Tom Senior M1 Mill Runout

Hi all

I’m hoping one of you fine people can assist with an issue I’ve been having with my Tom Senior M1 milling machine. I bought this mill several years ago and since acquiring it I’ve noticed the vertical attachment (knucklehead) shaft has significant runout, to the point you can see the endmill wobble/precession.

I’ve measured the runout within the internal taper and it reads approx. 1 thou. I then secure the collect chuck and take a reading within the bore of the collet holder. This measures approx. 2.5 thou. Measuring the runout with an endmill in situ is even worse. Despite testing the runout only half an inch from the internal bore of the collet holder the runout at the proximal end of the endmill is 6 thou!!

I then changed the collet chuck for a drill chuck and tested the runout on a round steel bar of ¼” diameter approx. ½” from the mouth of the drill chuck. This read 4 thou runout.

I don’t need the mill to be really accurate but I would hope I could achieve a total runout of no more than 3 thou.

Has anybody any suggestions on how I can improve this? I’ve already replaced the bearings within the knucklehead and cleaned the tapers/collets.

I was thinking of regrinding the internal taper of the knucklehead shaft however I doubt I would achieve much better than 1 thou runout which it is presently. Also I find it odd that it can be 2.5 thou runout at the internal bore of the collect chuck and yet 6 thou runout only ½” further away on the proximal end (close to the collect chuck) of the endmill.

Many thanks for reading this long post!

Best wishes

Luke

By your own figures the error is in the collet chuck/collets & drill chuck. Thats the short answer, you may want to buy a decent quality collet chuck if such a thing exists etc but that may be costly.

Tony

Edited By Tony Pratt 1 on 11/05/2020 19:25:05

Thanks for replying so quickly Tony!

Is it pretty normal/acceptable to have 1 thou runout in the internal taper of the spindle then?

I thought the same re: the chuck!

Thanks

That original 0.001" runout is being amplified by the poor attachments fitted to it. The error in the spindle taper is not that bad in itself, especially for home use.

If you reduced the taper runout to zero, the overall runout would only improve by 0.001".

Edited By old mart on 11/05/2020 20:43:37

I have just been tramming the head on my Tom Senior light vertical. Last night I spent ages. I clocked the MT2 taper which was fine. I inserted a Shaft in to a ER25 collet chuck. It was miles out. Same with a Diamond brand import chuck. Same with a Jacobs chuck. I also found my Clarkson to be a bit out. I ended up trying a cheap Chinese 27mm Arbor bought for a facemill. That was bang on with no run out at any point.

The side the underface were all perfect. I used this to hold a swing bar for the DTI . It just shows that a lot of gear is not perfect

I would at least expected a Jacobs chuck to be true. Forgot also tried a Albright keyless chuck too. I kept thinking the piece held in the chuck was out , but after trying various new dormer drill & new mill cutters. It was definitely all the accessories that were not as good as expected. So Tony Pratt 1 probably correct.

Steve.

You must have missed this one Stevie but good to know the Chinese tooling was the best of all that you have.

Another thing I had not taken into account ,Tony is that most of my stuff is used. How much of a hard life they have had , who knows. I guess it does not take much to knock a MT2 out of line.

Steve.

Yes Jason I was pleasantly surprised how good the Asian arbor was. It was a 27mm one I bought. I was going to move it on because it does not fit the cutters I bought, they are 22mm. But I will keep this for the mill setup for the future. I have seen that video before. Just to buy one of those induction heating machines would see my bank manager have a fit.

Steve.

Presumably the induction heater doesn’t heat tungsten carbide too effectively (for removal) or I expect the differences in expansivity are enough to free the grip.🙂

Mind you, dipping in liquid nitrogen might be better for fitting it in, as it is used in such fine tolerance applications?

Another suspect is how and what was measured. For example, I'd measure the run-out of something held by the Jacobs chuck, not the chuck itself, and that something needs to be a known precision round item itself. (Maybe that's what you did?)

However, a chuck only has to be accurate internally to position the drill in line with the spindle axis: it doesn't have to be externally accurate. Quite often chucks are internally and externally coaxial because of the way they're made, but it's not guaranteed! Any hoo, it doesn't matter how much the outside of a chuck wobbles.

Be good if some kind expert did a master-class on precision measurement for us. It's full of pitfalls, really easy to get wrong. One clue to faulty technique is getting contradictory measurements from the same set-up, which Luke might be experiencing. Maybe some of your results are misleading too - the accessories are actually OK.

When measurements get down to a thou or less tiny errors in technique intrude seriously. How the DTI or micrometer was held, choice of reference points, the geometry of the object and many other factors matter. In the tenths region, temperature makes an observable difference, or at least it should do. Remember a chap explaining temperature didn't interfere with his micrometer readings when a quick calculation showed temperature should have made a visible difference. He was probably subconsciously torquing the instrument to get the exact reading expected, not letting it stop on the ratchet for the true, slightly off, answer.

I'd love to set up a trial at an Exhibition were chaps measured a number of unknown slips with a few different micrometers, some calibrated, others not. The slips would be finished to non-standard sizes. I guess quite a few would make 9.99mm read 10.00, and there would be a scatter of results around an odd dimension like 14.385mm. I find it quite hard to work a micrometer truthfully and reliably, especially on rods. Be really good to learn how to do it properly!

Dave

If your Jacobs chuck is on a MT2 arbor, you may be able to improve its running. They are normally fitted to the arbor with a short taper and it could be separated and repositioned. The easy way to do this is to open the jaws and drill a 5/16" hole through the chuck body into the small cavity where the arbor taper fits. Then with a punch and supporting the rear of the chuck body, you can remove the arbor. Before separating the parts, mark both so you can fit them back together at 180 degrees from the original position. Make sure both halves of the taper are clean, fit them together, hold the chuck body in one hand and give the end of the arbor a smart whack with a copper hammer. If luck is with you, the runout will be a bit less.

Not with my skills. It can stay out.

Steve.