What's the standard technique for splicing spars?

A long diagonal cut to allow lots of glue area.

Les

I suppose I was wondering if there is some magical procedure to make these long diagonal cuts so that they match perfectly. That is, some nfty technique that doesn't require some big bucks power tool. Guess I just need to get out my ruler and protractor, huh?

abufletcher,

Actually its pretty simple.. Take the two pieces to be spliced and place them side be side. Pick your angle, I like less than 30 degrees, and cut them both at the same time... Voila! Perfect match!

Hibrass

It's that "cut them both together" part that I'll probably screw up on. The good news is that I've just realized that I don't actually need to splice the spars on my 63" wingspan Snipe since there is a separate center section. Sometimes it's better to think before I post!

Doh! [:'(]

I usually cut splices using a picture frame or mitre saw - the hand operated sort of thing that looks like a 'guided hacksaw frame'. I use a Nobex Proman. The Swedish ones like Nobex are reckoned to be the most accurate. Other makes are very cheap nowadays.
Of course they only adjust to 45 degrees, but if you clamp another fence to it at a very narrow (acute ) angle to the blade you can cut a long thin splice joint on thin strips. The point about these guided saws is that they cut absolutely vertically down as well as at the desired angle. One should use a very fine blade for this type of work.
Invaluable tool for all sorts of fine woodwork, not just picture frames.

For just a few splices you could cut roughly and use a ' Permagrit ' type sanding block in a small guide made like a minature carpenters shooting board - replacing the plane with the sanding block. Make the fence adjustable and lock with a wing nut.
Of course you can cut the wood over length and keep sanding until you get a perfect joint. Actually Permagrit tools cut very quickly so its only a minutes work.

I just tape my spars together with some masking tape and saw them at an angle. I'm not worried about the angle because I'm matching these two pieces together. I figure the longer the joint the stronger it is, so I make the longest cut that's practical.

The critical thing is the length of the splice (besides a tight straight joint). Eight to 12 times the thickness of the material is typical when used in a load bearing structure for a proper splice.

Foremost products make a really nice miter saw and miter sander. I don't know what I did without them! Makes splicing those spars easy...

Regards,

Bob

I use a small drop of thin CA to tack the spars/longerons/stringers/sticks together. and regardless of what angle they are cut, they will splice well.

Bill, AMA 4720
WACO Brotherhood #1

At least I am not alone.

My philosophy is that even silly questions can prompt useful answers.

For sailboat masts, (They call them "spars", also) where the Sitka spruce pieces are not longe enough to make the length needed, a 12% splice works well. The splice should be inline with the forces which will be applied (on wing spars this would be verticle). Bundling the two pieces together and sawing both at the same time works. You can also sand them when together to get a perfect fit.

Try a 4 to 1 splice on a piece of scrap spar. Bend it and see where it breaks; Odds are it will break outside the joint if glued properly. 6 to 1 is recommended but difficult to do on small spers like 1/4 inch.

I have always spliced with 2 Butt Blocks, 1 on each side of the straight cut.
Grain direction or quality mean very little in a 2 sided butt splice. Simple, VERY straight, stonger and VERY QUICK.

True, if the splice is to be seen, it is less pretty.
Acids in any wood types have no effect on the joint strength.

My suggestion along with those posted previously is to make two splices... Each splice out as far as possible near the wing tips. This reduces the loading to near nothing accross the splices.