Polymorph Half-nut

This topic has 25 replies, 12 voices, and was last updated 16 October 2015 at 14:34 by Bazyle.

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30 June 2015 at 08:09 #195402
James A
Participant
@jamesalford67616
I have almost finished settingup my Flexispeed lathe thatI received at Christmas, just needing to buy some polyeurethane belting and wire in the motor.

One modification that I would like to make in time is adding a half-nut so that I can disengage the leadscrew. Rather than trying to find a suitable left-handed tap, I am thinking about using polymorph to form the nuts instead. Does anyonehave any experience of using it for anything similar and, if so, how well did it last?

Regards,

James.
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30 June 2015 at 08:09 #17760
James A
Participant
@jamesalford67616
30 June 2015 at 08:31 #195404
Les Jones 1
Participant
@lesjones1
Hi James,
I think acetal would be more suitable than polymorph. Have a look at this information on making half nuts from acetal.

Les.
1 July 2015 at 07:48 #195455
James A
Participant
@jamesalford67616
Les,

Thank you for the link, which looks useful. I have a length of suitable material, so shall have a look at this method.

Regards,

James.
1 July 2015 at 10:02 #195465
Douglas Johnston
Participant
@douglasjohnston98463
I bought some polymorph a few years ago, but have not done much with it apart from playing with it. It might be worth a try for this application and I might give it a try myself. I don't know much about the properties of polymorph but the moulded objects are quite tough and not unlike acetal/delrin and would be easier to mould round a leadscrew since the temperatures involved are much lower.

If you have some polymorph, give it a go James and report back. When I get an odd moment I will try it myself on something smaller to see if it is a runner.

Doug
2 July 2015 at 07:48 #195540
James A
Participant
@jamesalford67616
Doug,

I shall be interested to hear how you get on, should you give it a try. I shall have a go myself with the polymorph and, if it is unsuccessful, try using delrin instead.

Regards,

James.
2 July 2015 at 11:38 #195562
DMB
Participant
@dmb
I have seen detailed instructions of how to make a new L/S nut with, I think, Delrin. I think it was on HMEM.
2 July 2015 at 21:35 #195627
DMB
Participant
@dmb
Hi James,

Further to my prev. post, I have just been into homeshopmachinist.net and typed "leadscrew nut" in the search box @ the top and immediately comes up with what I was remembering earlier – round black Acetal bar. They say bore a blank to thread OD less ONE thread depth, saw in 1/2 axially. Polish and oil L/S and clamp 2 halves of L/S blank on to L/S and grip the lot in bench vice.Use a hot air gun, NOT gas torch! to warm up L/S, and as heat travels along L/S, it will soften the Acetal so tighten vice jaws. Keep this up til 2 halves of nut close up.They reckon it takes 10-15 mins.There are further instructions for removing the nut and finishing it but you will have to look it up. I dont want to repeat the lot – someone may object. I note nothing said about OD of nut so I will guess it could need a wall thickness of thread depth X 2 + OD of L/S. If you try this, perhaps you could post description of how it went for benefit of anyone else needing to do similar. Good luck.

John.

Edited By DMB on 02/07/2015 21:37:57
2 July 2015 at 22:04 #195632
Les Jones 1
Participant
@lesjones1
Hi John (DMB),
That sounds like the link I gave in my post at 08:31 on 30/06/15

Les.
3 July 2015 at 10:23 #195670
DMB
Participant
@dmb
Hi Les,
U R dead right – I forgot 2 check 4 that.
John.
5 July 2015 at 10:53 #195798
James A
Participant
@jamesalford67616
Thank you all for the contributions. I shall have a go with the polymorph to see how well it works and post my experience for others to see. IF it fails to do the trick, I shall try the Acetal option.

Regards,

JAmes.
5 July 2015 at 11:03 #195800
Ady1
Participant
@ady1
Various plastics can be used but they tend not to last long, especially if you are a regular user

If you want an easy to machine material and decent longevity use aluminium
5 July 2015 at 11:17 #195801
James A
Participant
@jamesalford67616
Posted by Ady1 on 05/07/2015 11:03:17:

Various plastics can be used but they tend not to last long, especially if you are a regular user

If you want an easy to machine material and decent longevity use aluminium

True, except that my reason for wishing to use ploymorph or, perhaps, Acetal, is a lack of a suitable left-hand thread tap to make a metal half nut. To be honest, I have no idea what thread it is either. I suppose I could experiment with casting one in alumimium, but Ireally would rather avoid this route.

Regards.

James.
5 July 2015 at 21:35 #195874
Roderick Jenkins
Participant
@roderickjenkins93242
James,

If your Flexispeed is like mine then the leadscrew is 12tpi square form. I have no direct experience of this but my understanding is that square threads will not disengage from half nuts, they have to be ACME form. I hope others can confirm or deny this.

Rod
5 July 2015 at 21:57 #195875
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Roderick Jenkins on 05/07/2015 21:35:37:

… my understanding is that square threads will not disengage from half nuts, they have to be ACME form.

.

That's my understanding too, Rod

ACME, or similar [Trapezoidal, etc.]

MichaelG.
13 October 2015 at 22:50 #207740
James A
Participant
@jamesalford67616
I have now had a go at using polymorph to make a nut for the leadscrew, albeit not half nuts.

The leadscrew nut on my Flexispeed is a small, rather narrow, casting with the thread cut into it. Over time, this has worn and there is a lot of backlash in the nut. To try and remove this slack, I moulded some polymorph around the leadscrew and, once set, sawed and filed it square. I then screwed this plastic nut to the exisitng metal nut to bolster it. It has worked well and removed all of the slack whilstremaining loose enough to operate.

However, the impression that the material gives is that whilst it will last for a while, it is unlikely to cope with a large amount of use. Mind you, it was so quick to make the nut that even it has to be replaced each year, it is no hardship.

Regards,

James.
13 October 2015 at 23:54 #207745
Martin W
Participant
@martinw
James

Would there be any mileage in mixing in something like brass or bronze powder into the polymorph as a filler to increase its life and improve the bearing surfaces. There are lots of metal powders available here that might be suitable.

Cheers

Martin
14 October 2015 at 07:10 #207751
James A
Participant
@jamesalford67616
Martin,

To be honest, I had never even considered that, which seems like a good idea to me, especially as I imagine that it will make to polymorph easier to file and shape. When this version of the nut expires, or if I use the polymorph for anything else that is similar, I shall try adding some powders.

Regards,

James.
14 October 2015 at 08:15 #207757
John Haine
Participant
@johnhaine32865
Look up Moglice.
14 October 2015 at 09:41 #207762
Martin W
Participant
@martinw
John

Had a look at the Moglice site and it looks very interesting. At samples coming in at 10 euros for 50 grm (Ex VAT & Postage) it is cheap enough to have a play with. It was interesting to see that in their application sheets they were using it to repair/remake threads on lead screws etc. As they say, just ensure that the cast is on the least worn part of the thread or else the new nut nut will not run over all the thread.

Cheers

Martin

PS It sound like something a cat might catch !
14 October 2015 at 09:41 #207763
Ian S C
Participant
@iansc
A number of the plastics are available with various fillers such as bronze, graphite, and oil.

Ian S C
14 October 2015 at 10:32 #207768
Douglas Johnston
Participant
@douglasjohnston98463
Well done James, I'm afraid I never did get round to trying it myself, but I will move it further up my 'to do ' list. As a matter of interest did you use hot water to soften the polymorph or use a different technique?

Doug
15 October 2015 at 07:27 #207907
James A
Participant
@jamesalford67616
Posted by Douglas Johnston on 14/10/2015 10:32:40:

Well done James, I'm afraid I never did get round to trying it myself, but I will move it further up my 'to do ' list. As a matter of interest did you use hot water to soften the polymorph or use a different technique?

Doug

Doug,

I used boiling water. I had a mixture of fresh polymorph granules and a roughly moulded lump that was left over from making a plastic hammer head. The fresh granules melted perfectly well, but the formed lump proved much harder to soften.

Regards,

JAmes.
15 October 2015 at 09:20 #207931
Douglas Johnston
Participant
@douglasjohnston98463
Thanks James, I must dig out my polymorph and have a go.

Doug
16 October 2015 at 11:45 #208075
mark smith 20
Participant
@marksmith20
Ive used polymorph on occasional for work holding jigs, One thing i found is that it does tend to take a lot of heating for previously used lumps to be of use.It also doesnt tend to hold its shape very well . I think its a case of differential cooling but it is rather annoying ,when a curved jig straightens out a lot when cooling.. It may be more suited to small items .
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