Tips on tramming the nod of benchtop mill PM25MV

That's it. I'm gonna tram the nod and tack weld. If the nod stays trammed after the tacks, I'll put in small beads that I can easily grind off if I have to

Then maybe I'll do the X axis, too, if the plan works and the nod stays trammed for a month
 
Wonderclam said:
That's it. I'm gonna tram the nod and tack weld. If the nod stays trammed after the tacks, I'll put in small beads that I can easily grind off if I have to

Then maybe I'll do the X axis, too, if the plan works and the nod stays trammed for a month
Click to expand...
I wouldn't. Weld that is.

Iron can move under stress. By adding the shims, you are adding stress and the iron is relaxing in response. When you add a shim on one end, the column is no longer sitting flush with the base. Even if you placed the shims so they straddle the mounting bolts, the other end of the column is now pivoting on the edge. Tightening the off side bits will tend to bow the base of the column. The column will resist the bowing but slowly relax. The bolts themselves can also stretch under the load over time. We see that occurring when tightening head bolts and have to go back and retorque them after a period of run-in.
 
I had the same issue(just the tram though), and my solution was to make new tugger bolts for the head(used nitronic 50). It stays put now, do NOT weld it.

The hardware supplied with Chinese machines is junk. Replace all of that and go from there.

The Y I just keep within .003 over the width of the table, it does move but not much. Same with the Z, a couple thou over a foot isn't going to kill me.
 
Last edited:
bakrch said:
I had the same issue(just the tram though), and my solution was to make new tugger bolts for the head(used nitronic 50). It stays put now, do NOT weld it.

The hardware supplied with Chinese machines is junk. Replace all of that and go from there.

The Y I just keep within .003 over the width of the table, it does move but not much. Same with the Z, a couple thou over a foot isn't going to kill me.
Click to expand...

By Y, you mean X? and Z you mean the nod?
 
Wonderclam said:
By Y, you mean X? and Z you mean the nod?
Click to expand...
X is tram, Y is nod(column front to back), Z is column left to right tilt.

Tram is the easy one, and shims for the rest. I do like that epoxy idea shown above, maybe one day I will do that.
 
IMO, the solution that Stephan chose is a better one than shimming for the reasons he stated. However, bear in mind that once done, it would be very difficult to undo. You have to be certain that you can undertake the procedure flawlessly and that you have an excellent understanding of what is the cause of the misalignment.

A square column mill like the PM25MV actually has four alignment conditions which must be met, two more of you add the table surface. The table surface must be parallel to the x and y ways, the column motion must be perpendicular to the table surface in both x and y directions, the quill travel must be parallel to the column motion and the spindle axis must be parallel to the quill travel.

In simple tramming, it is assumed that the table surface is flat and parallel to the x and y ways and that the spindle is parallel to the quill which is parallel to the column motion. It is also assumed that the table doesn't do peculiar things when it is moved like lifting at extreme positions due to play in the gibs. In the real world, there is no such thing as a perfect alignment. The manufacturing and alignment processes deal with tolerances and as long as the machine is within the tolerances it passes. If a condition is misdiagnosed and the wrong adjustments are made and the result is an out of alignment machine, you can go back and redo the adjustments. Not so if you bond the column to the base with epoxy.
 
The guy said that the epoxy has a very fast set time. If I mess up, I practically need a new mill. I don't think I'll attempt to do that. I'll just keep working on this mill.

... Also, I tightened one of the T bolts too much and stripped the threads. M10x1.5 x 60mm T bolts. I'm not sure if these are hardened or not. On the head of the bolts, it says 8.8. Might be something to do with hardness?

I chased the threads on the bolts and tried to retap the nut, but the nut is pretty much done. I'm going to go get 3 M10x1.5 nuts tomorrow and I ordered some 404 stainless T-bolts on eBay, from China. It'll take 6 weeks for me to get it. In the meantime, I'l get a 12" of 1" stainless round bar tomorrow and see if I can machine some temporarily.

I took apart the head of the mill to take out the bolts.. that was a pain.. especially putting the head back in by myself. The spring that held the bolts straight forward broke off.

G9Vsc1S.jpg
 
So, the good news is you're learning a lot about the machine and will be able to use it far better when you are done than before.

Hardware matters.

8.8 is a high strength metric fastener spec. Unfortunately, fasteners like many other things made in China aren't always what they claim, sometimes they just copy the form without duplicating the spec. I have no information about the fasteners that came with your mill, or the ones you've ordered but I would highly recommend you replace the critical ones with known good quality from a reputable source. This is definitely one place where shopping by price (especially at the quantities you'll need) is likely to give you less than what you pay for.

Since you're in Santa Clara (where I was born BTW) you can go into Fastenal, Grainger, or possibly another supplier that caters to industry and purchase the right fasteners for the job. You will pay a little more than ordering online or at the local big box store but you will be able to ask questions and get the parts you need to make sure things stay where you put them.

The fact that your breaking fasteners may indicate that they are part of, if not the cause of, the problems you're having. Slow down and do your research before taking any drastic steps like welding or epoxying your mill. There's lots of very knowledgeable folks on here who can help you get the most from your machine.

If you want to learn more about fasteners I always recommend Carrol Smith's book.


You will be glad you read it.


Cheers,

John
 
You must log in or register to reply here.
Back
Top