# cmt 90 deg carbide



## dickhob (Apr 7, 2012)

I bought a cmt 90 deg router bit (815.660.11) from Amazon. It arrived in their usual 2 days and I was pretty excited. I'm trying to rout small 2x2x6x 1/8 boxes. 

When I pulled the bit out of the case, I noticed that one of the carbide sides does not go all the way to the very tip of the bit. It is about 1/16 short. I assumed it was a grinding error that got by QA, and contacted Amazon for a replacement. True to form, they shipped me a new bit overnight. (I really can't say enough good things about Amazon. They are a really great company).

Anyway the bit just arrived. It is exactly the same grind. One of the carbide edges is about 1/16 short from the point. I looked at the picture on Amazon and also on the CMT website. Both appear to show full length carbide edges all the way to form the point.

Before I send this one back again, Can anyone tell me is a short carbide edge on one side normal? Does it produce a clean cut and mitered edge? Or is it a quirk and I've gotten two defective bits in a row?

I've included a picture to show you what I'm talking about.
Thanks
Dick


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## Mike (Nov 22, 2004)

I haven't run into this before but I will check with the CMT Rep about this.


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## jim_hazel (Aug 7, 2011)

*Opinion*

I am not an expert at bits and the like, but if you think about the issue, grinding a 90 degree point with the cutting edge facing different directions (because they are on differing sides of the cutter) would result in a less than clean and perfect bottom. By designing the bit so that only one cutter forms the deepest part, that problem is avoided. My opinion is that this is a design feature and a good one.


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## Cherryville Chuck (Sep 28, 2010)

I downloaded CMT's catalogue a little while back. I just checked it and the picture in the catalog is not like your picture.


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## dickhob (Apr 7, 2012)

Thanks guys. I tend to agree with what's been said so far. I'll wait to see what Mike finds out, but I think Amazon may have a bad batch of bits.

Thanks again
Dick


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## Mike (Nov 22, 2004)

The Rep messaged me back yesterday that he is checking on this. It is so nice to get good information right from the source. I will post his response as soon as I get it. I suspect this is a built in chip clearing feature; most relief cut like this are.


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## wmpwi (Oct 13, 2012)

I just bought a CMT 90 V via Amazon (1/4 though) and it's the same design. I think it's intentional and might be for making some tiny or more precise line for shallow cuts. It too exact to be an accident.


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## wmpwi (Oct 13, 2012)

Oops, I kind of wish I had read this response before I jumped in w/ my opinion. Make more sense to me. 



Mike said:


> The Rep messaged me back yesterday that he is checking on this. It is so nice to get good information right from the source. I will post his response as soon as I get it. I suspect this is a built in chip clearing feature; most relief cut like this are.


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## MAFoElffen (Jun 8, 2012)

To me, logically, the full length carbide would cut what the shorter misses. On the other hand, the bit would tend to not center on shallow cuts, because of the shorter cut and less friction on one side of the bit, which would also affect the weight/balance. (unless they compensated for that elsewhere.)

??? Curious to hear what CMT says.


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## Phil P (Jul 25, 2010)

Hi Dick

I've used CNC tooling for the same purpose in the past which was specifically designed as single point tooling, i.e. only one side of the carbide ran to the tip, the other was shorter. This was supposed to make the cutting edge run cooler and the grind more accurate. It wouldn't surprise me if that were the reason for the design. It is interesting to note that replaceable-tip CNC tooling I've used for the same task is pretty much always single point, in that case woth a single carbide insert only

Regards

Phil


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## jw2170 (Jan 24, 2008)

I note the original post was back in June, so it seems no response from CMT rep back to Mike.


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