Joining boards end to end for shelves

[David Huston]

Looking at buying some reclaimed walnut to make some shelves out of. The shelves need to be 28 inches wide and 20 inches deep. The lumber is about 48 inches long most pieces around 5-6 inches wide. Can definitely get one shelf out of the pieces but hate to waste the other 20 inches or so. I think my dad has a biscuit joiner, would that be a good way to join the left over pieces in order to get another 28 inch wide shelf. I know this would be a great use for a domino but I don't have one and can't justify getting on for this project. Any thoughts would be great.

[John Blazy]

Simple scarf joints are stronger than you think. Scarf the narrow boards to your 29" length, say a pc @ 17 and another at 12" for all of them, then when edge gluing to make the 20" depth, stagger the scarf joints. super strong that way. Scarf joints are simple angled ends like wedge shims, but angle can be about 20 degrees +/-. clamp all boards together with scarf cut on common edge, then cut them with T-saw blade tilted, Plane the angles for fit, etc. Glue with epoxy for max hold (pre-wetting for ten minutes), but titebond will work, especially when staggering the joints in your edge gluing.

[Ole Anderson]

Single board end to end with a biscuit joint will make a good demo board for a karate chop. Obviously you would want to offset the ends when doing the glue up to get your 20" width. John has the right idea. If you could finger joint end to end the individual boards then offset them it would be ideal. Biscuits really don't add any significant strength whether end to end or on the long joints.

[Glenn de Souza]

I think a pair of deep rabbets, say 1 1/2-2" deep on each board would make a pretty strong glue joint. I guess this is basically a a lap joint. Fairly straightforward with either a dado blade or router. Staggering the joints and then gluing the long edges to get your final width should make a pretty strong assembly. You would basically have three glue surfaces (end grain, face grain, edge grain).

Maybe I'm a heretic here, but I think if you used your dad's biscuit joiner to join 5-6 inch wide pieces end to end, and then glued up several of these sections into a 20" deep shelf, AND if you were careful to stagger the end-end joints, you'd be fine. If I'm understanding it correctly, the end-end joint is supported by the long edge glue joint to the adjoining board.

I think maybe the karate chop demo board comment was for a situation where just one board was joined end to end and that was the end of the story.

[Bob Vaughan]

Finger joint the narrower pieces together then process like you would with pieces of that width for glue up.
You'll likely have to plan ahead and cut to rough length to allow for planing

[John Donhowe]

The weakest glue joint is end grain to end grain, and biscuits don't add much strength- they're mostly good for aligning glue-ups.

I'm having a hard time picturing the scarf joint suggestion. If the wedge cut is seen from the top of the shelf, it will give sideways stability, but I don't think will add much to load bearing strength. The only way a scarf would add much to load strength is if the bevels are oriented to meet at the surfaces- like matching chisels end to end. This seems like a hard joint to get to fit well.

I like the idea of finger joints, if you have the bit. However, I think the easiest way to get a reasonably strong shelf is just to glue up the strips, as in the attached rough drawing:
walnutshelf.png
It's like laying a wood floor. There's little strength at end to end (dashed line) joints, but by staggering, you'd get a lot of strength from the glued edge joints of the neighboring side pieces. That might be all you need, especially if you're able to support the shelf midway. I'd keep the outer pieces full length. good luck!

[Sam Murdoch]

The weakest glue joint is end grain to end grain, and biscuits don't add much strength- they're mostly good for aligning glue-ups.

I'm having a hard time picturing the scarf joint suggestion. If the wedge cut is seen from the top of the shelf, it will give sideways stability, but I don't think will add much to load bearing strength. The only way a scarf would add much to load strength is if the bevels are oriented to meet at the surfaces- like matching chisels end to end. This seems like a hard joint to get to fit well.

I like the idea of finger joints, if you have the bit. However, I think the easiest way to get a reasonably strong shelf is just to glue up the strips, as in the attached rough drawing:
walnutshelf.png
It's like laying a wood floor. There's little strength at end to end (dashed line) joints, but by staggering, you'd get a lot of strength from the glued edge joints of the neighboring side pieces. That might be all you need, especially if you're able to support the shelf midway. I'd keep the outer pieces full length. good luck!

If I (and John) understand your question correctly John's idea above is a good solution. Biscuits would help top/bottom alignment but the strength would all be in the glue up as John illustrates. Wonder if you really will get 48" of usable length from this reclaimed lumber. I would anticipate loosing as much as 3" off the ends but of course I haven't seen the stock.

[David Huston]

I think i will do it the way john drew up. The shelves will just be holding picture frames or whatever my wife wants to put on them. I am not sure if I will get the full 48 out of the boards either as I have only looked at pictures. I think I bought plenty though. Got 19 boards 48 inches or so long and most are between 5 - 7 inches wide. Just don't know how much I am going to loose getting them straight lined for the glue up. If i can get 45 clear in length and average 4 inches in width I should be fine.

Thanks for all the help.