Dovetail Jig Question

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Forum topic by WoodJitsu posted 12-31-2010 11:21 PM 1159 views 0 times favorited 4 replies Add to Favorites Watch
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49 posts in 2816 days

12-31-2010 11:21 PM

Hi All,
I have a general about dovetail jigs. Why is it when you raise or lower a dovetail bit for half blinds, it changes the fit? Logically, it seems like the fit would be the same, regardless of the bit height because you are cutting both sides with that same position. But, that’s not the case and I’m just trying to understand why. Any help would be great
thanks and HAPPY NEW YEAR!

-- Family, Friends, Jiu Jitsu, Woodworking. Order varies daily!

4 replies so far

View woodman71's profile


162 posts in 3347 days

#1 posted 01-01-2011 02:29 AM

Well I have the porter cable omni jig and my experience is that the angle of the dovetail bit is important porter cable says to use a 7 degree bit and by lower it and raise it you are changing the angle of your tails I guess it either right our wrong no in between and I guess any dovetail bit will do but I stay with want your dovetail machine owner manual says to use you will get best results .

View Mark Shymanski's profile

Mark Shymanski

5621 posts in 3736 days

#2 posted 01-01-2011 05:45 AM

It has to do with the geometry of the pins and tails. I don’t have the manual in front of me but I believe in raising or lowering the bit you are widening or narrowing the gap as the slope on the dovetail bit is either wider as you raise it or narrower as you lower the bit… picture where the top of the board intersects the bit if hits up high on the bit the gap will be narrower as the bit is narrower at that point, intersect lower down on the bit and the bit will remove more material making the gap wider. Leigh Jigs have a pretty good description, and pictures to match, explaining why this happens; you may want to check out their website.

-- "Checking for square? What madness is this! The cabinet is square because I will it to be so!" Jeremy Greiner LJ Topic#20953 2011 Feb 2

View Gator's profile


383 posts in 3699 days

#3 posted 01-01-2011 06:31 AM

I have the Leigh jig, and they use the 8 degree bits, and if you lower the bit on your pins it makes them loose, raising the bit tightens them up. The tail size remains the same. It is all about the depth of the pins that control the fit – like Mark said.. Geometry is a wonderful thing.


-- Master designer of precision sawdust and one of a kind slivers.

View kayakdude's profile


97 posts in 2800 days

#4 posted 01-12-2011 01:01 AM

i have a liegh d4 the older model but still work great you are making half blind dove tail right because you didn’t say what kind of joint you where making . it dose help to read and under stand the manual now i use a 8 dec bit i set my routor biy 1’’ as a starting point for 3/4 stock and you can always make the sockets deeper if you have to raising the dits for loser fit , also check you bushing make sure it 7/16 od and i don’t use a E bushing i think it a wast of money and see no diffents . i hope i help you guys out

-- kayakdude

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