Sliding dovetails – will this jig work?
kenrosenberg1
| Posted in General Discussion on
I am making a chest of drawers. I want to cut sliding dovetail ways in the case sides to house the drawer supports (web frames) and the narrow pieces that will separate the drawer fronts. I have devised this jig (see photo) to cut the sliding dovetails. The center opening is about 5/8″ wide, it will take two passes to cut the full width. The two sides are clamped together front-to-front to insure that the dovetails will be level and parallel, and to avoid tearout at the case front. Before I risk my workpiece, will this jig work? Any suggestions/advice appreciated.
Replies
You may want to use a straight cutter as wide as the narrow top of the finished opening, to remove the bulk of the material. Then follow with the dovetail bit, only cutting the edges.
I would not try to cut a dovetail the full width of the sides, cut your dovetail 2-3" in from the front and back of the side typically the width of the front and back rails of the web frame. A shallow dado between them can house the sides of the web frame if you wish.Mortise and tenon the web frame together and assemble it as you attach it to the sides. Do not glue the sliding dovetail at the rear of the case, let it float so the side can move. Glue only the blade at the front of the case, even then if your joinery is what it should be you will have to work quickly. Use plastic resin glue, especially if the temp is warm as it will give you more time to glue up. I also agree with wasting material with a straight cutter prior to dovetailing. I am speaking from experience here otherwise you might want to have a very large dead blow hammer nearby- and then maybe...
Your jig should work fine. I'm guessing that you are running a template guide on the router base? You'll go up one side and come back on the other.
I'm a little hesitant to run parts back to back, a catastrophe will effect both pieces. You should be able to take a measurement for the jig position and transfer that without any issues. You don't have a good place to clamp the joint between the two pieces and one could be pushed out of level/flush with the other. With sliding dovetails, you can't have any variation in depth of cut. Might be easier and safer to do one side at a time.
I don't trust those clamp bars, they can move just a small amount due to the slop in the fixture. They can also let go. The same is true with the Quick Grip clamps. A little vibration and you may be crying, it's happened to me.
I haven't always had the best luck removing waste with a straight bit first. The dovetail bit will be making contact on both sides of the bit. One side will be cutting against the rotation and can have a tendency to pull out of your control. I would prefer to make the female dado in one nice controlled cut. Don't lean on the bit, especially if it's a 1'4" shank. Even 1/2" shanks have a weak spot at the neck of the dovetail. 1/4" are known for slipping in the collet, particularly with a dovetail bit.
You can clamp some back up wood strips, front and back, with the parallel jaw clamp to prevent blow out on the edges. I would warn about making the fit of the dovetail too tight. You'll get the piece 3/4s of the way in and it won't budge, one way or the other. The sliding dovetail is one of those joints you need to get "just right". I try to get them cut and assembled in one day, a little humidity swelling can be enough to make life difficult. Sometimes, you may have to clamp some straight cauls to the side so it's perfectly flat when assembling. Make sure you do a practice session before starting on the good stuff.
Technically your jig uses the right principles as far as I can see. The difficulty you might encounter is assembly of a tightly cut and accurate dovetail housing anything longer than about 150- 170 mm (6"- 8"). Water based glue swells the wood slightly and makes the joint even tighter and then you have to overcome friction plus fight the curing glue. You can end up with the parts half assembled and the dovetail racked in the housings.
You might consider the form illustrated below which relies on short dovetailed sections spaced well apart with a simple tongue between the dovetails. The dovetails slip into a generous housing or mortice offset by about 25 mm (1") and then slide the 25 mm back into their proper place.
Another form you might consider is the tapered sliding dovetail. This form assembles easily and because of the taper in both the housing and the dovetail tongue only gets tight over the last 10- 15 mm of the assembly process.
Both these forms are harder to execute than the simple dovetail housing you propose, but if done well successful assembly is a great deal easier. Slainte.
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richardjonesfurniture.com
It's impossible for me to fit a long sliding DT for all the reasons listed above and tapered DTs have to be cut individually on each side of the case, which may prove difficult with a jig of fixed sides. This dado jig lets me set a taper angle across the piece, but I find them more trouble than they're worth.
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What does work for me is to cut a shallow dado in the sides (in a single pass, then rip them in half) and putting sliding DTs in the end panel stiles. Like this photo.
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At any rate, I suggest a few tries with scrap first,
Joe
Richard—Sorry to be off-topic, but that tongue-and-dovetail is a beautiful joint. Where have you seen it? Do you typically find it in apron joints?—Andy
Andy, the only circumstances I've seen it executed are:
A wide solid wood headboard (~600 mm) to the legs in a bed
Horizontal shelves or bottom in a deep carcase made of panels. In this case the gable ends were solid wood and the shelf was either solid wood or veneered board plus a front lipping.
In a desk where solid wood sides and back fitted into legs that ran from the ground to the top edge of the sides/back. The drawing I put up earlier was a solution I suggested to a contributor here for a desk construction of that type.
I've seen it in a slightly modified form used to hold heavy horizontal mouldings to the solid wood gable ends of a carcase. In this case a full dovetail housing was worked in the carcase, short butterfly pattern dovetail keys made that slipped into the housing and glued, then the interrupted dovetail housing plus widened slot/mortise was worked in the moulding. In almost every case described above the joint was only glued in one place; the exception is when used in an all solid timber carcase with horizontal dividers/bottom.
A few drawings and a worked example might be a useful addition on page 65A (sic) of your book Furniture & Cabinet Construction. Incidentally, my tome on timber tech is coming along-- only about three sections to complete and so far there are ~105,000 words, 230 photographs and 100 drawings, figures, charts, etc. Apart from some photographs by others that I have permission to use everything else used is written, drawn or photographed by me. Some sections have been peer reviewed by specialists, eg, a section on insects and wood was reviewed by a Professor in Entomology at the local yooni.
I've got to the point where I really want to get it done this year as I've been at the darned thing on and off since the autumn of 2005. A publisher that really has shown real interest in publishing it offered me a contract a few months back, but I declined the offer because I can only work at my pace, not a pace dictated by the publisher. Anyway, toodle pip. Slainte.
richardjonesfurniture.com
Edited 4/2/2009 3:22 am by SgianDubh
SG is right about the water-based glue. However you can get around that by using a polyurethane glue with a long open time of around 30 mins. Gorilla won't do -- they've changed the formula to drastically shorten the open time, as have Sumo, loctite etc. I have some Titebond with the longer open time. A lot of people don't like poly because it gives an inferior bond, but that doesn't matter in this application because the dovetail has an excellent mechanical hold -- the glue is as much for lubrication as for bonding. Last week I used this method on 24" half-dovetails to attach the top of a blockfront chest of drawers. I couldn't get the top on more than a few inches on a dry fit, but with the glue applied it went on like a rat up a drainpipe. I used K clamps to close the final half-inch. True the half-dovetail is easier than the full dovetail, but not by much, and I've used the same method for full-dovetail shelves. I can't take any credit for the idea -- I read about it somewhere. You need only a thin coat of glue on one surface, and if you don't overdo it there's minimal cleanup, by scraping when it's dry. As long as your dovetails are exact and you line up your parts well, e.g. using clamps to straighten the sides of a cabinet, it should go well. Doesn't stop you having a heart attack while you're putting it together, but so far it's always worked for me.
Jim
Certainly not with the all the answers but see link for some tips.
Use a Tapered sliding Dovetail. I love me routers!..
I do the taper on ONLY ONE SIDE. One side straight, the other tapered about 1/6" to 1/8" depending on the length. Longest one I make is about 90 inches. For that I use a 1/8 inch taper. Works perfectly on Veneered Ply. And my common glue, TiteBond II. Most I make are about 1/16" taper along the 4 foot length.
I DO make mistakes, so I make the 'slide in part' a 'bit' longer than the final. I 'Mark En' Trim' the final fit......
Sounds like you're getting some good advice here. Just to be a shameless promoter of the FineWoodworking.com archive, we do have a video and a slideshow on this topic.
Slideshow:
https://www.taunton.com/finewoodworking/SkillsAndTechniques/SkillsAndTechniquesArticle.aspx?id=27113
Video (free excerpt from a book)
http://www.taunton.com/finewoodworking/SkillsAndTechniques/SkillsAndTechniquesArticle.aspx?id=26741
Gina, FineWoodworking.com
Just to be a shameless promoter of the FineWoodworking.com LOL..
OK we still Love ya!
As others have pointed out, it can be hard to assemble this long a sliding dovetail, which should not be glued along its full length. Only glue the first few inches, leaving the rest to slide due to changing MC in the wood.
If you find the joint is too tight to assemble easily, you can lubricate the part that needs to be left dry with paraffin, then use epoxy, if you need an extra hour of assembly time.
yes it will good job
Thanks to all for the helpful advice, especially the reference to FWW issue number 163, which addresses this question. After considering the options, I decided that cutting sliding dovetails the entire width of the sides would weaken them too much and would make the web frames too difficult to fit, so I decided to cut a 3/8" wide dado for the web frames, and to cut dovetail sockets about one inch deep at the front of the sides, to allow the drawer dividers to be dovetailed in. To hold the jig centered when cutting the dovetails, I made a runner that fits into both the slot in the jig and the dado in the case side. (See photos; I removed the clamps and the backing piece to see the setup more clearly.) The web frames will be glued only at the front of the cabinet; as long as they fit properly they should be plenty solid.
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