Lathe question!

I've got a project going in another thread. There are a few parts I'm considering turning on a lathe. In itself, no big deal: I've got quite a bit of lathe experience. The question is one of materials used. While I've turned wood and metal, I'm considering using plastic on these parts. I've never even considered using plastic on a lathe until now. Is it even possible? My first thought is it would take a slower r.p.m. to cut down on heat issues, but beyond that I'm frankly clueless. Anyone here have any experience with plastic lathing? Or is it no big deal, and I'm just over-thinking this?

Plastic can be lathed just fine. As you said the speed needs to be reduced, the speeds used for wood or metal will melt plastic instantly. I've shaped plastic parts by spinning them in my drill press.

Ah, great! That's kind of what I was thinking, robn1. Everytime I've drilled plastic I've had to cut down the r.p.m., so yeah it would be crazy to go full-bore with plastic on a lathe!
Looks like I'll be giving my Eagle engine bells a go, then!
Thanks!

Also depends what type of plastic you plan on turning. At work we often pour up a blank of urethane plastic to turn on the lathe. Cuts beautifully.

I'll keep that in mind about the urethane, swgeek. I'm going to see what's available to me. Thanks!
I definitely don't want to attempt anything too soft.

swgeek said:

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At work we often pour up a blank of urethane plastic to turn on the lathe. Cuts beautifully.

I do this all the time, it smells like hell but it machines great...

You will likely find that Delrin is the most popular machining plastic it has a lot of favorable qualities...

I would suggest delrin as your material. solid & very easy to machine. Your cutting speed should be between 150-300 feet per minute. To get your rpm the formula is CSx4/diameter.
Multiply your cutting speed by 4 then divide that number by your workpiece diameter. To find cutting speeds just google something like "delrin cutting speed". Most of that info is readily available for materials.

Great advice, everyone! Hard to beat the rpf "brain bank" for handy tips to improve ones' craft!
This sounds like it's going to be a lot of fun, certainly moreso than turning machine parts, brake discs or table legs!

I lathe PVC rod. works great. my tank build has some gun barrels i did in PVC. also besides the slower speed. use a very sharp bit.

I also agree with others regarding delein Turns like a dream!

Delrin is ok if your going to mold the part but if your using it as a finished painted part i wouldnt. delrin has a tendency for the primer or paint to peel off over time.

Interesting. Peeling paint would be an issue, of course. I could play it safe and go with urethane. Decisions, decisions...

I've had delrin parts made, but since I wanted clear colored items I never painted them. I found that they were tough and stood up well under use as long as you didn't use them as an impact tool. Urethane would be better if you want to paint, but there is a latex water-based primer you can get at home painting supply places that seems to stick to everything. I have used it on slick brass and other metal types of items with great success-it might be good for delrin.

Delrin is considered self lubricating. ive used an adhesion promoter and it helped a little. still ended up peeling after a few weeks. we did a bunch of tests with delrin when making aircraft parts.

i find it mind boggling that you ask this question.

all i have ever turned on my lathe is plastic.

PVC rod, cast smooth-on, cast alumalite, acrylic rod, polycarbonate rod.

all turn very nicely, except for acrylic. one wrong move (chatter) and the acrylic will shatter.

i have my taig lathe set at its slowest speed.

Yeah, I felt crazy asking it, as I've turned so many other substances over the years! Actually it's hard to believe that plastic has never presented itself to me on a job! And your acrylic comment confirms my suspicions about it, thanks!

My first impulse was to go with aluminum, but I figured the potential howling coming off that might wake up every dog in the neighborhood!

swgeek said:

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Also depends what type of plastic you plan on turning. At work we often pour up a blank of urethane plastic to turn on the lathe. Cuts beautifully.

Um, are you suggesting I pour my own blanks? I'm going to need at least a 2 1/4 inch diameter rod, and I know not where to acquire such a thing around here, short of using liquid urethane. Possible? Or am I getting dumber by the post?

try a plastic supply house. they usually carry all sizes of rod. in what ever plastic you may need.

PVC rod for me. Makes great barrels and easy to remove waste. Has strength.

TazMan2000

How's the PVC rod with paint? I can get that readily, and won't have to journey half way across the state for that...

Depending on the size of your part you
could use acrylic pen blanks. I have turned many acrylic blanks to make pens years ago. Easy to turn.

I use DELRIN for any part that I am prototyping (super easy to work with except that the chip always seems to get all tangled up). I have spun it up to 1200rpm with no melting problems at all. Cast ACRYLIC for any clear/transparent parts. you can machine it and then polish it up to almost glass clear with sandpaper and Novus plastic polish.

If you need to paint it I would just prototype the part in DELRIN and cast it in resin. I have never had much luck getting paint to stick to any plastic parts I have machined (except cast acrylic, automotive paint seems to stick to that pretty good).

I am not a pro and just talking trial and error. I would listen to the people who do it for a living .

Well, I used to do it for a living... but I too am in a fog about this! As I've said, plastic on the lathe is just something that never came up! I'm wondering if something to "dull down" the machined finish (i.e. hand sanding, steel wool, etc.) would aid in paint adhesion...?

First off if you use PVC theres no issue with paint sticking. second if your that worried about the paint sticking go to any auto supply store and get Bull dog adhesion promoter. spray a light coat of this first, let dry and then sparay whatever you want over it. should do the trick. theres no real trick to turning plastic except for the speed.

Well, this all sounds like all the advice I'll need to make a go of this! Now it's just a matter of doing it. Thanks a billion, guys!