# Spiral Bit Breaking in Router



## MikeMa (Jul 27, 2006)

I am having issues with a 1/4" spiral bit use in the router table. I had the bit set for a 3/8" cut depth. Feather boards were used to keep the work piece flat to the table and to the fence. The cut started out well, and I was not using a lot of force to push the piece through, in fact it was going through fairly easily. Mid-way through the cut the bit breaks in the collet! I just purchased this bit this week and this was the first time I used this bit.

Any thoughts as to why this would occur? Defective bit? Collett too tight? (I tend to make sure they are good in tight as I have sign spiral bits pull themselves out.) Too deep of a cut?

The bit was a Bosch bit purchased from Lowes.


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## jschaben (Jun 21, 2009)

NiceG316 said:


> I am having issues with a 1/4" spiral bit use in the router table. I had the bit set for a 3/8" cut depth. Feather boards were used to keep the work piece flat to the table and to the fence. The cut started out well, and I was not using a lot of force to push the piece through, in fact it was going through fairly easily. Mid-way through the cut the bit breaks in the collet! I just purchased this bit this week and this was the first time I used this bit.
> 
> Any thoughts as to why this would occur? Defective bit? Collett too tight? (I tend to make sure they are good in tight as I have sign spiral bits pull themselves out.) Too deep of a cut?
> 
> The bit was a Bosch bit purchased from Lowes.


Hi Mike - tough luck on the bit. 3/8" is a pretty big bite for a 1/4" bit, I would suggest doing that cut in two or even 3 passes. I try not to make a single pass deeper than the diameter of the cutter. On larger bits it is even less.


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## jlord (Nov 16, 2009)

Hi Mike, 
It sounds like to much at once for such a small bit. Try taking a couple of passes to your required depth.


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## bobj3 (Jan 17, 2006)

Hi Mike

That is common with spiral bits, if the bit comes up just bit it will jam and it will break in a heart beat 

A good way to tell if that did it look in the slot and see if it's a little bit deeper in one spot.  they do like to creep up..
Also if you are using the wrong type of bit in the router table it will pack the slot up and jam the bit.. (upcut / downcut thing) 
==


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## MikeMa (Jul 27, 2006)

I am using an upcut bit for grooving out 1/4" dado 3/8" deep. Is the upcut not the appropiate bit?


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## MikeMa (Jul 27, 2006)

I took a close look at the piece that went through. I am thinking the cause is too much at one time. The sides of the cut are very rough throughout. You can see where the bit itself start to rack in the cut about 2/3 the way through the cut, then at the very end you can see where the bit dug in to the piece. I am going to get this bit replaced and will try with smaller cuts next time.


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## jschaben (Jun 21, 2009)

NiceG316 said:


> I took a close look at the piece that went through. I am thinking the cause is too much at one time. The sides of the cut are very rough throughout. You can see where the bit itself start to rack in the cut about 2/3 the way through the cut, then at the very end you can see where the bit dug in to the piece. I am going to get this bit replaced and will try with smaller cuts next time.


Upcut should be fine, try it with a max of, say 3/16 and make two passes.


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## BigJimAK (Mar 13, 2009)

Mike,
John is dead-on.. A good rule of thumb is to limit your max cut to no deeper than the diameter of the bit or the shank, whichever is smaller. Also, by cutting shallower you can cut faster, minimizing any burning of the wood. As the diameter of the cutter grows significantly wider than the diameter of the shank you should further reduce the depth of each cut when you are cutting the full cutter-width, as the stress on the shank goes up. As a side-note, long cutters should be reserved for trimming the edge of a piece of wood, where you're not removing the full width of the cutter.


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