Spindle Runout Issues on PM-728VT

The first two are just radial bearings. The latter is an angular contact.
 
Gasp! 6005 and 6007 non-ABEC Chinese cartridge bearings? Those are $15 bearings retail, probably $5 each in bulk.

On a good day, you could probably replace all three (including the ABEC-5) with German precision replacements for $50 each if you comb ebay. Retail on any one of those with a clearance rating for precision machine use can go $150-$300 each or even more.

I see it like this, and it's not nice: PM gave you a slightly lower machine price by using those cheap bearings, and in the process, made the fatal assumption that you either wouldn't notice or wouldn't care. But you did, and now it gets interesting.
 
It would appear you have an easy upgrade to your mill by installing better bearings however I would be a little surprised if bearings could cause the amount of error you are seeing unless they are loose. Others may may have better information on this. It seems likely to me the taper is damaged or not machined correctly. Following is some more information from that book on how accurate spindles should be in general, how to test the fit of the taper and finally measuring runout. It seems likely there could be a whole batch of them that were machined incorrectly. perhaps you could measure the spindle on V blocks with test bar to confirm if its the bearings or spindle?


I am curious if the test bar you purchased is hollow, does it feel lighter than it should be for that diameter and length?

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All I have to say is WTF is going on here. I am ******, this spindle should be .0002. Let me check in to what is going on here and we will get back to you. Every single one of these is tested with a test bar just as you show and recorded. I hear nothing from people other than how they can not believe how good the specs on these are. I will dig that up and get this solved, I do not know what the heck is going on here but I will find out.
 
1. Inspect/test these machines before shipping out and provide a report (for ex. max runout @ 4" from spindle face = .001, tested .0007, etc.)

2. Provide what the tolerance should even be. I'm just assuming that I shouldn't have 3 thou of axial runout 4-5" from the spindle when checked with a precision ground test bar. Maybe it should be that bad. . . Who knows. To be fair, they did send another spindle to try when I raised the issue, but my question of "what should good look like", has gone un-answered. If good is .003 TIR @4-5" from the spindle face, then define it. I sure hope max tolerance is more like .001 at 4-5" on an ultra-precision machine, but who knows. Again, the tolerance is not defined.

Every one of these mills IS certainly tested, I will get that information for you once I get your serial number and dig that up (I have a guess but still not certain who you are, I will get that from the tech people)

I am so irritated right now that I was to scream at someone, but I just need to calm down and get to the cause of the problem and handle it. It is my reputation that is being messed around with here and I do not take that lightly. We advertise these the way we do because that is what they are and people have absolutely loved this machine over the years. And we have strict standards that are to be met, and this factory is very very trustworthy. But something happened with this one, and I have to figure out who let me down and get it handled.
 
As far as the bearings, I actually watched the video now and I spoke too soon. The bearings in there are correct, the bearings are listed in the manual and that is what was in the video. I thought you were saying there was no angular contact bearing. There is the angular contact at the bottom like there should be. That is the proper arrangement. At first look, I thought you said that all the bearings were plain ball bearings. There is no need to change any bearings, bearings have never been even the slightest issue and spindles have been designed like this for many years. But, I do have to get this spindle figured out and how that happened. I will stop reply now while I am frustrated and looking at things too quickly.
 
My Tormach PCNC770 came with test tolerances and results. The spindle runout was specified as .02 mm near the spindle face and .03 mm at 100 mm from the spindle face. It tested at .01 mm and .02 mm, respectively. Unfortunately, one of the spindle bearings failed prematurely so the spindle was replaced under warranty. Tormach replaces the entire spindle cartridge rather than a bearing replacement so I got a new spindle as well.

Since the cartridge had never been installed in a machine prior to my receipt, I don't believe it had been properly tested. This was evident in the fact that there were burrs from the balancing holes on the face of the spindle that prevented the TTS tooling to properly seat, giving rise to atrocious runout. My spindle has about .0008" TIR at the spindle face but about .003.1" TIR at 4".

This runout bothers me but I have been using the mill for the last decade in spite of it The only tools that I use with a 4" stickout from the spindle face are drills and reamers. Drills are by nature an imprecise tool and a reamer can flex enough to still align properly. A fix would be to re-machine the R8 socket in the spindle which could be a perilous undertakng and might actually make things worse.
 
qualitymachinetools said:
As far as the bearings, I actually watched the video now and I spoke too soon. The bearings in there are correct, the bearings are listed in the manual and that is what was in the video. I thought you were saying there was no angular contact bearing. There is the angular contact at the bottom like there should be. That is the proper arrangement. At first look, I thought you said that all the bearings were plain ball bearings. There is no need to change any bearings, bearings have never been even the slightest issue and spindles have been designed like this for many years. But, I do have to get this spindle figured out and how that happened. I will stop reply now while I am frustrated and looking at things too quickly.
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I agree. We ended up on a bit of a tangent with the bearings because there seemed to be some interest in understanding what was in there, but the radial runout, as delivered, at the bottom of the taper was only about a tenth. So, while the bearings might not be impressive, I also don't think they are the root cause, especially since I did check the spindle with v-blocks (first vid).
 
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