Spindle thread wont engage ml10...

I bought a myford backplate for proxxon chinese 4 jaw chuck last august and successfully machined it to fit. However trying the chuck and backplate now it is very tight and I cant get it to thread on any suggestions...

Well if it fitted ok once but does not fit now, there must be something on the thread preventing it screwing together. Most likely rust, dirt, swarf or a small dent or burr. Careful examination of both threads and cleaning up as appropriate should fix it.

Cleaning both threads with a clean tooth brush may improve matters.

If not, examine the threads for damage.

It should be pretty difficult to cross thread a 12 tpi thread (Assuming that the ML10 uses the same as the 7 Series.

Howard

This happens a lot on my lathe (an ml10 coincidentally).

The chuck has to be pretty well exactly aligned to screw on.

I put a squared blank in the tailstock, and gently hold this against the chuck jaws , then the chuck will screw on.

The blank is about 1" dia. I guess you could just use a flat bit of metal to the same effect.

Worth a try

John

That used to happen a lot on my Speed 10 (ML10 variant) too, but only with the 3-jaw chuck.

It was the register, not the thread, that was the problem - and it was necessary to present the chuck very concentrically to avoid it sticking and failing to engage. I just accepted this because it meant the concentricity of the chuck grip was preserved as well as it practically could be across chuck swaps.

The 4-jaw went on much more easily. I never measured it, but assumed there was a few thou more clearance in the register counterbore on the backplate, justifiable because you'd have to set up any workpiece manually anyway.

In the OP's situation, it may make sense to ease the counterbore a little.

Edited By Mick B1 on 11/04/2021 09:22:46

Or maybe just a chamfer on the edge of the register counterbore in the backplate would be enough to guide things in? Could be done with a three-sided scraper or three-sided file with the end ground to a sharp edge.

Great idea John, I think I have a tailstock drill pad that might work.

As others have said I will check the threads for swarf and perhaps chamfer the thread on the backplate.

I bought an ML10 in 1976 from Myford and used it with a three jaw chuck and in 79 I bought a 4 jaw from Myford that would not go on.They were most helpful and sent a gentleman who came and used a thread chaser to ease the spindle thread with a good result.The journey from Myford to us must be 35miles,I wonder if the new Myford would be so helpful.

Frank

bricky:

If I understand you correctly, the Myford engineer ran a tap through the backplate thread? Or did he use the chaser on the spindle itself?

The taps are available and I have found them useful for fine-tuning backplate threads.

You could bore 0.002" out of the register of the backplate without any bother, just check the running of the backplate and skim if necessary. There has to be some clearance to fit, but as already mentioned, make sure there is absolutely no trace of swarf in the mating parts first.

Edited By old mart on 11/04/2021 15:20:09

If it is the register that is tight be very careful about lubrication and not putting the hot chuck on the cold spindle or you will have a shrink fit. Rather than taking 'taking 2 thou off' it should be a case of very gentle application of fine sandpaper.