The biscuits do absolutely nothing as far as strength is concerned
But they sure make it a lot easier to align the boards...
This comment is typically made about biscuits. Most often when referring to gluing together a top etc.
Saying this too often will eventually give the idea to the newbie that there is no reason to own a biscuit joiner. Biscuits can successfully replace M&T joints in many places. They are faster $$$$ and easy to make etc. They are most useful when making kitchen cabinet boxes, face frames etc.
Don't be misled as to how worthless biscuits are! They can be your friend $$$$$!
Agreed. I use biscuits all the times (well, almost), especially when the goal of the project is the "end product". Frankly, I feel that other joineries like dovetails, through tenons, box joints, etc. are pretty much "just for show" rather than the necessity in many applications (except for reproduction work.)
I built my workbench base with wedged tenons and I don't think I'd feel safe having replaced them with biscuits. That being said, biscuits do have their place. As a matter of fact, I did use them on the workbench top to attach the aprons slightly offset at the top and then planed them flush. That's one use for a biscuit that most other joinery can't do.
But a comment not necessarily "typically made" by anyone who knows what they're talking about. On long grain to long grain glueups, like on the table top in your quoted text first above, the quote is basically correct with regard to both "strength" and "alignment".
There was an article a couple of years back in one of the trade mags, plus there's a ww site (that I can't find at the moment - but will try if needed) that ran a test on the various types of woodworking joints. From dowels to variations of the M&T and the test included biscuits.
Certainly you can use them for joinery but if good strength is necessary for the joint - then biscuits are a poor choice. A rail and stile cabinet door doesn't have or need much strength in it's joints in a typical cope and stick construction but make that a deeper M&T joint and it is one of the strongest joints available. A biscuit added to a butt joint (rail to stile for instance) certainly adds some strength (end-grain to long-grain glue joint) but it was not much according to the test results as I recall.
The dovetail makes a good strong joint for many applications where pull-apart strength is a necessity - such as in drawers. Yes, other joinery can be used but I would disagree with your statement about being "just for show". You only need to look at some of the works by Sam Maloff and look closely at the joints he uses in his chairs for instance. Not much to see unless you pull it apart or see it before it's assembled but they're dovetails and M&T's and nothing shows. He uses them for strength and does not draw attention to them.
first is about biscuits in corner joints of Particle Board and MDF furniture. It basicially says Biscuits actually weaken the joint so wider spacing of biscuits leavs more room for edge gluing.
The second is a study in solid wood, replacing tenon joinery for entry type door frames. In this case they show how going to 3 biscuits is actually nearly as strong as a tenon in Pine. The most interesting facts from this study are that putting the biscuit deeeper in the edge grain side is more effective (see how the joist fail by tearing the edge grain) and that the gap at the bottom of the slot is another weak point so poly glue might be better, as it fills gaps better (still not good). Epoxy might be best huh?
I agreed with you on the M&T for chairs and tables, that's why I wrote "many applications" not "all applications". But I think I should be more clear; I was thinking about dovetail joints for a jewelry box or drawers in a side table that get opened a few times a week.
> The first is about biscuits in corner joints of Particle Board and MDF
Both studies make sense. Biscuits significantly increase the glue surface. In solid wood that makes it stronger. In particle board that makes it weaker.
doesn't have or need much strength in it's joints in a typical cope and stick construction but make that a deeper M&T joint and it is one of the strongest joints available
Double stack your biscuit and you have the strongest joint.
It doesn't...it's a misinterpretation of the results of the test...
In the MDF joint, the thickness of the remaining material around the biscuit slot was insufficient given the strength of MDF. Wood w/ its continuous fibers isn't subject to same problem.
Didn't somebody here come up with some study that proved that biscuits in a joint are actually stronger than glue alone? Or is age causing a brain fart? twitch, jo4hn
A few years ago Norm was using more biscuits than Uneeda could bake. (We old timers know the reference here :)) Then someone said he wasn't too keen on them lately because of "swelling problems" or somesuch. What is his position now?
Biscuits sure beat a butt joint but I personally think they sometimes make panel alignment more complicated. Perfect alignment during glue drying can be had with clamps and cauls.
jo4hn, your brain is working just fine. There are numerous studies of biscuits and joint strength. You might start, as I just did, by Googleing with[ "biscuit joinery" joint strength study] in the search criteria[just use what is in brackets]. You can find more if you massage the search words a bit. Larry
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