half nuts

[Trevor BeamondParticipant @trevorbeamond52280]

I am looking where I can get a couple of half nuts for the transfer of an old AVO coil winder.

Half inch diameter, 40 tpi, left hand buttress thread.

Thank you,

Trevor

[Trevor BeamondParticipant @trevorbeamond52280]

[Michael GilliganParticipant @michaelgilligan61133]

Welcome, Trevor

Frankly, the old joke "over there in the corner, next to the rocking-horse manure" springs to mind … but of course, there is no harm in asking.

My guess is that they will need to be custom made.

The good news is that people claim great success 'heat-forming' Delrin to make such things.

MichaelG.

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For convenient reference; may I assume that the machine is one of these:

https://archive.org/details/AvoDouglasCoilWindingMachinesManual

Edited By Michael Gilligan on 05/07/2018 07:59:12

[Anonymous]

What model of winder? I think my AVO coil winder is a "Douglas" No. 1. I've never looked before but on close inspection the half nuts on my winder do look to be buttress thread, LH and 40 tpi. You learn something every day!

Unless you get lucky with a scrap machine I expect you'll have to make them. Depending on the facilities available one could screwcut them, or it may just be easier to make a tap. In my,manual it is explicitly pointed out that the half nuts have a chamfer across the threads so they sit snugly on the driving thread.

Andrew

[GeorgineerParticipant @georgineer]

There's a highly regarded method for making half nuts from delrin/acetal here:

http://www.denfordata.com/bb/viewtopic.php?f=50&t=3727

It was originally given on the Home Shop Machinist forum and there is still a 29-page thread discussing it (search for delrin half nuts), but the instructions and pictures were removed from the beginning of it some time ago.

George

[Trevor BeamondParticipant @trevorbeamond52280]

As I understand it, the "Dougias" No 1 is a hand driven machine. Mine is belt driven with a round belt like a sewing machine. I doubt if it would wind thick wire.. It has a brass plate label 931.. It has a large retrofit counter mounted on a on a piece of RSJ, all very heavy. No motor or drive system came with it.

I have fitted magnets and reed switches but not built the circuitry to drive electromechanical counters.

I am most interested in the use of Delrin. I had thought of using Araldite but was worried about it getting stuck to the lead screw. Tracy Tools have a pricey left hand thread tap with normal thread profile which would probably not give sufficient bite.

Trevor

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Trevor Beamond on 05/07/2018 22:24:37:

As I understand it, the "Dougias" No 1 is a hand driven machine. Mine is belt driven with a round belt like a sewing machine. I doubt if it would wind thick wire.. It has a brass plate label 931.. It has a large retrofit counter mounted on a on a piece of RSJ, all very heavy. No motor or drive system came with it.

.

The pages at the end of the Manual that I linked may help with identification.

MichaelG.

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Edit: any chance it's this one ?

https://archive.org/details/AvoDouglasNo.6CoilWindingMachine

Edited By Michael Gilligan on 05/07/2018 22:35:59

[Sam StonesParticipant @samstones42903]

A word of WARNING.

Without even reading through the entire method for forming (pressing) threads into Delrin (polyacetal), which is clearly a smart way; just a word about applying heat to this material.

The fumes from over heating are extremely noxious. Get a whiff and you'll never forget it.

Good luck with your 1/2 nuts.

Sam

[Speedy Builder5Participant @speedybuilder5]

Trevor, have you looked at replacing both nut and leadscrew ? And is a LH thread necessary ? If you replace both screw and nut, the choices may open up a bit.
BobH

[Trevor BeamondParticipant @trevorbeamond52280]

I am not capable and do not have the equipment to do an extensive modification. The butress thread is needed as the direction change is done with an over centre system. If I were fit, I might consider running one of the lead screws in the two directions using a stepper motor drive.

To change a lead screw would necessitate dismantling the frame and my hammer may not be big enough. I am interested in repairing valve radios and this is a diversion. This week I have been given a fan to repair, I might get it going before winter.

I have used the winder to make some pick up coils for a geetah and to rewind some solenoids for slave clocks (30 thousand turns) and to make an inductance for a car low voltage ignition. I initially got it to rewind the mains transformer in an Alba valve radio but changed the transformer instead.

Trevor

[Sam StonesParticipant @samstones42903]

Coincidentally and way off topic Trevor, it might be useful to know that a buttress thread is a highly recommended and much used thread-form for plastic materials’ applications. The reasoning relates to radial creep.

By the way, I admire your tenacity with regard to winding those fine wire coils. I recall my electrician father claiming that he was the only one in the workshop with the patience to handle the extremely thin wire. Besides suffering numerous wire breakages, other maintenance chaps who tried came close to nervous breakdowns.

Only wish I could help with the half nut problem.

Sam

[Trevor BeamondParticipant @trevorbeamond52280]

I show a photo of the winder, I assume it is No2 but came without any drive. I tried three motors and settled on a 12V motor driven by a Variac and battery charger.

The pulley came from a Ford timing belt and has a very nice bearing.

I show the rocker with old nuts fitted.

But I can't see how to attach a picture obtained from my computer. Where is the paper clip?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Trevor Beamond on 08/07/2018 15:30:27:

But I can't see how to attach a picture obtained from my computer.

.

Here's a Frequently Linked Thread, Trevor: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=103028&p=1

… It's become a sort of Initiation Ceremony

MichaelG.

[Author]

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