Myford spindle alignment

Hi folks, I noticed my Super 7 chucks were visibly not seating properly against the shoulder on the spindle nose. Fearing a bent spindle, I clocked the shoulder and the parallel portion of the spindle but there was no measurable run out. Clocking a lathe test bar also showed nothing amiss with the spindle taper. I clocked the face of my 3 and 4 jaws and the faceplate and this showed a consistent run out at the same position relative to the spindle (the outside edge of the faceplate gave a TIR of 0.2mm). My threaded ER32 chuck gave the same results.

I have scraped and the male and female threads and can't find any muck in there, but the 4 jaw and face plate are very tight screwing onto the spindle; the ER32 chuck is free.

I suspect something wrong with the spindle thread, but can see nothing obvious. Do I dare run a die or threading tool along it? I could also pass a tap through the chuck threads to clean them up - is this wise?

I would be most grateful for any thoughts on what might be wrong and what I might do about it. I have some work coming up that requires a true running 4 jaw and faceplate. Many thanks for reading this!

Alex.

As Gray stated: the thread does nothing other than pull the chuck onto the register, however, if the thread feels tight it is likely you have got swarf into the threads, and under these conditions the thread certainly can throw the chuck(s) out of alignement. It is not always easy to see the swarf - if it was a broad ribbon that got trapped it is almost like electro-plating in there! If all your chucks now seem tight then it's likely the swarf has attached itself to the spindle thread rather than inside the chuck.

I would be very wary of using a die on the spindle (and a tap in the chuck for that matter, but I don't think the problem lies there) unless as a last resort. Try using a pointed tool - scriber or something - and work all around from start to end.

In future, if there is any hint of the chuck feeling tight as it's screwed on then stop and remove it. A short session with an old toothbrush will work wonders. Once you have forced the chuck on it becomes much more difficult to get off (yes, I learned the hard way on this one).

Hi
I aquired an old rusty S7 the front face of the register was pitted / rusty . after setting the spindle
Using a tipped tool i faced it nice and true about 4 thou off . I coud not touch the diameter of the register as Gray says thats the locating part not the thread.
Nobby

Hello Alex,

Another possibility might be a shallow bruise on the chamfered mouth ot the chuck register if this trouble was confined to only one item. But as it appears to be across the board then I go with the others on the thinking of fine embedded swarf now incorporated with the spindle thread.

A suede brush with brass wires might shift it, a little kinder to use than a standard wire brush. I would use taps on chucks only with reservation, a threading nut on the spindle would be best avoided I think.

As Chris says, don't force it on, big mistake. A little moly grease on the spindle thread might help ease things a trifle but look out for it breaking down and allowing 'pick up' in metal to metal contact, leading to a seize.. It it feels tight with moly grease, undo it pronto. The grip on the thread should NOT be that tight, the register does the alignment.

I hope you get it sorted out satifactorily

Brian.

Gents, many thanks for the suggestions. I will have a closer look at the threads for embedded swarf and other bruising/damage. I will report back!

Alex, just for peace of mind you cold try running an indicator one the register faces. A 'blip' on the indicator might detect a bruise you can't see.

Neil

All - just following up on the above for those who are interested! I spent the evening examining the spindle thread following the suggestions above. I couldn't see anything wrong, but gave the thread plus those in the chucks a good brass-wire brushing - no improvement. I finally decided to fit a threading tool to the tool post and run this up against the spindle thread with the appropriate gearbox setting (rotating spindle by hand). This approach highlighted a significant bruise on the thread, which I 'screwcut' away. The result of this was that the jamming chucks and face plate now screwed on freely, hence this must have been the problem. How it happened, I dread to think! Tests with the DTI showed a much improved, but not perfect, run out.

I'm not sure I would have found this without your help, so thank you!

Alex.

Hello Alex,

Thank you for the update, it is always heartening to have an explanation for puzzle like that.

I can see no reason now why negligible run out should not be possible. Stub Mandrel's advice above should show the way. If the register and shoulder are all as they should be, then the final move is to look again at the chuck and faceplate registers which might also be revealing after your 'rethreading', I would try marking surfaces with felt tip markers and run them together to see where any high spots exist..

Remember it is the register and shoulder together that does the location, the thread merely holds things together.

Regards

Brian