Wednesday, April 12, 2017

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.

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