# What are the causes?



## john heff (Sep 7, 2008)

I broke the tip off one flute of my 1/2" solid carbide spiral upcut bit and would like to understand what I did wrong so I don't repeat it with any of my other solid carbide bits. I have read that carbide will break if dropped, but are there other percautions that must be taken when using solid carbide bits? 

I was using a table mounted router and fence to rout a 1/2"Wide x 3/8"Deep groove in 8ft lengths of maple, making multiple passes 1/8" deep. I had made 7 passes before breaking 1/4" off the tip of my bit.....I hadn't noticed any difference between that pass and the previous 6 passes. 

It is a brand new bit and I have never dropped it.
There is no discoloration anywhere on the bit.
The bit was manufactured by one of the top three recommended by RF members.
I had a 3/4" brass insert installed in the base-plate.
The router speed was 10,000 rpm.....I *thought* the speed was 23,000 but later I found I had the rotary speed switch set to the wrong end of its rotation, therefore the speed was set only to 10,000 rpm.
I'm not sure what my rate-of-feed was......I'm guessing it to have been around 1/2" per second, or 1" per 3 seconds. The work-pieces were kept tight against both the fence and tabletop.

Can the broken bit be repaired?

Thanks for your help. - John


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## dovetail_65 (Jan 22, 2008)

It sounds like you did nothing wrong(except the speed). 

I have had that happen on brand new bits every now and again and they usually will take them for an exchange.

You can not repair that and I would not try they are brittle bits.


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## bobj3 (Jan 17, 2006)

HI John

You can repair it but it would be cheaper to just replace it..

The harder the bit the more brittle it is.. 

I have my share of bits just like that,, most of the load is right at the tip of the bit, it just takes a little tap in the slot to break one...the real key is not to over load the bit  small cuts, it will take longer but it's cheaper in the long run..don't forget it's doing two jobs at one time , making the bottom flat and cleaning the edge at the same time...chips do like to go around and around and they over load the bit.. 



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john heff said:


> I broke the tip off one flute of my 1/2" solid carbide spiral upcut bit and would like to understand what I did wrong so I don't repeat it with any of my other solid carbide bits. I have read that carbide will break if dropped, but are there other percautions that must be taken when using solid carbide bits?
> 
> I was using a table mounted router and fence to rout a 1/2"Wide x 3/8"Deep groove in 8ft lengths of maple, making multiple passes 1/8" deep. I had made 7 passes before breaking 1/4" off the tip of my bit.....I hadn't noticed any difference between that pass and the previous 6 passes.
> 
> ...


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## Skyglider (Nov 2, 2008)

deleted post.


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