Tramming and Table Locks

[ajmacdon]

Hi, first post here but it's been a really helpful site to read so far!

I just got my new PM-932 up and running today and started tramming the head. I find that the table and column locks (all of them, X, Y, and Z) seem to have a pretty big effect on the reading. When I lock and unlock the column X changes by 5 thou and Y by close to 8 thou. The X and Y locks each throw things off by a couple thou but aren't as big a concern as the column locks.

I've used mills for years but never maintained my own (school, work, friends, etc) so this is new territory for me.

I gave it some thought and can't see how the machine could tram the same when locked and unlocked unless there were absolutely zero clearance in the gibs which is impossible.

How do most people approach this? My strategy was to dial it in with X and Y free but the column locked since that's how I will use it most often. My first project was to face a 6x8" transmission adapter and with a 2" face mill it turned out as well as the factory job (barely a click as you drag a fingernail over the overlap) so things seem to be working, just curious on the standard practice.

Pic of the new machine and my beloved old southbend just for fun:


Thanks,
Alex

 

[darkzero]

I have a PM-45M. 5-8 thou is a lot. You may want to check if your gibs are loose. When I lock my gibs for any of the axes I only get 2-4 tenths movement shown on my DRO. But I just easily manipulate the locks to compensate for that when I feel a need to. Then again, I also have balls installed between the gibs & the locks. When I lock the X or Y, I may get very little side to side movement but not enough lift on the table to really affect tram. For the column & the quill yes so I tram with those locked.

 

[T Bredehoft]

Nice looking shop. Too clean, though
Have you adjusted the gibbs? They should apply just a touch of drag on the hand wheels (when cranking by hand) I found that my (PM25) Z gibb has a problem with which I live. it's either loose, or so tight the head won't drop on "crank down" by itself. And Yes, it has .008 movement in x and .002 in Y when tightening the clamps. I do not machine moving Z, it's locked whenever I machine anything. I have a spring loaded brass plug in the quill clamp, also, to keep it snug against the opposite side, else it moves .002. But I'd rather use my mill the way it is than do without.

 

[darkzero]

.008 & .002? Um, ok, maybe I'm not understanding clearly what you guys are talking about? So for your table, if you snug down one or both locks for whatever axis, that's how much it moves?

 

[T Bredehoft]

I loosen the two Z clamps, mount an indicator in the spindle and zero it for X movement. I tighten the two Z clamps and it reads .008 The same on Y movement, .002 So long as I cut with both clamps tight everything comes out fine. If the two clamps are loose I can see the head moving as it cuts. Not much, but moving.

Edit, correct typo.

 

[darkzero]

I see. You got me curious now. I'm going to check with an indicator mounted in my spindle for locking Y & X when I get home

 

[ajmacdon]

Dug into it a little further, hard to figure how tight the Z gib should be with the power feed doing all the work. The problem is that it seemed fine even with the gib adjusted all the way tight (bottom bolt almost out) and never really dragged. That cleaned up the movement with the column locks to about 0.0025 which seems reasonable for this kind of mill. Just kind of concerned that the gib is adjusted completely to the tight side and it never produced any drag. A couple other people observed the same thing but nobody seemed to come to any conclusion.

For now it's academic because I always use the column locks but I do have to figure out a way to attach the column cover with the gib screw so far out.

Alex

 

[darkzero]

I misread some of the OP. Just tested mine.

Indicator in spindle, when I engage both locks on the column, X moves .002". Y doesn't move at all, well when I engage one lock, it moves .0005", then when I engage the other it goes back to zero.

I haven't touched my column gib in a long time so I'll test it again whenever I do.

And for what it's worth....

When I engage just one of the locks on my column, head moves down about .0004", then when I engage the other lock on the column, head moves back up about .0008" so total movement from zero after snuging both locks is about .0004" on my PM45M.

For my quill, if I extend it a bit then lock it, it moves .0005" in Z, .0002" in X, & .001" in Y.