Dimensioning sliding dovetails

[Oskar Sedell]

Hi all.

I'm planning to build a shop bench, for sawing, sitting on while chopping or coffee drinking. The drawing shows the rough design in a side view: Two leg frames, dovetailed into the top and two stretchers in between.

I'm thinking that only the leg frames will be glued up, and that the bench can be knocked together with the tapered sliding dovetails between legs and top and the wedged stretchers between the legs.

I have little experience in dimensioning furniture and I hope to get some advice from you.

I want the bench to be pretty sturdy and of normal height for sitting on. My idea is to make the leg frames strong enough to resist racking in the cross direction and the stretchers high enough so that when they are wedged in place there is no racking in the lengthwise direction.

Therefore I imagine that the dovetail connection to the top does not have to take that much load. Am I wrong here?

Furthermore, is there a rule of thumb for laying out the sliding dovetails with respect to strength? What about the width (A) of the tail and the depth of the dovetail dado (B)? Does this depend on the choice of wood? I will probably make the bench out of a cherry board I have, and the top will be somewhere between 1 and 1 1/4 inch thick.

Looking forward to hear your views on this.

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[William Fretwell]

If the legs are substantial and the stretchers wide enough then you are correct the sliding dovetails will have little force. Many benches don't have dovetails just some wooden pegs at the front so the bench top is free to move, that is all you need really.
The middle of the stretchers should be at the mid point between the bench top and the floor.

[Brian Holcombe]

1.25" Thick is very light for a workbench top, IMO. 2.5"~ would be my minimum.

I'd want a pretty good overhang, so the legs could be set in from the ends further than your drawing shows. Mind you, your feet will tuck under the bench and you don't want to constantly feel that you have to step back from the bench to position yourself.

[Robert Engel]

If I were doing it that way (which I wouldn't) I would leave the pin part as wide as possible with about 1/4" of shoulder and about 1/2 the thickness of the top. I think you're over complicating it. I would use a simple fastening method used to fasten a table top that accounts for movement.

If possible I would at least double the thickness of the top, perhaps 2 layers laminated together. In this cast the DT's would be quite simple just using the bottom layer in separate pieces to form the DT.

BTW, for sawing, I find a knee horse far superior due to mechanical advantage and ergonomics.

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[Oskar Sedell]

If the legs are substantial and the stretchers wide enough then you are correct the sliding dovetails will have little force. Many benches don't have dovetails just some wooden pegs at the front so the bench top is free to move, that is all you need really.
The middle of the stretchers should be at the mid point between the bench top and the floor.


Thanks William!

[Oskar Sedell]

1.25" Thick is very light for a workbench top, IMO. 2.5"~ would be my minimum.

I'd want a pretty good overhang, so the legs could be set in from the ends further than your drawing shows. Mind you, your feet will tuck under the bench and you don't want to constantly feel that you have to step back from the bench to position yourself.

Thanks for answering Brian. I'm not sure if it was clear that the bench is for sitting on, or kneeing on while sawing. I edited the original post just to be safe. Maybe 1 or 1.25 inch is still too thin?

[Oskar Sedell]

If I were doing it that way (which I wouldn't) I would leave the pin part as wide as possible with about 1/4" of shoulder and about 1/2 the thickness of the top. I think you're over complicating it. I would use a simple fastening method used to fasten a table top that accounts for movement.

If possible I would at least double the thickness of the top, perhaps 2 layers laminated together. In this cast the DT's would be quite simple just using the bottom layer in separate pieces to form the DT.

BTW, for sawing, I find a knee horse far superior due to mechanical advantage and ergonomics.

356261

Thanks Robert! It may very well be that my plan is overly complicated. On the other hand, the end result is only part of the joy. I've never made any wedged stretchers, or any bigger project with structural sliding dovetails and I look forward to try it out.

Also, I thought that fastening the top by unglued dovetails would allow for wood movement.

[Bill McDermott]

Oskar, Your bench looks like a great project for a woodworking class, especially if the legs are mortise and tenons top and bottom. Have fun building that, and enjoy sitting on it, pondering. My only comment is that you might want to intentionally make the dovetailed rails extra long so that you can make the sliding DT a bit tapered. It will be a lot easier to assemble the top three pieces. Then you can align things, cut those rail to length and chop the mortises for the top of the legs. My saw bench top is 1 1/8th inches thick and works perfectly well for the purposes you propose. Looking forward to seeing a photo of your finished bench with that cup of coffee on it.

[Oskar Sedell]

Oskar, Your bench looks like a great project for a woodworking class, especially if the legs are mortise and tenons top and bottom. Have fun building that, and enjoy sitting on it, pondering. My only comment is that you might want to intentionally make the dovetailed rails extra long so that you can make the sliding DT a bit tapered. It will be a lot easier to assemble the top three pieces. Then you can align things, cut those rail to length and chop the mortises for the top of the legs. My saw bench top is 1 1/8th inches thick and works perfectly well for the purposes you propose. Looking forward to seeing a photo of your finished bench with that cup of coffee on it.

Bill, thanks for your comment. I indeed plan to make them dovetails tapered, and M&T the leg frames together. Thanks also for commenting on the top thickness. The mandatory coffee-break pic will be posted as soon as I get it all together.

[Pat Barry]

I would make the dovetails into approx 2/3 of the thickness of the top, so for the 1.25' thick top, I would go about 7/8" deep. This would be fine for hardwoods such as ash or oak. for softwood, I would want more thickness though, 1 1/2 inches for example - basic BORG 2x4, 2x6 for example and then go with 1 inch deep dovetail. Make a quick test joint though to verify before committing to your project.

[Brian Holcombe]

Ah-ha! 1.25" will be fine for that. I think the bench will work well as planned

[Brian Holcombe]

I would make the dovetails into approx 2/3 of the thickness of the top, so for the 1.25' thick top, I would go about 7/8" deep. This would be fine for hardwoods such as ash or oak. for softwood, I would want more thickness though, 1 1/2 inches for example - basic BORG 2x4, 2x6 for example and then go with 1 inch deep dovetail. Make a quick test joint though to verify before committing to your project.

1/3 max for sliding dovetails,otherwise the trench removes too much strength from the top.

[Pat Barry]

1/3 max for sliding dovetails,otherwise the trench removes too much strength from the top.
1/3 depth might be fine for furniture, however, 1/3 would not have much strength with respect to racking forces for the stated application. This was the reason I opted for deeper in my earlier post. I don't see a big reduction in strength for this application with a deeper dovetail but will adjust my thought a bit to go to 1/2 the thickness of the top based on you feedback. No matter, I would still opt to mock this up on a test piece and then stress it a bit with lateral racking forces to see how it holds up

[Brian Holcombe]

If you don't see a big reduction in strength then trench out 2/3 from a board then see how strong it isn't. I know this from experience and having made the mistake of taking out 2/3.

1/2 is even too much. 1/3 is plenty of depth for a sliding dovetail to be strong without weakening the table top.

Sliding dovetails are inherently weak against racking, they would do fine in the above application because the stretcher will work against racking forces.

[Oskar Sedell]

Brian: thank you for your insight. Exactly what I was looking for. Indeed I want the stretcher to take most of the racking forces. My intuition tells me a wider dovetail (i.e wider dado) would have more racking strength, or in other words; withstanding more momentum. What are your experiences here?

Pat: Thanks for chiming in. A mock-up is a good idea, maybe I'll make a model first.

[Brian Holcombe]

Wider will help a lot in that respect, I would make them as wide as reasonably possible

[Oskar Sedell]

Wider will help a lot in that respect, I would make them as wide as reasonably possible

Thanks Brian! Going to finalize the drawing (and make sure my cherry board is big enough).