# Tips on tramming the nod of benchtop mill PM25MV



## Wonderclam (Oct 18, 2019)

I have a PM25MV mill.  I'm using Edge industries tramming tool. It goes in the spindle and has 2 indicators on both sides. I calibrated it until I got it to about .0002

I trammed the X axis and got to around around .001. Good enough for me. 

Now it's time to do The Z axis and it is off by .006

So I decide to shim it. I added .006 feeler gauge on the left and the right side of where the front bolts are. 

Then it was off by .009. so I redid the shims to .009. 

Then it was off by .012. so I redid the shims by .012. 

Then I needed to take off .009 from front, then I took off all the shims. 

Now, I'm off by .007...

You see where I'm going with this. Anyone have this mill and have some tips?


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## bill stupak (Oct 18, 2019)

start with a smaller gage, .002" or ,003". it doesn't take much to move it.


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## RobertB (Oct 18, 2019)

Wonderclam said:


> Now it's time to do The Z axis and it is off by .006
> 
> So I decide to shim it. I added .006 feeler gauge on the left and the right side of where the front bolts are.
> 
> ...



So if it was off more after you shimmed it the first time, why would you use even thicker shims, and then do the same thing a second time?


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## tweinke (Oct 18, 2019)

You need to remember that the Y axis is not directly in line with the spindle and that a small shim at the column will make a large change at the spindle.


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## higgite (Oct 19, 2019)

Which was lower when you started and then after each new set of shims… front of table or back of table?
Were all sets of shims in the same spot?
Where exactly was that spot relative to the bolts and the front or rear edge of the casting?
Pictures of the shim locations would help us see what you see.

Tom


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## Wonderclam (Oct 19, 2019)

The back was lower by .006 at the beginning. When the front indicator was at .050, the rear one was around .043.

I'll take pictures and post them in a little bit


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## Wonderclam (Oct 19, 2019)

so this is where I've been adding the shims. and I add another shim of the same thickness on the same spot on the other side of the mill


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## RJSakowski (Oct 19, 2019)

The Pro Tram has a separation of 5" between the indicators so your original difference is .006"/5".  It looks like you would be about half that distance between the pivot point and your shim location at the base of your column so the required shim will be .006"/5" x 2.45" or .003".  From your description, it sounds like you shimmed the wrong end.  

One thing that you have to remember with your type of mill is that a loose column gib will cause head sag.  You should always lock the column when you are tramming.


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## Wonderclam (Oct 19, 2019)

Looks like the magic number was .004

got both axis to a hair under .001


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## Wonderclam (Oct 19, 2019)

Bah, it's off tram again after a little bit of work. Not sure what happened, everything was as tight as can be. Very discouraging.


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## Wonderclam (Oct 20, 2019)

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


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## RJSakowski (Oct 20, 2019)

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


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.


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## RJSakowski (Oct 20, 2019)

Here is a good video on tramming issues.


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## Wonderclam (Oct 20, 2019)

RJSakowski said:


> Here is a good video on tramming issues.



I want to try that, but hat seems like a very daunting task, especially for a new machine hobbyist. Too many things can go wrong.


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## bakrch (Oct 20, 2019)

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.


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## Wonderclam (Oct 20, 2019)

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.



By Y, you mean X? and Z you mean the nod?


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## bakrch (Oct 20, 2019)

Wonderclam said:


> By Y, you mean X? and Z you mean the nod?


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.


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## RJSakowski (Oct 20, 2019)

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.


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## Wonderclam (Oct 20, 2019)

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.


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## matthewsx (Oct 20, 2019)

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.





__





						www.CarrollSmith.com -- NUTS, BOLTS, FASTENERS, and PLUMBING HANDBOOK
					





					www.carrollsmith.com
				




You will be glad you read it.


Cheers,

John


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## Wonderclam (Oct 20, 2019)

Can you guys help me find the bolts I need? I'm looking through Grainger and McMaster and I'm having problems navigating and finding the correct ones.

Also, was wondering how much torque is too much. I have one of those extendable 3/8" ratchets and that's what I used to tighten it down.

I was also thinking of maybe repairing the damaged threads on the bolt by TIG welding using stainless filler rod, then turning it down to size, and re-thread with a die


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## matthewsx (Oct 20, 2019)

Precision Matthews should be able to give you the size bolts you need, you'll probably have to contact them for that spring anyway. And, the reason I suggested Fastenal or McMaster is that they actually have knowledgeable folks there who can help you navigate their catalogs. I know they are daunting, especially when you're searching online but as soon as you get the size and length and thread pitch you can give them a call and they will hook you up.

As for torque that's another question for the folks at PM. Buy a decent quality torque wrench, or get one from Harbor Freight if you're on a budget, it will be money well spent.

Welding a bolt with any kind of filler is unlikely to provide satisfactory results. If the fastener is hardened in any way you'll anneal it (make it softer), the materials may not be compatible with each other, and cutting new threads is going to be a job for a lathe or thread forming die, both of which cost more than just replacing the fastener not to mention the time you will waste doing it. 

Stainless is probably not the material for this job, it has high strength but is usually more brittle which may not be desirable in this application. Usually stainless fasteners are needed only where rust or corrosion are a problem like outdoors or on a boat. 

Read Carroll Smiths books if you can, he writes in a very easy to understand way and the knowledge he shares is useful way beyond race cars. Particularly "Engineer to Win" has tons of information on materials and how to build structures that will hold up under high loads.


Cheers,

John


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## Wonderclam (Oct 20, 2019)

I might forego replacing the T bolts altogether. The threads don't look so bad, it's more one of the nuts that is chewed up

Another option I just thought of is to turn some high grade bolts down to size on the lathe and mill the rest for the T slot head.

I got some large grade 8 bolts that might work....

Maybe even make some nuts out of these large bolts. I'm thinking a "longer" nut would be harder to strip since there's more threads to bear the burden of tightening.


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## RJSakowski (Oct 21, 2019)

Wonderclam said:


> I might forego replacing the T bolts altogether. The threads don't look so bad, it's more one of the nuts that is chewed up
> 
> Another option I just thought of is to turn some high grade bolts down to size on the lathe and mill the rest for the T slot head.
> 
> ...


For high strength nuts.  Grade 12 is strongest.








						McMaster-Carr
					

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.




					www.mcmaster.com


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## RobertB (Oct 21, 2019)

matthewsx said:


> 8.8 is a high strength metric fastener spec.



8.8 is approximately the same strength as an sae grade 5, a 10.9 is about the same as a grade 8.

It will vary by application, but a 10mm 8.8 should be torqued to about 55nm/40 ft-lbs.


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## matthewsx (Oct 21, 2019)

RobertB said:


> 8.8 is approximately the same strength as an sae grade 5, a 10.9 is about the same as a grade 8.
> 
> It will vary by application, but a 10mm 8.8 should be torqued to about 55nm/40 ft-lbs.



8.8 is 800 MPa minimum tensile strength which converts to 116030.190405776 psi, grade 5 is 120,000 psi so you are correct they have roughly equivalent specs which are fairly high strength. Provided the fastener in question comes from a reputable supplier it is most likely sufficient for the application and far better than the unmarked fasteners I've seen installed on many Chinese tools. I've trusted 8.8 fasteners to hold together the racing karts I built for my customers as well as in many other applications.

However the key thing I was trying to get across is this.



matthewsx said:


> 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.



and



> 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.



I'm fairly sure that PM can give the OP information on the fastener in question, and the torque spec. The challenge is that unscrupulous parts suppliers could possibly introduce counterfeit fasteners into the supply chain. I'm not trying to say this is the case here, just that when replacing fasteners it's worthwhile to go with known suppliers rather than whatever is cheapest on Amazon.

Also it's worth noting that using a higher tensile strength fastener that what is specified can cause it's own problems. There are many applications where it's preferable to have the fastener deform rather than snap off. Choosing fasteners, like selecting any material is a trade-off between hardness, toughness and strength.

Here's an info-graphic about it.





Getting these trade-offs correct is where engineering comes into play. I'm not an engineer but I was raised by one and I'll always remember as a kid crossing a bridge with my dad while cars were driving across it. I was concerned by the fact the bridge was moving under my feet and told him so. He said "son, if it doesn't flex it will break". 
I miss that man....

Cheers,

John


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## RobertB (Oct 21, 2019)

matthewsx said:


> Provided the fastener in question comes from a reputable supplier it is most likely sufficient for the application and far better than the unmarked fasteners I've seen installed on many Chinese tools.



You mean like those unmarked fasteners that come with wrenches that are 3" long and stamped out sheet metal to assemble them with because any decent wrench will twist the heads off?


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## matthewsx (Oct 21, 2019)

RobertB said:


> You mean like those unmarked fasteners that come with wrenches that are 3" long and stamped out sheet metal to assemble them with because any decent wrench will twist the heads off?



Yep, those ones for sure


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## Wonderclam (Oct 21, 2019)

Turns out the bolts weren't damaged. The nuts were the ones that stripped. Bought 3 new stainless nuts and tightened the mill head as much as I can, thinking it would strip the bolts. I gave it all my strength, but could not strip them. I guess they're fine now.


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## matthewsx (Oct 21, 2019)

Wonderclam said:


> Turns out the bolts weren't damaged. The nuts were the ones that stripped. Bought 3 new stainless nuts and tightened the mill head as much as I can, thinking it would strip the bolts. I gave it all my strength, but could not strip them. I guess they're fine now.



So, you used the Armstrong torque wrench?


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## Wonderclam (Oct 21, 2019)

I thought for sure I'd strip the bolts considering how much force I was putting into it. I sure hope it will KEEP the tram now. I got both axis to around a thou


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## RobertB (Oct 22, 2019)

Besides breaking or stripping fasteners, one of the reasons they should be torqued to manufactures specs is to prevent damage or distortion to the parts being held together. On many things damage can occur at far less torque than the fastener is capable of handling.


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## Firstgear (Oct 26, 2019)

I would have gone with Grade 8 nuts and as well as 10.9 socket head cap screws....I wouldn't worry about issues with those anymore and you can crank on them without fear of breaking or stripping....but thats me....


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## Firstgear (Oct 26, 2019)

you might ask PM what torque settings are suggested for those fasteners....


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## coffmajt (Oct 26, 2019)

The epoxy for trimming that has been mentioned is available with a compatible solution that you can brush on any surface that you don't want the epoxy to stick to, such as bolts or flange surfaces.  With this, if you screw up the first attempt at least you haven't done permanent damage to the mill


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