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.
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.
