The latest FW — and coincidentally AW also — has another feature on tapering sliding dovetails. Is there some convincing reason why this is still the method of choice?
For the past few years I’ve been cutting sliding dovetails straight and snug, and joining them quite easily using polyurethane glue. The poly acts as a lubricant, and the dovetail goes in like a rat up a drainpipe. Well, a rat with a boot up its backside in the shape of a tap with a mallet. The long open time doesn’t hurt either when you’re fitting several shelves in a case.
I got the idea from an article by Jack Gray in WJ (April 2002). He was promoting a set of jigs he built for cutting dovetails in prototype furniture for L & JG Stickley, where apparently all case goods used sliding dovetails. He mentioned the glue only in passing, with no details on its use. The only tricky part I’ve found is deciding how much glue to use. Too little, and you break into a sweat; too much, and you’re scraping foam. I’ve been gluing the pins and wetting the channels on the theory that this won’t force extra glue to the front of the case where it would show. You could make a good case for gluing the channel instead to provide even lubrication all the way through.
I suppose you wouldn’t want to use any glue method where you’re mixing wood and plywood, and I’ve never had to use it on shelves deeper than 12 inches. I had assumed that this method was quite common. How many people actually use it?
I never did try Gray’s jigs. One involved sticking a 3 and a quarter router upside down in a vise to make the tails. Not for the faint of heart or the weak of wrist. (Arthritis)
Replies
Jim,
If it is working for you, don't change. After having a desk's writing surface "sliding dovetail" bind up about 6" from being home, I have since combined a dado with a 3" or so wide sliding dovetail in deep carcase construction, combining ease of assembly with the looks and security of the dovetail.
And I did see an old flatwall cupboard top that utilised tapered dovetails. The shelves themselves were tapered in thickness, back to front, so that the show edge of the shelf was only about 5/8" thick, and the back edge an inch or so. The shelves were a tight fit over the last inch or so of assembly. Dainty looking from the front, thick enough not to sag, plenty of meat to nail backboards onto. Really a good concept.
I knew all those Ritis boys, and Arthur was the worst of the bunch.
Ray
Like the sound of the tapered shelf -- makes more sense than leaving a gap, however small. Bit like the dovetail stiffener used under tables. I've seen a few older pieces where shelves were dovetailed on one edge only -- upper or lower -- with the other edge flat. Those might have been easier to hammer home? Nowadays they'd involve more work for those of us who rely on routers, though.
Cheers, Jim
I agree. Sliding dovetails bind because the wood swells from the water? in the glue.
You must have paied attention in woodworking class!
WG,
No need to worry about using glue on sliding dovetails and having the joint swell. Forget the glue. Just put a couple of lag-bolts through the two boards, from the outside. The bolt heads give the appearance of sturdiness, and the metal and wood make a nice contrast, yielding an artistic look to the piece.
MelMeasure your output in smiles per board foot.
For longer sliding dovetails, I generally put glue at either end. I begin to advance the tail piece into the pin and tap gently, when I am about 1 to 2" from having the entire joint in place, I apply glue to the part of the pin that has not yet been advanced, and the part of the tail (on the opposite end) that has not yet been engaged. This has several advantages- 1) If the joint won't go in, I still have a chance of disassembling it and refining the tails for a better fit before putting on the glue 2)the strength of the joint (properly fitted) is largely mechanical- it's not clear to me that I need a 9" glue line on a bookshelf or chest- the 3-4" of glue is more than enough 3) there is less squeeze out to deal with.I don't know if this is "by the book", but I haven't had a book shelf fail on me- and the shelves are fully laden with test books.Glaucon
If you don't think too good, then don't think too much...
Glaucon,
I have seen your approach to assembling sliding dovetails before. I am not sure if there is a book to go by, but if there is, you don't seem to be far off.I have not yet used sliding dovetails, but it's coming. Here is what I was thinking about. Given your experience, what is your reaction. I was thinking of adjusting the tail until it goes in all the way, and even a tiny bit too far, and have this happen with no force. Then put glue in on the front and in the back and let it sink in for a few seconds, and then tap the tail into final position. I figured that the glue will swell the wood. If it didn't fit without glue, it wont fit with it. If it fits tightly without glue, it wont fit with it, so there should be an easy fit without glue.It sounds to me like you might make things a bit tighter than what I am thinking of... What is your reaction?
Thanks,
MelMeasure your output in smiles per board foot.
You don't really need glue on a tight sliding dovetail joint because it holds mechanically. I've always assumed that's why you use such a joint; a simple dado joint has end grain on one face on all three sides -- not the best situation for glue. Most people seem to prefer using a tapered joint just because it's so difficult to insert a shelf where the fit is snug. It tends to bind, with or without conventional glue, and then you're in dire straits. Like having your head stuck in the school railings. Even a tapered joint should be so tight at the front that you'd need only a dab of glue as a safety measure. In most cases there's no incentive for the shelf to move because the pressure on it is vertical.
When I first used poly glue on one I was bothered by having to water one surface to cure the glue. I assumed that even a minor amount of swelling would cause a problem. However, it doesn't seem to. Or perhaps I've been lucky. Poly takes a long time to cure -- 20 mins -- and in the meantime it lubricates enough to insert the shelf before any swelling takes place. You may need a tap or two for the final inch or so, but you need that anyway even for a tapered joint. You don't really need the gluing effect, you need the lubrication. The beauty of poly as a lubricant is that it cures to a glue, and doesn't hang around to cause problems later, as a regular lubricant might.
Jim
Jim,
Thank you for that information.
Let me see if I understand what you are saying:
1) use a tapered sliding dovetail
2) it need to be a snug fit
3) use polyurathane glue to lubricate the fitting of the joint.
4) the fit ought to be snug enough to require a couple of taps with a mallet, using polyurathane glue as a lubricant and glue.Can you give me any tips on judging how much of the poly glue is enough. I have never used it because it foams.
Is my description of your technique correct?How long a tapered dovetail is too long?
I am going to make a hutch for my daughter. I thought about putting the shelves in with sliding dovetails. IT would be a step back hutch. The depth of the shelves on top would be about 13", and about 18" on the bottom. Any suggestions?Thank you.
MelMeasure your output in smiles per board foot.
Right except for one thing. The point of the polyurethane glue is that it lets you use a non-tapered dovetail. I suppose that by definition a tapered dovetail can't be a snug fit, except for the last couple of inches. That's why I was interested in trying something else. I cut the grooves with a hand router, both together, then do the tails on the table with the same bit. You have to fiddle with the tails till they're the right height and width. If you can push the tail in a couple of inches into the groove without herculean effort, and without it rattling around loose, it's probably right. (Pause for unseemly laughter.) If you try to hammer it all the way home with ordinary glue or no glue, chances are it'll bind. It'll certainly give you a workout. It'll save you a lot of work if you can do all of the sockets first, then leave the bit set up in the table for all of the tails. (With most versions of the tapered joint, as you'll see in this month's FW, there's an extra step in cutting the grooves.)
I don't normally like using Polyurethane glue either, mainly because it turns into a bowling pin if there's a long time between jobs. I'm afraid the amount is trial and error to some extent, though I began with the conviction that scraping off excess was preferable to a jammed shelf. I put a thin coat on the part of the tail that's in the socket, and slightly dampen the socket. I don't see why the reverse wouldn't work either. Why not try a mockup? Better than an irreparable disaster.
I think I mentioned in the original post that I've never had to do a shelf deeper than 12 inches, so I can't say how 18 inches would do. Again, I'd try it out on some scrap. For such a long shelf you could try the hybrid joint suggested in an earlier response. I gave the source for this way of doing dovetail joints in the original post, but I doubt that it's worth checking out. It says nothing at all on how to use the glue.
Good luck, Jim
Jim,
I understand now.
Also, my FWW came, so I have the article.
Now I need to do some practicing.
Thank you very much.
MelMeasure your output in smiles per board foot.
Jim,
Your suggestion that a hybrid joint (part dado part DT) in longer joints is a good one, I think. That 18 inch non-tapered sliding DT taught me a lesson!
Still, with a good router table and set up, a very precise-fitting non-tapered DT sliding joint can be made. Generally mine will push home (sometimes with the help of the rubber hammer) and have no slop when dry. But they can also be unslid (again, maybe with a rubber hammer giving a hand).
AFter I read in Knots about taking the points off the DT corners, I do find the joint will slide and unslide together a bit easier.
I just use ordinary yellow glue usually, but just a front and back dab as Glaucon mentioned. As long as one doesn't bugger about too long, the wood does not swell before the joint is tapped home. (That 18 incher was the exception, of course. One who buggers about like moi should have known better). :-)
Lataxe
I did a BIG cabinet once where I used 1/2 dovetails. Angle at the bottom with long and wide shelves. I made the daddo a bit higher than the shelf and glued a strip of wood (contrasting wood, so nobody got the idea it was a 'fix'. ) Worked well!
Mel,
Glaucon is the wise sliding dovetailer. I have made a number of the things and early on made the mistake of gluing the whole DT - all 18 inches of it in one case. Naturally the bluddy thing jammed and it was curse, swear, mallet to get it undone (damaged).
I learnt Glaucon's trick (I did read it somewhere at the time of the disaster but can't remember where). Also, a Knotter mentioned that it helps to knock the pointy corners off the tail, which gives excess glue somewhere to squodge out and does help prevent mechanical jams. I have used this technique since. The DT stays mechanically tight without the corners.
Them DTs do need to be well-fitting when dry - they should push home but with effort. The glue does swell the wood when it's wet but it all shrinks back again when it dries out. You do not want flop-joint. The joint must be tight enough to enable the glue to do its thing - bond mated surfaces, not part fill a gap.
One day I will try a tapered sliding DT; although why bother if the precision of router cutters and such can let you make well-fitting sliding DTs without a taper?
I can imagine (and it is imagining, not real knowledge) that it would be difficult to make a precision straight-sided sliding DT with handtools. Perhaps a tapered joint is more forgiving of any less-than-flat joint surfaces?
A tapered sliding DT that was not entirely even (ie had a few gaps between the tail and the keyway) would still be strong when slid together, as the sliding automatically creates the good fit where there is one.........? (Assuming you have got the taper angles and the sizings more or less correct).
But I am guessing, so it would be interesting to hear from anyone who has made tapered and straight ones as to what the respective advantages and disadvantages are. Experience counts.
Lataxe
Lataxe,
I appreciate your post.
Let me check my understanding of what you said. Did you attempt to make an 18" sliding dovetail that was NOT tapered? As I said, I have not done sliding dovetails yet, but am planning a hutch and was going to use them for the shelves. I plan to use tapered sliding dovetails.From what you said, I should
1) make a snug dry fit.
2) remove the points on the ends of the tails
3) only glue the front and back, as Glaucon said.
Note that I am tempted to try polyurathane glue that was recommended by Jim because it as a lubricant. I am planning to do a number of test joints before making them on the actual hutch. Please let me know if I described your recommendations correctly.
Thank you for the help.
MelMeasure your output in smiles per board foot.
I took a handtool class from Scott Wynn (sp?) once. We made a bench hook that used tapered sliding dovetails to attach the feet to the board. The taper allowed you to adjust the tightness of the fit but still be able to take the piece apart when needed. He also had an amazing portable workbench that used this type of joinery. He could break the whole thing down, move it, and knock it back together in 15 minutes, or so he claimed. So I always assumed (please no one respond with that old saw) that the taper was best used when you want to be able to take the piece apart.
I use straight sliding dovetails in almost every piece I make. Some are almost 20 inches long. I never use any glue. I just use a plastic-faced deadblow mallet and some sweat. I have not yet damaged a piece, but some have given me a good workout. I tip for getting a great fit: Have an extra piece of wood the same thickness as your dovetail. That way, you can dial it's size in on the router, and then simply mill your piece without risking the dreaded sloppy fit.
Paul
I just use a plastic-faced deadblow mallet and some sweat.. Geee... that sounds like hard work!I have made more en' a few 48 inches long. I go for a 'nice' but not to tight fit. If I cannot fit dry cuss at myself a bit and use one of my dovetailed sanding blocks with 120 grit paper and lightly sand each slot. I guess I could use a dovetail plane but I don't have one.The block is narrow and I just use rubber cement on a strip of paper. Usually just a 'swipe' along each edge will allow a nice fit dry. I only glue the front edge (front of the project) about 6 to 12 inches or there about depending on the length.For these long dovetails it is usually plywood for cases with shelves.To be honest, I have never cut a tapered dovetail. Not sure why but I see no reason to try and glue the entire length of a dovetail for case work.Just me..
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