VMC Mill spindle runout

[LathejackParticipant @lathejack]

A useful diagram of the milling head from John Purdy, looks impressive with five bearings supporting the spindle. It does appear to be a diagram of the slightly larger turret mill, that uses a quill of the same diameter, about 86mm I think, for its full length.

The VMC mills such as the Warco have a 75mm diameter quill that increases to 100mm diameter at the bottom, and the Myford VMC quill looks similar to this although the head casting and depth stop are different.

I've just had another closer look at my VMC quill through the depth stop slot in the front of the head casting. It looks to have one castelated nut sat on a tab washer above the top bearing to secure the spindle.

 I have owned this mill for about 24 years and it is a long time ago when I removed the quill. I didn't remove the spindle but i think it uses two bearings in the bottom 100mm diameter of the quill, but I am not sure if there are two in the top or just one. They are not taper roller bearings, they are ball bearings of some type and I am not sure if they are designed to take preload or not.

Edited By Lathejack on 14/11/2022 10:39:18

Edited By Lathejack on 14/11/2022 10:46:28

[John PurdyParticipant @johnpurdy78347]

Further to my last and to elaborate on Lathejack's post my quill is a constant 80 mm in diameter. The top two bearings supporting the pulley are 6208 radial ball bearings. The spindle runs in two 6206 radial ball bearings at the top and two 7207B annular contact bearings at the bottom preloaded by the ring "M108" in the diagram. Although the diagram and parts list shows three 6007 radial ball bearings at the bottom, when I disassembled the spindle I found that the design had been changed to the two annular contact bearings. You will see that I have hatched out the top of thee bearings at the bottom of the spindle and amended the parts list.

John

Edited By John Purdy on 14/11/2022 18:14:40

[John DParticipant @johnd]

Thank you all for your further replies. I have now managed to strip down the quill and spindle which was indeed very straight forward. Placing the spindle between centres on the lathe I am getting in the range of .0075-.01mm runout in the centre. I am getting the same when testing with it on two vee blocks. (Supporting it on the lathe on a centre in the spline and and on its bearing on the other I was getting pretty much no run out in the taper.). I have therefore concluded that it is indeed very slightly banana shaped.

Spindle services prices were reasonable for a simple taper regrind but climbed to well over 1k if doing anything involving bearings too.

Any thoughts on straightening this fairly small amount without machining would be welcome. New bearings are on order.

[Mike PooleParticipant @mikepoole82104]

It may be worth a call to Warco to enquire the availability and price of a new spindle. Our maintenance shop had some magicians at straightening shafts that had been bent, it may be worth a try if you have access to a press but probably not a job to learn on.

Mike

[Tony Pratt 1Participant @tonypratt1]

You need to support the appropriate bearings in vee blocks and rotate the spindle checking runout to get an idea of what is going on, be very careful how you check things.

Tony

Edited By Tony Pratt 1 on 15/11/2022 19:45:59

[LathejackParticipant @lathejack]

John D.

The quill assembly on your Myford VMC is a very similar design to the quill on my later type Warco VMC. Now you have dismantled it, just out of interest, what type of bearings does it have? Does it have two bearings in the bottom housing of the quill, and how many in the top?

The rather poor manual that came with my Warco VMC claimed that it had two bearings in the bottom, if I remember correctly, but the manuals are not always accurate.

[John DParticipant @johnd]

Hi Lathejack

starting from the bottom up:

At the bottom end of the quill

1 x 6207zz (confirmed on removed bearing)

1 x 2907 thrust (from myford manual)

 

at the top of the quill

1x 6206zz (confirmed on removed bearing)

 

and then, I think, under the pulley

2x 6009zz

 

Edited By John D on 15/11/2022 20:57:55

[John DParticipant @johnd]

I don’t have access to a press but think that may be my best option. I just need to find someone with a press near me (Herts/Bucks).

Tony, you make a good point about how I measure. How should one get bearings on and off a shaft without damaging things? I could heat the bearings or chill the shaft I guess.

Edited By John D on 15/11/2022 21:13:53

[Tony Pratt 1Participant @tonypratt1]

John, you are now talking about less than .01mm runout?

Tony

[JasonBModerator @jasonb]

Not even sure if the OD in the middle of the shaft is something you can trust for any measurement. Looking at the drawing above it could be possible that the middle is not finished to the same standard as the two diameters that the bearings fit on.

Also can't see how 0.01mm deviation in the middle equates to 0.035 at the socket end if it is just a bend particularly as the bearings are placed towards the ends.

[Tony Pratt 1Participant @tonypratt1]

Posted by John D on 15/11/2022 21:12:55:

I don’t have access to a press but think that may be my best option. I just need to find someone with a press near me (Herts/Bucks).

Tony, you make a good point about how I measure. How should one get bearings on and off a shaft without damaging things? I could heat the bearings or chill the shaft I guess.

Edited By John D on 15/11/2022 21:13:53

I think using a press on your spindle is about the worse thing you could do, you quote 'I am getting in the range of .0075-.01mm runout in the centre', I'm not really sure of your checking method but that is damm good on a maybe unimportant diameter as per Jason B. Just wait for new bearings and rotate the spindle in them with the installed bearings on vee blocks, you can then check the R8 taper.

Tony

[Graham MeekParticipant @grahammeek88282]

The critical items on the shaft are the bearing locations, or registers and the R8 socket. The relationship of these items is what matters.

Checking between centers on the central portion between the bearing registers proves nothing.

To check this properly, place the bearing registers on vee blocks, (you will need to pack one vee block due to the difference in diameters), and clock the R8 taper off these. An alternative would be to mount in the lathe using a fixed steady on the front bearing journal. The splined end held in a 4 jaw is then adjusted to get the other bearing register running true. Once this is done the R8 taper can be clocked.

I would also be inclined to check for a cracked spindle at the cone end. Over tightening of the R8 collets can cause this to happen. Especially if the hardening process on the spindle nose has not been carried out correctly.

Regards

Gray,

[HopperParticipant @hopper]

A big +1 on what Graham Meek said above ^^^^^^

Only the bearing register surfaces and the R8 taper surface would usually be precision finished at the factory, probably ground. The area in the middle of the spindle could well have been left "rough machined" and not precision ground because is does not contact anything, It just sits there in space. So runout there is ok.

Graham's very handy suggestion of setting the spindle up in the four jaw and fixed steady so that both the bearing register surfaces are running dead dead true, then clock the taper is a much more stable setup than trying to rotate the spindle on V blocks that are not bolted down and clock the taper at the same time.

Then atfer this above test has shown the spindle is (hopefully) running true, when you get the new bearings and install them, I would set it up similarly with one bearing held in the chuck and the other in the fixed steady and then rotate the spindle and clock the R8 taper. It should run dead true if all is well.

Installing the new bearings is usually done using mild heat to expand them so they slip easily onto the spindle. Heating them up in a tin of oil over a flame is the traditional way. An electric heat gun can do the job too, with care. If you do have to gently tap the bearings onto the spindle, support spindle on block of wood and use a tube etc so you are tapping only on the inner beraing race and not transfering shock through the balls.

I would then do a final test with the spindle and bearings installed in the quill and lay the quill down or clamp it down to something or hold it in the four jaw and fixed steady again etc and clock the taper as the spindle turns in its bearings in situ. If runout mysteriously shows up at this stage, it must be due to bearing installation not being quite right somehow. Very unlikely though. But best to check anyway.

Definitely leave the press alone at this early stage!

[Andy_GParticipant @andy_g]

Posted by John D on 15/11/2022 21:12:55:

How should one get bearings on and off a shaft without damaging things?

This video on spindle rebuilding might be of interest:

[Graham MeekParticipant @grahammeek88282]

One thing I forgot to mention in my above post was that there are two diameters to check with an R8 taper not just the cone, or tapered part.

Should the cone be running true and the inner register be running out then this is down to one of two things.

a) The R8 register was never machined on the true centreline of the spindle.

b) There is a bend in the shaft.

This latter condition would show up using a good clock, (0.002 mm or better) and the part set-up in precision Vee blocks as a run across the bearing register. This run would be along the spindle centreline and the check would only be performed on a static shaft.

Rotating the shaft through 180 degrees should show this defect up but in the opposite sense, (Think Banana shape).

regards

Gray,

[John DParticipant @johnd]

Some good news. I think I have now reduced runout to a workable level.

I cleaned everything, and ordered new bearings. When testing with various methods and setups I was clocking run out at .005mm on the bench. Fitting the lower bearing to the shaft was difficult. Even having heated the bearing up to 80 degrees C it was still difficult getting it onto the shaft. I drifted it on and it took more effort than i would have liked (from the point of view of risking damage somewhere). I used SKF bearings other than for the thrust bearing where I used NSK as this was readily available. The thrust bearing was subtly different in that the one of the 'washers' was an tight fit on the shaft whereas the other just slipped on. I put the tighter one in the lower position (i.e against the face of the lower bearing) as I assumed that this one should move with the shaft whereas the other contacts the step in the quill.

I tightened the nut the at the top of the quill so is to created just the slightest amount of resistance when turning the shaft by hand in the quill. I then backed it off and re tightened it once again slightly less to again just the start of perceptible resistance. Is that correct? How would i know if it was too loose or tight?

All done I am now getting .01mm runout measured at various points on the lower taper. I don't have a long enough knob piece for my indicator to measure the upper surface on the R8 at this stage. Next step is to use a collet with a ground bar and measure 200mm down from the nose and see how things are looking – but I am really pleased at this stage.

Doing my time again I would have heated the bearing for longer (in the oven) to more like 90 degrees C before fitting to see if that reduced the problems fitting the bearing to the shaft and therefore reduced the chances of introducing some runout at that stage by rough handling of the bearing while drifting it on. I'm not sure its worth stripping again and buying new bearings to find out.

[HopperParticipant @hopper]

That's a pretty good result. Reduced the original .035mm runout to .01mm. Not perfect but should work ok for home hobby use.

I would not worry too much about runout 200mm down from the nose. How many milling cutters that long will you be running? Try a piece of ground bar about as long as a typical milling cutter for a more useful idea of what to expect under cutting conditions.

You could heat bearings up a bit more than that for installation, as long as they have steel or brass cages etc and not the plastic ones. 120C would be ok in most cases. And you can freeze the spindle overnight too. But probably would not make a great difference in fit from 80C on such a small diameter.

 

Edited By Hopper on 21/11/2022 03:48:00

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