What bit to cut 1/2" plexiglass?

[signtist]

The search does not seem to work.
So can someone set me straight.....I need to cut out 8" letters from black plexiglass.
What 3/16" bit?
Single edge or double?
What speed?
What depth per pass?
Conventinal or climb direction?
This is a $500 a sheet .....so I can't afford to screw it up!!!!

[jerry_stanek]

you could try this bit and ask Onsrud what speed to cut at they are pretty good at this. I used a 9/64 bit to cut some as I needed to keep the inside as small as possible. It also depends on what you require for the edge finish.

[signtist]

Jerry....What bit? Do you have a number for it.
I could use a 1/4", but would 3/16" is better.

[knight_toolworks]

a o flute bit is best. myself I like a 1/8" bit it's easier to keep the plastic in place. 1 to 2 ips 8000rpms is fine. 1/4" per pass.

[woodworx]

This works the best for me. Surface the table.
1/4 downspiral to score the top at a depth of .1" to prevent chipout. Change bits to a compression or upcut and make 2 passes leaving a .03 skin on the bottom so you don't loose vacuum and cut through but with a .01 allowance removing the lines on the edges left by making 2 passes. I have cut acrylic like this many times and this is the fail safe way...I wish it was 1 pass all the way through with out the letters moving, but that isn't reality.

[knight_toolworks]

that's not a bad idea on the downcut. though I don't remember having any chip out though. I pretty much only cut cast and that cuts far better.

[garyb]

Onsrud 63-520
3/16" spiral O flute for hard and soft Acrylic

[geneb]

My last project required cutting knobs from a 1" thick block of acrylic. I used a 1/4" "O" flute bit from Centurion Tools at 10,000 RPM with a feed rate of 1.2in/sec.

This was the result:
http://www.simpits.org/geneb/wp-content/uploads/2009/09/brfs_knobs.jpg

g.