Nod Tolerance For Milling Machine

[coffmajt]

Happy Thanksgiving to all - I was checking my Grizz milling machine for tram and found it a few thou off which was easily reset, but got curious about the nod direction [ Mine is a 3616 which has no adjustment for nod] and I found it was .005 in out across a 9 in span. In order to correct this I will need to shim between the head and column if this is too much to live with. Just need some feedback from more experienced than me to see if it needs to be fixed. I do plan to remove the head and overarm assembly from the column and check the mating surfaces to see what they look like before I do anything else. Thanks in advance == Jack

 

[Billh50]

If after checking the surfaces and they looked good. I would then calculate how to grind the mounting plate to get rid of the nod. But that is because I was always taught to never use a shim to correct something unless there was no other choice.

 

[chips&more]

I would never grind or modify anything until I was absolutely sure there was a problem. And I knew exactly what the problem was. And then I would still just leave it alone. Shim it, maybe scrape it later on, but not grind it. Cannot control progress as well with grinding. With scraping, you can control your progress better. Good Luck, Dave.

 

[Billh50]

I have never had a problem controlling progress with grinding to within .0001. But I am also not talking about grinding with hand tools either. And as I stated, only if everything else looked good (no nicks, gouges etc. ). But that is my preference and the way I was taught to build machines when scraping was not necessary.

 

[coffmajt]

If after checking the surfaces and they looked good. I would then calculate how to grind the mounting plate to get rid of the nod. But that is because I was always taught to never use a shim to correct something unless there was no other choice.

That would be my plan also - the shims would only prove the amount of grind needed== Jack

 

[Bob Korves]

The head on a machine that does not nod and rarely gets swiveled is not likely where the problem lies. The ram and the turret have also likely rarely been used. The problem most likely is somewhere else. and that would be in the knee vertical slides and in the Y axis slides. If the ways do not show a lot of wear, check that the gibs are adjusted properly, and that they are all locked when testing. Many times on machinery the symptoms do not point directly to the real problems. If your knee is sagging and you shim the head so it is square to the table, from then on the quill and the knee will not be sliding parallel with each other and the work will move fore and aft relative to the tool when raising and lowering the knee. Think about the problem more carefully before changing anything...

 

[Wreck™Wreck]

There is no "tolerance" aside from what you desire, therefore do whatever works for you and the work that you commonly do.

Many people will tell you not to screw around with a machine as designed and built, ignore them and do what works best FOR YOU.

 

[British Steel]

One caution, is the nod measurement high at the extension of the ram or low? If it's low there will be added "leverage" due to cutting forces in use which may cancel at least some of the nod... Could be worth attaching a skyhook to the head to load it upwards and re-measuring

If the nod was measured by sweeping a DTI against a parallel on the table, mills are often built with the "far-from-column" side of the table a little high to compensate for the load from adding a part* - I can't recommend too highly Connelly's "machine tool reconditioning" and Schlessinger's "machine tool accuracy" for explanations of how what seem to be inaccuracies are built in as compromises to make machines more accurate!

Dave H. (the other one)

* set up the DTI on a parallel at the front of the table, add a hefty load and see how much movement there is - there *will* be some, likely more than you expect!