Plastic for gears

Would it be possible to use plastic for a lathe change gear, if so what is the best material to go for ? My old Harrison had a large fibre gear in the train, so I'm assuming there could be a suitable plastic type material that is machinable and readily available.

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Delrin.??

I posted this only yesterday. **LINK**

Nick

Cheers Nick, I missed that post.....Delrin it is then

We used to use tufnol on larger dp gears or nylatron on smaller ones.

I've succesfully used Delrin.

Tufnol is excellent if you use the right grade in the correct grain orientation. Allegedly stronger and better able to cope with shock loads than delrin or nylon. But ideally needs proper attention to lubrication for long life. Delrin and nylon are, up to a point, happy run dry if kept clean.

Chocolate fireguard time if you use wrong grade and / or wrong grain orientation with Tufnol.

Clive.

I take It this is with regards to sheet tufnol rather than the round bar?

Michael W

Edited By Michael-w on 20/03/2017 10:59:28

Tufnol is surprisingly strong if the correct material is used (Woven sheet for gears, not rod which is rolled). I once had a vintage sports/racing car that used a Tufnol gear for the camshaft drive, admittedly the works racing team used a steel gear as they were not concerned with the noise but failures were very rare.

However these days I would use acetal (Delrin).

Russell.

we used sheet woven tufnol

Tufnol gears are/were used to a great extent on printing presses, the ideal lubricant happened to be printing ink.

Ian S C

Nylon PA46 and PA66 are widely used for gears in demanding applications like high temperature automotive actuators. May be an option depending on availability.

One problem with the specialised plastics is locating them in small quantities at a reasonable price.

All plastics have rocketed up in price over the last few years. Tufnol used to be available for pence. I have seen works offices thrown up in a corner of the shop and sheeted in with tufnol sheet it was that cheap but now a piece of 1M x 300mm 10mm Whale Tufnol which is what is used for gears is over £100.

The cheaper grade is paper based and the dearer is fabric based.

I can only assume they are using £20 notes for the paper grade and Armani for the fabric grade.

What would Tufnol rod be used for then, if not gears? I only ask as I was fortunate enough to pick up a fabric based rod for peanuts at a car boot sale and it's 76mm diameter by 512mm long, so fairly big. Been looking for use for it since I bought it!

Good for electrically insulating standoffs, knobs, handles and anything that doesn't need to be metallic. Rather like wood but without quite the same directional weakness. Machines nicely and polishes up with a bit of oil to show the colour textures. The phenolic smell isn't entirely pleasant but it's not particularly hazardous.

Some ideas and data here.

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Further to Muzzer's suggestions: Bearings

MichaelG.

The rod is made by rolling up a sheet of paper or cloth in the resin, before hardening it. This means the layers are like the rings of a tree, so a gear will have the weak direction (between the layers) running across the teeth, making it easy to lose teeth. Gears made from flat sheets have the weak layers aligned so they only have to cope with forces trying to 'spilt' the gear - an unlikely situation in normal use.

Thanks for the replies guys, I had worked out the strength issue with making gears from rod, which is why it is still sitting on my shelf, sooner or later I'll be making something and realise that I can use it. Until then I suppose it will just have to lie there and stare at me! I did think of selling it but you know how it is, sell something like that and the following week it's just what you needed...

I've not used them before but small quantities are available here...

**LINK**

HTH

Jon

Strewth! That chunk of Tufnol sitting on my shelf would cost somewhere north of £200 to replace!

I have several nylon gears in my Harrison L5 changegear set and when i needed one of them for cutting the thread in the backplate for a new chuck I was a bit worried if it would stand the load from cutting a 1.5 " X 6 TPI thread in cast iron but it did it fine , dont know if it would have done it if it had been a tufnol gear though , and a bonus is the geartrain runs a lot quieter with a plastic gear in it because as anybody with a Harrison knows the steel gears can ring a quite a bit at higher speeds.

regards Geoff

Edited By Kettrinboy on 21/03/2017 18:03:38