Dovetail theory and glued up panels help

I am fixing to dovetail up a case. The top and bottom (horizontal pin boards) are two pieces with one glue line. The vertical side panels, tail boards, are three pieces with two glue lines. Species is American Beech, KD at purchase and seasoned inside my house for three years before glue up. The panels have been stickered in my shop for about a week now with no visible stupidity.

I am inclined to pass the glue line through their respective pins or tails, and leave some meat on both sides of the glue line in both the pins and tails.

On the one hand those London pattern dovetails with the microscopic pins sure are pretty. On the other hand American Beech moves a fair bit seasonally, and my shop has a fairly wide seasonal humidity/ temperature/ equilibrium moisture content swing.

My fundamental question is how small can I make my pins on the horizontal pieces with the one glue line, while being prudent about wood movement but tipping my hat to the micro pin London style?

I do have a 1/10 LN mortise chisel, but that seems like a precious small pin given movement on Am Beech with a glue line in the middle one. I routinely see plus 55 degrees F and 6-8% RH in the winter but plus 80 degrees F at 70-80% RH in the summer.

I will try for a pic tomorrow. I set out for my glue lines to be symmetrical and think I hit in the 1/8 to 1/4 window. All the panels are edge to edge. I considered slipping in a quarter sawn ribbon more or less on center during glue up but chickened out.

Appreciate the help folks. I started my “vacation” at 1630 on Friday. I got called in Saturday morning at 0420 and got home at 2000. Sunday I spent 8 hours moving snow, today I finally got to sleep. Hope to be in the shop Tuesday laying out dovetails.

I wouldn't over think it. Assume this is a decorative case? +1 on pic or drawing.

What is a 1/10 mortise chisel and how does that apply to dovetails?

Structurally, whichever sides of the carcase I'm worried about spreading I make the pins. IOW in a chest of drawers, I would make the pins in the sides. Probably not a super big deal, just seems more sound to me.

I wouldn’t worry about differential movement or where the glue lines end up. If your panels glued up with tight joints then it shouldn’t impact anything if you end up with a glue line in the middle of a pin or tail.

Hi Scott

The glue joint should be stronger than the wood, so no issue with one or more glue lines.

With regard London style (skinny) dovetails, while I like the look for drawers, I do not do this for cases. Equally, I dislike the look where pins and tails are the same width - this looks machine made. Make the dovetails slimmer, but do not go overboard.

http://www.inthewoodshop.com/Furnitu..._m5913ec9b.jpg

Regards from Perth

Derek

So here is my glue joints on end grain. I am off by 1/8 top middle and lower right, off by 1/4 lower left. Considering what little stock I have left to work I will take it and like it. The four panels will be the outsides of a wall hanging saw till, I was thinking tails would go on the vertical boards. It will hang from a French cleat near the top, but just about all the weight of the saws and accessories will be born by the lower panel, the floor panel.

Quote:

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Originally Posted by Robert Engel

What is a 1/10 mortise chisel and how does that apply to dovetails?

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The one tenth inch wide edge is the most narrow chisel I own for cleaning out the cuts in tailboards. I really don't want to go that small for this project.

So next question, do I need to fill my gaps? I got this same carcass glued up this morning from the four panels. Nominal 30x40x11 inches. Each of individual corners was going home with light taps from 20 oz mallet after paring.

I assembled with fish glue from Lee Valley, carefully applied glue to all joining surfaces with a popsicle stick. I needed my engineers hammer and some pretty firm whomping to get the case together. Once I cleaned up the joints it was out of square, the diagonals measured 50.0 and 49.5. Got a strap on the long diagonal and pulled it to square at 49.75 on both diagonals.

On the corners that are not strapped (like the one in the picture) the joint is tight inside the case and I have consistent 1/16 inch gaps outside the case. On the opposite (strapped corners) the outside is tight and I have a 1/16 inch gap at the joint inside the case.

Do I need to fill these gaps with perhaps epoxy after the fish glue is thoroughly dry before I take the clamps off?

Plan is for a 9 inch wide board on the back at the bottom, and a three inch wide board on the back at the top. I can't install either until the strap comes off, but I can install both backboards with the X brace still nailed in.

FWIW I am asking about the structural aspects of filling the gaps with glue. The outside of the case will be painted, and I am OK with the small visible gaps on the inside of the case as a reminder to do better next time.

Thanks

Attachment 471270Attachment 471271

Structurally that will be fine. If you paint it, I bet they won’t be that noticeable. If you want to fill the gaps for cosmetic reasons you can, but that is entirely up to you.

I’ve had the best luck filling gaps by gluing a little sliver of wood in them. If you match the grain direction it can blend in really well. You can smear glue and sawdust in the gaps too, but that tends to show if you aren’t painting the piece.