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Drawbar - different threads at each end ?

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Boo:
Hi,

I amd just about to make a drawbar for milling cutters etc in the lathe and remember reading that it can be beneficial to use a different thread at the nut end from the tool end in order to reduce the chance of the drawbar unscrewing itself in use.  My questions are:

Is this really a thing ?

Should the nut end be finer or coarser than the tool end ?

I have an M12x1.0 metric fine tap as well as the normal M12x1.75 taps for making the nut so could do either.  The nut is a casting from Hemingway.  Tool end must be M12x1.75 to suit the cutter holder.

I'm sure I'm overthinking this but if it makes a difference I might as well do it as not.

Thanks,

Boo

awemawson:
I made the (7/16 UNF) drawbar for my Bridgeport probably 25 years ago. Nut end is (I think) a half inch whitworth  thread and it’s never unscrewed in all that time.

I suspect I used Loctite on it. It must have been a decent bit of steel as it’s still going strong.

Sea.dog:
I turned mine from hex bar,m so not an issue. You could through drill and pin the nut.

Boo:
Hi,

Thanks for the replies, I should have said that the tooling end is MT3 which has 2 different threads applicable and since the nut is a cast item from Hemingway, I wanted to use the same nut with two different bars having the same thread at the nut end and M12 or 3/8Whit on the other end.

So, really I just need to know whether thre is any advantage of using a finer thread at the nut end than at the tooling end, and specifically whether M12x1.0 is OK or should I stick to ISO M12 ?

As I said, I'm sure I'm over-thinking it :-)

Thanks,

Boo

John Rudd:
The drawbar on my mill, a 626, has an M12 to secure the mt3 chuck, the tightening end has a nut on it ( threaded but not known what thread) and is cross drilled and pinned…a nip with a spanner sees it tight enough.

Personally, I wouldn’t worry whether it’s M12 fine or standard…

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