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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 29th Apr 2012, 11:58 am   #1
M0FYA Andy
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Default Paxolin Disks

Has anybody got any hints or tips on how to accurately cut disks from thin paxolin, accurately circular with smooth edges?

I have a dozen or more Colvern wirewound potentiometers with bakelite bodies which should have a paxolin disk back glued in place into a rebate in the bakelite. Unfortunately over time the glue has failed and the backs have gone AWOL.

Depending on the power rating the disks need to be from about 1.25 to 1.75 inches in diameter.

Any ideas welcome, please!

Many thanks,

Andy
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Old 29th Apr 2012, 2:23 pm   #2
TrevorG3VLF
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Default Re: Paxolin Disks

Not easy, I do not see how this can be punched without a press to locate the punches.

The way I would try is to cut out a disc oversize, place it between two wooden discs and place in my wood turning lathe attachment with a large end load and turn to the required diameter.
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Old 29th Apr 2012, 2:24 pm   #3
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Default Re: Paxolin Disks

Hi Andy,

Drill a hole for a 4 or 5 mm nut and bolt in a piece cut roughly to size then "turn" it to size with a file in a power drill. Then glue up the hole. A neat way is to cover one side of the hole with tape and put glue in the other side. I.ve used double sided tape to hold a disc to the face of a lathe chuck. You could do that on a drill, with care.
Peter
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Old 29th Apr 2012, 2:54 pm   #4
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Default Re: Paxolin Disks

Yes, I can see ways of doing it by starting with a hole in the middle, but it seems rather counter-productive to make a hole which then must be filled, and difficult to achieve neatly!

I imagine when these were made the backs were churned out by the thousand in minutes using a punch made for the job.

Andy
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Old 29th Apr 2012, 4:48 pm   #5
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Default Re: Paxolin Disks

If the paxolin is thin enough, won't scissors do the job?

Alternatively, if you clamp the paxolin sheet to a piece of wood you should be able to use a hole saw in a bench drill set up so that the central drill bit doesn't stick out of the saw. Maybe use an old pot spindle instead?
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Old 29th Apr 2012, 4:57 pm   #6
M0FYA Andy
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Default Re: Paxolin Disks

I tried cutting a piece with scissors, but I just wasn't happy with the accuracy of the end result!
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Old 30th Apr 2012, 6:02 pm   #7
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Default Re: Paxolin Disks

Hot glue is strong enough to hold the paxolin to a round block of wood or metal bolted to a countersunk bolt used as a spindle. You can then turn this in an electric drill and file round, best to use a tool rest to help hold the file (tool) I used my drill stand on its side with a block of 3x3 timber as the tool rest. Do be careful though with fingers and use goggles, and don’t allow it to become too warm.
I now have a small lathe so it is a bit easier and not so dangerous.
When you have finished just warm up the disk and slide the paxolin off.
Mike

PS. you could use an old car engine valve to glue the paxolin to.

Last edited by crackle; 30th Apr 2012 at 6:04 pm. Reason: added ps
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Old 30th Apr 2012, 6:46 pm   #8
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Default Re: Paxolin Disks

I recently did exactly this to make a new back for one of my Colvern pots. I marked the circle I wanted on the paxolin using a compass, rough-cut it out with a hacksaw and hand-filed it circular. If had wanted to do 12 it would probably have been worth making jigs and support pieces and/or drilling holes then filling them again and/or rooting out my hot-melt glue sticks. But to do just one took perhaps 15 mins with the compass, hacksaw and file and ended up a very neat precise fit (I kept checking the size against the actual pot as I was carrying out the job).

Cheers,

GJ
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Old 30th Apr 2012, 7:10 pm   #9
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Default Re: Paxolin Disks

Make a plywood disc with a bolt through the centre to hold the paxolin whilst you turn it in a lathe (if you have one) or, as a previous poster has suggested, an electric drill can be used as a stand in. Stick the thin paxolin sheets to the plywood disc using double sided tape and off you go...

Steve.
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Old 30th Apr 2012, 7:14 pm   #10
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Default Re: Paxolin Disks

I've long since had an idea for a tool that will do exactly what you're talking about. If I had access to a lathe I think I could easily make one.

The idea is simple - I'm sure most of you guys are familiar with the concept of a panel pin pusher? It's a spring loaded rod inside a tube that you load with a panel pin (small nail), and then push the plunger, and therefore the panel pin, into the job.

Ok - so imagine, the reverse. Instead of pushing a plunger that is inside the tube, the tube is pushed over the plunger - it is the tube itself that is sharp and acts as a cutter. The centre plunger being sharpened like a pencil (or centre punch) to allow for precision placement, the tube then slid down over the centre plunger to cut the work-piece. With a very light spring load, the centre punch wouldn't mark the surface of something like paxolin.

I want something like this to allow me to make small washers in polystyrene "plasticard" to allow me to fabricate my own home made coils. I see no reason why, anybody with a lathe and a little patience couldn't make such a thing. The tube can be sharpened like a saw-blade or honed like a chisel - so ling as it's quite thin and the centre plunger is a very good fit, I can't see how accuracy will be an issue either

Last edited by DragonForce; 30th Apr 2012 at 7:15 pm. Reason: spooling misttok :D
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Old 1st May 2012, 8:58 am   #11
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Smile Re: Paxolin Disks

Hi,
It might be worth putting an appeal in the "Wanted" section. I'm sure folk may have kept the discs that fell off the pots, or the scrap pots themselves. I know I had a few kicking around somewhere.
Just an idea.
Cheers, Pete
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Old 1st May 2012, 9:39 am   #12
M0FYA Andy
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Default Re: Paxolin Disks

DragonForce, that sounds like an improved version of a 'wad punch' used to cut a hole in leather or similar, although usually it is the hole that is required rather than the disk. I agree that your concept should work if it is made.

Tractorfan, good idea!

Andy
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Old 1st May 2012, 1:17 pm   #13
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Default Re: Paxolin Disks

Turn or file some metal discs to the correct diameter. Alternatively you may be able to find coins or washers of the correct size.

Clamp paxolin betwen the discs and file to the correct size.

Achieving alignment of the discs might be a problem. You could try glung then to the "jaws" of a 'G' clamp. The paxolin might be transparent enough to see through with a bright light behind it, then you'll be able to see both discs to align them.

Have a go with a couple of washers or coins first to see if the idea works for you.
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