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Help with worn tailstock

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rbertalotto

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#1
The bronze threaded insert on my Jet 1236BD lathe is stripped. I want to order a bronze nut to replace the worn part.

My lead screw measures either .558” Dia x 8. Or 14.2mm X 3mm threads apart.

It appears the leadscrew is metric ...14 X 3......correct?..
 

P. Waller

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#2
Possibly a square thread, if so it will be difficult to find an off the shelf part with such threads.

If a trapezoidal thread form, 30 Deg. ISO or 29 Deg. Acme it should prove less difficult. Make sure that you are not measuring a burr on the screw Major Diameter, .2 MM is a good deal over the nominal diameter which is always the maximum.
The thread dimensions may be found here https://mdmetric.com/tech/thddat16.htm
 

RJSakowski

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#3
.558" is only .0025" under a nominal 9/16". You should be able to determine whether the lead screw is metric or inch fairly easily. 8 tpi would be .125" pitch. You should have exactly 16 threads, not counting the first thread, in two inches. If the pitch is metric, 3mm, you will have 16.93 threads.

To make it easier to keep track,, I mark every fifth thread with a Sharpie.
 

benmychree

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#4
It should be easy enough to make a new one, using the screw to gage the new nut's threads.
 

whitmore

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#5
The bronze threaded insert on my Jet 1236BD lathe is stripped. I want to order a bronze nut to replace the worn part.

My lead screw measures either .558” Dia x 8. Or 14.2mm X 3mm threads apart.

It appears the leadscrew is metric ...14 X 3......correct?..
Maybe correct, but not complete; it's a LEFT HAND thread, isn't it? And, single start?

If at least some engagement is still possible, use a dial gage to find the advance with 1.00 turn of the handle,
that'll give you the best pitch measurement. 3mm and 3.175mm == 8tpi are the candidates.

In a pinch, ink the screw and press it against paper, it's easier than getting calipers to
read the sloped edges.
 

derf

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#6
Contact Jet....that's probably a standard common part.
 

rbertalotto

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#7
Thanks everyone! All great feedback. I'll measure again and then order a bronze nut to repair.
 

rbertalotto

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#9
I took a chance and ordered a metric ACME nut. Hope I was correct.
 

Richard King 2

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#10
how does the screw look?

You may have to make a new one of those too....

Good Luck
 

rbertalotto

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#11
Well, the metric Acme nut I ordered was the wrong size. I searched everywhere for an 11/16 X 8 nut. No joy.....And all the Jet parts places could not help.

Here is how I fixed it.

I turned a a piece of aluminum to 1.0” OD and 11/16” ID
Then I found a pice of welding wire that fit perfectly into the threads on the screw.
I sprayed the screw with release agent.
Wrapped the wire tightly around the screw.
Covered the whole mess with JB Weld and inserted into the aluminum bush8ng I made.
Let it set overnight and the next morning the screw turned out easily.
I bored out the tailstock and using LocTite 620, bonded the bushing into the tailstock

Works fantastically!

Absolute zero felt lash. Amazingly accurate on the DRO I have installed on my tailstock

Been using it now for a few weeks and even with high loads it is holding up fine.
 

Richard King 2

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#12
Good luck, please let us know how long it lasts say in 6 months.
 

rbertalotto

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#13
The bronze nut in the tailstock lead screw on my Jet 12x36BD was totally stripped out.
I measured the lead screw and believing it was metric, ordered a metric, left hand, ACME nut to fix it.
Well, the metric Acme nut I ordered was the wrong size.
Turns out is was American thread. I searched everywhere for an left hand, 11/16 X 8 nut. No joy.....And all the Jet parts places could not help.

Here is how I fixed it.

I turned a a piece of aluminum to 1.0” OD and 11/16” ID
Then I found a pice of welding wire that fit perfectly into the threads on the screw.
I sprayed the screw with release agent.
Wrapped the wire tightly around the screw.
Covered the whole mess with JB Weld and inserted into the aluminum bushing I made.
Let it set overnight and the next morning the screw turned out easily.
I bored out the tailstock and using LocTite 620, bonded the bushing in place of the worn bronze nut in the tailstock

Works fantastically!

Absolute zero felt lash. Amazingly accurate on the DRO I have installed on my tailstock

Been using it now for a few weeks and even with high loads it is holding up fine.
 

chips&more

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#14
That was very ingenious! But I wonder how long before the JB stops working? And the welding wire pulls away/out. Was there a reason why you did not just make a new nut on your lathe?
 

rbertalotto

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#15
I do not have the ability or tools to grind a cutter for those ACME type threads. Otherwise that is exactly what I would have done.

Let's see how long the JB Weld holds up.
 

hman

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#16
I like your fix. About the only thing I could think of that I might have added would be to (somehow) mask the leadscrew contact areas of the coil, then lightly sandblast the "outer" surface (as well as the inner surface of the bushing), to increase adhesion. But what you did sounds like it should work pretty well. Hope it holds up!
 
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