Splines or biscuits

[smorris]

I'm working on a new project and have several pieces I'll be gluing into panels and I'm not sure if splines or biscuits would be better.

I have 2 10" x 20"x 1 1/2" pieces of mahogany to edge join into a 20x20 panel. I can do biscuits or a spline. Off hand I'd say they have the same level of effort so that isn't a decision point. Normally I'd just use biscuits but it occurs to me maybe a spline(s) would work better this time because of the size. Is there any significant difference in strength between the 2 methods assuming the faces are properly jointed and clamped and I'm using TB III?

[Tom Miller]

Edge gluing alone will be every bit as strong as if the piece was 20x20 to begin with. You may find biscuit are helpful for alignment, but with a single joint that's not too big, you should be able to keep that lined up with little trouble.

A spline needs to be cross-grain to the pieces it's joining, if it's going to add any strength, so making it from hardwood is problematic at that size. I think plywood for splines is the only practical approach.

Regards,
Tom

[LCHIEN]

I'm working on a new project and have several pieces I'll be gluing into panels and I'm not sure if splines or biscuits would be better.

I have 2 10" x 20"x 1 1/2" pieces of mahogany to edge join into a 20x20 panel. I can do biscuits or a spline. Off hand I'd say they have the same level of effort so that isn't a decision point. Normally I'd just use biscuits but it occurs to me maybe a spline(s) would work better this time because of the size. Is there any significant difference in strength between the 2 methods assuming the faces are properly jointed and clamped and I'm using TB III?

just mulling it over, my thoughts are:

the strength is in the glue, not the spline or biscuits. I would expect the strength to be close to identical either way.

the biscuits would seem to be a bit easier, setting up the joiner is almost automatically aligning and the biscuits are premade and bought and should perfectly fit the joiner blade slot. The spline requries making a spline that matches the grooving tool - an extra step.

Finally the biscuits should be invisible. The spline, if used correctly, may be visible and be a decorative touch if you desire, especially when done with contrasting wood.

[poolhound]

I agree with everything Tom said. In my experience a jointed and glued edge is often stronger than the actual wood. I tested this one time with some off cuts from a glued up panel made from 4 x 4" wide pieces (3/4"). I set them across a step and stomped on them. Every time the wood broke but never the joints. Hardly scientific but interesting none the less.

Some biscuits wouldnt hurt to help with alignment and you also may want to add a caul, although with only one joint keeping them level shouldnt be too tough.

[pelligrini]

A spline or biscuits won't help with strength. Biscuits would be quicker & easier for alignment. The times I've used my biscuit jointer on something similar there was a a little slop in alignment too. I've found dowling to be tighter on alignment (once I learned how to drill straight.)

The best thing I've found for alignment, as poolhound mentioned, are a few cauls.

[cabinetman]

Here's another vote for just glue and clamps...cauls would be good too. You might do a preliminary dry fit clamp up to see how the mating edges fit. You could do it flat or standing on edge. Once clamped, see if both pieces are flat. Look at the seam on both sides, and lay a straight edge across them. IOW, your mating edges may be slightly off. This will give you the opportunity to correct.
.

[smorris]

Thanks everybody. I'll go with biscuits for alignment and I have plenty of caul stock around the shop. I even know where everything is since I spent the last few days straightening up from the last project.