Adjusting and squaring a 1965 Millrite MVI

Another report from the field:

When I first got the vertical mill in November 2006, I trammed it, and all seemed well. But I soon started to notice little symptoms of a non-perpendicular spindle, like the fly cutter cutting in two steps if the work moved left-to-right, and only one larger step if the work moved the other way.

I also noticed that the spindle seemed to have considerable runout, especially angular wobble, but this varied with what R8-shanked tool or collet or chuck was mounted. Very strange.

I had to shorten the drawbar by about 1/4" so it wouldn't bottom out on my brand new 1" stub arbor for tools for a horizontal mil, and while I had the head tilted horizontal to remove the bar, I inspected the inside of the mill's spindle, the R8 socket. The taper part wasn't smooth, between 40 years of battering while inserting collets and shanks, and some tightly adhering hard spooge. Cleaned it off with acetone and a half-round swiss file, so it's now smooth the the finger. This helped a lot, cutting the wobble in half or so. But didn't solve the wobble.

Most of the big problems seemed to involve the 1/2" R8 collet, so I looked at it closely. It has had a long service life, with damage here and there, but nothing that could cause the observed wobble, something like 0.006" peak to peak at 5" from the face of the collet. Then I noticed that the bore of the collet had two sections, fore and aft, separated by a little groove, and the diameters were not exactly the same, the front section being slightly larger. Huh? Looked at all the other collets - only one section, and one diameter, as one would have expected.

Now the 1/2 inch collet gets by far the most use, so I bought a new US-made (Lyndex) collet. What a difference. Now the wobble is more like 0.0005", a tenth as much. Bingo!

I'm wondering if the 1/2" collet I had was a soft collet that had been machined to fit something special. Anyway, it is now retired.

Now, it was time to re-tram the mill. (This was done with the now-retired collet, but it shouldn't matter.) I trammed it to less than

0.001" offset in about 15" along the table (X-axis). So far so good. Then I measured front to back (Y-axis) - it was off by 0.010" in ~7". Ouch! Perhaps the knee is loose.

Tightened the knee locks, observing the effect with a knife-edge square between the vertical dovetail on the machine base and the horizontal dovetail on the top of the knee. Not perpendicular when unlocked, closes up and becomes almost square when knee gib locks are tightened hard. The gap at the top looks to be about 0.010". Hmm. Time to tighten the knee gib adjuster screws.

All the gib adjusters have their jamnut glued to the hex-socket setscrew adjuster with hard-caked spooge, perhaps decades worth. Take them out one by one, clean, oil, reinsert, and tighten. Cleaning required scraping the spooge out of the threads with a 3/8-16 tap and die, and acetone. Scrape excess paint out of the spot-faced bearing area for the jamnuts.

Now the knee tilt is within original spec, but I may have it a bit too tight, as the knee doesn't come down smoothly, instead lurching. Going up is smooth.

Next weekend, I will re-tram the mill, using the new 1/2" collet and a well-clamped knee and table. As well as a few bits of hardware I bought for rigidly attaching dial test indicator to spindle.

I recall a year or two ago someone on rec.crafts.metalworking saying that with Chinese machine tools, one needed to spend ~40 hours taking the tool apart, cleaning all the swarf out, finishing the machining, and adjusting. I believe that may be true, but it's turning out that the old iron is requiring the same thing and taking about the same amount of time. The difference is the machine one ends up with.

Joe Gwinn

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Joseph Gwinn
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