Thursday, June 19, 2014

Mill: Large Table Upgrade

I installed the large table from Little Machine Shop on my mill. It's the larger table with LMS' own mills use. Let me say I can't think of anything I can do on the larger table that I couldn't do on the stock table, however, the large table is a lot nicer to work with and makes setup easier. It also has a much more robust Y axis gib which is a lot longer than stock and has two additional set screws to adjust it.

Close up of the Y axis gib set screws.

Installation is pretty easy, and I took the time to drill all the holes for my DRO setup before removing the old table from the mill. I also made my standard modifications to the gibs, as described in a previous post.

All in all, I really like this upgrade and it makes the mill nicer to work with. It surprising how much of a difference a couple extra inches makes. My biggest issue with the upgrade was the poor quality of the Y axis dovetails; there is enough variance that you can feel the handwheel get significantly tighter as you move the table toward the column. Fortunately I don't usually move the table that far toward the column, but it's still something I may try to address later.

The larger table installed. The power feed is visible on its left side.

Mill: New Mill Base

My X2 mini mill sits on a wooden work bench, and I noticed the mill's tram would change from day to day. Finally I figured out the wood bench was flexing and changing from temperature and humidity enough to effect the mill sitting on top of it.

To test my theory I took a big piece of 1/8" steel and put the mill on top of it, helping to decouple the mill from the bench. That fixed the problem quite nicely.

To make the fix more permanent I took a 1/2" steel plate and, with the help of another machinist with a bigger mill, milled both sides of the plate flat.

1/2" steel plate milled flat, with locations for posts marked.

I then drilled four countersunk holes in the plate for the mounting holes in the mill's base and JB Welded M6 studs into the holes. The mill was then placed on the plate and nylock nuts were loosely tightened down. They're left a little loose because I want the mill to be able to move slightly on the plate in order to keep it decoupled from the bench.

The new base in place and bolted down.

Tuesday, June 17, 2014

Mill: Gib Set Screws

Please read the complete article:

I don't like the how the stock set screws use a locking nut. Tightening the nut loosens the set screw against the gib. Instead I threw away the lock nuts and use green Loctite. Green is specifically designed for set screws and works very well at maintaining consistent locking even as you turn the set screw. You also apply it after installing the set screw as it's drawn in by capillary action.

UPDATE: This technique worked ok, but the set screws could still loosen over time, so I ended up going back to locking nuts.

Tuesday, June 10, 2014

Mill: Power Feed

I've wanted a power feed for the X axis for a while now, not only because it gets pretty tiring cranking away, but also because a power feed is much smoother than I could ever be and that will produce a better finish. I decided to wait until I installed the large table upgrade since that would effect how the motor mounted to the table.

I had been looking at using a car's power seat servo as motor for a while, and I finally committed when I saw apointofview's post at Home Model Engine Machinist use the exact same motor to create a very elegent and simple power feed:

The new large table's lead screw extends through a bushing at the left end of the table and has a slot cut in it. I pinned a steel key in place in the slot. I then took a 14" flanged nut and milled a slot in the middle of it, just large enough to fit onto the key.

Key fitted to the slot in the X leadscrew.
14mm nut with slot milled into it.

For the motor itself I used a widely available servo for a power seat in a car. You can get them from several places including Amazon: The motor is reversible from left hand to right hand orientation. I used this for the speed controller: since it was cheap and had good reviews. If I were to do it again, I probably would have bought this to save a couple of dollars:

For the direction switch I bought a DPDT DC switch that's center off. That way I can set the switch to center to stop the feed. I found a DPDT switch on eBay specifically design to be used as a direction control for DC motors, so that saved me a couple of wires and a bit of soldering. For the table jog I decided to just use the speed control and wired in a switch set the control's speed adjustment pot to maximum.

Wiring diagram.

For the power I used an old 15v laptop power supply since they tend to be pretty good quality. I wasn't worried about using 15v since most cars run between 13-15v anyway.

The whole mess of wiring was then packaged into a project box from Radio Shack and attached to the side of the lathe. The extra switch on the top right of the control box is the on/off for the spindle light.

Upper left is power, lower left is jog, center is direction.

A piece of aluminum plate was machined to bolt to the end of the table, and to accept the bolt pattern of the motor's housing. The back of the motor mounting holes in the plate were countersunk to provide clearance for the end of the table. The motor's leadscrew was removed and four sides milled flat so that a 3/8" drive socket can easily slide onto it. The leadscrew was then cut down so it would clear the end of the table's leadscrew's key when mounted in place.

Leadscrew machined down and motor bolted to mounting plate.

A 12 point 14mm socket was slid onto the leadscrew and then everything was mounted on the table. To engage the power feed I slide the socket forward until it engaged the 14mm nut. To disengage I simply slide the socket back. I purposefully made everything with very loose tolerances to allow easy engagement and to prevent any binding from misalignment. I cut some grooves into the socket on the lathe for a little more traction.

Power feed assembly bolted to the table. In the picture the power feed is engaged.

The latest beta version of Android DRO (now called Touch DRO) will display the feed rate for a selected axis. When using that with the power feed I can set the feed rate very exactly. As the power feed is configured now it will hold a speed to within 1/2" per minute, which I'm quite happy with. I think if I remove the X hand wheel's handle before using the power feed that variation will go away, as I suspect the weight of the handle is speeding up the feed for half a revolution and slowing it down for the other half.

FOLLOW UP: After a couple of days I started getting some vibration in the motor when running in a certain direction. I was able to fix the issue by taking out the plastic screw which supports one end of the motor's shaft and pressed a small ball bearing into its bore. This gave the motor's shaft a solid and smooth surface to push on and rotate against.

UPDATE: I've since relocated the control box to the side of the top of the column. It's a lot easier to maintain the mill and access the controls.

UPDATE: I added a small cover to the leadscrew engagement to keep chips off it. It's mounted via magnets on the underside of the cover.

Cover in place over leadscrew.

Cover upside down to show the mounting magnets.

Thursday, June 5, 2014

Mill: Spindle Light

I wanted a spindle light to try and reduce shades on the work as much as possible. So far I'm a pretty big believer in you can have enough light on the work.

People apparently install LED rings in their car's headlights to try and make them look like BMW headlights. So on eBay I found a LED ring with an 80mm diameter, which is about the largest the bottom of the mill's head can accommodate. It cost $22. There were cheaper ones, but I bought this because the LEDs and electronic were sealed, while on others the LEDs were exposed, and I was worried about swarf shorting it out.

I used 5 minute epoxy to glue 4 neodymium magnets to the back of the ring to mount it to the mill. It was then that I discovered the cover surrounding the spindle on the X2 is made from plastic. However, with a bit of maneuvering I managed to get three of the magnets on metal and get the light mostly centered.

Neodymium magnets epoxied to the back of the LED ring.

The wire from the light runs up the left side of the head, to the top of the column, and then down to the control box which houses a simple switch to turn it on and off.

Spindle light mounted and turned on.