Myford spindle rectification or replacement

Diogenes II has spotted the bruise on the thread, it is on the flank of the first turn. I will try the marker tip.

Thanks for comments

Yes definitely something showing up on the thread as Diogenes II mentions.

Tony

Hello again, I have tried marking the threads on the spindle nose, and blueing the chuck registers, still feel that its a nose thread problem.

Does anyone know of any engineering firms able to inspect spindle and correct and issues with the thread if I send it to them.

I don't want to mess with this much, and risk irreparable damage!

Thanks

If the bruising is causing the chuck to run ot why not get a Whitworth form thread file and apply the 12 tpi portion to the bruise, until it has been removed.

This can be done with the mandrel in situ, and will avoid the problems likely to be caused by stripping the headstock and then reassembling.

If the bruise IS causing the run out, I would expect the chuck to become tight as the register tries to align the chuck against the misalignment caused by the bruise. Indeed it could even make it impossible to screw the chuck fully home.

Does this happen?

The alignment should be by the register, not the first thread, so it would probably not matter too much if it were entirely removed. The thread is the means of holding the chuck against the register faces, which minimise eccentricity and axial run out.

Do not expect any 3 jaw chuck to hold work absolutely concentric. A good one will show 0.005" (0.125 mm ) or less.

If a new 2MT runs out in the headstock two possible causes come to mind

1 ) Accuracy of the male taper to the register being clocked ( i e manufacturing defect ) Check between centres if there are centres bat both ends

2 ) Possible damage to the internal 2 MT taper. Cure? Gentle cleaning with a 2 MT reamer

Howard

Hi Peter, sanity check, I did this sort of thing for nigh on 50 years & also owned a Myford Super 7, I believe there is little wrong with your spindle, all the register DTI readings look good but maybe the thread is damaged, difficult for us to tell? I can't believe any engineering firm will be able to help you for less than the cost of a brand new spindle. I would suggest taking the advice of Howard Lewis above, a back plate should go on with little or no resistance to turning.

Tony

Thanks for your advice Howard and Tony; the newest and least used chucks, faceplate, backplate only become tighter for the last mm or so of tightening. Still can snug them easily down by hand.

Given the hourly rate I am paying for classic car work, Tony's comment re cost of checking the spindle sounds right - I messed up a fuel control system repair last year and had to send it back to the guys who rebuilt the car in the first place.

I had not heard of Thread Restoring Files, so will try this, and if there is no improvement, accept that this is the accuracy I will get from that lathe.

Regards

If a bruise shows on the thread as a shiny area, it is ok to dress it down locally with a little cheap half round diamond file, using the flat side. An ordinary file might not be hard enough if the spindle is heat treated. This 1 1/8" thread is plenty large enough to be unaffected by localised repairs.

+ another for the advice above - the tightness at the last turn makes sense if the damage is at the end of the spindle, it's probably only making it's presence felt as the register tries to seat and pull everything into line..

As noted, it's okay to dress the bruised area down even if you go very slightly below the level of the surrounding metal, a small localised 'dip' won't cause any problems as the untouched thread surfaces will support the chuck regardless.

Thread files are made in TPI and Metric pitches, about 8" or 10"long, square with 4 thread sizes at each end, 8 in total. They are very good for repairing threads in ordinary steels Etc .mine are made by sykes- pickavant. If as I believe the myford S7 has a hardened spindle then a thread file will be spoit the first time you use it ! I have trued many a duff thread using a good all hard hacksaw blade and it would work well in this application. All you have to do is follow the original thread. Noel.

Peter,

If you can clearly see and feel the bruise on the thread, a diamond needle file might help. I bought a set of different shapes and they are excellent.

I didn't look through all your clips but I did see a few that clocked the spindle. I thought it was running really well and not worth disturbing if the thread clean up works ok.

Hello again, quick update, after considering everyone's advice got a thread restoring file and a 1/2 round diamond file. Ran the thread restoring file over the spindle running slow in reverse backgear with lots of cutting oil mainly to make sure any trapped swarf was removed. Then worked at the suspected bruised area with the half round diamond file, cleaning threads, refitting the collet chucks, measuring runout and repeating. Definite improvement, Myford Collet chuck now consistently giving 10 micron/0.0004" runout on the taper,

The new Eccentric Engineering Collet chuck now runs onto the register all the way up to the shoulder with little resistance, (previously started to get tighter about 3mm from the shoulder) and is giving consistently 50 micron/0,002" runout.

There is actually nothing wrong with this chuck

It is worth quoting the following from Gary of Eccentric Engineering regarding its accuracy - I have his permission to do so on this forum.

The collet chucks were designed for work holding when using the Turnado rather than as a high precision collet chuck. We hope to get any runout to under a thou or two which is fine when making things with the Turnado System, but as you have experienced it will depend on the condition of the spindle thread and register which we have no control over. If the collet chuck is fitted to a spindle nose that is old and worn that is likely to add to any runout........It was never designed to be a high precision work holding device, more a convenient way to hold material out over the middle of the Turnado table and minimize catch points to protect fingers that are close to the work when hand turning.

So to sum up, very nearly there with sorting this issue, thanks to advice from forum members.

I am not chasing high precision; however its useful to know the accuracy of my lathe and its accessories so I can gauge how closely my work approaches what is possible and where errors lie.

Regards

Peter

Edited By Peter Turvey on 27/01/2021 18:26:23

A good result which saved you worry and possibly money. The runout you now have is well within expected norms.

Get ready to make swarf!