Breaking bits too often

My xcarve is still being assembled, once its up and running with my dewalt 611 my bit issues may go away.

however currently I am working on a shopbot with 4x8’ sheet size. Although I typically only run 4x4’ sheets at a time.

I am only running 1/4" and 1/2" baltic plywood at the moment. Here is what happening and any advice is appreciated.

Im using Rockler or Freud solid carbide bits mostly in 1/4 shank size. Either up or straight shank in 1/4" or 1/8" bit.

Im running 34,000 rpm, 1 in per sec and usually 3 steps on 1/4" and 5 steps on the 1/2"

I’m only getting 1-2 sheet cuts per bit before its either dull or breaks.

Its costling me $18 a bit and i need to buy one every time I run a new job (1-2 sheets).

This doesnt seem normal. Any advice would be appreciated.

60 inches per minute and 34k rpm…slow down the spindle and increase the feedrate.

You are doing a lot of rubbing with those settings…which dulls the bit. Try halving the spindle speed.

Second that.

Chip Load = feed rate ( ipm ) ÷ ( cutting rpm x number of cutting edges )

Assuming you’re using 2 flute - you’re getting about .0008 chipload which means you’re probably making a a fine dust instead of chips. Your bit is getting real hot (dulling) and losing it’s temper (breaking).

You should be able to pause the machine, stop the spindle, and the bit shouldn’t be that hot. Disclaimer: it may be hot so don’t burn yourself. Whenever I have done this I’ve been able to hold onto the bit just fine and I would consider it warm.

Ok thats been my problem then. I’ll make those ajustments and report my results. I appreciate the advice guys. I’ve been using single flutes lately. Also read some folks who use downcuts with better success in ply and mdf.

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@Corey- yes fine dust, no chips.

The chips remove the heat from the bit and the dust will not do that. I don’t have much experience with mdf and plyboard but I’ve also seen that about downcut. The downward motion will prevent tear out on the ply so you should have a nice clean top surface.

Posting results from this morning.

I ran a job this morning on 1/2" baltic birch ply and got excellent results.

Home Depot didnt have a downcut spiral so I used a Freud 1/4" upcut spiral with climbing direction on.

4 passes at 12,500 rpm and 6 ips.

Cut like a dream, wood chips- no dust, bit stayed cool and no rainbowing on the metal or burning on the wood.

I’ll continue to fine tune as I continue but cant thank you guys enough for the feedback.

Ill share photos of my work soon. :slight_smile:


The X Carve is great, but these forums are even better. If it wasn’t for helpful people in here providing assistance, I’d have given up long ago…