# Why a 7 degree dovetail bit for PC Omnijig?



## Harvoc (Dec 10, 2010)

Can someone tell me if it is necessary to use only a 7 degree dovetail bit for the PC Omnijig, or whether bits of different angles can also be used.

All of Porter Cable's dovetail bits are 7 degrees. I cannot find any words of caution in the instruction manual against the use of bits of any other angle. However, I am wondering if there is some intrinsic design in the Omnijig that makes use of other angles prohibitive.

Thanks very much,
Harv
New Haven, CT


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## jw2170 (Jan 24, 2008)

Harvoc said:


> Can someone tell me if it is necessary to use only a 7 degree dovetail bit for the PC Omnijig, or whether bits of different angles can also be used.
> 
> All of Porter Cable's dovetail bits are 7 degrees. I cannot find any words of caution in the instruction manual against the use of bits of any other angle. However, I am wondering if there is some intrinsic design in the Omnijig that makes use of other angles prohibitive.
> 
> ...


Hi Harv,

If you use other angles, wont the ends of the pins and tails be different widths for a set depth?


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## bobj3 (Jan 17, 2006)

Hi Harv

The 7 deg. and the 8 deg. dovetail bits are used for though dovetails the norm 10 deg.,12 deg.14 deg.,18 deg. dovetail bits are used for the blind dovetails the norm but the 7 and the 8 deg. can also be used for the blind dovetails also..in 1/4" to 1/2" thick stock the norm..

http://cgi.ebay.com/16-pc-1-4-Shank...489703982?pt=Routers_Bits&hash=item20b5d6c22e

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Harvoc said:


> Can someone tell me if it is necessary to use only a 7 degree dovetail bit for the PC Omnijig, or whether bits of different angles can also be used.
> 
> All of Porter Cable's dovetail bits are 7 degrees. I cannot find any words of caution in the instruction manual against the use of bits of any other angle. However, I am wondering if there is some intrinsic design in the Omnijig that makes use of other angles prohibitive.
> 
> ...


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## Ralph Barker (Dec 15, 2008)

The 7° DT bit matches the angle of the fingers on the pin side of the template for through dovetails.


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## Harvoc (Dec 10, 2010)

Thanks Ralph. I "see" the geometry of it now. I didn't realize those fingers were offset to a matching 7 degree angle, and now it is very apparent why. Through dovetails can only be 7 degrees on the PC Omnijig, but half blind dovetails can still be any angle as both tails and pins are cut with the same dovetail bit. Do I have it all correct?
Thanks,
Harv 
New Haven, CT


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## Ralph Barker (Dec 15, 2008)

Harvoc said:


> Thanks Ralph. I "see" the geometry of it now. I didn't realize those fingers were offset to a matching 7 degree angle, and now it is very apparent why. Through dovetails can only be 7 degrees on the PC Omnijig, but half blind dovetails can still be any angle as both tails and pins are cut with the same dovetail bit. *Do I have it all correct?*
> Thanks,
> Harv
> New Haven, CT


Yep. You'd still want to give consideration to the spacing (adjustable on the OmniJig) and the nature of the material, though.


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## bobj3 (Jan 17, 2006)

Many of the dovetail jigs that use the 7deg..dovetail bit also use the strait cutting on the other side of the dovetail joint to match the 7 deg.cut of the dovetail bit, Katie jig for just one of many..


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