Domino for a coopered backrest - compound angle issue

[s1nglemalt]

I searched the net for anything dealing with a coopered backrest / headrest and Domino, and found nothing. I am building Maloof-inspired lowback dining chairs and will cooper the backrest to get more angle as well as make the chair better looking since the flow of the seat goes into the same lengthwise flow of backrest. For several of the backrests, clamping the entire backrest assembly was fine, but for two remaining backrests, every time I clamp the 2 pieces (they have 3 pieces each already glued together at 5 degree angles, so really there began 6 pieces of 2-4.5" wide x 7" tall x 8/4 thick walnut) together they fall apart, even with clamps holding them together against their faces.

I thought the Domino would work fine, and it could with your help. Where I need help is the front of the Domino XL bumps into the "next" piece and throws off my angle.

From the photo, I am trying to put a Domino into piece 3, but the front of the XL bumps into 4, throwing it off. But, only by a half inch or so.

Is there a way to make a spacer between the XL and the backrest, so it cheats the fence off of the piece 4?

Any non-Festool ideas out there are also greatly appreciated. I have no idea why 4 backrests using the exact same formula worked fine, but now the hotter angle or something is causing the other 2 headrests to pop out of my clamps.

I know my nuclear option will be to glue 4 scrap pieces 10" long x 1" thick to the front and backs of 2 and 3, about 3 inches apart, and just glue those scraps together as a poor man's way of solving this, but I would rather hear from the internets what you would do.

 

[chris mann]

Put a spacer under the fence the width of the piece you're dominoing and adjust fence depth. I've used 12mm mdf before on the domino 500 and then screwed into on from the back thru the triangular holes.  Not sure if 700 fence has same holes.

 

[rvieceli]

Is there a reason you can't reference off the other side of piece three?

Since piece 4 would then angle away from the fence instead of into it.

 

[s1nglemalt]

Yes, I could, but I never plane that side square, since it gets bandsawed off. I only need 1 side square,  and that is always the front.

I was hoping someone would say this so I could ask, "Would you use the back knowing it is a bit rough?" I really do not care about this precision, since I am solely doing this to help glue up. Of course, I will ensure the domino does not get cut when I round out the coopered headrest, but it is really only helping me glue up two halves of a backrest.

 

[Stoli]

What about a tapered spacer under the fence? 

 

[tjbnwi]

I agree with Chris, a simple spacer, adjust the fence to make up for the spacer.

Tom