Tramming Tolerances

[Navy Chief]

I have been working on getting my Grizzly G0755 mill trammed accurately. I am struggling with the Y Axis tramming, currently I have it within .001 over a distance of 8.25 inches. I would like to get it closer than this but with having to shim the column to make adjustments this is as close as I have been able to get it.

What does everybody consider an acceptable tolerance for tramming to be? With my current setup I am within .00012 in an inch.

I am considering adding some adjustment bolts to the column for adjustment without needing to shim the column, but I have not been able to find any examples of somebody having done this before and I don't want to screw up my new mill...

Thoughts?

 

[Tony Wells]

I seriously doubt you will actually need it any closer. I don't fret about my mill if it's that close and I do commercial work all the time on it. I think you've done well getting it as close as you have. I'd definitely stop.

 

[Navy Chief]

I seriously doubt you will actually need it any closer. I don't fret about my mill if it's that close and I do commercial work all the time on it. I think you've done well getting it as close as you have. I'd definitely stop.

Thanks, it is hard for me to turn off the OCD perfectionist side of my personality sometimes. I will commence to making chips with it then.. Maybe sometime in the future I will add the bolts to the column and try to get it perfect, but for now I want to build some things.

 

[JimDawson]

I'm guessing you could adjust that last 0.001 out just by tightening bolts. But unless you are doing work for NASA, you should be good to go the way it is.

 

[RJSakowski]

You will most likely find that by pushing on the column, you can cause variation larger than you are measuring. All machines flex when force is applied. Most hobby class machines aren't massive enough to prevent flex in the frame.

 

[brav65]

Tom Lipton just reviewed a super accurate level and showed that it was so sensative that hand pressure on his 4" surface plate could deflect the bubble on the level. I think he said it measured 1/10 of a second of arc.

 

[chevydyl]

I have a Bridgeport clone knee mill, and it's trammed 0's in both planes, when I take a cut about 20 thou with a face mill it's enough force to deflect it during the cut. I too am ocd and will spend any time necessary getting those 0's on the tenth indicator. I don't do work for nasa lol but I am assured that it's flat. When I put parts on the grinder it usually takes about 5 tenths to flatten it out from face milling.

 

[fgduncan]

You might also consider that the very heat from milling will create enough of a temperature change to warp your work by that much! As mentioned above, that small amount can be corrected by simply tightening some of the bolts. Trying to do tenths with a hobby machine is a good way to wind up in a padded room. When I am trying to get a sliding fit, I bring the work in to +.001 and then polish to size. That might not be the professional way to do things, but then I can only offer that I am an amateur.

 

[chevydyl]

there other day while tramming, I was standing on the back side of the table to see the indicator, I rested my hand on back of the ram, the needle moved.... lapping is for that last little tiny if you need it. talking with a shop owner that has the big PROTOTrak knee, 5hp, he wont take a job if there isn't a thou tolerance, let someone else waste time chasing tenths