Just got my HiTorque Mini Mill

[macpod]

After dreaming of buying a mini mill for years, I spotted the HiTorque Mini Mill at LMS and after learning it had a belt drive (and taking a shot of courage) I decided to buy.That mill came in a few days ago and after a few flights of stairs now lives next to my toaster.

The unit arrived undamaged (connected only with two bolts to the bottom of the cheap plywood box) had just a light coat of oil on it vs the packing grease I'm accustomed to with stuff from china. I cleaned that off with mineral spirits and lubed the leadscrews and column gear rack with white lithium grease. Next I lubed the ways with mobile one 10w-30 (I would have used Mobile One vactra 2 oil if I could find it locally), and coated the other bare metal surfaces with a gun rust barrier spray (G96 seems popular).

The little machine shop manual did not mention breaking in the spindle, but I see the grizzly does so I'm doing that now. This has spurred a few questions which I hope you all could answer:

1. I plan to adjust the gibs, square the head, and then tram the mill next in that order. Is there anything else that the manual does not mention which I should do next (or in a different order?)

2. I have installed a collet +tool in the mill and tightened the draw bar with a wrench while holding the spindle with my hands only. I believe this is the proper way (although I feel I should be tightening it much more like a meathead!). Is this right?

3. While the tool does not appear to wobble noticeable and my dial indicator shows the bottom portion of the spindle has at least less than 0.001" of runout, the draw bar at the top of the spindle and the spindel nut is off center by a few millimeters. Is this ok?

Thanks all, I have a software/electrical background.. but virtually no mechanical background so these forums and some posters here have been a real help in getting started. As I go along in setting up, modifying, and then cnc-ing this mill, I hope to document it well.. hopefully it will be as useful as some of the other scattered info I have found.

[TXFred]

1. I plan to adjust the gibs, square the head, and then tram the mill next in that order. Is there anything else that the manual does not mention which I should do next (or in a different order?)

Start designing a column brace. Lots of good designs are to be found on this forum.

2. I have installed a collet +tool in the mill and tightened the draw bar with a wrench while holding the spindle with my hands only. I believe this is the proper way (although I feel I should be tightening it much more like a meathead!). Is this right?

There is a hole on the right side of the head, and a stick in the toolkit that fits the hole. The stick looks like a spare handle for the Z axis feed, but isn't threaded on the end. This will let you lock the spindle and apply more torque to the drawbar.

3. While the tool does not appear to wobble noticeable and my dial indicator shows the bottom portion of the spindle has at least less than 0.001" of runout, the draw bar at the top of the spindle and the spindel nut is off center by a few millimeters. Is this ok?

Initially it is, but you'll want to fix it.

If you remove the drawbar, you should see that there is a metal spacer that holds the drawbar centered. The problem is that its center hole is way too big, so the drawbar can sit at an angle. The solution is to make a new spacer that just barely slips over the drawbar.

You can run with it as is for a long time. The problem is that the off center drawbar puts the spindle out of balance. At high spindle speeds, it will make the whole mill vibrate. Replacing the spacer will fix this. If you want to be really obsessive, you can also make a new washer as well. I did.

[macpod]

Ah yes, I have read quite a bit about the column support issues. It seems they are rumored to involve:
-Only having the giant column bolt supported on one side
-The stock washer
-The actual bottom of the column getting squeezed and flexed (see the attached pdf for a demonstration of this)

Hoss's website has a nice collection of the different column support mods out there: (see the X2 Column Rigidity and Support section):
Shop Info

At least for the moment I plan to make a support structure that will not require any column modifications, but will involve tapping two holes in the base. After reading that pdf I'll probably abandon the stock washer completely and make this out of 1/4" or 1/2" pieces of steel.

I'm also giving serious consideration to filling the first 6" of the column with epoxy (west systems 105 epoxy with 209 extra slow hardener) and possibly an additional media. Before I do that however, I want to make sure it won't impact other potential improvements.

Links of the day:
To square the head, I found this a nice read:
Mini-Mill Spindle-Column Alignment

On mcmaster you can buy 1/2"x6" (1031K12) or 9" (1031K12) aluminum rods with a ceramic coating for under 7 bux. These rods have a diameter tolerance of -0.0004" to -0.0012". They also sell brass shim stock sheets for about 2-3$ a pop.

To tram the mill, this was a good read:
How I tram my mini-mill | MachinistBlog.com


As far as the drawbar issue, I'm glad to hear that isn't a total show stopper

[RobosaurusRex]

I'm also giving serious consideration to filling the first 6" of the column with epoxy (west systems 105 epoxy with 209 extra slow hardener) and possibly an additional media. Before I do that however, I want to make sure it won't impact other potential improvements.

macpod:

I've read John Pitkin's column flex fix and I have a problem with it. He was able to achieve a reduction in his column's flex, but which of his two fixes helped the most? He substituted a thick steel plate for the bell washer AND he filled the bottom of the column with epoxy. He should have added the plate and measured how much it helped and then added the epoxy and measured it again.

My understanding is it is the filler/aggregate mixed with the epoxy that provides nearly all the strength and he didn't add any. I'd mix the epoxy with finely crushed glass or granite so the epoxy only made up about 10 or 15% of the volume. It would also be a cheaper fix because glass or granite costs a lot less than epoxy.

I bought a 1/2-inch thick steel plate and a digital luggage scale so I could reproduce his experiment, but I haven't gotten around to it yet. I'm just guessing, but I suspect that steel plate was responsible for nearly all the improvement.

Rob
MachinistBlog.com

[macpod]

There's a familiar name

I have been totally sidetracked by a few other projects so I haven't done much tweaking of this machine yet. Just manually milling non-dimensional critical stuff and playing with the electronics:
http://www.cnczone.com/forums/bencht...achometer.html

I plan to do the steel brace fix first, and then the epoxy eventually.. and I'll certainly test between those two.

I've been wondering if instead of epoxy, if just a metal tube stuck inside would help keep the column from getting squeezed and hence flexed. (after installing the metal brace of course).