Mill spindle runout

[Steve355Participant @steve355]

Thanks to everybody who has taken the time to post and try to help me solve my problem.

Yesterday I acquired a new 0.0001 DTI gauge, and I thought I would redo the measurements with that. So I cleaned up everything, got rid of the mag chuck, and used a proper M&W surface gauge. Most frustratingly, I got completely different results. Luckily, in the right direction. What I learned was:

According to the new set up, the bearings on the spindle are within a reasonable tolerance
The MT2 test bar also seem to be giving reasonable and consistent readings along its length

Lessons:

1) Tenths are really, really small, and the slightest knock or piece of dirt, or burr, will make a significant difference to the readings, as it should.

2) It’s incredibly important to turn the spindle in the V blocks very gently and carefully

3) When a large, rapid jump occurs on the DTI dial, it is probably not due to a wear situation, more likely due to some manual or physical anomaly with the set up

4) just because a measurement shows up in a particular area of the test piece, does not mean that that area is the source of the measurement anomaly. The source of the anomaly may well be elsewhere (for example at the other end of the spindle)

5) in my case, the shoulder between the spindle shaft and the nose was not machined to a completely sharp right angle. I believe that this pressing up against the V block was causing a lot of the anomalous measurement.

So with everything clean and carefully deburred with emery paper, and the shoulder of the nose of the spindle away from the V block, I am getting much better results. Here is a New Video showing the new measurements.

 

After everybody coming up with sage advice on remaking the spindle, I am hoping that in fact it is acceptable. Opinions on the video would be welcome. To be honest I’m feeling pretty stupid at the moment! But I guess that’s why I posted it in the beginners forum, working at tenths is not easy, and obviously requires a lot of experience, and I am definitely a beginner at it.

I also mentioned before that once any preload is put on the bearings with the preload nut, the bearing will not turn easily. What I have discovered, is that that is in the horizontal position only. When I hold the quill in a vertical position, the bearings all run freely. However, in the video I have tried to illustrate a tiny amount of play that seems to exist, I am not sure whether this is play in the upper race bearing, or whether it is between the race bearing and the quill. The lower race bearing is a very firm fit in the quote and requires quite a lot of effort to get it out. The upper bearing on the other hand, is an easy push fit, and there may well be a tiny amount of play there.

Thanks again for all the help everybody. Any further comments on what I should do next would be very welcome. It’s a journey!

Steve

 

 

 

Edited By Steve355 on 14/09/2022 09:51:35

[old martParticipant @oldmart]

Your latest figures are excellent, within 0.001" tir. That will be plenty good enough for home use. If the cutter shanks end up more than that, it may be possible to find the sweet spot between the spindle and collet holder by trying different positions and the one that gives the minimum runout can have alignment marks on the tooholder and spindle end. When you repack the washed bearings with lithium grease, leave at least 50% air space between the spindle and quill bore.

 The bearing preload is best adjusted until the spindle gets just warm after running fast for about 15 minutes, slacken the preload very slightly if it feels hot.

Edited By old mart on 14/09/2022 20:04:04

[not done it yetParticipant @notdoneityet]

The upper bearing on the other hand, is an easy push fit, and there may well be a tiny amount of play there.

If it is actually able to move, use of loctie ‘bearing fit’ grade would stabilise the bearing within its seating pocket.

[old martParticipant @oldmart]

The upper bearing in a two bearing mill spindle has to be able to move to allow the preload to be adjusted.

[Neil LickfoldParticipant @neillickfold44316]

Now that you have the spindle cartridge sorted out, how much clearance is between the spindle and the bore that it runs in.? In my case it was around 0.07mm of clearance. I got the outside of the spindle flash chromed and lapped the OD down , hindsight I should have ground it. The upper section was not true to the lower section so it needed a small amount of honing to get it corrected. Now the spindle runs true better than 0.01mm over its 100mm stroke. So ai am very happy with it. It's no Bridgeport but is very repeatable. I am still getting it sorted for the shims and levelling to get it as best I can to the table run out. The mill I am using has a rise and fall table, with some irregularities in the table assembly. But is very repeatable when wound up, and locked or unlocked, is not changing the height of the table. Mine has a tapered bearing on the bottom of the spindle and a angular contact for the top bearing. Some replace the top angular contact with taper bearings, while others recommend replacing the bottom taper roller with a higher precision angular contact bearing. To get better precision from the spindle, the bearing housings need to be as round as the tolerance that you are trying to get the spindle to run to. So if you are looing for roundness from the spindle of 5um 0.005mm, the spindle bore in general will need to be round to 0.0025mm and the same with the spindle shaft as well. It does not take long and trying to get things really correct become a serious amount of work to achieve , along with the price of the bearings etc. I have added the extra spindle cartridge bearing support on the bottom of the casting as well. It did not change the linear runout of the quill, but when it locks in place using the flexure clamp, the quill movement at the end of its travel is less than 0.01mm , again, I am very happy with that.

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