machining epoxy

[bob golding]

has anyone tried turning a epoxy cast rotor? i have cast my magnet rotors but didnt get them level while the epoxy was curing so i have around 2mm more on one side. i have access to a lathe large enough to fit the rotors so i can true them up. no experience of turning epoxy though. anyone got any clues on speed and type of cutting tool needed. do  i need coolant?  i know keeping the heat to a minimum is important. any other things to look out for, apart from not putting the rotor down on the bed of the lathe of course this is why i am doing the job myself.  don't want the machinist phoning me up and asking how to get the rotor unstuck from side of the lathe. i know 2mm is not a lot but as i have ghad the offer of a free lathe to use thought i would at least try it unless there is a good reason not to. in which case i will live with 2mm runout happily.

[fabricator]

You won't need any coolant and heat will not be a problem, as long as it's cured good and hard it'll machine a lot like most plastics, I suspect getting a rotor set up so it's taking off the high side will be the biggest job. You would almost be better off doing it on a mill.

[bob golding]

You won't need any coolant and heat will not be a problem, as long as it's cured good and hard it'll machine a lot like most plastics, I suspect getting a rotor set up so it's taking off the high side will be the biggest job. You would almost be better off doing it on a mill.

thanks fabricator,
 i have an old hub from another project that will fit the rotor holes with a nice 3 inch diameter 4inch long machined end that will fit into the chuck so lining it up shouldn't be a problem.  epoxy is nice and hard had around 3 weeks to cure.

[fabricator]

Well just because the hub fits and you have a machined shaft does not mean the high spot on the rotor will be the high spot when you get it chucked up, I hope it works out for you, if you have problems you can try changing to different hub holes or just turning the shaft in the chuck to get it right.

[bj]

   Bob---never tried a lathe, but do lots of epoxy/die grinder stuff, and it's never been an issue.  Different epoxies
do behave differently though.  Never have had to use coolant, but sharp carbides are always cutting, and chips
don't get a chance to heat up.
   

[ruddycrazy]

Hi bob,
 I always machine the extra epoxy off when I've made both stators and rotors, all I use is HSS tool ground up with a knife edge.

cheers Bryan

[oztules]

Bob...... BEWARE

If you have anything like my luck, you will find out how to stick iron filings to every bit of the lathe, tool post, chuck, tooling, and anything else within a small distance of your turning rotors.
It seems unavoidable.

You will likely need a degaussing device to neutralise the lathe and your magnetic tooling....... think big AC electromagnetic.

I used a microwave transformer core (cut the "I"'s off and used just the EEEEs and the primary. Drove it from a 48v transformer into the 240v primary... Worked a treat.

I know you are only turning the epoxy off...... but when the owner turns up and uses it on steel..... all the chips try to migrate into the spiral of the chuck, and binds everything up.... he won't love you anymore thats for sure.



..................oztules

[Flux]

Epoxy is no trouble to machine, without filler any tool will do as long as it is sharp. With certain fillers it can be abrasive and carbide will hold up better but HSS should be fine unless you have loads to get off.

Machine tools, chucks tool holders etc and made of hardened steel and as Oz has warned they are quite good permanent magnet materials so if it is a friend's lathe then watch how you mount the rotor and be careful not to let any form of tooling get direct contact with the magnets. Demagnetising is difficult even with this very poor carbon steel magnet material. Those who have used magnetic chucks on grinders for steel parts will know only too well.

Flux

[bob golding]

mmm hadn't thought of the effect on the lathe. i don't wont to upset him being as he has been generous enough  to offer.  think i might just try to file it down with a rasp instead. its only a couple of mm so might be better to not risk it.

[tanner0441]

Hi

 What is wrong with a long flat  bed sander as used in body shops? You could fix the rotor to a flat piece of board, like a bit of counter top, then fit strips of hard timber round the rotor and sand down to the wood. The harder epoxy will sand off quite quickly and youwill see if you are hitting the wood.  Then finish by hand.

Just a thought...

Brian.

[fabricator]

Epoxy is EXTREMELY hard to sand, almost impossible, unless it has special fillers in it to make it sandable.

[bob golding]

job done. lathe is still ok . no problems with swarf in the chuck. finish looks like an old 78 record. but its at least flat now.  had to have the  cross slide all the way out to get it to fit.  will  slap a coat of epoxy on it to finish it off.

[fabricator]

Good deal.

[RP]

will  slap a coat of epoxy on it to finish it off.

Be sure to level it this time...