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 Post subject: A better box-joint jig
PostPosted: Wed Mar 28, 2018 5:35 pm 
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Most of you are familiar with the shop made box joint jigs that rely on a single pin to locate the workpiece as you shift the part down after each cut. The problem with this style jig is that any error you make in spacing the pin or setting the dado width multiplies with each new cut, so that by the end of the piece the error has been multiplied to the point of being a real problem.

I made this new style jig that relies on drilling a series of holes very precisely, then uses a steel dowel pin to step the workpiece across the fence. No more cumulative error. Of course, you need to locate the holes accurately. I used my CNC router to do this, but you could probably do it with a drill press and an Incra jig to accurately space the holes. This jig is set for 1/4" pins/slots. A replaceable zero-clearance backer sits in a dovetail slot in the jig.

Very first joint off the jig fit better than anything I ever achieved with the old style jig.

The jig is attached to the slot of an Incra 1000SE miter gauge, but pretty much any miter gauge (or a sled) would work.

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PostPosted: Thu Mar 29, 2018 10:14 pm 
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Brilliant, I like it. Next time I need box joints I gonna make one. Thanks


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PostPosted: Fri Mar 30, 2018 11:26 am 
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Great idea! Thanks for the tip.

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PostPosted: Fri Mar 30, 2018 8:05 pm 
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Hey drstrip,

Interesting, but I've never had the problem that you describe. Even if there is a slight error that propagates down the board, it makes no practical difference as the same error propagates on the mating board so the fit is the same all the way down the joint.

I've never understood the need for all the fancy adjustable box jigs out there. To me, they just seem to be a tremendous waste of time required to adjust them.

I have three extremely simple box jigs made from scraps, one is for 1/4", one 3/8", and one for 1/2". Those are the only size box fingers I have ever needed to make. Each one is a piece of MDF with two notches and a tight fitting stick in one of them. Actually, one is two jigs in one, 1/4" on one end and 3/8" on the other (the stick is removable).

The bottom line is that there is more than one way to skin a cat, so do whatever works best for you. :wink:

Cheers,
Tom

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PostPosted: Fri Mar 30, 2018 11:14 pm 
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tms wrote:
Hey drstrip,
Interesting, but I've never had the problem that you describe. Even if there is a slight error that propagates down the board, it makes no practical difference as the same error propagates on the mating board so the fit is the same all the way down the joint.


The problem I've had with error accumulation occurs when trying to mate two boards of a given width and want the joint to begin and end on pins/slots. If you don't care about the width of the board or whether you start/end on pins/slots, then the error isn't a big deal.

And for whatever reason, when making jigs like you describe, I've had problems getting the notches spaced exactly by the width of one slot.


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