Lead screw nuts

[Peter Simpson 2Participant @petersimpson2]

Hi,

My Tom Senior light vertical (metric) milling machine has a fair bit of back lash in the X and Y lead screws. Has anybody out there had new lead screw nut manufactured ? If so could you suggest a suitable supplier of these items.

Mant thanks Peter

[Peter Simpson 2Participant @petersimpson2]

[John HaineParticipant @johnhaine32865]

You could look at this thread…

http://www.practicalmachinist.com/vb/general-archive/casting-leadscrew-nut-91107/

[_Paul_Participant @_paul_]

The X axis leadscrew nut in my old Geo. Taylor Mill was badly worn with over 0.050" backlash, I looked at buying replacement 10 TPI Acme stock and a new nut with a view of machining to suit.

Then I came across this thread Acetal leadscew Nuts the easy way with nothing to lose other than the small cost of some Acetal bar I tried it, that was some months ago the machine has less than 0.002" backlash now and is very smooth to use.

It was surprisingly easy to do.

I now intend to do the same with the Y axis.

Regards

Paul

[JohnFParticipant @johnf59703]

Hi Peter, I don't know what other equipment you have but probably a lathe so why not make a nut from scratch and screw cut it to suit. Check your lead screw for wear first — not 100% method but is the backlash the same at the two extreem's of travel as it is in the centre? If so then the wear is in the nut, if a little different then the screw is worn as well and it may be best to replace both.

I used to recondition small lathes many years ago and made many of these, it is a little more difficult if it is an acme thread because you need an acurate tool ground to suit but Tracy tools do some acme taps –never used one but its worth a look and if available in your size you could screw cut to near size then finish with the tap.

Best of luck. John

[Russell EberhardtParticipant @russelleberhardt48058]

…or you could make anti-backlash delrin nuts similar to those described by Brian Pitts in the Yahoo

hf47158toCNC_Moderated group.

Russell.

[Tim StaceyParticipant @timstacey83769]

Turning up a replacement is not a huge job and very rewarding if you have got a lathe. RDG also do a range of ACME taps at sensible cost if they match your leadscrew dimensions and could avoid the need to get into internal cutting.

Regards

Tim

[Ex contributorParticipant @mgnbuk]

If your leadscrew is worn & your lathe is long enough to traverse the thread length, you could re-cut the thread slightly thinner to get it even along the length & screwcut a nut to suit. That was the method employed during lathe refubishment by a company I was seconded to as an apprentice to widen my experience – I was paid car mileage rates to deliver the worn screw & nut to the machine shop & collect the refubished screw / new nut on my motorcyle. I had the screw (the cross slide screw from a Herbert lathe IIRC) strapped length-wise along the bike.

Regards,

Nigel B.

[Ian S CParticipant @iansc]

One method of dealing with a warn lead screw (in ME)was to turn the lead screw end for end, The right hand end does'nt get the wear that it does near the chuck. Ian S C

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

(1) On all their early machines Tom Senior used solid whitemetal or whitemetal lined bronze feed screw nuts . Later ones had solid bronze nuts . A very few (probably wartime) had iron nuts .

You could cast white metal in the existing nut around the existing leadscrew just like it was done in the past but better would be to use a controlled engineering approach – fill the nut with whitemetal , bore out , roughly screwcut the thread on the original lead and finish with tap .

A variation of the old idea may be possible using one of the modern metal or PTFE filled high strength engineering repair materials .

(2) It is possible to do an improvised repair on a bronze nut by a cut and shut operation . Depends what your nut actually looks like but basically put some cuts in the right place and close up the threads either by squeezing together end wise or squeezing radially . Many feed screw nuts have a longitudinal or cross cut slot and screws to close up for adjustment as standard .

(3) Making an all new nut is not at all difficult but you have to screw cut the thread . You can choose to screw cut to a finish or screwcut a little undersize and finish with tap . You are not likely to have any success directly using an ACME tap to produce the entire thread form unless its very small size .

Edited By MICHAEL WILLIAMS on 21/04/2012 18:35:05

[GoCreateParticipant @gocreate]

Hi

This method looks great, would it be a good compromise for a cnc conversion? Provided you can accept a very small amount of backlash. Save allot of time and expense changing to ball screws. Maybe friction would be the issue though so more cost on bigger steppers and drivers.

Nigel

[dcostaParticipant @dcosta]

Hello Nigel.

Please look here to see another possibility for replacing the feed screw nuts.

I used Delrin (or POM) in the feed screw nut in my shapper machine. But I did not use the above method. I made the thread using a tap set and as far as I can see there is no sign of backlash.

I have yet to test the nut in service.

Best regrads

Dias Costa

[GoCreateParticipant @gocreate]

Hi Dias

Thanks for the link, actually that's what I was referring to, it's the same link given by Paul above, sorry I did not explain myself fully.

Looks a very easy method, reading through that thread it seems the Acetal is surprisingly durable.

I would be interested in how your Delrin nut performs.

Thanks

Nigel

[dcostaParticipant @dcosta]

Hello Nigel (and Paul).

I apologize for this lack of my to the Paul's post.
I've done dozens of hours of tests on empty and there is no sign of backlash. There's still a little time for the tests under load.
If you are interested I can join a photography of the nut with a little more detail (and quality…) to my photo album of the shaper machine here.

Best regrads

Dias Costa

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