home made tiny pot knobs

[dentaku]

I got some tiny pots with "Shaft Diameter:3.18mm; Shaft Length:5.59mm" which of course is in trimpot territory.
They plug in nicely into a breadboard but they're difficult to turn without using a screwdriver SO I made some knobs out of HDPE by turning them in a high speed hand drill as if it was a tiny lathe.
The metal tubes that go in them fit perfectly on the 3.18mm plastic shafts. I think they're spacers for big multi deck rotary switches.
So far I haven't found a way of completely removing the tool marks. It's not like you can sand and polish HDPE like wood

It would be interesting to see any cobbled together solutions people on this forum have come up with for very specific problems.

[JackOfVA]

That's a standard 1/8" pot shaft - been around for decades and off-the-shelf knobs are readily available.

[SeanB]

You can polish it with a cloth and some fine grinding paste, and that will get most of the marks out. Otherwise hot air from a gun will slightly melt the surface and with care you will get a smooth surface.

[dentaku]

I was wondering about heating it up. I might try that.

Today I made a knob for a regular sized pot after finding a big chunk of thick white plastic (it might even be PTFE) in the basement. It works perfectly and doesn't melt at all no matter how fast I turn it unlike other white nylon I've tried.
It's not hard to find leftover stuff from fish processing plants around here and that's probably where this came from.

You can polish it with a cloth and some fine grinding paste, and that will get most of the marks out. Otherwise hot air from a gun will slightly melt the surface and with care you will get a smooth surface.

[dentaku]

Yeah, but I don't have any and it's way more fun to make your own

That's a standard 1/8" pot shaft - been around for decades and off-the-shelf knobs are readily available.

[Dongulus]

Ha, hand drill as a tiny lathe. I love the idea.

[dentaku]

Ha, hand drill as a tiny lathe. I love the idea.

This is the drill. It's a flexible shaft Foredom with a triac based foot pedal speed controller.
https://www.eevblog.com/forum/beginners/is-this-a-custom-pot-in-this-drill-speed-controller/msg387018/#msg387018

It works fine as long as the material doesn't stick more a few CM out of the drill.
I could use a dead harddrive as a makeshift tailstock if I wanted to turn something longer.

[dexters_lab]

Yeah, but I don't have any and it's way more fun to make your own

That's a standard 1/8" pot shaft - been around for decades and off-the-shelf knobs are readily available.

indeed, i call it 'creative engineering'

nice work, hdpe can feel a bit slippy but i'm sure they will work great

[kc9qvl]

My just built knobs to repair my SA.

[SeanB]

If it was used in food processing it likely will be a Nylon 6.6 or HDPE, as these are food safe. PTFE will be soft and slippery. I have some PTFE stock I use to turn out bushings for food grade equipment, and some Vesconite that is used for the inner bushes away from the product. Nice thing about the Vesconite is it is both self lubricating and water lubricable, though you find the shaft wear is a lot more. PTFE is just soft unless glass filled, when it turns into a pretty good grinding media.

[dentaku]

Nice. They're even knurled.
I see someone's got a real lathe

My just built knobs to repair my SA.

[ampdoctor]

I was wondering about heating it up. I might try that.

Today I made a knob for a regular sized pot after finding a big chunk of thick white plastic (it might even be PTFE) in the basement. It works perfectly and doesn't melt at all no matter how fast I turn it unlike other white nylon I've tried.
It's not hard to find leftover stuff from fish processing plants around here and that's probably where this came from.

It's probably a material called Delrin. As far as I know it's similar to PTFE but not quite the same.  It's frequently used for commercial cutting boards in deli's and meat processing plants.

[dentaku]

If it was used in food processing it likely will be a Nylon 6.6 or HDPE, as these are food safe. PTFE will be soft and slippery. I have some PTFE stock I use to turn out bushings for food grade equipment, and some Vesconite that is used for the inner bushes away from the product. Nice thing about the Vesconite is it is both self lubricating and water lubricable, though you find the shaft wear is a lot more. PTFE is just soft unless glass filled, when it turns into a pretty good grinding media.

This stuff is very slippery. I made a tiny conical knob out of it that fits on the tiny pots with the 1/8" shafts and it's too slippery to use. It's nice on big pots though.
I can push a chunk of it against a table sander and it doesn't melt at all. Regular plastic just turns to goo if I do that.
Do you now if Nylon 6,6 is THAT tolerant to heat?
From what I can find... "Type 6,6 nylon melts at 255-265°C" but I have no clue what temperatures are created when sanding plastic.
It's a thick chunk of scrap and I doubt it's anything expensive. PTFE is probably a bit pricey to use in large quantities.

This is becoming quite interesting, talking about plastic on the EEVBlog

[jh15]

My first encounter with DuPont Delrin was on my first turntable. Garrard advertised Delrin as the surface that the trip lever rode on towards the inner grooves so as to not disturb the anti-skate by causing drag.

[SeanB]

Probably HDPE, it machines well and is both non contaminating and resistant to disinfectant cleaning. If it is nylon it strings and builds up a crud layer on grinding, though machining with sharp cutters makes a nice finish. You generally will have trouble with any plastic in getting close tolerance cuts though, especially on things like thin wall bushes.

I did buy a small half kilo block of PTFE to make bushes out of, it was around $30 for that.

[dentaku]

I did buy a small half kilo block of PTFE to make bushes out of, it was around $30 for that.

Aah, that's a good clue that it's probably not PTFE because it's a thick 2.5cm chunk that looks like it came from a very large piece of fish plant or boat shop garbage and they wouldn't bother using overly expensive stuff for no reason.

[dentaku]

I made a pretty decent regular sized knob tonight with my makeshift lathe.
The blue dot is made of rather soft plastic so it looks a bit rough in this macro shot but in real life it looks fine.

The dots are simple, drill a small hole, shove in a round plastic plug, lathe it all flat.