Re: [CAD_CAM_EDM_DRO] Routing speeds and feeds for plastic "sign" material

On 09/23/2010 02:48 PM, Alan Rothenbush wrote:

> I'm tired of having a CNC milling machine and a CNC PCB router and still labelling things with a Dymo labeller!
>
> So I bought some of that standard sign material .. you know the stuff, soft plastic, thin black layer on the top, white below.
>
> First step was to route a hole for a fuse, next step engrave some lettering below the hole.
>
> I'll be darned, though, if I can figure out the speeds and feeds and whatnot for this material.
>
> Everything I do just seems to melt the plastic onto the cutter!
>
> Any advice or pointers to some reading material greatly appreciated.
>
>
> Alan
>
> --
> Alan Rothenbush
> Client and Research Services
> IT Services
> Simon Fraser University
>

Free advice, worth what you paid for it!

Try cooking spray, then spin your bit to full speed with paper towels
around it to allow excess to come off. Often, the microscopic layer of
oil will make bit cleaning easier.

It sounds like you are spinning too fast or feeding too slowly. Why?
If you spin too fast, the friction melts stuff. I have seen machinists
cutting steel which was throwing brown chips (they said this was good.)
When the chips turned blue, they changed cutters. Scary stuff!

A test: DO NOT SPRAY THE BIT FIRST! Take a tiny drill bit in your
drill press, put a hunk of scrap on a steel block. Run it as slowly as
the press will run and try to make a curl of waste. You will probably
succeed as the chips carry off the heat and friction is low. Now,
increase the speed until the plastic either starts to melt or you can't
get good chips. With each speed increase, you will feed faster to
maintain the chip formation. When the plastic starts to melt, try
treating the bit with cooking spray and try again. If the melting
stops, you know a secret.

DO NOT SPRAY THE BIT FIRST! On the router using scrap and a bit that
you don't really care about, run it at very shallow cuts and the lowest
speed the router will do. Slow feed will result in a gummed router.
Clean and increase the feed rate. Repeat until you get to your feed
limit or you get clean cuts. WARNING: Too deep a cut will guarantee
broken bits.

You now have a feed and speed, try slightly deeper cuts until you get
melting. This should be near a sweet spot. Now back off a few percent
and increase the router speed and see what happens. Eventually, you
will reach a point where the router speed will just be too high, or you
won't be able to feed fast enough.

Now spray the bit, let it dry and spin it into paper (any loose oil will
hit the paper, not the work.) See if it helps (it probably will), drop
back to where you have some margin and you should be good to go.

If you REALLY are masochistic, you can graph speed and feed combinations
and you will see you have a maximum bit speed, a minimum and maximum
feed rate, and a maximum depth of cut. Given that, you will probably be
able to find a safe operating area and stay within it.

Dave 8{)

P.S. Or you could just try the spray and see if that fixes things
enough... :-P