Height tolerance on Y axis travel?

[starr256]

I have had my PPM-727V mill now for almost 2 years. I have found that the table has a 0.010" variation on height measured from the mill head to the table when the table is moved along the 6" travel along the Y axis. I am sure of my numbers and the method of attaining them. Surely this is not acceptable. The question is, how do you address the issue?

 

[higgite]

I don’t know how to fix it, but I have 3 questions that might help in troubleshooting.
1. Are the X and Y gibs adjusted so there is no slop in table movement?
2. Is the X-axis locked during the Y-axis travel and measuring?
3. Have you checked for table top flatness with a straight edge?

Edit: More questions:
4. Is the height variation gradual and proportional across the table? That is, does it measure .005” off at mid-travel?
5. Are the Y-axis measurements consistent at different spots along the X-axis?

Tom

 

[starr256]

1. I believe the gibs are suitably adjusted.
2. Measurement take with X axis locked and unlocked.
3. Table is flat.

 

[Jim F]

I have a G0463, similar to yours, I had to shim the column to get the nod out of mine.

 

[higgite]

I have a G0463, similar to yours, I had to shim the column to get the nod out of mine.

I don’t think the OP is describing head nod. He’s describing what sounds to me like the table and/or ways are tilted front to back relative to a stationary head/spindle. At least that’s what I read into it. Maybe he can clarify it.

Tom

 

[starr256]

Mr. Higgite...
You have correctly identified my issue.

 

[starr256]

Answers to question 4 and 5.
4. It is a constant linear variation.
5. The variation is the across the x axis.

 

[RJSakowski]

What is being described is that the table surface is not parallel to the ways in the y direction. This has absolutely nothing to do with the head or column. One possible cause is that the gibs are loose enough so that when the table is moved to a forward position the center of gravity is hanging over the support of the ways, the table tilts, lifting the back of the table.

To check if this is the problem, lock your table down and remeasure. This should remove any gib clearance issues.

This is more common on the x axis as there is a greater chance of overhang in that direction. I had this problem on my Tormach 770 and was able to improve it by adjusting the gibs. Unfortunately, there is no provision for locking the table on a CNC mill.

 

[Reddinr]

My mill RF-45 type had a similar problem but about 2-3 mil across the 8" table width. Still has the problem as a matter of fact. I've learned to shim parts when it is important, which is usually never for the stuff I do.

So, I think my table surface is not parallel to the Y axis ways. Yours is probably the same unless it is the gibs. as mentioned above.

The only way I can think to fix it is to get the table re-ground parallel to the ways.

 

[starr256]

Well, more or less have taken Mr. Reddnir's approach. Since 95% of my milling uses the vice, I shimmed it flat. Phooey. I'll deal with it during the next pandemic surge lockdown.