I've finally got both of my radius dishes made (15' & 25') when I noticed something peculiar. I placed the back pieces (unjoined) in the dish and pressed them down, the joint opened up!!  I spent a lot of time between the joiner and the shooting board to match these edges. The fit was very good (on a flat plane). 

The dishes were made with a router on a homemade rotating table. And yes, I've rechecked the radius of the dish with the template.

Am I to assume that when the pieces are joined and thickness sanded that this will not be an issue?

My question is this, is the stress of the individual backs pieces pulling apart going to be problematic in the future? From what I've read, here and in books, the backs and tops are joined with the pieces laying flat, not inside the dish. Right?

This is my first build so I just thought I'd ask before proceeding.

Rob

Thank you kind sirs.  I sure appreciate all the help I've received on this forum.

The process continues..........

Here's a question. Do you radius your sides, back and X-bars for a dreadnought or leave flat?  Plans say you may radius top up to 3mm or leave flat.  If left flat what are the chances of a sagging top?  Robert O'Brien on DVD for OM style uses a 30' radius sanding dish for top and 15' for the back.

Yes its a mess alright.  I made a 15', 25', 28' and a 30' last summer in my garage.  It was great how the MDF dust clung to my sweety arm hair in the 90 degree heat to create a nice sticky paste, and I'm not even that furry.

Sounds like you're off to a good start.

When I made my own 15' and 25' dishes, I noticed, on the very first one, a tendancy of the new dish to curl, or cup, toward the routed side.  I put this down to a condition similar ro casehardening, or reverse CH, because who knows what unholy stresses are squashed into MDF during manufacture? Also, I had exposed that new raw surface to humidity fluctuations.

I sealed, and then recoated, both sides of my new, and hard-won (what a MESS!) dishes with epoxy.  First coat disappears, second coat lays out the nicest glue-releasing layer you could hope for: glue-ups pop right off, and self-stick sandpapers, or Spray-77 or -90, hang on just fine until you point a heat gun at them.  The best part was that the routed dishes stayed flat, preserving the true(-ish) radius that was won so dearly, and dirtily.

Whatever you do to one side of a board, real or fake, you should do to the other.

Dan

[QUOTE=MichaelP]Sides? No. Now if you mean do I sand the radius into the linings, neck block and tail block yes I do, but is not absolutely necessary on the top but would on the back because of the slope. Top and back braces are profile radiused with the exception of finger braces and upper transverse braces on the top if you wish.[/QUOTE]

Yeap, that's what I meant to say.  Seems like there is no end to buying more tools or a gadget.  I did like how WaddyT made his go-bar deck I saw in his shop pics.  I think I could do that using water pipe and dowel rods.

Thanks again MichaelP