. The read head needed 1.5mm machined off the cover's mating surface to lower below the height of the cross slide. The read head is secured by two screws to insure it can't rotate.

New iGaging scale mounted to cross slide

The tachometer, like the mill's, uses a Hall effect sensor since they're much easier to set up than an optical sensor and are just as accurate in this application. The lathe previously had a spindle extension installed, and for the tach's magnet I drilled a hole on the extension and used JB Weld to mount a small neodymium magnet in it. 
Spindle extension with magnet mounted.
 The tach's sensor was mounted to the outside of the lathe's gear cover. I considered mounting on the inside but space would have been an issue and it works perfectly well on the outside. I covered the top of the sensor with epoxy putty to protect it and keep any swarf from shorting it. If you look closely you can see I've bent the sensor itself up and away from the spindle to provide a better orientation to the magnet. The sensor's USB cable is run down the back of the lathe to the Arduino's case.
Hall effect sensor mounted on gear cover.

Unlike the mill's Arduino, I constructed this one using a prototype board. It's much cleaner and easier and I highly recommend it, even though it added $8 to the build. I used standard USB A connectors for the scales' interface since both connectors and cables are much easier to find. This forced me to change the cables on both scales, but that didn't cost much. The tachometer's plug is also USB to avoid the issue I had using a 3.5mm headphone jack for the tach on the mill. Everything was mounted in an old Dell laptop power supply brick's case I had on hand. Neodymium magnets were glued to the case's top for mounting on the back of the lathe.

I'm using a Motorola RAZR phone as the Android device running the TouchDRO application. Since the lathe only has four readouts (X,Z, diameter, and tach) the phone is adequate. It's currently mounted with magnets to the top of the headstock using a bracket I fabricated.
All done.
Like with the mill, setting up a TouchDRO system has made the lathe a lot easier and nicer to use, and I would hate to ever be without it.

Friday, May 26, 2017

Rolle's Dad's Method

Rolle's Dad's Method (RDM) is a brilliant way to accurately measure the alignment of a spindle to the bed/column, and is extremely useful for aligning the head on the mini mill (with the column removed from the base) and the headstock on the mini lathe. It's great because it takes run-out completely out of the equation and only measures the assignment. However, I haven't found a description which I felt practically explained the method to me, and therefore it took me a little while to figure out what it meant. Here's how I do it:

1. Chuck as straight and smooth of a rod in the spindle as you can. Using RDM the smoothness and straightness of the rod doesn't actually matter, but it does make doing the measurements easier.
2. On a lathe mount a DTI on the carriage so it can indicate the rod. On a mini mill I'll move the head to the bottom of the column and then mount the DTI on the column right below the head so it can indicate the rod. You hcheck the X and Y alignment separately, determined by whether you're indicating the side or the top of the rod.
3. You want to indicate two parts of the rod as far apart as possible. On the lathe this means indicating it with the carriage at the chuck, and then as far to the tailstock as possible. On the mini mill it means indicating with the head all the way down and then all the way up. Generally I can get about 7-8" of separation. I'll mark the two points with a Sharpie so I can easily hit the same spots.
4. With the DTI at the head, I turn the spindle by hand and observe the DTI dial, and adjust the dial so the needle is traveling the exact same amount above and below zero; I call this "average zero".
5. Then, without touching the dial, I go to the opposite extreme of the rod. With the lathe this means moving carriage and with the mini mill the head.
6. Again, I turn the spindle by hand and observe the DTI. The needle will usually move a lot more, but that's ok. I mentally determine where the new average zero would be. The difference between the old average zero and your new average zero is how far out of the alignment you are. Again, it doesn't matter how much the needle moves, all the matters is where your average zeros are.

For example, I'm going to check the horizontal headstock alignment on my mini lathe. I chuck the rod and mount my DTI so it's indicating the side of the rod and move the carriage with the DTI on it all the way to the chuck. I turn the spindle and see the needle is moving a total of .004", and I turn the dial until the needle is traveling exactly 0.002" above zero and 0.002" below zero. I now have my average zero.

Average zero set at the headstock. You can see the Sharpie on the rod marking where I measured.
Without touching the indicator, I move the carriage to the end of the bed. I again turn the spindle by hand and observe the DTI. It's now traveling 0.004" below zero and 0.008" above zero. Mentally I calculate the new average zero is +0.002" on the dial. That means the headstock is 0.002" out of alignment with the bed. If the needle had actually traveled 0.006" below zero and 0.006" above zero it would have meant my headstock was perfectly aligned with the bed.

The needle at average zero at the far end of the bed.
It's reading +0.002", so my headstock is 0.002" out of alignment with the bed. 
Remember, the key is the difference between your average zeroes.

Wednesday, April 12, 2017

Mill: Vises

While prefer clamping directly to the table, I like vises because they're already trammed, so anything I clamp with it I know is already aligned. I primarily use two: a screwless precision vise and an angle drill press vise.

The 3" screwless precision vise fits beautifully on the mini mill and has more than enough clamping power for the machine. Be sure buy one with slots on the sides instead of just holes, since it makes clamping the vise at angles much easier. I purchased mine from Shars and paid about $54 shipped.

As soon as it arrived I made two modifications. I removed the holder the bolt threads into, and removed the cross piece from it which hooks into the grooves on the bottom of the vise. I then turned a new cross piece on the lathe whose length just fits. This keeps the assembly from rotating when tightening or loosening the vise. Second, I put a spring the bolt. This keeps tension on the bolt at all times, making it much easier to move and hook the cross piece. 

One of the biggest annoyances using the precision screwless vise was loosening the jaw and accidentally unscrewing it from the T bracket which holds the cross bar that hooks into the base. After having it happen it again in the middle of a project I took the screw which connects the jaw to the T and turned it smooth starting 5 threads from the end.

Middle section of screw turned smooth.

I then ground a flat on the T right where it threads onto the screw. I then assembled the vise, threaded the screw into the T, and peened the flat to capture the screw. Now, no more accidentally unscrewing it.

Another reason I like the screwless vise is because I don't need a swivel base to rotate it. I can just loosen the clamps, rotate the vise on the table, check it with my protractor, and tighten the clamps back down. This provides more rigidity and more space between the head and table. Making the clamps is a good project for the mill.

The angle drill press vise isn't a milling vise, and has a whole set of issues because of it. The moving jaw will always want to lift when tightening, so I need to tap it with a hammer once it's tight and also make sure the work didn't move, thought using parallels helps since I can carefully tap the work back down until it's resting fully in the parallels. The vise also isn't super stiff, but for the power the X2 has it's adequate. Finally, it can be a bit of a chore setting the angle on it, and usually requires a bit of tapping it back and forth with a hammer. However, the angle adjustment is dovetailed, hardly has any play, can be locked very solidly, and has basic angles preset with the use of a pin. To set a precise angle I just zero my Wixy digital angle gauge on the table and then stick it on the vise and set my angle. Some operations on the mill would be pretty difficult to set up without an angle vise, so I'm happy to deal with its shortcomings, especially since it only cost me $43 brand new from Sears.

My preferred vises.

I also ended up getting a 3" Kurt-style milling vise. The Kurt-style vise forces the moving jaw downward as it's tightened, which keeps the part from lifting. While it's not quite as precise as the screwless vise, it's faster to use. It did need a lot of cleanup work. The Casting for the jaw where it meets was the nut was deformed with extra material in the jaw, so I Dremeled away the extra. Also with the Dremel I smoothed out the location where the hemisphere rides in the jaw. After this I lubed it up and reassembled it.

Ultimately, the precision screwless vise is what I prefer over the Kurt-style vise. It's very easy to set up and square up, it's high capacity is really nice, and with my modifications it's not much slower than the Kurt-style.

Mill: Speed Control

NOTE: If you're not comfortable working with electrical component and AC power, then do NOT attempt this modification. Touching the wrong thing can potentially kill you.

My mill is a Grizzly G8689 with the standard brushed motor. All its wires are numbered, I assume for ease of assembly, so I'll refer to the wires by their numbers. I assume the wiring is the same for all brushed motor mills, but your mileage may vary.

The stock controller. You can see the numbered tags on the wires and the terminals.

The X2 mill's DC motor speed controller is the weak link and not the motor itself. Short of doing a treadmill motor/controller upgrade, you can upgrade just the speed controller and see good gains in both torque and speed. Although the stock controller is a PWM unit, it's not a very good one and is quite limited. It's also a much easier and potentially cheaper upgrade than a treadmill motor.

The common DC controller you'll see in searches if the KBLC-19PM which is just a custom version of the KBIC-120 rated for 125VDC out instead of the standard 90VDC. The KBIC-120 is only rated up to 0.5 HP without a heatsink and the X2's motor is actually 0.5 HP or less, regardless of what the sticker on it says. so you can safely use the KBLC-19PM or the KBIC-120 using the 0.5 HP resistor (0.25 ohm, PN#9841). You can also use the KBMM series of controllers, but the cheaper KBIC works fine. Since I was able to get the best deal on it, I went with the KBIC-125B, which is a KBIC-125 uprated from 90VDC to 125VDC. Aside from the KBIC itself, I also needed a 5k potentiometer. Forunately my KBIC come with a motor fuse, otherwise I would have needed to add one (the mill should use a 7.5A fuse).

The stock controller is screwed to the back of the mill's electrical box, with a small accessory board next to it. The accessory board converts AC to 20VDC to power the fan. To remove the controller loosen all the terminal screws, remove the wires, remove the four screws and remove the board. To make room for the KBIC I also removed the accessory board, turned it, and mounted it to the side of the box using a couple newly drilled holes, some plastic washer, and a pair of pop rivets.

To mount the KBIC I reused one of the vent holes on the side of the box, then measured and drilled a second hole, and using two screws and nuts secured the KBIC's side to the side of the box.

KBIC mounted in box with accessory board mounted on the side.
In this picture it's already been wired.

Inside the small controller box I disconnected the motor leads from the switch and connected them to wires 1 and 2 running back to the electrical box. The 5k potentiometer was wiring in using the old potentiometer's wires with a direct swap over. The old potentiometer also incorporates a switch with three wires going to it (AC neutral), I took those three wires and soldered them all together and heat shrinked them.

The three wires on the old potentiometer which I wired together.

Back in the electrical box I soldered spade connectors onto the wires to make installation and troubleshooting easier. I then wired it up per this diagram:

On the 20VDC accessory board I connected wire #3 to the AC neutral terminal and connected #4 wire with a short jumper to the AC hot terminal. I removed the yellow LED which was wired in series with the accessory board since it was disrupting its operation. Now the fan runs whenever there's power. I don't think the added cooling is needed, but I didn't see a reason not to.

The emergency cutoff switch is still used and turns AC on and off before it connects to any switch or board. The AC fuse in the diagram isn't used as the mill's existing fuse is used instead.

The "Inhibit" function on the KDIC allows the motor to be turned off electronically. I decided to take advantage of it, as it allows me to set a RPM, and then use the switch to turn the motor on and off without having to reset the speed every time like on the stock controller (note: the switch's direction is now reversed so you might want to relabel it). The KBIC also gave me much finer control over the motor, which was a pleasant surprise. The stock board was frustrating to try and adjust, since the adjustments frequently overlapped. However, on the KBIC they're all nicely separated and discrete.

Once the KBIC is connected, I needed to adjust it for my motor specifically. The first thing I did was adjust Max Speed so the output was 110VDC at full speed. I then adjust the Min Speed so the motor stopped just before the speed knob hit zero. The factory Accel setting was good, but could be adjusted if the motor either spun up to speed too fast or too slow. I left the Current Limit at it's factory value of 1.5x the HP resistor. I also left the IR Compensation as is, but might look at it later if I find the motor RPMs dropping under heavier load; it allows the KBIC to compensate (to a degree) for load to keep the RPMs steady.

However, a couple weeks after upgrading to the KBIC I again upgraded to a KBWS which uses PWM to control the DC voltage.There are two commonly used ways to power a DC motor from AC voltage: SCR and PWM.In short, an SCR will essentially chop off half the AC input and feed that to the motor, with the speed being controlled by where in the AC waveform it starts to feed it to the motor. When the motor is set to full speed this is fine, but at anything less than full speed the motor won't be getting the full voltage. While with PWM the AC is rectified to DC, and then the DC is very rapidly switched on and off to control the speed, so the motor sees rapid, brief inputs of full voltage.

The KB PWM control I use produces a peak voltage of 160VDC which is very rapidly switched on and off to produce a lower average voltage. I was worried about the 110VDC motor being hit with 160VDC, but after research I found if the frequency is high enough, then it doesn't really matter (assuming the peak voltage isn't absurdly high). In fact, a high frequency PWM drive will actually allow the motor to run cooler while producing more torque.

In real life this means SCR controllers are cheaper, more robust, and able to handle more current, but are louder (they produce an AC buzz), the motor runs hotter, and the brushes and commutator have a reduced lifespan. PWM controllers are more expensive, have lower current limits, are somewhat easier to break, but they run very silently and the motor runs cooler with a longer brush and commutator life.

Since both the KBIC and KBWS use the same chassis, it was very simple to swap them out. Please note newer KBWS controls come with a shorter capacitor which doesn't require modification of the control box, while the older KBWS would need modification to accommodate their height. 

KBWS installed in the mill.

The quieter operation was immediately noticeable and very welcome. After an extended run the motor was still cool to the touch, unlike with the KBIC. Ultimately, I think it was a worthwhile upgrade.

Both the mini mill and mini lathe mostly use PWM controllers stock. However, the stock controllers are very limited and prone to die. If my choice was the stock controller or a KBIC/KBLC I would go with the KBIC/KBLC, even though they're SCR simply for the significantly greater performance and adjustability they offer. However, if you can get a KBWS for a good price, that's a better the way to go.

A quite note, KB Electronics makes a cheaper version of the KBWS called the KBWD. However, while the KBWD will work, it doesn't have an electronic stop like the KBWS has. On a mill/lathe the electronic stop is very handy, since you can set a speed and then use it to turn the motor one and off without disturbing the speed setting. That feature is useful enough to me to specifically seek out the more expensive KBWS.

Mill: Gibs

I think the gibs which come with the mill are fine, except the divots for the set screws are woefully inadequate. Because the set screws aren't pushing against a flat, they tend to rotate the gib, which compromises rigidity and creates uneven wear.

To fix this I decided to machine proper flats into the gibs for the set screws to sit on. First I removed all the set screws for the gib, then installed and positioned the gib. I sharpened the end of two M4 set screws in my lathe and first installed one and tightened it down, and then tightened the other one in each hole in turn. This left exact center marks for all the set screws. From measurements it looks like the gib angle is 55*, so I used my Wixey angle gauge to set my angle vise.

Since the gib wanted to rotate when the vise was tightened, I placed a section of 1/2" steel rod in the corner formed by the gib and vise jaw, and then used my table clamp set to push down on the rod, effectively locking the gib in place. I then machined the flats using a 3/16" end mill with a plunge cut. For the lock's flat I used a 1/4" end mill.  By the way, that gouge you see is what happens when your vise decides to let go of the work.

The set screws were also upgraded from the stock dog point to cup point. The last couple millimeters of the set screws were turned down so they just fit in the gib pocket. This helped position the gib horizontally and keep it from sliding on the set screws.

I also took the opportunity to lap the gib slightly, but it turned out it was pretty flat to begin with. Once everything was reassembled, the gib has much more contact with the dovetail, and I can tighten the set screws tighter without making it hard to move. It was well worth it in my opinion.

I didn't like how the gib locks looked either. They have a rounded nose which pretty quickly becomes deformed through use. 

I figured if they had a flat nose to push against a flat surface, they'd work a lot better and wouldn't deform. So it was disassembled and thrown in the lathe where its end was extended and faced flat. Since its end turns on the gib I greased it just before assembly.

I also substituted the mini mill Z-axis gib for the Y-axis gib. It needed to be cut to length, but it sits much better and takes up nearly all the space available.

To adjust the table gibs on my mini mill I move the table to the middle of the X axis and set a dial indicator measuring horizontal play at the end of the table. I then lock Y and loosen all the X set screws. I adjust the two outside set screws until I have about 0.0015"-0.002" of measured play in the table. I then adjust the two inside set screws individually by tightening them just until I feel resistance in the hand wheel, then easing them off just slightly.

For the Y axis I lock the X and loosen on the Y set screws. If you have only two Y set screws then adjust them until you have about 0.0015"-0.002" play in the table. If you have four set screws then adjust the two outside ones until you have about 0.0015"-0.002" play, and then individually adjust the two inside ones same as on the X axis.

Of course, when you're machining be sure all the axis are locked except the one you're moving.

Mill: Spindle Bearings

The mini mill uses deep groove radial bearings. They're not ideal for a mill spindle, but they'll work adequately. There are essentially three options for replacement bearings:

1. Deep Groove Radial Ball Bearings (6206 for MT3 spindle) - These are the same as the stock bearings and come as either sealed or shielded. Shielded actually have a tiny gap between the shield and the inner race, so they don't protect as well, but they also produce less heat and have a higher top speed. Sealed protect the bearing better, but they'll produce noticeably more heat and, once they're installed and preloaded, their top speed will be about the same as the top speed of a belt driven mini mill.

ABEC-3 bearings should be used in the mini mill for the lower runout, though most Japanese bearings, even if they're listed as ABEC-1 will actually be ABEC-3. A lot of replacement bearings you see are C3 tolerance. The C3 indicates they have greater clearance inside the bearings. On the mini mill they should be ok to use since the bearings are preloaded. You can also use CN (normal internal clearance) or C2 (reduced internal clearance).

The downside of deep groove radial ball bearings is they cannot handle a lot of preload, and preload is what produces a stiff spindle. In addition, as you preload them their runout increases.

2. Tapered Roller Bearing (30206 for MT3 spindle) - A popular upgrade are tapered roller bearings (TRBs), with people often using cheap car axle bearings. These bearings are incredibly rigid and allow virtually no deflection. They can take huge loads (much higher than a mini mill is capable of). The problem is those axle bearings have a max runout of 0.001" which is pretty bad. On a mill low runout is especially important, as it effects tool chip load, especially on small diameter tools. You can buy higher TRBs (minimum grade C or P5) but they're not easy to find and can be quite expensive. Additionally, TRBs are very sensitive to preload, and have a very small window of acceptable preload. TRBs are also 1.5mm deeper than the stock bearings, which can require some modifications. There are no sealed versions, so some form of seal needs to be fabricated to keep contamination out and grease in. Considering their mounted vertically in the mini mill, keeping the grease in place can be a challenge. Finally, they cannot spin nearly as fast as ball bearings.

Tapered roller bearing cutaway.

3. Angular Contact Ball Bearings (7206 for MT3 spindle) -  Unlike deep groove ball bearings, ACs are able to take both axial and radial loads. However, AC bearings are directional, meaning they can only take axial load in one direction. In fact, there is play between the bearing races until preload is applied. ABEC-3 precision 7206 ACs (roughly equal to TRB class C or P5) are fairly readily and relatively cheaply available. They're also the same dimensions as the stock bearings, which make it a direct swap. ACs are much more tolerant of a wide range of preloads, which makes setting the preload much easier and more forgiving than with TRBs. While ACs are less rigid than TRBs, for a machine as small as a mini mill it shouldn't matter at all.

Angular contact ball bearing cutaway.

Because of the vertical bearing orientation in the mini mill, grease retention is an issue, and I also found contamination of the lower bearing is an issue. That's why I ultimately used sealed AC bearings. While they're readily available from an over-seas vendor, those bearings are ABEC-1 which have 0.0005" runout. SKF makes a 7206-BE-2RZP ( sealed AC bearing which is ABEC-3 and is supposed to have ABEC-5 runout. The one place I could readily find them (and for a good price!) was

On a related note, you may have seen instruction for installing ACs on the mini lathe on other sites. The problem with those instructions is they have you pressing in the bearing through the rolling elements. In other words, you're applying pressure to the inside race in order to press the outside race into its bore. You should never do this. The manufacturers will always tell you not to press the bearing through the rolling elements because, while the bearings can handle high dynamic loads, the high static load from pressing can damage both the races and the balls themselves, greatly reducing the life of the bearing.

Before starting, I chucked the spindle in the lathe and sanded the top bearing seat with 400 sandpaper then a Scotch-Brite until the bearing was a light press fit. It's important to accurately set the preload later on, and apply less static force on the bearing while doing so.

I made a press for the bearing so I wouldn't have to remove the mill head. Since both the outer and inner races are a press fit, I needed to make adapters for the press which would push both inner and outer races equally. You never press a bearing through the rolling element or you'll destroy it! The adapters were made using two 3" diameter by 3" long pieces of aluminum rod, and a 2" diameter by 1" long steel rod. The press itself is a 5/8" long piece of threaded rod with a nut red Loctited onto one end.

The aluminum was faced on both sides, and then a 5mm long section was turned down to 60mm . The center was then drilled and bored out to 31mm. This allowed it to slip over the top of the spindle and press evenly on both inside and outside bearing race. It also allowed it to center over the top bore of the spindle head when pressing in the bottom bearing. The bottom adapter was again faced on both sides and the end of the OD turned down to 60mm. The center was drilled and bored out to 43mm, which is wide enough to not touch the inner bearing race. The steel rod was faced on both sides, and had the center drilled and bored out to 16.5mm, wide enough to clear the 5/8" threaded rod.

I then thermal fit the bottom bearing onto the spindle (freeze the spindle overnight and heat the bearing to 180*). Alternatively, it can be pressed into the bearing, but care must be taken to only press on the inner race. Make sure the wide part of the outer race faces the top of the spindle, and the wider part of the inner race faces the bottom of the spindle. Remember that the angular contact bearings have play between the races until preloaded. With the aluminum bottom adapter fitted in place I wanted roughly the midpoint of the play in the bearing to put the spindle's nose flush with the adapter's surface. I kept taking facing cuts on the adapter until I reached that point. So with the play removed one direction the nose sat slightly under the adapter's surface's level and with the play removed the other direction it stood slightly proud.

To press the bottom bearing and spindle into the mill head I put the 5/8" threaded rod through the center of the spindle, put the top adapter in place (the top bearing is installed later), put the bottom adapter in place over the spindle and bearing, placed the steel adapter over the bottom adapter, and ran the nut down on the threaded rod, holding everything together. The steel adapter supports the spindle's nose, which in turn supports the bearing's inner race. Since we adjusted the bottom adapter so the inner race would sit in the middle of its play, we can now press the bearing into place without applying any force to the inner race. I lightly oiled the bearing and the bore and tightened the 5/8" rod until the bearing pulled and seated into it's bore.

I then disassembled the top of the press, lightly oiled the top bearing and bore, and pressed it into place as well. On the top I needed additional clearance for the spindle, so I used a PVC pipe fitting; it worked just fine.

Bearing press assembled using old spindle and bearing.

Honestly, the system the X2 uses for preload adjustment isn't all that great or accurate. The absolute first thing I did was face both side of the adjustment nut. From the factory it's pretty far off. This will allow even pressure to be applied to the bearing. Next I took the set screw, cut the point off, and faced it. This would still provide enough holding power to keep the nut from turning, but wouldn't damage the spindle threads. To make adjusting the nut easier, I took a 32mm socket and ground it down until I had four teeth to interface with the nut; it's much easier than using a lock ring wrench.

32mm socket ground down to fit the spindle nut. Regarding the finish, I did it with an angle grinder, so what do you expect?

Adjusting the preload is tricky, since I wanted to get between 100 and 125 pounds of preload. Using a torque wrench I measured how much torque was required to remove the play from the spindle, then I added 20 in/lbs of torque to that, and tightened down the nut. It was roughly 55 in/lbs of torque. Using a DTI attached to the mill head I checked for play in the spindle (if the DTI is on the table then it'll also read flex in the column, of which there is a surprising amount); on the mill you shouldn't see any play with properly preloaded bearings.

I then checked the preload by measuring the breakaway torque, meaning the amount of force required to make the spindle start to turn. This can be fairly easily calculated using a thin feeler gauge, a strong magnet, and an scale. You fix the end of the shim to the spindle using the magnet, measure the diameter of the spindle in inches where it's attached, hook the scale to the shim, wrap the shim around the spindle as far as it'll go, and then pull on the scale and see how much force in pounds is required to start turning the spindle. If you multiply that by the radius you get the breakaway torque in in/lbs. For example, I measure at the lock rings, which have a radius of 0.815". My breakaway force measured at 1.25lbs. Therefore, the breakaway torque was 1.02 in/lbs. For a mini lathe or mini mill using AC bearings, about 1 in/lbs is good, and I'd estimate a range of 0.6-1.5 in/lbs being acceptable.

Since grease can effect the breakaway torque I'll turn the spindle in the opposite direction I'm going to measure and then turn it back just slightly and then measure. I've found this technique creates a "dead spot" in the grease and almost completely eliminates its friction.

Measuring the breakaway torque on the mini lathe.

Then I ran the mill at high speed for 30 minutes while monitoring the temperature of the mill head right next to the bearing. I used a IR thermometer which I pressed against the side of the mill head right at the bearing. I've checked the temperature at that location versus the temperature right at the bearing's outer race using a thermocouple and there is only a couple degrees difference. If the temperature stays under 60* C then you're fine on preload. On mine the temperature barely even reached 45* C. I then made sure to put a witness mark on the nut so I could tighten it to the exact same point every time.

Sunday, April 2, 2017

Lathe: Power Cable

I really dislike how the power cable goes through the motor cover and lathe bed to get to the control box. It means whenever I want to remove the motor cover I also need to remove the control box to disconnect the power cable. It makes much more sense to me to simply connect the power cable directly to the control box.

Power cable in place and bolted to the control box.

With the chip tray removed there was plenty of room to route the power cable under the lathe and to the bottom of the control box. I drilled a 1/2" hole and made a bracket out of aluminum which was riveted into place. The old cable hold down bracket was then used to bolt the cable to it.

Lathe: Chip Tray

I hate the chip guard on my lathe. It's not shallow enough, and the chuck can easily grab the chips and throw them around. I've ended up with chips in my hair too many times because of it. So I removed it. The motor cover has vent holes on its end, so I formed a piece of aluminum to cover it and deflect chips.

Aluminum chip deflector riveted in place.
While I was at it I also removed the chip tray. It serves absolutely no propose and just made things harder to clean up. It was fairly easy to remove the tray and reinstall the legs themselves.

Both chip guard and chip tray removed.

It hasn't been any harder to clean up, and it definitely makes it easier to work with and to clean up afterward. The only downside is I'm still looking for a good place to put the DRO control box.

Monday, March 20, 2017

Lathe: QCTP Rotation

I have a 0XA QCTP installed on my mini lathe. Instead of using the included nut to bolt it to my carriage I used the handle off the stock tool post. This allows me to quickly rotate the QCTP into a new position, an option which I use a lot to either provide clearance or give the tool bit a better angle.

Tool post in rotated position.

Saturday, March 18, 2017

Lathe: Gear Reduction Pulleys

I realized I never used the high speed on my mini lathe, and I really needed a lower speed on there than what I had for parting and knurling. In addition, the mini lathe belt is a proprietary part which I'm not a fan of.

There are a lot of sellers on eBay selling ratio reduction pulleys for the mini lathe. They'll drop the low speed to 700 RPM and high speed to 1800 RPM with an increase in torque and lower low speed.

I bought the cheapest one I could find expecting it to need modification to be usable, and it did. I needed to turn the large pulley down to 10mm wide to fit. I then needed to cut a keyway in the motor pulley. However, once I was done they fit nicely and use a standard xl (163xl037) belt which is easily available on Amazon.

Pulleys and belt in place.

In low speed it's now usable down to about 150 RPM which is a really nice change from before, and should really help parting and knurling. I may eventually experiment with the ratio and go up a tooth on the motor.

Wednesday, March 8, 2017

PWM Control Notes

Peak Voltage:
The KB PWM control I use produces a peak voltage of 160VDC which is very rapidly switched on and off to produce a lower average voltage. I was worried about the 110VDC motor being hit with 160VDC, but after research I found if the frequency is high enough, then it doesn't really matter (assuming the peak voltage isn't absurdly high).
"As long as the PWM frequency is fast enough, it's average voltage is what counts. No, the average PWM voltage should not exceed the motor's rated voltage, at least not for long. This is no different that applying a DC voltage to the motor.

Using a high voltage supply and then less than 100% PWM to compensate is a perfectly legitimate way to run a motor, again, as long as the PWM frequency is fast enough. In effect you are creating a switching power supply that converts the high voltage to the lower one used to drive the motor. It may not look that way because the induction of the motor windings are a integral part of this power supply.

- Olin Lathrop

The things which kill a motor are overloaded bearings, bearing run too fast, brush arcing, and damage from overheating. None of those is really a result of voltage, and a high frequency PWM drive will actually allow the motor to run cooler while producing more torque.

Adjusting Max Voltage:
The high frequency a PWM motor control outputs to the motor can leave a digital multimeter confused or inaccurate if you're trying to measure the max volts, while I've found using an analog multimeter will respond accurately to the PWM output.

If you have a digital multimeter which can read duty cycle and you know the peak voltage (160VDC in case of the KBWS using 115VAC), you can multiply the duty cycle by the peak voltage to get the average voltage, which is what the motor should see. 

To set the max volts to 110VDC for the mini lathe and mini mill's motors I first used a analog multimeter to set the max output to 110VDC. Then to double check I calculated the motor RPMs from the spindle RPMs since I knew the gear ratio; the lathe has a 5000 RPM motor while the mill has a 6000 RPM motor.

Tuesday, February 28, 2017

Lathe: Headstock Bolt Torque

The mini lathe's headstock is a very poor design. Tightening it to the bed puts a lot of force on the channel in the headstock's bottom which mates to the bed's prism, and the outer side of the channel is not well supported. Even worse, a square relief was cut in the channel which concentrates the stress at the corners of the relief. Ultimately, if you tighten the headstock down tight, you run a good chance of cracking it.

After some research by Grizzly, a recommended torque of 96-144 inch pounds is recommended for the bolts, and I would stay toward the bottom end of that. I torque them to 102 inch pounds, or 8.5 foot pounds.

Crack originating from inside corner.

Bearing Preload

Bearing preload is critical for machine tool spindles since it keeps the spindle rigid, especially under load. It's the amount of compressive force placed on the bearings at rest, and is usually expressed in pounds force or newtons force. For example, my mill spindle has approximately 100 pounds of preload.

High end machine tools use angular contact (AC) bearings which are ground such that, when clamped together back to back, automatically provide the required amount of preload. Unfortunately, the design of our mini lathes and mini mills makes setting the preload extremely difficult since setting it via the spindle nut is very imprecise, and you're also fitting the press fit of the bearing on the spindle.

Now that I've replaced my spindle bearings quite a few times, I've found several different ways to check the bearing preload. In practice I'll usually end up using all of them as double checks.

1. Calculate the torque required for the desired clamping force. I use the this online calculator. The problems with using torque is you need to account for the addition force necessary to move the bearing's inner race on the spindle and the amount of torque needed can change while tightening the nut.

2. Check the breakaway torque, meaning the amount of force required to make the spindle start to turn. This can be fairly easily calculated using a thin feeler gauge, a strong magnet, and an scale. You fix the end of the shim to the spindle using the magnet, measure the diameter of the spindle in inches where it's attached, hook the scale to the shim, wrap the shim around the spindle as far as it'll go, and then pull on the scale and see how much force in pounds is required to start turning the spindle. If you multiply that by the radius you get the breakaway torque in in/lbs. For example, I measure at the lock rings, which have a radius of 0.815". My breakaway force measured at 1.25lbs. Therefore, the breakaway torque was 1.02 in/lbs. For a mini lathe or mini mill using AC bearings, about 1 in/lbs is good, and I'd estimate a range of 0.6-1.5 in/lbs being acceptable. If you're using tapered roller bearings, then a breakaway of a little under 10 in/lbs is good (which also illustrates the much higher friction inherent in tapered roller bearings).

Since grease can effect the breakaway torque I'll turn the spindle in the opposite direction I'm going to measure and then turn it back just slightly and then measure. I've found this technique creates a "dead spot" in the grease and almost completely eliminates its friction. This is especially useful if I'm using sealed bearings.

Shim in place, wrapped around the spindle, and just starting to pull with the scale.

3. Bearing temperature run at top speed won't tell you if the preload is correct, but it can tell you if it's too high. Run the spindle at the top speed you'll be using and measure the temperature on the head directly next to the bearing (I've found it's only a couple degrees cooler there than directly on the bearing's outer race). If the temperature stabilizes below 60 degrees Celsius then it's ok.

Another method which I haven't tried yet, is using the power consumption of the motor to estimate the preload on the bearing. Since power consumption will go up with preload, you can increase the preload until you start to see the power consumption start to rise.

If you're setting preload on tapered roller bearings, then you want to make sure you snug down the spindle nut and then turn the spindle at least 10 times to insure the rollers properly seat in the racers. Otherwise, the preload will drop significantly, if not completely, as the rollers seat.Then you need to measure the axial end play of the spindle. To get the best measurement, shove the spindle in one direction while rotating it, and then shove it in the other direction while rotating it, and be sure to measure at the same spot on the chuck/spindle every time to account for tolerances. You want to keep adding preload until the end play just reaches 0. If you tighten it any more at that point friction and heat will rapidly rise.

Lathe: Speed Control

Apparently most of the newer 7x12 mini lathes are now coming with a KBIC-240D speed controller stock. Unfortunately, mine was not one of them. While the power of my lathe is adequate, I wouldn't mind a little more torque, especially at low RPMs.

The lathe came stock with a PWM controller, and for the same reasons as with my mill, I decided to stick with a PWM controller for the lathe upgrade. Since installing the KBWS-25D in the mill went so well, I decided to do the same thing with the lathe. I eventually picked up a well used KBWS-25D on eBay for a great price. While the mill has a 350W motor, the lathe only has a 250W motor, so I installed a 9849 HP resistor on the KBWS.

NOTE: The older version of the KBWS-25D come with a very tall capacitor, while the newer versions come with a shorter one. The shorter one definitely makes mounting easier, especially on the mill.

My eBay find.

The tall capacitor kept me from simply installing it in the control box, so I marked out the KBWS chassis on the exterior of the box and cut it out with a Dremel and some files. Then I used UHWM strips to space the KBWS out a little more and clean up the hole. The KBWS then slides in from the outside of the control box, and is bolted into place. If I was using a SCR controller from KB (like the KBIC or KBLC) then I could have just bolted it directly into the control box since they lack the tall capacitor of the KBWS. A hole was cut in the clear plastic protective sheet to provide clearance for the capacitor and the armature fuse holder was mounted to the side of the box.

Cuts and holes marked.

Hole cut and drilled. It's not clean since I did it with my Dremel and the spacers will clean it up nicely.
Bolted in place along with the spacers.

Plastic cover and fuse holder mounted.

 Like in my mill, my lathe's wires are numbered which made things easier, though different lathe's might have different numbers or no numbers at all. For me, wire 1 (AC hot) went to L1, wire 2 (AC neutral) went to L2, wire 3 (motor +) went to A+, and wire 4 (motor -) went to A-. The potentiometer wires are in reverse order so P1 goes to P3, P2 to P2, and P3 to P1. I removed any extra wires I wasn't using to keep things clean.

Labeled connections on the KBWS.

Since the mill doesn't come with a pre-installed run/off switch like the mill, I needed to add one to allow me to set a speed and then turn the spindle on and off independently. A mini toggle switch from Amazon worked nicely, and fit in the existing hole above the direction switch, and connected to the inhibit connectors on the KBWS.

The IR trim pot controls how much compensating voltage is given to the motor to maintain RPM, so I goosed it upward a little.

Like with the mill, I really like this mod. The board is more reliable, gives me much more control and adjustability, and allows me to set an RPM and then turn the spindle on and off. Considering if you bide your time you can find these boards for not too much, I think it's a great upgrade and definitely helps with the usability of the lathe.