# PM-25MV nodding off



## Steven57 (Dec 25, 2014)

Check to see if my 7x27 bed was trammed to the head and it was dead nuts. However, the head is nodding forward to the tune  of .003" in 7". 

What is the correct solution?

Side note : I am doing the MachineChick (CNCZone) mod for tramming the head and will finish that prior to loosening the head up.


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## tmarks11 (Dec 25, 2014)

It depends if the "nod" is off because the column is tilted forward or because the headstock (PN238) is not mounted squarely to the z axis slide (PN 1).





To tell the difference, you would need a cylindrical square.  With it sitting on the table, and a DTI on a noga chucked into the spindle and zeroed to the back edge of the square, you raise the head and watch the indicator.  If the column is inclined, than the reading will change as the head goes up.  If the head isn't squared, than the reading should stay at zero.  All of course within the normal variation you see because your gibbs are not completely tight.

Here is a haas being setup on youtube, at 5:00 they are using a cylindrical square to check the column square to both the X and Y direction (not it is 0.0005" off in the Y direction).

https://www.youtube.com/watch?v=KtX9_9bSsJs


You could also chuck up a piece of ground drill rod in the spindle as a reference, although that will not be as accurate, since now you have the inaccuracy of your collet chuck that could affect your readings.  The DTI would be mounted on a mage base attached to the table.

Hossmachine has a set of videos on tramming his Grizzly version of your mill.  

https://www.youtube.com/watch?v=40Q61UAnOTA&spfreload=10

Chances are that the 0.003" you are off is just a paint chip or a burr.  Disassemble the offending surface, inspect the mating surface, stone it lightly in a figure 8 pattern with an india stone.  That being said 0.003" is not much, although if you were surfacing a wide part, it would probably leave a visible line where each pass overlapped.  Chances are the machine is going to be flexing at least that much (so a nod forward would be self correcting... a nod back would make the flexibility worse).


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## TomS (Dec 26, 2014)

I have the same problem on my PM-932.  I've got .005" of nod in 6" of Z axis travel.  See my thread - http://www.hobby-machinist.com/showthread.php/28216-Options-for-Checking-and-Adjusting-Quill-Tram.  I realize gib clearance contributes to the nod issue but I'm still not convinced it is the entire issue.  Still need to investigate the problem further.

BTW - I used the method shown in the Hoss video.

Tom S


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