Broken Bits

[terryb]

Hi all ... breaking a couple bits today....I'm using a material made by Rowmark...its 1/8" thick its used for ADA signage...(soft plastic)I'm trying to ingrave a oval inside a oval number plate 1/32" deep... the bit is a onsrud 1/16" 1/4 shank...(63-700)any suggetions on a feed rate , spindle speed , Z plunge ...currently set at 1.5 feed ,0.5 z plunge ,10,000 rpms......image attached..

Terry B
7030

[kerrazy]

What kind of spindel?

[jsfrost]

Terry,

I have never tried with a 1/16th bit, but I think you can get the effect you want with a 90 degree V. Plunge depth of 1/2 the desired line width.

Unless this is a two color plastic. If so, make the depth enough to display both colors.

[terryb]

dale ...5 hp colombo

[terryb]

Jim ...its a revesable material ...I'm try to duplicate a part made sevral years ago ...got it to the excat match with bit ...cut about 70 parts then the bit broke..I have an other one, just curious ...on what would cause the bit to break

Terry B

[patricktoomey]

I usually run 1/16" bits at 0.5 ips to maybe 1.0 ips. On RPM's it depends on material but I usually crank it up a little higher, maybe 12,000-15,000. I think the chipload calculations breakdown on very small diameter bits and it seems like you have to get the RPM's up to reach the minimum cutting edge velocity to avoid overloading the bit and breaking it. That or run really slowly on the feed rate. That's my experience with little bits but I'm definitely not a bit expert so take all of this with a grain of NaCl.

EDITED: I forgot to add that when the bit does eventually dull it's going to overheat/overload and break if you keep running it. I can get hundreds of a particular part out of wood before breakage but maybe only a few dozen of the same part in Corian or HiMax.

[jhicks]

Terry, I too run the copolymer materials for signs and agree with Patrick .5IPS maybe.7 max at 12,000 RPM with .062" cut depth for fine details on an .062 bit and we cut/clear starting on the outside of the letters moving with an inside offset to get the cleanest outside edge definition. Unfortunately this means 2 passes when surface color exceeds .062" which is the case on anything over 1/4" stock. 1/2" stock is supposed to have top color at .05 but we have seen enough variation to go 2 passes and avoid any failure to clear the top color. Maybe trying a bit deepoer like .075 cut would work but you would have to experiment to be sure.

Usually a conventional vs climb cut gives us the best results. Stepover at between 30 and 40%