Cutting plastic discs

[simonfilm]

I need to cut a disk like this http://www.dfocussystem.com/images/marking2_thumb.jpg.

It can be nylon, polythene, kevlar, etc. The big diameter is almost 100 mm ( 4 inches) and 5 mm thik. I have thought two aproachs. With a round bar. Here the problem is to part it on the lathe. The other aproach is with a plate. Cut a cirle and put it in the lathe. Here the problem is that is very thin and can bend in the chuck.

Any idea?

Thank you very much!

[rowbare]

Do you have a drill press? Get a couple of hole saws and cut them out of flat stock. Do the small hole first and use the same guide hole for the large saw.

bob

[pofo]

I'm no machinist, so don't listen to me. But there is a video on the M.I.T. site with a series of machining videos. He shows how to cut thin material on a lathe using a plate with double sided sticky tape instead of a chuck. He cut aluminum on it. He cut a disk with a hole just as you show.

I would think it would be even easier with plastic.

It's one of the videos in this series. http://techtv.mit.edu/genres/24-how-...machine-shop-1

[SanDiegoCNC]

Originally Posted by simonfilm I need to cut a disk like this http://www.dfocussystem.com/images/marking2_thumb.jpg. It can be nylon, polythene, kevlar, etc. The big diameter is almost 100 mm ( 4 inches) and 5 mm thik. I have thought two aproachs. With a round bar. Here the problem is to part it on the lathe. The other aproach is with a plate. Cut a cirle and put it in the lathe. Here the problem is that is very thin and can bend in the chuck. Any idea? Thank you very much!

This is probably best cut on a waterjet or cnc laser if you have access to either.

The next best way would be to use double-back tape and cut them on a cnc mill.

Lastly, if you cut them on a lathe, you'll have to do so with a chuck since the diameter is so large. Using nylon will be a problem with a lathe because it has a tendency to flex while cutting, even with a sharp insert like an NPR parallel (0.004 R). Also, you would need to use a cutoff blade (0.123 wide) to reach the desired depth during cutoff. That presents the biggest problem... having the cutoff blade extended out so far makes for a less rigid tool. If you do decide to machine this on a lathe, be sure to adjust your home position in 'X' away from the sheet metal, otherwise you'll crash when the tool indexes.

Hope that helps!