Rule of thumb on biscuit size?

[Stan Calow]

I am gluing up a table top of 3/4" oak, and want to use biscuits to help with alignment. I normally use smaller size biscuits, but I'm considering whether #20s are OK to use for this thin a top. My concern is the biscuits telegraphing through the top. Is there a rule of thumb for this?

[Jerry Wright]

Never had luck with biscuits for aligning a top. I use dowels. With a good jig they are dead nuts on center and strong enough to force some deflection in line. Just my 2 cents.

[Peter Christensen]

I don’t usually use anything to align when gluing but if you are worried about the biscuit telegraphing through offset them closer to the bottom. They won’t show on top and if they telegraph it will be under where it doesn’t matter.

[Jim Morgan]

All biscuits are the same thickness, so a #20 is no more likely to telegraph than a #10. Telegraphing occurs when the moisture in the glue causes the biscuit and adjacent wood to swell, and the joint is leveled before the moisture equalizes. Then the biscuits and adjacent material shrink a bit, leaving a visible depression at each biscuit site. The solution is to wait 2 or 3 days before leveling the joint.

Like most tools, biscuit joiners require some tuning to perform optimally. I used a micrometer & shims to make sure the fence and the base were dead parallel to the blade (used blue tape to shim the base). When I use biscuits for alignment, I get dead-on results.

[Jim Morgan]

P. S. I later spent 4-5 times the cost of the biscuit joiner to purchase a Domino, which is superior in just about every way. Like biscuits, however, Dominos may be subject to telegraphing when joints are leveled immediately after glue-up.

[Doug Dawson]

P. S. I later spent 4-5 times the cost of the biscuit joiner to purchase a Domino, which is superior in just about every way. Like biscuits, however, Dominos may be subject to telegraphing when joints are leveled immediately after glue-up.

So it sounds like you aren't using the Lamello. (DeWalt perhaps? that's a piece of...) When the whole "domino" thing goes public domain, it should get more interesting.

[Frank Pratt]

I have a biscuit joiner, but don't use it for alignment cause it just isn't that great for that. Clamps & cauls will align the boards much better. Where biscuits excel is in joining sheet goods.

[Doug Dawson]

I have a biscuit joiner, but don't use it for alignment cause it just isn't that great for that. Clamps & cauls will align the boards much better. Where biscuits excel is in jointing sheet goods.

If you use junky clamps and crooked cauls, you will get a bad result. I'm sure that doesn't apply to the work you do.

[Stan Calow]

Thanks for input guys. I've used dowels before and prefer biscuits. I should have realized that they're the same thickness since the cutter doesn't change. Dohhh! Most previous work has been in wood thicker than 3/4" so hadn't worried about it before.

[lowell holmes]

My experience with biscuits is they are used for alignment. I never depend on them for strength, that comes form the glue joint. I have
not used it since Harvey came through. I do have a big plastic jar of biscuits. I glue the joint and clamp it. I clamp the glue joint with cauls
during the glue up as well as horizontal clamps. Just for what it's worth