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This winter I bought a Leigh Tool D4R Pro Dovetail Jig c/w VRS Vacuum & Router Support. I am relatively new to routering, but replaced a Lee Tool’s Harbour Freight jig.

Well made, jig, with an exceptional, detailed owner's manual and available video's on their website.

I am having an issue obtaining a 90 degree inside right angle on my through dove tail joints in ¾” Maple. If I make the joint tight, my angle is approx. 85˚.

I use a 3/4" spacer board (provides support the rear of the finger comb) and see no play in the finger comb to allow the offset from 90˚.

Any thing I should look for?

Any quick check that I can make to ensure the router bit is perpendicular to the finger comb before routering?

An help or suggestions would be appreciated. Thank you.

David
 

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Just speculating because I'm not quite sure what you mean by an inside right angle on a dovetail joint. But I think you mean that the cut isn't straight through the piece, but the bit is somehow not going straight through the workpiece.

I would check to see if the workpiece is shifting as the bit passes through. This would be caused because the clamping pressure is insufficient, or the material is so slick that the pressure you're useing just isn't holding it perfectly still during the cut.

If that's the case, you might consider using some reasonably fine grit sandpaper to hold it still. Your backer might also be allowing the workpiece to slip. One other possibility I can think of is that somehow, sawdust is getting on the jig between workpiece (or backer) and the jig.

You might also check to make sure the jig is dead flat. That requires a good straight edge. I doubt that this is so, but check anyway.

Are you using a solid "comb" or individual fingers you can set at any spacing. If the later, are they cinched down tight enough? Are all of them exactly 90 to the jig? You need a precise engineer's square to be certain of this.

I once had a jig for cutting box joints on a router table that allowed the workpiece to slip from the spin of the bit. So that's my best guess as to what's happening. I think I'd focus on that first. If it's slipping, it's not by much, so sandpaper would be my first fix.
 

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I assume that your spacer board is of uniform thickness, so not throwing the angle off. The first thing I'd do is check the angle between the spacer board and the bottom of the fingers (set at maximum projection). It's possible that the support brackets on either end of the jig (that the finger assembly is clamped to) are not perfectly square, or might not be tightened firmly against the frame. Also, make sure that the spacer board is not pushed too far up, to prevent good seating of the finger assembly when clamped in position.

I have an older incarnation of the D4, and don't have the dust collection accessory, but is it possible that the dust collection support beam is raised a tad, relative to the top of the fingers? That would tilt the router base slightly, preventing a good perpendicular cut.
 

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Hi David, could you post a picture of your work, showing where the error happens?
I am having trouble visualising your problem...
 
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