Bits breaking problem

[GlacialWanderer]

I've been cutting a lot of 1/4 and 1/2 inch plywood. My bits have been lasting for an hour or two and then they snap. Using 1/4 and 1/8 carbide endmill bits.

Do people have any suggestions on what sorts of issues with my machine might cause this?

[jalessi]

GlacialWanderer,

Are you settng your depth of cut to agressively for the size cutter you are using?


Jeff...

[wizardrule]

that would be my first thought as well. How deep a cut you doing?

[GlacialWanderer]

I'm setting the depth of the cut equal to the width of the cutter. I read this was a good place to start. Is this reasonable? What feed rates do you suggest for plywood. I'm using Models a Porter Cable 690 (27,500 rpm) router.

I new to the whole CNC scene so I'm just looking for ideas on what the problem might be. This was a good idea. What other things might cause my bits to break?

[LeeWay]

You can try shortening the amount of bit you have exposed. Try different styles of bits as well. I cut lexan with a 2 flute carbide 3/16" router bit cutting 3/32" deep @ 150 IPM.
I would not use a 4 flute bit in wood or plastic. Not sure what yours is, but 2 and 3 flutes seem to work best for me.
I have tried a single flute bit too, but it doesn't seem to be as good.

[ger21]

Are you using metal cutting endmills, or spiral router bits? Most likely, you're breaking bits because you're RPM is too high, and your feedrate is too low. You should never be able to break a 1/4" bit. If you use the correct bit for the application, a 1/4" bit is capable of cutting 1/2" plywood at 1000ipm in a single pass. Obviously your PC 690 won't be able to do that, though. Ideally you want to cut as fast as possible, and adjust your rpm to match. So we need to know your max feedrate you can cut at.

Cutting depth = tool diameter is OK, you can go deeper if you like. But it's important to clear the chips out of the cut between passes, especially with the 1/8" bit. If you don't, you'll be creating a lot of heat, which quickly dulls and weakens the bit, which can cause breakage.