Spindle Runout Issues on PM-728VT

[qualitymachinetools]

So I think what they are saying is that:

1. The runout is probably within spec, but what you are measuring is coming from the difference in the test bar diameter and the bore diameter the Top of the spindle. (The top of the spindle dimension range is 24.125-24.145mm / .9498-.9506")
2. You had a problem with our drill chucks, which I know are a bit smaller, usually those measure around .947" - .948" at the top. R8 collets are usually .9485-.9498 when I have measured over the years.
3. They said to send you a new drawbar and try that first, if the drawbar is distorted it could be pushing it off to the side at the top of the bore there.
4. We will figure it out, it may not be what we / I thought at first, but we will get it worked out!

What is the diameter measurement of that test bar at the top of the R8?

 

[netmagi]

So I think what they are saying is that:

1. The runout is probably within spec, but what you are measuring is coming from the difference in the test bar diameter and the bore diameter the Top of the spindle. (The top of the spindle dimension range is 24.125-24.145mm / .9498-.9506")
2. You had a problem with our drill chucks, which I know are a bit smaller, usually those measure around .947" - .948" at the top. R8 collets are usually .9485-.9498 when I have measured over the years.
3. They said to send you a new drawbar and try that first, if the drawbar is distorted it could be pushing it off to the side at the top of the bore there.
4. We will figure it out, it may not be what we / I thought at first, but we will get it worked out!

What is the diameter measurement of that test bar at the top of the R8?

Also note the ring on the taper of the test bar (and bluing still visible in same location as the ring) that I referenced in my post from a few minutes ago on the taper angles, showing that the taper isn't seating past the spindle nose.

EDIT: converted to inches that's - .949

 

[netmagi]

So I think what they are saying is that:

1. The runout is probably within spec, but what you are measuring is coming from the difference in the test bar diameter and the bore diameter the Top of the spindle. (The top of the spindle dimension range is 24.125-24.145mm / .9498-.9506")
2. You had a problem with our drill chucks, which I know are a bit smaller, usually those measure around .947" - .948" at the top. R8 collets are usually .9485-.9498 when I have measured over the years.
3. They said to send you a new drawbar and try that first, if the drawbar is distorted it could be pushing it off to the side at the top of the bore there.
4. We will figure it out, it may not be what we / I thought at first, but we will get it worked out!

What is the diameter measurement of that test bar at the top of the R8?

First, I really appreciate your continued personal attention to this matter and commitment to resolve it. THANK YOU. This is why myself and so many other people keep coming back to the PM website to click 'buy' after looking at so many other vendors. You guys care and are willing to engage with your customers, which is everything to us 'hobbyist machinists'.

Previously, PM technical support suggested that I increase the size of the bore the factory is referencing in that diagram with a wooden dowel and some sandpaper, because that upper bore doesn't matter in the registration of the tooling. I agreed that it "shouldn't" matter in the registration of the tooling, but declined to do it because I do think that upper bore would at least 'limit' a tool moving under a really heavy cutting load that might unseat the taper. If I'm understanding correctly, the factory is suggesting that the upper bore 'is' responsible for tooling registration, even without any significant radial load on the tooling, only the small amount of radial loading from the drawbar (which is mostly pulling in the axial direction).

I'll break up how plausible I think that is into two instances:

Instance 1 - Full or at least 'good' taper contact

I disagree that a small radial load caused by the drawbar would cause tooling (or test bar) to not run true. I believe the axial force (pull) from the drawbar would keep the taper seated, resisting any smaller radial load from imperfect threads or a bent drawbar.

Instance 2 - 'Poor' taper contact (for ex., only contacting at the spindle nose, like mine is)

I agree that pretty much any radial load is going to cause tooling (or test bar) to have runout because it's just going to rock on the spindle nose until either the shank hits the bore at the top, or the top of the taper makes contact. In theory, if the shank and upper bore were a perfect fit, it would run true in testing, but runout under load since it could flex till it rocks into full contact with a wall of the taper.

 

[G-ManBart]

I can't help one bit, but I'm learning a lot from this thread!

 

[qualitymachinetools]

I care a lot, trust me, I want everything to be perfect, every time.

So we will assume that the spindle top bore of the R8 is at the Max tolerance, .9506"
And your measurement of .9486", max possible difference of .002"
Which assume they are centered, .001 on each side at the top from runout.

So if its pushed to one side up at the top, if you measure the runout of the test bar at equal length from the spindle face, about 4" down, it should be equal to what its pushed off center up top. (If that is what is happening)

If that was the case, no matter what the taper, or even if there was no taper, with that top bore holding it still, it should not be able to move more than the .001" off center.

I will ask what the taper spec is on those. I've seen a lot of different info. That is a good point if it only looks like its contacting at the end.

Thats assuming everything else is dead on, which it seems to be. But you need a long indicator to reach up inside of that spindle to get that internal bore.

Also - When they said to sand inside of that bore, that is to remove any burrs left if there are any, no to enlarge it. If they said to enlarge, thats not correct, but on some of the Chinese mills over the years we have had burrs left on the bottom edge of that top bore which the R8 fits fine at first, but then later on the burr sort of folds up from that ledge and tooling gets stuck or tight.

Some more things to check, take out the set screw key in the R8 so you can put the test bar in any way you want. Put it in where the key is first and record what you get, mark it, then flip it around 180 degrees and see if that repeats or if it changes.

You don't have to do any of that, we will have a spindle assy coming for you after its assembled and checked out so its an easy swap, but I am just curious. Once that gets to you and its all settled, I will also check it out here later on

 

[G-ManBart]

Also note the ring on the taper of the test bar (and bluing still visible in same location as the ring) that I referenced in my post from a few minutes ago on the taper angles, showing that the taper isn't seating past the spindle nose.

I re-read this entire thread this morning and your earlier post about the ring visible on the test bar, plus this one, is what stands out to me. I measured some of my R8 stuff (collets, face mill adapter, Albrecht drill chuck) and saw quite a bit of difference in diameter at the drawbar end. What I didn't notice was any of them having a ring where they are clearly making single-point contact like you're seeing.

If the taper of the spindle and taper of the tool/holder fit properly the drawbar end diameter really should be irrelevant once you add a reasonable amount of tension to the drawbar....the taper shouldn't be able to move. What you're seeing is simply a pivot point with a single point of contact. The fact that you tried other things like collet chucks and none of them fit differently than the test bar suggest the taper of the spindle is incorrect.

 

[higgite]

If it was covered earlier, I apologize for overlooking it, but has anyone measured the runout of the spindle taper itself? (See step 3 in pontiac428’s post #11) Or is that a moot point at this stage?

Tom

 

[WobblyHand]

It doesn't take much of a taper error to mess things up! Bought a taper adapter that looked ok, but the taper was (slightly) too steep. This meant it only seated at the very top of the taper, with a tiny contact ring, like the OP is mentioning. The taper adapter would slip and was not concentric under load. Fortunately it was the adapter and not the spindle taper. Good luck with getting this all sorted. PM will take care of you.

 

[ShagDog]

If it was covered earlier, I apologize for overlooking it, but has anyone measured the runout of the spindle taper itself? (See step 3 in pontiac428’s post #11) Or is that a moot point at this stage?

Tom

I have the same mill. I have measured my spindle taper (assuming reference is to lowest part of spindle), and mine looks to be less than .0001" runout.

 

[pontiac428]

This thread has been fascinating; I am sorry it came at the cost of time delays and frustration. I have learned a very important lesson about R8 tooling in general. I have R8 shank tooling from many origins. I have made the naive assumption that they were either close enough or, being a taper, were tolerant of variance. I intend to measure and blue my tooling to assess the fit and open my third eye to all of the inputs of variance.

It makes much sense to look for problems suspecting the cheaper part (the shank) and to trust the expensive part, at least initially. It follows the principle of parsimony that the correct solution is usually the simple one.