How deep to set biscuit slot depth?

[NewCabMaker]

I recently bought my first biscuit joiner, a used Porter-Cable. The previous owner had apparently set the depth too shallow because when dry-fitting boards the biscuits bottom out before the joint closes.

I increased the depth with the fine adjustment for my first test joint so the joint closes when dry fitting. But when I added glue to the slots I started to wonder if I ought to cut a little deeper yet to give more space for the glue.

How can I set the depth to the ideal, or am I worrying about something that's not critical?

Bill

[Rumpty]

Cut a test slot, insert a biscuit, using a sharp pencil make a line on the biscuit on top of the wood, remove the biscuit, turn over and reinsert, draw another line, remove the biscuit, the lines should match. Adjust the depth until the lines match. You can set the depth so the biscuit is just a hair deep for ease of assembly.

[Joe Wilding]

I am sure someone here would probably make some cuts and measure it for you. I could do that in a day or to if you need me to. In the mean time, my Porter Cable biscuit cutter is still set up in the factory default setting. I think it cuts 1/16 - 1/8" extra depth (For a size 20). This is handy as it allows for almost 1/2" of missalignment of the two slots (length-wise, not thickness-wise) and still allows the joint to come together. You wouldn't want to get too carried away on this extra depth becasue at some point the biscuit won't be centered properly (located more in one baord than the other) and you will loose joint strength. I think the 1/16" - 1/8" is about right though, in my opinion.

Joe In Denver My Woodworking Website:

[NewCabMaker]

Thanks for posting this technique. Makes good sense to me -- and I wouldn't have thought of it!

Bill

[Bob]

Isn't there a mark on your joiner that has settings on it for 10's 20's etc.??

[max]

Extra s good. The biscuits do nothing on the edges so you don't need them in contact with anything. max

[Andy Dingley]

There's usually a rotating cam, but there's also a screw adjust in the stop.

If you buy a cheap biscuiter then it's worth checking this, as they're often inaccurate. I've recommended Screwfix's Ferm biscuiter to a few people as a really cheap but usable machine, and then had them report problems with it. Fixing this adjustment solved the problem.

[Leon]

Umm Deep enough that you can close the joint with a biscuit and glue in it. Practice on a pieces of scrap wood.

[Phisherman]

There's no concern about "space for the glue." In fact, too much glue can cause issues. Always take the time to do a dry fit--after the glue is applied it's too late.

[Allen]

Dry fit after the glue is applied? .... Hmmm, let me get back to you on that. :)

Allen

[Allen]

OK, never mind I reread that .

Allen

[Krunchy]

dyslexic..?? "after the glue has dried its too late"

now give yourself the compulsory slap on the forehead

[Unquestionably Confused]

Uh, Allen? Read his post one more time, carefully. Feel free to move your finger along the page and you can even move your lips if you wish. LOL!

[Allen]

Did that. Now sitting in the corner.

Allen

[Phisherman]

Ah...Look at the dash (double hyphen) that separates two independent clauses. Probably I should have made them separate sentences.

[Lawrence Wasserman]

You're right, it should be just a little deeper than the width of a biscuit. What I've seen recommended is to cut a slot, seat a biscuit in it, and draw a line across it with a sharp pencil where it crosses the top of the slot. Pull the biscuit out of the slot and reverse it and put it back in. If the line ""just" disappears into the slot the depth is good.

[Bob]

Your joiner should have a depth setting for each biscuit number. My Makita does.