Mill

From Fusselman.org

If you've been here long, you've seen my off-and-on obsession with building a CNC mill to do my bidding. Unfortunately, it "takes a mill to make a mill", sorta. If you're trying to do it on the ultra-cheap (I am), you end up making lots of your own parts. In my case, I've even gone so far as to build that "ladder mill" to help get me there.

A while back (think like 2003), I had a drillpress donated to me, which I had to do some work on to get it running. Since then, I've added a depth stop, and a cross-slide vise to help hold and align work.

This week, I finally got around to finishing the "mill conversion" by adding a z-axis feed, and setting up an indicator to measure that travel. The indicator setup still needs some work as I'm not really happy with the bulky setup using the magnetic stand. The indicator seems plenty rigid and all, it's just a lot of junk stuck to the side of the mill. I have in mind something more elegant, but we'll see.

Z-Axis Feed

The z-feed itself was the "hard" part. Basically, I just removed the handles from their hub, and turned the shaft down to accept a gear I had handy (out of a pressure washer, if I recall). I would have also bored the gear a bit (to leave more shaft) but I don't have boring bars, and the gear was didn't have a ton of space to give. My "worm gear" was a piece of 3/8-16 all-thread, with one end turned to accept a bearing, and another gear bolted to the other end as a handle. Initially, I'd intended on putting bearings on both ends, but there were some issues with that, when it came to mounting.

All the parts used for this project were stuff I had laying around. They're not perfect (the gear and the all-thread engage every other tooth (the gear skips a thread on the screw, because it has pretty coarse teeth)), but they seem to get the job done. To that end, I didn't have an appropriate pair of matched bearings for the feed screw. I had a small bearing that I'd turned the back of the screw to accept, and had a larger bearing that cleared the threads as-was. I didn't have a real plan for the front (larger) bearing, though.

Without that plan, I figured I'd work on mounting the rear bearing so that the screw and gear meshed, so I could test that before I got too worried about that front bearing. I was going to build real bearing blocks (think shaped like pillow blocks), but didn't have any solid stock of appropriate size. I started looking for angle, or strap that I could turn into angle. I ended up cutting an old bed caster frame in half, and knocking out a big hole in one half for the bearing (which thankfully had a shoulder on one side). I bolted that bracket to the side of the drill head with #4-40 screws (actually pcb standoffs, since they're hex) for no particular reason. In retrospect, should have used #6, as 4-40 sucks to tap. Thankfully, cast iron is soft.

Once I got the rear block in place, I noticed that there really wasn't any force on the front at all, as the spring force (wanting to wind the quill back up, and turn the gear backwards) is entirely against the rear bracket and bearing. I realized that a front bearing probably wasn't really needed. I drilled an appropriate clearance hole in the other bracket half, and bolted it to the front of the head. The screw turns freely, as all of the quill's retraction force is against the bearing at the rear.

For normal drillpress operation, it's still possible to remove the screw (wind it "up" past the spring, and tilt it out) and operate the shaft with a vise-grips. Unfortunately, too much material was removed to screw any of the existing handles back in. Sometime, I'll build a new hub to bolt onto the end that has handles.

Z-axis Play

One thing I noticed was that there was a bit of vertical play once the mill touched the surface of the work. This seems to be caused by slop between the rack and pinion that drive the quill itself. I was able to eliminate this by adding a stiff spring to pull on the depth stop (directly attached to the quill) and hold the integral rack against the proper tooth-face on the pinion.

Rotary Table

The 3" Rotary Table has been moved to its own page.