Biscuiting a miter joint?

[Toller]

I made my first biscuited miter joint last week; with two 15" wide panels and three biscuits. It did not come out well; no matter how much I fussed with it I couldn't eliminate the gap. Possibly no one would have noticed it, but I sure didn't like it. (it couldn't have been too bad, as it held my full weight jumping on it...) So, I am redoing it, being more careful that my cuts are perfect, and only using two biscuits.

Well, when I dry-fit it, there still a gap I can't get rid of; the gap is uniform all across, so my cuts are good. I marked up a biscuit with a central line, and the central line falls exactly on the edge of the slot. I have thinking that maybe the clamping on 90degree joints is adequate to make it work, but the clamping on 45degree joints won't push them together, and I have to make my slots a hair deeper.

Does this make any sense, or is my problem likely to be elsewhere?

I am not thrilled about the recutting my slots, as they are likely to end up a bit wider than I would like; maybe I can get away with just deepening one side?

[Duke of Burl]

What size biscuits? If they're 20s and you substitute a 10, does it go away?

[Jim Stuyck]

My experience is that, within reason, neither the depth nor the width of the slots for biscuits is of concern. Only the distance of the slot from the edge of the workpiece matters.

In fact, having a tad extra width means cutting slots EXACTLY on the mark isn't a concern...close counts. "Perfect" isn't part of the equation.

Therefore, given your description of the problem, I'd say your slots aren't deep enough. And that puzzles me because, with my buscuit cutter, "depth" is preset and I've never fiddled with that.

Jim Stuyck

[The3rd Earl Of Derby]

Precision flatness of both sides of the wood is the key. ;-)

[Swingman]

Lay some 80 grit sandpaper on your workbench, rub the edge of a biscuit on it until, when placed in the slot, the gap disappears.

[Leon]

Snip

How do your joints fit with out the biscuits? The cuts/angles can be dead on correct but if your parallel sides are unequal in length the joints will not close.

If the joints close properly with out biscuits, adjust you cutter to cut a bit deeper and closer to the inside of the joint.

[Teamcasa]

Are you sure the biscuit is preventing the mating surfaces from closing? Cutting the slots deeper is not a big deal unless the slot emerges from the end. You should be able to tell if the (dry) biscuit is more than halfway into the slot on each side. I routinely cut my slots a touch deeper to allow for glue expansion and to prevent hydraulic the joint.

Dave

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[Leon]

Hot enough for you? Bryan and I spent from 9:00 a.m. to 4:00 p.m. Saturday replacing our water softener on the west side of the house. I have been kicking back today.

[Swingman]

It's punishing outside ... been in and out all day overseeing a framing job. At least I can leave ... those poor bastids have to stay and work!

BTW, this is one of the best, and fastest framing crews, I've ever used. Frame1 package was delivered last Monday at 9:30 AM, they missed one entire day of work for punch-out on another job, and on Friday morning I had to order a building height survey!

Come by and take a look for yourself ...

[Jim Northey]

[Leon]

I'll try to get by there in the next couple of days.

[Toller]

Excellent idea! Why didn't I think of it? Anyhow, the gap dissappears with the sanded biscuits, so all is well. Now the only issue is whether I should add a third biscuit in the middle that is cut deeper.

[Leon]

In the instance of using biscuits in mitered corners, the biscuits do add considerable strength to the joint in addition to helping with alignment if the joint is end grain to end grain or if the panels are plywood. The more the better if the joint runs perpendicular to the grain.

[Swingman]

That's why I get paid the big bucks ... yeah, right! ;)

Splines and biscuits are two of the best ways to reinforce the inherently weak miter joint. I would put as many, evenly spaced, that would not structurally effect/weaken the parts.

I did the job for years with spines, but when finally brought kicking and screaming into the modern technological world of biscuits a couple of years back, it was Tom Watson who assured me that biscuits were fine for this particular task. I haven't had a problem with them doing the job.

Seems you have a problem with biscuit size, or your plate joiner's depth of cut ... you need to figure out which because this gap business shouldn't be happening.

[Toller]

I have done a thousand biscuits (PC joiner/PC Biscuit) with no problem, but they were all 90 degrees. I think the clamping was adequate to bring them together. Since clamping is at an angle to the biscuit on 45s, it just isn't enough. But making the cut a bit deeper for all biscuits would probably be prudent.

[Leon]

Keep in mind that the 90 degree angle does not require a deeper cut for the biscuit than any other application of the biscuit. If you find that the holes are too shallow on the 45's you may not be holding the joiner perfectly perpendicular to the miter glue surface. You should insure that you joiner is indeed tilted to the same degree as the miter cut to insure that the biscuit is 90 degrees to the surface that it protrudes from.

Also band clamps work VERY well when clamping a container that fully closes on all sides and again insure that your parallel sides are equal in length.

[Joe Bemier]

Someone above mentioned using sandpaper and that can work.

I do a lot of stair tread nosing and run into the problem you describe from time-to-time. When I see the gap in dry fit I just run the fine side of a rasp over each edge of the biscuit. If I were building a bridge I might worry about anything less than full contact of all bicuit surfaces but for most applications these small deviations will not become an issue.

I found that this is generally caused by operator error. If I slow down and use the tools more precisely it does not occur. But I am talking about gaps 1/16 and

[Toller]

I went though 100 biscuits and pulled out the narrowest ones. They varied from 1.917 to 1.945, with most between 1.924 to 1.931. Everything fits fine now. I even upped the count from 2 per joint to 4.

One of these days I will increase the cutter depth a couple thousanths, but it hasn't been a problem except on the angled cuts.

[Toller]

' er.. 0.917 to 1.945 etc.

[Tex]

Lemme see! They varied 0.018" (WOW! EIGHTEEN WHOLE THOUSANDTHS!). You actually sorted 100 biscuits and took the time to measure some of them to 3 decimal places when you could have reset the depth an eighth of an inch or snipped off an edge? I don't mean to pry into your inner thoughts, but I'm amazed you went to all that much trouble -- it ain't brain surgery cutting biscuit slots. Besides, they're on the inside, the slot is filled with glue, and the biscuit is going to expand with the glue moisture. WHY??????