dovetailing.bookshelves

I just.closed a project with a client for a large set of built ins in their new.family room. The base will consist of a desk, file cabinets a run of base cabinets for a/v storage and such and some bookshelves. The uppers will be open staggered shelving with a vee groove back. all will be from southern yellow pine. i will have to assemble several parts onsite.
I came up with the thought.of dovetailing the shelves into the sides. I am ordering a 14 degree cutter from molding knives.com to fit my delta molding head so i can cut the dovetails on the ts. Then ill dadoe out the sides and run a 14 degree dovetail bit down each side to make the pocket to receive the shelf.
Any thoughts? My.thinking is i may have to make the shoulder cut on the ts first then come in with the moldong head cutter to avoid tearout. Anyone ever tried this?

First, I don't think you can cut dovetail females with a moulding head. You may be able to do the male parts, coming from the side of the shelves, but I just do them with the same router bit I use for the females.

I have never had luck doing the entire female slot with the dovetail bit, even in a shaper. I always start with a straight bit (typically 1/2 inch) to hog out the dado, then make a separate pass to trim the bottom and do the undercut on each side. I use a clamp on guide, and have a selection of shims that I put along the guide so that I don't move the guide between the center cut and the two side cuts. I don't remember which shims I use for this sliding dovetail process, but let me describe how I cut dadoes for plywood shelves (of mystery thickness). I start with the guide clamped to the workpiece, offset enough to allow me to run the router against the guide with a 1/2 inch bit. Then I try a shim 0.20 inches thick against the guide, and cut the second side. If the plywood is thicker than .70, I make the next pass with a 0.21 inch thick shim - my dado is now .71 inches wide. If the plywood is really 23/32 rather than slightly less (0.71875") I make a third pass with a 0.22 shim - and know I can use the .22 inch shim for the rest of the job. If this is a really cheap plywood where the thickness varies over the sheet, I may start each dado with a 0.21 shim).

To cut the male dovetails (on the shelf) I put the dovetail bit in the shaper (router table) and run the boards vertically on both sides, micro adjusting the fence until the shelf fits easily in the groove.

You don't need to worry about modest amounts of tearout in the female part, since it will be hidden. If you are getting tearout on the male part, make the first pass very shallow, to just scribe a line, then cut deeper to form the tail.

Thanks Charlie, I know what you mean about the plywood. I usually use a dado set in the table saw and that was my intent for the shelves. Cut out the dados first then with a jig and template guide run the dovetail bit down the the dado to give me the female joint. (I ordered a 3/4" dovetail bit to keep it simple) and I was planning on just the males on the ts with the molding head. I found that moldingknives.com will make the custom profiles for the delta and corob cutterheads. This way I can run the shelves in the horizontal position and use my sliding table to keep them perpendicular to the fence. With the amount I have to run and all solid stock, I know I would mess up a few of them trying to run them vertically and my shop has low ceilings so I would still have to run several of them on the flat anyway.
The plywood can get quite frustrating at times. Even the good stuff can vary from one batch to the next by quite a margin. The last big job I did I got the set up perfect, or so I thought, until I started assembling and found that even though most fit the way I set it up some were too tight and others had compounded and I had almost a sixteenth of play! YIKES! I was none too pleased having pre cut an entire kitchen!!

I too was scratching my head as to how a moulding head could do either male or female dovetail profiles ;-) Cutting a dado to hog out the waste and then cutting the dovetail works fine although I usually just run a full kerf saw cut and then the dovetail to assure a true profile cut. that being said the idea of sliding dovetails in plywood makes me cringe. As you point out the ability to get a good, consistent, reliable fit is a real shot in the dark regardless of your care during setup. I'd stick with a dado and in ply, to assure a good looking joint I make the dado about half the thickness of the shelf and rabbet the shelf to create a tongue. This way if (I should say "because") the ply is irregular in thickness, any gap is hidden by the overlay.



This could be a stopped dado to give you a clean front on the verticals.

Rich Soby said:

...Cut out the dados first then with a jig and template guide run the dovetail bit down the the dado to give me the female joint. (I ordered a 3/4" dovetail bit to keep it simple)...

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I use a 1/2 inch 14 degree dovetail bit so that I can adjust the width of the female sliding dovetail - even when I am putting 7/8" runners between drawers, dovetailed to the side of the cabinet. If you use a 3/4 inch bit, then the widest part will be a full 3/4 and you won't have any room to adjust for shelf thickness - such as the nominal 3/4 inch plywood that is actually 23/32 (.719")or 18 mm (.709") or 19 mm(0.748")

good point. in this particular case though I am using solid 5/4 stock milled to about an inch thickness. I typically use plywood only for carcase work and overlay with a faceframe of the specified wood for the project. This project calls for all solid syp the only plys will be for the 2 cabinet boxes that will not be seen other than when the cabinet doors are open.

Rich Soby said:

good point. in this particular case though I am using solid 5/4 stock milled to about an inch thickness. I typically use plywood only for carcase work and overlay with a faceframe of the specified wood for the project. This project calls for all solid syp the only plys will be for the 2 cabinet boxes that will not be seen other than when the cabinet doors are open.

Click to expand...

Doh! Sorry about that Rich. I don't know how I got off on the plywood thing.

no biggie, actually it raised very good points and even though it doesnt apply to this particular project it is certainly quite relevent for many others.

Just set up the cutters in my molding head and the bit in the router to make a test piece and i have to say it worked really slick! Minimal fuss and the two pieces slipped right together with just the right snuggness. Would recommend it to anyone making sliding dovetails.

Wunderbar! I am having trouble picturing how a moulding hewad can cut that sort of profile. Treat us to a couple pics if you get the chance

Here is the knife mounted in the cutter head. I set it up in the TS using a rabbeting fence and my miter fence on my sliding table. (sorry no pic of that as the saw is set up for a different operation at the moment) the fence would be to the right of the knife exposing only the depth of the dovetail


Here is a piece after the cut


The dovetail dado cut with a matching dovetail bit on my router (I used 14 degree)


And the mating


being yellow pine and Im sure other species will do the same, there is a little blow out on the end of the cut, my intent is to over size the pieces and rip them to width when ready for assembly.

I like to make a stop cut on the front of the carcase - say 1/2 inch short of the front. With the round bit cutting the female part, you need to cut extra - say 3/4 inch - off the front end of the male part.

Minor tear out in the back can be ignored. some of it may be cut away if you create a rabbet for a back.