# Twist (pun intended) on an existing jig.



## GulfcoastGuy (Feb 27, 2012)

Gotta make a jig for the project for my wife. I've seen the existing plans for a rail type mortising jig and the self centering post style. This should do both. I'm planning on adding adjustment to the width of one of the wooden rails. This should allow me to set an offset from center line of the stock for the center line of the mortise.

 jig SM by pat w1, on Flickr

Thoughts?

GCG


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## GulfcoastGuy (Feb 27, 2012)

Added the moving fence. To set an offset from center line all I'll have to do is set the gap between the movable fence and the stationary bar and lock it down on both ends.

 Jig SM MOD by pat w1, on Flickr

The question is ... will the dog hunt?

GCG


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## jschaben (Jun 21, 2009)

Hi Pat - I think the first drawing would have worked for you, not sure what the second one does for you. When I want to offset mine, I just shim under one of the clamping legs, effectively makes the stock wider and offsets the jig by half the thickness of the shim.


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## AndyL (Jun 3, 2011)

I think that's a great idea, looks very usable. You wouldn't actually need a finger-nut at the pivot end of each rail, just tightening the screw that rides in the slot would hold it steady.

I can see the usefulness of the adjustable fence to allow you to put your mortice in any position... if you incorporated a couple of screws you could get really precise adjustments. However I agree with John, a set of shims of different thicknesses would be simpler. A set of 1/8", 1/4", 1/2" and 1" shims would allow you to shift the mortice off centre by up to 15/16" in increments of 1/16" - how often do you need to position a mortice more precisely than that? I guess you'd need to screw the shims to the face of the fence to stop them slipping out as you move the jig.


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## GulfcoastGuy (Feb 27, 2012)

@John, The shim idea went through my mind but I had the same concerns of how to keep one in place. 

@Andy, I see the point about the unnecessary knob/finger nut. Guess I was going for a belt and suspenders. 

BTW calibrating this before use should be easy.

Cut some round bar stock to make a calibration post and get some like sized MDF - 2 pieces
Invert the router and loosely mount the plate of the jig.
Chuck up the calibration post and plunge to expose some of the free end.
Set the two MDF pieces one either side of the post and clamp the rails down with the fence pulled all the way back.
Tighten down the jig to the router. Done.


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## GulfcoastGuy (Feb 27, 2012)

John, I'm a little confused. Why would the shim offset by half the width?

GCG


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## jschaben (Jun 21, 2009)

:blink:


GulfcoastGuy said:


> John, I'm a little confused. Why would the shim offset by half the width?
> 
> GCG


Hi Patrick - Well, pretty simple math really. The jig self centers so on a 3/4" board it will center 3/8" from each edge. If I wanted to place the mortice 1/2" form one edge, I would need to shim the other side to make the total thickness 1" or a 1/4" shim, but I've only moved the mortice 1/8". That's the long answer, short answer is because you are dividing things in half. Short answer doesn't explain much:bad:


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## GulfcoastGuy (Feb 27, 2012)

Makes perfect sense. Don't know why I didn't see it.

GCG


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