Another Biscuit Question

[phrog]

The explanation I have read & heard from at least a couple of sources that might look like this is biscuits swell after being wetted with glue. They will shrink back down some after the glue has dried. If sanding is done too soon after gluing, when the biscuits shrink back down there can be slight depressions visible.

I think the reason using biscuits for edge gluing boards became popular was because Norm Abram used this method frequently on NYW. As C-man pointed out already, they are not required for strength. I have even heard people saying biscuits might weaken an edge glued joint. Not enough to make any diffierence, mind you.

Makes sense to me. I think I will use C'man's method of only glues, cauls, and clamps on long-grain to long-grain. Sounds easier and avoids many problems.

[phrog]

The affectation for biscuits is based on what is thought of as a quick easy method. I'll throw pocket screws in that hat too. Biscuits can shrink in place, leaving a divot, or they can swell, and leave a bump. As for any strength, their intention was to help keep parts from pulling apart. They provide little axial strength.

They aren't uniform in thickness, and can vary from brand to brand. With their shape, and shape of the cut, there is not much more than a "tab" resulting in a gluing surface. They have an allowable movement factor when used, and don't insure alignment. In a multiple use project, their positioning can get offset, and not allow a mating of the two edges.

For where ever a biscuit can be thought necessary, a spline would serve a better purpose. It can be made with a specific species of solid wood or plywood, better fit, and more surface gluing area.

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I had been using dowels, but after reading your opinions, I think I will forget those also in edge-to-edge joining and just depend on the glue to keep the joint together.

[cabinetman]

Makes sense to me. I think I will use C'man's method of only glues, cauls, and clamps on long-grain to long-grain. Sounds easier and avoids many problems.

AND...you have that extra gluing surface without all those biscuits being in the way.

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[Cochese]

Edit: Not worth my time or effort

[cabinetman]

Biscuits work for some. The best thing you can do is try all the different kind of joints is to use what works best for you, regardless of what someone else may think of it.

Along with that, to have the benefit of information from those that can offer it from their experience.

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[JimD]

I've used a lot of biscuits to help align boards during glue-up of a top. I've never had one show up on the finished project. I'm not saying it can't happen, just that it hasn't happened to me. I don't really worry about it. Maybe the fact that I am a weekend woodworker so my projects often go from weekend to weekend helps.

My bottom line for biscuits is to use them more for alignment than for strength. I have stopped using them as a replacement for mortise and tenons more because I think mortise and tenons are better than because biscuits don't work, however. My current computer desk and chair are all biscuit joints. The joints are not as solid as I would like but the furniture still works fine and has for about 10 years. You may be helping out a different generation by using mortise and tenons. But I like making things as well as I can and that indicates to me that M&T are preferred.

Jim

[cabinetman]

I've used a lot of biscuits to help align boards during glue-up of a top.
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My bottom line for biscuits is to use them more for alignment than for strength.

Jim

A better alignment method is with cauls and clamps. OTOH, if you use biscuits and cauls, and one or more biscuits are off, the cauls will not be of much help. But, using cauls can be very advantageous in that small wedges can be used (with the absence of biscuits) for boards that are slightly off in relation to the others.

With all aspects being near perfect, I wouldn't use biscuits, splines, or any dowels, as the slightest offset with them will prevent alignment at their location. Biscuits don't insure alignment, and are intended to help the mating boards from pulling apart...not worth the hassle, IMO. I use the wording "don't insure alignment"... if you have boards with multiple biscuits, and just clamp them together, you most likely will not have the boards in alignment. I've done that many times and there always seems to be some nudging involved.

About the glue up. So, the process is ready for clamps. It seems at this point it's a simple matter of just setting the clamps and cauls and tightening them up. Well, what can go wrong? Clamps, like pipe clamps for instance have a closing pressure from the clamp ends that can exert more pressure on an upper or lower edge of the board other than the center, if not positioned properly. Many of those clamps the ends do not close under pressure absolutely parallel to each other.

When tightening one of those its a good idea to see how the mating edges are reacting as the clamp gets tight. Alternating the clamps position on top of the boards and the bottom of the boards help in creating a straight line of pressure to bring the boards together.

As an example of an improper clamp attachment, lets assume that there is slightly more pressure along the top portion of the edges versus the bottom. As the clamps tighten, the pull can make the combination of boards bow, or curve into a "U" shape. This would be indicative of all the board edges (that may be flat to each other) and the faces take a shape other than horizontal. The other side...meanwhile...will show that the glued edges are not tight but slightly separated allowing the board to tip away from its mating board. Over clamping (too much pressure) can do this.

The whole point to this drawn out description is when setting clamps to the outer edges of a group of boards, insure that they are set to exert centered pressure to the boards.

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[woodturner]

I've used a lot of biscuits to help align boards during glue-up of a top. I've never had one show up on the finished project.

It's like any other tool or technique - if used correctly for the appropriate application, it works fine. If used improperly or for the wrong application, the results might not be satisfactory.

For edge glue up, biscuits perform better than dowels. Dowels provide alignment but essentially no glue surface, while biscuits provide both accurate alignment and glue surface. Biscuit jointers assist in accurate placement of the biscuit slots, resulting in more accurate alignment. When gluing up a large top, such as an 8' conference table, biscuits are nearly essentially - it's almost impossible to adjust clamps quickly and accurately enough before the glue skins to ensure a flat, true surface.

For legs and strength-bearing applications, mortise and tenon is definitely stronger - and more complicated and difficult to make. Biscuits are fine for lighter duty applications, but I would still choose mortise and tenon for higher end pieces and heavier duty applications.

[LCHIEN]

Biscuits will "telegraph" if they are placed too close to the surface but I've never had that happen. If you put the biscuit correctly in the middle of 3/4" material then it won't show. Try and join material too thin or try and put the biscuit 1/8" from the top you might have problems.

I don't use biscuits for strength. For me they provide an easy way to align pieces. They vertically align perfectly (if you cut them and hold the fence tight to the board) and provide a smidgeon of lateral adjustment. Sometime when you have glue in a joint the joint will just float on the glue (yes maybe I had too much but its better than starved) when you tighten the clamps (may a bit too much also) and shift all over the place. You can back off and even remove some glue but its a pain in the neck to have to keep realigning (esp if the piece has a slight wave in it). Biscuits avoid that.

I don't think it really compromises anything by using biscuits, - no drawbacks and properly done, there's no way to tell in the final product that they were used at all.

[cabinetman]

I don't think it really compromises anything by using biscuits, - no drawbacks and there's no way to tell in ths final product that they were used at all.

By the time the glue dries, or some time thereafter, if it leaves a dent or bump in the face, you can tell. But, by that time it's a bit too late.

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[phrog]

Alternating the clamps position on top of the boards and the bottom of the boards help in creating a straight line of pressure to bring the boards together.

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Another gem I hadn't thought of (but should have). Thanks. I learn so much from this site.