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Leadscrew material ?

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Richard Cox01/10/2019 21:55:05
60 forum posts
19 photos

Evening I’m thinking about making a new leadscrew for the lathe cross thread is

m16x4 l/h trapezoidal I think , what is the best material to make it from thanks

Rich

old mart01/10/2019 22:00:27
4655 forum posts
304 photos

EN24T is strong and not too bad to machine.

not done it yet02/10/2019 09:14:05
7517 forum posts
20 photos

Nowt to add to the material choice but I would make a feed screw as a square thread - particularly if a new nut was required at the same time. I see no advantage of a trapezoidal thread in this application. Both my Raglan lathe and mill were fitted with square threaded feed screws as OE.

So much easier to make a cutter to do the job.

Martin Kyte02/10/2019 09:49:07
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3445 forum posts
62 photos

Can you fit a ball screw into the space?

regards Martin

Pete Rimmer02/10/2019 10:22:19
1486 forum posts
105 photos

I like EN8DN for screws. it's free-machining EN8.

Edited By Pete Rimmer on 02/10/2019 10:24:15

Richard Cox02/10/2019 17:21:44
60 forum posts
19 photos

Thanks for the replies I didn’t think of changing the thread to square good point don’t suppose it matters if making new of each I was going to make a spare as I have took the measurements while lathe was stripped for a repair

Rich

Tim Stevens02/10/2019 17:26:44
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1779 forum posts
1 photos

I'm not sure a square thread is easy to arrange with a split-nut attach & release system. Of course, yours might be different. But remember that square threads were abandoned long ago as sodding difficult to machine ...

Cheers, Tim

HOWARDT02/10/2019 17:47:25
1081 forum posts
39 photos

Also square thread has no compensation for wear.

Chris Evans 602/10/2019 17:48:29
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2156 forum posts

Richard, it is easy and very cheap to buy off the shelf. I bought a 1 metre length of 16 x 4 l/h plus nuts. enough for three leadscrews around £60

Richard Cox02/10/2019 19:00:51
60 forum posts
19 photos

46d77de7-5d85-47d3-b8b5-81845f6c3da5.jpeg20388f5c-7f8d-4cb2-80c7-511bc5e0e3e8.jpegEvening all on closer inspection it appears a square thread does it look like it up you lads ? 16dfbbbf-04cd-41c6-8065-415333149368.jpeg

old mart02/10/2019 19:13:28
4655 forum posts
304 photos

Richard, that thread of yours looks like ACME or trapezoidal, (29 or 30 degree angle), not square. If it is imperial pitch, it is ACME, and if it is metric pitch it is trapezoidal.

Chris Evans mentions that 16 X 4 TR leadscrews and nuts are easy to get hold of, this would be the easiest option, just a little machining of the ends needed. And an opportunity to incorporate antibacklash if there is room to do so. 

Edited By old mart on 02/10/2019 19:18:27

Richard Cox02/10/2019 19:28:36
60 forum posts
19 photos

Ok thanks for the advise like you say easy enough to machine the ends do you mean incorporate the a backlash in the nut ?

Chris Evans 603/10/2019 18:49:25
avatar
2156 forum posts

I bought mine from Automotion Components and bought two nuts thinking the wear would be rapid. Four or five years on there is no sign of requiring the fitting of the spare screw and nut. The lathe is used around three hours a day about four times a week Look at the position and design of your machines nut to see if it can be split to move apart for backlash. Some Colchester lathes use a wedge pushed into the split nut by a grub screw.

not done it yet03/10/2019 19:32:05
7517 forum posts
20 photos

I read this thread as a mis-named feed screw, not a lead screw. It is certainly ambiguous and with the word ‘cross’ included, to me, indicated he actually meant feed screw for the cross slide - not the lathe lead screw. Also, an someone explain exactly how any feed nut, on its own, is “adjustable for wear”. As I see it backlash simply increases as wear takes place until unacceptable or the nut threads fail.

I can clearly understand the need for a non-square thread for a lead screw, but not for a simple feed screw. Square is stronger than alternatives, cutters are simplicity to make (and it matters not a jot if slightly too narrow as the thread can be corrected by the odd division or two on the compound slide).

not done it yet03/10/2019 19:32:06
7517 forum posts
20 photos

I read this thread as a mis-named feed screw, not a lead screw. It is certainly ambiguous and with the word ‘cross’ included, to me, indicated he actually meant feed screw for the cross slide - not the lathe lead screw. Also, can someone please explain exactly how any feed nut, on its own, is “adjustable for wear”. As I see it backlash simply increases as wear takes place until unacceptable or the nut threads fail.  Half nuts should be adjustable, to a point, obviously.

I can clearly understand the need for a non-square thread for a lead screw, but not for a simple feed screw. Square is stronger than alternatives, cutters are simplicity to make (and it matters not a jot if slightly too narrow as the thread can be corrected by the odd division or two on the compound slide).

Edited By not done it yet on 03/10/2019 19:35:50

old mart03/10/2019 20:17:12
4655 forum posts
304 photos

Cross slide leadscrews have left hand threads, and the exact configuration of the front end varies from lathe to lathe. Buying a length of new leadscrew is only part of the whole. It would be best to carefully measure the existing leadscrew to produce a drawing. The new leadscrew is nothing more than threaded rod, like a large piece of studding, and one end will have to be machined to fit a replica front end. This is easy if you have access to another lathe or your lathe is put back in working condition. This is why a drawing is essential.

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