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Myford Super 7 Tail stock problem

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Simon Williams 307/05/2020 10:47:04
728 forum posts
90 photos

FWIW my take is that you have the symptoms of a piece of debris jammed in the cast iron thread, about 1-1/2 or 2 turns in. Brushing with a tooth brush won't shift it. Cast iron, being relatively soft, will be locally bruised allowing the fleck of debris to nestle in a crevice, jammed in place by trying to force the male over and past it.

Borrow a small mirror, go looking down the thread for a foreign object. It will be obvious because it will be a different colour to the adjacent cast iron, having been burnished by running the male thread up to it.

Once you've found the bit, it'll take some shifting. Think pointy something with a 90 deg bend in it. It'll be surprisingly reluctant to let go.

Don't go cutting or filing, you know it fitted before, it'll fit again but there is a mechanical obstruction.

Once you've got the fleck out of the surface of the thread, go looking for another!

Good luck

HTH Simon

John P07/05/2020 11:03:38
451 forum posts
268 photos


Hi Trevor

Looking at your photo's the 2nd one down of the external thread it looks to me as if the
first two threads have become a little rounded on the crests and in the 3rd photo
the thread looks a little deformed the first thread in at about the one o'clock position.

I took my 7 tailstock apart to have a look more clearly at this and noticed the the external
thread was very sharp with no lead in chamfer , if yours is the same it needs to be dressed
down ,i used a three edged diamond file this one was from Arc euro these are quite
good for this as they leave a clean polished edge.
In my photo you will see a thread cleaning tool that i use for cleaning the internal chuck
threads ,i think this came from Sparey's Amateur's lathe book it is made from 1/8 inch
welding wire , this also fits the thread in the rear of the tailstock as i have already tried it.
When you get the thread started at least 2 threads in and you can turn it in no more lock
the tailstock down to the bed and using a flat piece of hardwood resting on the end
of the end cap and with a small ball pein hammer give a sharp rap and see if it
moves around a little more,don't go pounding it with hammer blows just one at a time
and carefully ,it wont be quick but will free up the thread eventually , you can carefully
lightly tap around the sides of the cap four places using some wood to protect the
surface again don't overdo this and keep the cap on the move ,you must make sure to
clean the threads often whilst doing this cellulose thinners and a toothbrush.
These parts do fit together quite well ,there is little clearance in these threads
so care is required.
While that you have the tailstock apart check the two grub screws that hold the
nut in the barrel as the can work loose over time.

Good luck
John
myford tailstock.jpg

Trevor Rushton 207/05/2020 19:39:35
avatar
9 forum posts
5 photos

Dear All

thank you so much for your helpful suggestions. You were all correct about the contaminated thread; as I mentioned before it caught me out.

Very careful cleaning followed by a variation on the grinding paste method using a small amount of metal polish very carefully as a final clean. I could then screw the cap in by hand - success.

So having enjoyed a spell cleaning in the sunshine I took the whole thing back into the workshop for final assembly - 1 turn and that was all I could get.

Whole thing out again and another cleaning session- success again.

So, most certainly some important lessons there and next time I shall be more careful.

This forum has been very helpful so thanks again.

Michael Gilligan07/05/2020 20:51:56
avatar
23121 forum posts
1360 photos

Well done, Trevor

Thanks for letting us know yes

MichaelG.

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