If "there is some unevenness and roughness when turned manually" and this is at a low preload, the bearings ar worn or damaged.

You should measure the runout at the inside of the spindle taper. If that is not possible, then on the outside of the chuck taper.

If you use a drill chuck (not a collet) than the runout of the drill chuck is probably more than the runout of the spindle.

When you say "took it to bits" was that just removing the spindle or stripping the spindle and cleaning the bearings?

If not a complete strip then that may be worth a try and at the same time inspect the bearings for damage if they look OK then regrease, adjust, run for a while and adjust again if needed and then take readings with the spindle in place.

While apart you can also see if the builder got a better surface finish where the bearings fit.

You should measure the runout at the inside of the spindle taper. If that is not possible, then on the outside of the chuck taper.

As per Huub, above, measure the taper runout. A commercial blank 2MT arbor would suffice, for this.

ONE OF THESE

Does the mill cut metal satisfactorily or has this fault been found by measuring?

I see measuring machines in the workshop as the second or third stage in a diagnostic process, never the first. After finding the machine doesn't cut as expected, measurement is a good way of isolating the fault, but only after trying more basic tests first. Unfortunately it's all too easy for amateurs to lead themselves up the garden path due to measurement errors. You can guess how I know! Trouble is accurate and reliable measurement is a difficult skill in itself. (Manufacturing is organised to check parts. In general they don't poke about with dials and micrometers as we have to.)

Huub commented: If "there is some unevenness and roughness when turned manually" and this is at a low preload, the bearings are worn or damaged. I agree.

Michael said: My ‘working hypothesis’ is that inherent runout in the spindle has abused the bearings. It's a good hypothesis that would account for the bearings premature demise, assuming of course that the mill wasn't worked hard during it's life.

Steve suggests himself: Unfortunately I think I have to conclude that when it was made, it was turned around, either in a chuck or between centres or something and wasn’t perfectly realigned. Quite likely – as we know, Model Engineers often do their best with limited equipment and skills. And some of us make mistakes, such as not using the technique needed to avoid introducing runout!

Hobby-end machines are what they are, so perhaps the root cause of this problem isn't worth fixing? I'm inclined to put up with minor faults until they stop me doing what I need to do. Assuming the mill was performing reasonably before runout was discovered, only because the machine is in bits, I'd fit new bearings and carry on. As a Dore-Westbury is likely to be at least 30 years old, it hasn't done too badly!

For most hobby purposes it's not necessary to own top-quality equipment in perfect condition. In my workshop tools are 'good enough' if they do what I need, and I don't fuss about their imperfections!

Dave

Edited By SillyOldDuffer on 09/09/2022 10:16:11

To prove if it is the bearings at fault rotate the spindle in a matched pair of vee blocks. The bearing registers resting on the vee block. If you get the same run-out it as was present in the assembled spindle and then it is not the bearings.

Also put a clock in the centre between the bearing registers and see if there is a high spot. Mark the high spot with a felt pen. Move either side to see if the readings are the same or less.

If the readings are the same magnitude then it will be safe to assume this portion is running out from manufacture.

If the readings either side are occuring at the same point but are less then the spindle may well be bent.

If the high spot in the centre is opposite the low point at the Spindle nose then this would confirm it.

Hope these notes help,

Regards

Gray,

Edited By Graham Meek on 09/09/2022 11:09:57

Point 1. I'm not sure magnetic mounting is the ideal for this test.

Point 2. Do you not just need to remachine the 2 Morse internal taper with the spindle running in it's own bearings? It has got to be spot on after that.

All that said, it's not terrible and I would say the machine is perfectly useable as it is.

regards Martin

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Boring or grinding would probably give a better chance of a good result.

… pleased to see that others have come to the same general conclusion

MichaelG.

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P.S. __ You might find inspiration, encouragement, or even lust … here:

http://anglo-swiss-tools.co.uk/gepy-centres-spindles/

[ start by understanding how it’s done properly … you can always work backwards from there ]

Edited By Michael Gilligan on 09/09/2022 12:29:13

Whilst it needs to end up as mt2 (probably) it doesn’t have to be mt2 whilst fixing it.

I would bore the spindle to a suitable cylindrical diameter (probably large end of mt2 ish)

Then loctite or shrink fit a plug in and finally bore and ream that using the spindles own bearings.

Probably worth replacing the bearings whilst your doing it – modern new bearings of reasonable quality are not expensive and are sufficiently accurate for the job.

Dave

A DTI is not an absolute measuring device. It is a comparator. A dial gauge actually provides a proper reading.

Bill,

It is my belief that the distinction is entirely artificial: Both instruments are more logically classed as Indicators; unless and until they are mounted in such a way that there is a Zero reference and the ‘system’ is calibrated.

Even then, the dial mechanism and the [likely] cosine error both serve to make them poor Gauges.

The use for which both were originally devised was that of a Comparator … a reference point is established, and the deviation from that is indicated rather than truly measured … The uncertainty can be high at any point other than a return to that reference.

Semantics make this a tricky concept to grasp, but that’s my best effort at this time in the morning !

MichaelG.

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NPL Good Practice Guide No. 11 is a useful essay on Uncertainty of Measurement

Downloadable here:

https://www.npl.co.uk/special-pages/guides/mgpg11.aspx?ext=.

Edited By Michael Gilligan on 11/09/2022 07:11:52