Can I turn a part from hard clear plastic?

[twhite]

You will also want to have a nice radius on your turning and facing tools. That will help with the finish and keep from chipping.


Cutting oil is my blood.

 

[whitmore]

I'd vote for considering a casting, with dye to color the stuff; Tap Plastics has transparent dyes
for this sort of thing... an epoxy or urethane casting would be nice and durable, compared to acrylic,
and you can get a good mechanical bond to the machine part by embedding it while
the resin is still soft. Machining to finished shape, or turning a mold, will satisfy the need to
make swarf...

 

[dbb-the-bruce]

Personally, I'd do it on a wood lathe with hand tools. But I have a lot of wood turning experience. It will be grabby. Probably would mostly use scrapers. It would be easy to sand and polish by hand. As many have said, watch the cutting speed as you don't want to start melting / softening it. Another thing with plastics is you can/will get one continuous strand of swarf that can range from a nuisance to dangerous.

You do not state why you are committed to sticking with plastic/acrylic, why? I'm guessing that you want it to look original. It may be hard to match it anyway. So why not just use a piece of wood?

 

[cazclocker]

I don't know how big your end piece is, but here's a link to some 1" diameter red acrylic rod on ebay. Plenty to experiment with and to get things correct.

Thank you for the link. The final piece needs to be around 0.5" OD at the largest diameter. I think 1.0" diameter would be a little too large, but I noticed the same seller has both 0.5" OD and 0.75" OD rod, in the same red color. I put both OD sizes in my eBay "watchlist". Much appreciated!

A couple of thoughts:
1. I've never tried to turn plastic before, so I might chuck up a piece of this stuff because there's enough material to try again if I screw up.
2. The knob I'm trying to replicate is only one of 3 knobs that shipped with these little lathes, and I want the color to match exactly, if I can. From what I can tell, the handles of the Millers Falls "804 series" screwdrivers were made from the same material as the Rivett 1R knobs. They are also from the same year, too, so they stand a good chance of being EXACTLY the same color. So, what I think I'll do is order some of those rods to practice on and then make the real thing with the screwdriver handle.

 

[cazclocker]

Sure you can turn plastics on the lathe; you may have some polishing to do afterwards if you want the part to have a clear shiny finish.
Also drill to size, don't use a pilot drill as is often done with metals. Plastics can crack and shatter when trying to enlarge an existing hole
-Mark

Yes, I'll have to polish it. I'm hoping successively finer grits of wet/dry paper will do the trick.
THANK you for the tip about drilling to size - I did not know there was an increased chance of shattering when trying to enlarge an existing hole, but it makes sense, now that I think about it.

 

[cazclocker]

They can also crack and shatter if you get greedy with a cut too….

View attachment 420575

YIKES!!!!

 

[cazclocker]

I'd vote for considering a casting, with dye to color the stuff; Tap Plastics has transparent dyes
for this sort of thing... an epoxy or urethane casting would be nice and durable, compared to acrylic,
and you can get a good mechanical bond to the machine part by embedding it while
the resin is still soft. Machining to finished shape, or turning a mold, will satisfy the need to
make swarf...

I've considered that approach! But as I mentioned, color matching is important to me, so I think my best chance of success will be to get a piece of the same material the other two knobs were made from. That kind of forces me to resort to a Millers Falls "804 series" screwdriver, which was made the same year as the Rivett 1R.

 

[cazclocker]

You will also want to have a nice radius on your turning and facing tools. That will help with the finish and keep from chipping.


Cutting oil is my blood.

I have several cutters that I keep nice radii on... one of them will end up on the front lines!

 

[cazclocker]

Personally, I'd do it on a wood lathe with hand tools. But I have a lot of wood turning experience. It will be grabby. Probably would mostly use scrapers. It would be easy to sand and polish by hand. As many have said, watch the cutting speed as you don't want to start melting / softening it. Another thing with plastics is you can/will get one continuous strand of swarf that can range from a nuisance to dangerous.

You do not state why you are committed to sticking with plastic/acrylic, why? I'm guessing that you want it to look original. It may be hard to match it anyway. So why not just use a piece of wood?

Why I'm committed to using plastic is a fair question. You're correct; I want it to look original. The first picture (of the three I posted) is NOT my Rivett 1R - it's someone else's. But it shows the appearance of an undamaged 1R. That's my end goal. Well, one of them, anyway!

 

[stupoty]

They can also crack and shatter if you get greedy with a cut too….

View attachment 420575

Ive had that issue with milling thin (5mm) perspex sheet.

Lots of hold downs and no letting it vibrate !

Stu