Help, biscuit joint shows 0.010" glue line on one side

[Clark Magnuson]

I am trying to make a 22" long by 20.5" wide by .75" thick cabinet bread board cutting board.

I have a bunch of 1x10 [.75" x9.25"] rock hard maple cut in 24" lengths.

To practice joining, I took two pieces of scrap and ran them the the Delta DJ-15 jointer with one board getting it's top run against the fence and one board getting it's top away from the fence in case I did not have the fence and blades perfectly square.

I cut three biscuit joints over the 24" length with a Porter Cable plate jointer model 555.

I glued up with Porter Cable size 20 [24 x 58mm] biscuits and Tightbond II glue.

I jointed the outside edges and then ripped down the middle a piece of old growth Douglas Fir 1x4 take off decking in half to insulate the clamps from the work.

The joint looked tight on top and the joint looked very flat when compared to a straight edge.

But when the glue was hard and I took the work out of the clamps, scraped off the glue beads and belt sanded, there was a ~ .010 glue line gap on the bottom. The sander takes out glue faster than it takes off Maple, so there is a ~ .010" trough as well.

This crevice is not good for food preparation.

Should I plan on filling gaps with some product?
Is there a way to avoid gaps?

Thanks in advance.

[keith micinski]

Two suggestions. I always use the same face for reference on every machine. If your machine isn't set up square then stop what your doing and get your machine setup right. A lot of people say that the machines don't have to be setup to as tight of tolerances as all of the digital gauges allow these days and I say those people are over 50 and can't be helped. The day I started getting all of my digital do-hickies and setting all of my machines up properly is the day my life got a lot easier. Admittedly you can build some mighty fine work with old machines that are setup by eye, but it takes a lot more skill and a lot more time to do it. Every thousandth of error you take out of the machine is another thousandth you can be wrong by and still have a piece turn out nice. The other thing I would suggest is when you clamp a glue up like that put two clamps on top of the board to counteract the bottom three. I would guess that the gap is on the face of the board that was facing up in the glue up.

[keith micinski]

As far as the gap, if it is a cutting board cant you just keep the gap on the bottom and make it a one sided cutting board. That one side should last longer then your going to be cutting I would guess. I don't think anything as far as a filler goes is a good idea on a food prep surface.

[Chuck Wintle]

i would rip it in down the glue line, rejoint the edges, test fit the pieces checking for flatness and no gaps and finally recut the slots for new biscuits and reglue. What I noticed during one of my glueups was one of the biscuits was a little tight and became "stuck" while the clamps were being tightened to bring the wood together. It caused a small gap to remain such as the one you have.

[Nelson Howe]

I agree that dividing your clamps top and bottom should help eliminate the gap. I don't agree about always jointing off the same face. I'm no expert, but reversing faces seems like a simple solution for a just in case problem, no matter how careful you are with your machines. It also seems that biscuits aren't necessary for strength in that joint, and I don't find them precise enough (maybe my biscuit jointer has too much slop?) to rely on for perfect board alignment anyway.

Nelson

[Terry Welty]

+1 for all the above, Set up your jointer accurately, table saw down the glue line, re-joint, check, re-glue, re-clamp. I wouldn't use the biscuits either.

[Chuck Wintle]

+1 for all the above, Set up your jointer accurately, table saw down the glue line, re-joint, check, re-glue, re-clamp. I wouldn't use the biscuits either.

I have heard biscuits add a lot of strength to a woodworking joint...is this wrong?

[glenn bradley]

If your faces are flat and there is no gap in the joint on one side but there is on the other, your face to edge joint is not perpendicular. If the gauges you are using to setup your jointer are declaring a true 90*, set them aside. Joint two edges of some face jointed material and lay them on a known flat surface with the edges together. You should have no gap regardless of orientation. If you have a gap, adjust your machine till you solve that. Then just for curiosity's sake you could check the machine with your gauges and see how far out of true they are.

+1 on solving the current problem by ripping and re-gluing. Many folks here (me included) get glue ready edges off the tablesaw. As mentioned, some folks scoff at getting your machines adjusted to within Nths of an inch or degree. I am not one of them. I'm in the over-50 crowd (I thought we didn't trust anyone over 30. Its 50 now? ) and can say that taking the time to really dial your machines in tight pays you back in saved time and material 10 fold.

[Mark Rakestraw]

No argument from me that your machines should be set up properly, but Nelson's point about not referencing the same face off the jointer fence is a good standard practice. What that means is if you're looking down on the unglued joint run the board on one side of the joint through the jointer with the "face" against the fence and the board on the other side of the joint with the "backside" of the board against the fence. Whatever error there may be in the 90 degree setting of the fence will now cancel itself out.

[Peter Pedisich]

Clark,

I've dealt with this before by placing a track-guided saw (ANY type) with the blade splitting the glue line, and rip away - the resulting halves should mate nicely for a new glue-up.
Good luck!

Pete

[Bill Orbine]

I have heard biscuits add a lot of strength to a woodworking joint...is this wrong?

Sure the biscuit makes the POOR panel joint strong.....especially like the one with gap problem shown above. In reality, with a good joint the biscuits aren't necessary because glue is stronger than the wood. In this case such as above, I only use the biscuits for alignment and I do not use glue on the biscuits.

[Ken Fitzgerald]

Clark....does the gap occur the entire length of the board or just in a small area?

The reason I ask...your tactic of swapping faces should have canceled out any differences in the jointed edges not being at 90º. I am wondering if the gap could have been caused for a couple possible reasons: 1) a biscuit hole wasn't machined deep enough or 2) the board warped after being cut or 3) the board wasn't flat after glue up if the joint runs the full length of the board.

I have never had a biscuit joint hold a board apart during glue up but I have not paid enough attention when cutting the biscuit slot and wound up with a really loose slot and on another occasion I ended up with one that would not align well as it wasn't 90º to the jointed surface. These were obvious operator errors on my part.

If you have some more scrap, it might be worth another attempt.

[Terry Welty]

hmmm... no glue on the biscuits... is that to avoid biscuits swell that could cause the jointed board to swell? Just curious.

[John Coloccia]

It can swell enough to telegraph through the board, actually, and you get a little bump. It's frustrating because you sand away the bump, and then it shrinks and you end up with a little low spot. I personally don't use biscuits anymore, not for this reason, but I just don't find them all that useful.

[Clark Magnuson]

OK, I ripped the glue joint.
MY 28 year old Delta contractors saw with Jet fence and Harbor Freight blade did anything but cut straight.
The jointer with opposite fence sides looked like it made a straight cut.
I glued again without biscuits this time.

After a half hour, I pulled it out and scraped down the joint. Both side look like no gap, except for ~ 1" where the gap is ~ .001", probably from operator error at the jointer.

So it looks like I had success, but why?
Was it the lack of biscuits?