Having trouble fitting the back to the sides

[nkwak]

I'm at the point where I am about to glue the back on the sides and the taper is giving me trouble with getting the ends to both come in contact without having to use a lot of force.

Is there something I need to fix? I feel like I did something wrong leading up to this. I used a 15' arched sanding caul (made by tracing a brace radius jig) in much the same way that you would use a radius dish. This is what the setup looks like:



I also have nuts on the central threaded rod that set the height of the wooden caul as I rotate it around the circumference of the rims. Since the back has a taper I propped up the neck block with some wooden blocks.

That taper is not a straight line however; it's an arc. Because it's higher in the middle of the length of the body I have to basically bend the back plate in order for there be 100% contact. Is that wrong?

If it's not then I'm finding that my gobars do not exert enough force to deform the plate to set up a tight joint. I'm trying to find a workaround and recall that Jonathan Kinkead made a halo-like caul that screws into the mold. Has any of you ever tried this?

[tippie53]

you have a lot of movement. The dish is the best way for a better fit and finish.
how well does your bar fit the back braces?
https://www.youtube.com/watch?v=pz6xzVRA51E&t=68s

[BlindBo]

Hey Neil. After prepping the rim with the appropriate radius dish, I use the radius dishes in the go-bar deck to ensure the rim is in complete contact with whichever joint you are gluing (top or back). It normally results in complete contact and a solid joint. I made a short set of go-bar rods for this and just shim under the lower radius dish as needed to get adequate pressure from the bars.
Hope this helps.

[nkwak]

you have a lot of movement. The dish is the best way for a better fit and finish.
how well does your bar fit the back braces?
https://www.youtube.com/watch?v=pz6xzVRA51E&t=68s

I'm inclined to agree with you. The radius dish serves about 3 different purposes. I'm hoping that I can just move forward from this point or if I have to go back and do a step or two over.

There was movement but have a nut and locking washer underneath the table top with another nut/washer on the surface of the table. I also have a nut/washer beneath the caul (so that I didn't create any low spots) and a wing nut on top to keep it from creating high spots. I removed much of the raised areas with a block plane and relied on the caul to serve as a reference and for final sanding.

The braces came pre-radiused from Martin, but only along the length of the brace, not the cross section. The result is that length of the plate is a straight line with the sides curling up in the radius; it's not bowl-shaped. THat's probably the bigger problem.

[nkwak]

Hey Neil. After prepping the rim with the appropriate radius dish, I use the radius dishes in the go-bar deck to ensure the rim is in complete contact with whichever joint you are gluing (top or back). It normally results in complete contact and a solid joint. I made a short set of go-bar rods for this and just shim under the lower radius dish as needed to get adequate pressure from the bars.
Hope this helps.

Yeah, I was thinking if I were to buy a radius dish that I would use clamps around the perimeter. I have 8 cam clamps (4 deep throat, 4 regular depth) and about a dozen F clamps of various bar length.

[BlindBo]

Hey Neil. You are correct, the radius dishes are multi-use. Besides sanding the correct geometry into the rim, they can be used to sand the correct radius on your braces, provide a gluing caul for installing braces and provide the correctly radiused caul for gluing the top and back. All the steps help you produce the correct geometry. Here is a shot of how I use them:

IMG_1075.jpeg

This is the setup I use to glue the back and top in my go-bar deck. The radius dish supports the top (or back), then the rim goes in place and then the other radius dish goes on top. This gives you complete contact and the upper dish provides a solid top platform to distribute the go-bar rod pressure around the rim/top joint. Works the same for the back, just reversed. Same goes for gluing your braces in place.
Having used a lot of other methods including the spool clamp method, I find this to be the most simple to do.

[MaineGeezer]

I do a similar thing, except instead of using go-bars I pile about 50 pounds of assorted Heavy Things on top of the stack