Tramming the ST mill head

[dahui]

Hi folks,

I've been working on the machine a lot and finally got to checking the tram on the mill head. The first thing I checked was to see how flat the table was...it's .002 out in the X direction across the short side of the table. Not great. I wasn't sure how to check the Y direction...other than traming.

So what did I find? Out of tram: Y rotation .007 / X rotation .018. (I'm not sure the correct nomeclature for this, but I mean rotation around the X axis etc.) I can understand .007 but .018? Okay, so bust out the shim stock. I managed to get the X rotation down to less than .0015, pretty decent. After some more shiming the Y rotation is still about .005. Figured I was getting close, only issue is shimming one side tends to screw up the other side.

For some reason I decided to run the mill head up and down at this point...only to find MAJOR binding and sticking. I thought I had bent the shafts or the mounting plate so I pulled out all the shims, re-tightened and discovered the mill head ran perfectly smooth. Soooo...it seems that I can probably get tramed well enough, I just won't be able to move the mill head up and down. Not quite super duper.

Any suggestions?

This machine would be great if they just paid a little bit of attention to quality control. I'd happily pay another 500 bucks for a machine that is straight. I could hardly care if the motors run at this point.

[bicycleboy]

On my Tri-Power which is somewhat similar I started with about .008 front to back (your Y?) and .018 left to right, your x. After 7 iterations I got it down to about .0015 total variation with the head about 1/2 way down. In doing this I noticed that it's important to lube the quad tubes and always move the head upward a little before locking to get a consistent head orientation.
I used forked shims from McMaster -Carr that fit around the bolts between the black plate and the lathe head. Also be sure to always add or subtract shims at the same time of the same thickness on adjacent bolts so the plate remains in the same plane. I torqed the bolts to 30 ft-lb after each adjustment. I noticed no binding in the quadra-lift tubes after finishing.
Did notice that the cheap bolts start twisting at about 35 ft-lb. I think the bolts should have been at least double this strength, but I don't trust the shallow tapped holes so will leave as is.
Haven't checked the lathe taper (or seen any problems in several parts) but I guess it would be better to straighten that out before tramming the head. I don't know if they have alignment pins in that connection or not. Every place around my x and y acme feed screws the alignment pins were grossly out of position and multiple attempts made I don't understand how the manufacturer can come so close to making a great product and screw it all up in the alignment and getting cheap at the wrong places
Good luck!

[dahui]

Hi again,

Yes I'm getting .007 front to back and .018 side to side.

I tried moving the column up and down before locking, and locking seems to make the head come down about .002 regardless of what I do.

Here is the wierd thing...I have my indicator in the spindle, indicating the right side of the table. I lock the 5th column and see the indicator move .002. Then I flip the indicator 180, zero it out, and rotate 180 again. Now, I still see exactly .007 difference...shouldn't that be .009? (or .005?)

In any case, how did you check the alignment of the pins on the leadscrews?

cheers

[dahui]

Well after a couple of hours futzing around the best I can get is .0015 side to side and .0045 front to back. I haven't had a chance to take any cuts yet, need to turn some setp pulleys first, but at least it's an improvement. Wish it was easier. I just bought a 2.5" face mill but I'm not that confident that it will make a good finish with the head being 5 thou. off.

I found that making my shims cover the entire length of the shimmed side got rid of the binding problem I was having. The first time I tried shimming, my first post, I was actually using aluminum foil. It's .00065 thick and very consistent. My last attempt was with .006 brass shim stock. Three sheets on the back side and two on the chuck side (standing in front of the machine). Same results with aluminum foil and shim stock, amusing.

[Rainman229]

Any chance of getting pictures of what you did?