I was watching a Youtube video on Ishitani making furniture. He was making trash cans. Mitered corners. He cut slots through the miters and put keys in them. The interesting part was the keys were slightly too thick. He hammered them gently on a flat surface, put glue on them and slipped into place. This seems like a good idea to me. Rather than making the keys the perfect thickness, make the a few thousandths too thick, mash then slightly, and let the glue swell them back up for a perfect fit.
I have done lots of keyed miters. Spent a lot of time and stock trying to rip keys to exactly the right thickness. I have ripped them on the TS, Sanded them in the Performax, scraped them, hand sanded them and I don't know what else. Just never thought to hammer them just a little thinner. Have not tried it yet, but it seems like it will work.
But I don't have a metal vice. Does seem like it would work, especially if you had one with smooth jaws. This really did look like a few thousandths. Would not want to get carried away but it might make for nicely snug keys.
Anybody that uses an ax knows that wood crushing and reswelling is irreversible. Fit an ax head perfectly and then get it wet. It will never be tight again when it dries out. The crushed cells never regain their original size.
Water from the glue will swell the crushed spline some but then it will shrink right back to the original state when it dries out. How is this better than fitting a properly fitted spline in the first place?
I think you are correct it the cells are crushed, their integrity destroyed, but I am talking pressing them down a few thou.
It's a fairly common practice to swell a small dent back up by wetting it. I have don't it a few times and seen no evidence the dent reappears when the wood dries. I have seen that practice recommended here. I have also seen steam recommended, but have not tried it.
I saw Roy Underhill make a water proof box by hammering a nail on it's side into the bottom edge of the side, creating a groove and them planing away the wood to the level of the bottom of the groove. When the box was assembled the compressed wood would swell when water leaded into the joint and seal it. He did not say if this would seal the box when subsequently dry.
I have also seen wood flooring ruined by flooding where the boards swelled and crushed each other and it never recovered. Also seen the ax handle effect you mentioned.
I think the difference is in the degree of compression. If the wood is crushed, I don't think this will work, but if the compression is slight I think it will, but you raise a good point. Fitting the keys properly is probably the best practice, but sometimes you need a bigger hammer.
A friend's father working in the shipyards in WWII. He said "A good machinist knew how to lean on his lathe to get the last 1/10000"."
My dad was one of those ax head soakers - it never bothered him that it didn't work, he would do it anyway.
I've also seen biscuit shaped indentations in a table top - they finished the top in a hurry (that shop was always delivering at the last minute) and after a month or so had to make a new top for the customer - biscuits dried out and shrunk, pulling the outer surface back with them.
On the other hand, we had a planked and caulked row boat when I was a kid. Throw it in the water and it would promptly fill up with a foot or so. Bail it out after three days and it was tight for the rest of the summer. I think the planked bottom did not swell so much as to crush the fibers, just enough to squeeze the caulking material really tight. It was some kind of cotton as I recall.
I had to watch that twice. Pretty slick, but it appears to waste a lot of stock, or does it?
I made a little push block to cut them. Once I got the width/thickness tuned I could slice them by the dozens and did. I have used them up. Need to do more, wish I had taken notes.
I make lots of special purpose jigs. A year later I look at them and go "What the heck did I made that for?"
What I found with the splines was that on a given day they would fit, and on another day they would be tight or loose. Maybe it was the humidity or maybe the saw blade cuts a different slot in pine than in walnut. Or maybe an end grained slot is different that a long grained one. It's important to use the same blade every time or cut new splines
Re: I think it's in the extent of compression too.
Barry Irby
My uncle had a flat bottom boat he left with my grand dad. Same deal. Put it away for the winter and it would dry out and leak. Put it in a pond in the spring and it would swell and seal.
I mentioned hardwood flooring. I saw a room addition that was 24' wide and 32' long. 2 x 8 joists lapped on the center beam. Joint in the plywood subfloor fell over the same beam. They installed new very dry hardwood in the room. A spring surfaced under the room and flooded it. The flooring swelled and burst the room open far enough that one set of joists fell off the beam. Amazing.
"Anybody that uses an ax knows that wood crushing and reswelling is irreversible."
There is this thing called the proportional limit. Beyond that point permanent change occurs, up to that point you can cycle it. Trees sway back and forth in the wind, or in say bows when drawn and released. The cycles to failure are incredibly high, compared to almost anything you can imagine. They are stretched and compressed, over an over, though mostly on the 0 axis.
Who knows what the point of biscuits is. Swelling is not that convincing, because it eventually dries out. The dimensional change isn't necessarily permanent. Two issues are that the biscuit needs to be undersized enough to be an easy but not sloppy fit. Tight enough to bond the glue. After that not much maters.
The axe case is different from the biscuit. The biscuit is dry fit slightly tight, swollen to be tight. The axe is tight fit dry, then cycled with water, and the amount of water is unspecified.
I believe all biscuits made for the biscuit joining operation are "crushed" by the manufacturer. I also know the biscuits expand when water based glue is applied. I have had the biscuit expand enough to prevent assembly when I was careless with the glue application. I had to remove the expanded biscuits with vice grips and a mallet. Apparently these do retain the "expanded" dimension after being glued into the application.
