Pm935tv Accuracy?

[HighWall]

My spanner arrived from Enco along with my R-8 collets. I adjusted the alignment pin on my PM935TV, which was totally easy with the spanner. I then took a new 1/2" collet (import) and mounted a .500 gage pin (also imported). When I put a .0005" dial indicator on the pin, it was within .001" concentricity, just barely. Is that good runout for this kind of setup? It's the only collet and gage pin combination I've measured so far. When I measured my quick change MT3 collet and Glacern keyless chuck with a 1/2" drill, it was more like .003 to .004, which didn't excite me that much.

My only other milling machine was a Grizzly 6x26, but I never tried to measure runout on it, so I don't have much of a basis for comparison. I do know that the outside of the spindle on the 935 spins with no measurable runout on this dial indicator. I'd need one calibrated for tenths in order to measure that at this point. My mentor suggested the more useful test would be to measure the runout of the taper inside the spindle, but I've not had time to pursue that yet

 

[wrmiller]

Your mentor is correct. To accurately measure the spindle run out on on your machine, measure the spindle. Using a collet and something stuck in it just adds tolerance stackup and is only indicative of that particular setup's accuracy . Put a DTI right on the taper inside the spindle. That will tell you the spindle TIR.

And just FYI, but drill chucks are not very accurate.

 

[qualitymachinetools]

Enco Chinese Collets are NOT ALLOWED in a PM-935T Mill!!!!!

The spindle runout on that machine will be dead on, just like the part you measured on the outside. The runout you are seeing is going to be the Enco collet, they are OK, but not that great I am sure. Measure runout in the spindle, it will be just like the outside of it was, pretty much nothing.

That Glacern I thought would be better than that, but its hard to measure with a drill in it. The keyless drill chucks I have are .002 or better, thats about as good as you will get with a drill chuck.

 

[tmarks11]

When I measured my quick change MT3 collet and Glacern keyless chuck with a 1/2" drill, it was more like .003 to .004, which didn't excite me that much.

As mentioned above, chucks don't tend to be very accurate. A good Jacobs chuck will be better than a Chinese import (I have some strong doubts about the real origin of Glacern tools), but you still don't use a chuck for milling. Drills aren't the most accurate tool to begin with, so 0.003" run-out isn't really going to make a difference.

"my quick change MT3 collet and Glacern keyless chuck"? You aren't stacking the chuck into a collet are you? MT3? Your mill has an R-8 arbor. Does your chuck have an MT3 arbor, and you have an R8-MT3 adaptor?

 

[HighWall]

Of course, I was only using the chuck or the quick change collets one at a time. LOL. I did just measure the runout of the inside of the taper in the spindle....and there really isn't any. I was using a .0005 indicator on it and the needle didn't move even a single line width

 

[tomh]

( it was within .001" concentricity )

You will be hard pressed to do better with inexpensive collets. Don't let this TIR business run you nuts!
Use and enjoy your mill.

Remember .001 TIR = .0005

Tomh