Kreg 720 Jig Measurements

[Tim Booher]

I'm making pocket holes to connect wood together with a jig, the Kreg 720. The 720 works by moving at an angle (which I'm trying to measure) to ensure the hole is drilled higher on thicker pieces.


The 720 works like this:


472130


I'm trying to calculate the length of the drill bit which I can set with a stop. The 720 has stops included for common wood, but I like to be exact and I need to understand the geometry of how the 720 works. I zeroed out an angle meter and found that the case is exactly 57 degrees.


472131


But! I wanted to make sure that the drilling jig block moved at 57 degrees, so I used my caliper to measure the board thickness block at the bottom and the top. That gave me these measurements.





s
d
▲


high point (mm)
43.9
54
10.10


low
10.1
0
-10.10


accuracy (+/-)
0.1
0.1



Θ
-45
deg






Per this geometry:
472132


So I'm going with 45 \deg which is intuitive for a jig like this. However, the case seems mounted to match the 57 deg that I measured. I also measured the picture in photoshop and got the 57 deg for the case as well.


I'm confused with how these could be different. Obviously the case doesn't have to match the internals, but 12 \deg is a big difference. I'm curious if anyone has looked at this. I'm sure folks would go with the 45 deg measurement, since that makes sense and is directly measured, but I would love any experience.

Btw, I'm making a calculator online and I'll share the link here.

Tim

[Tim Booher]

ok -- the pictures aren't showing up here, so I'm linking to a stackExchange post I wrote up as well.

https://engineering.stackexchange.com/questions/49380/figuring-out-geometry-for-kreg-720

[Jim Becker]

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