Geometry Obstacles

Hi Everyone,

I am in the process of designing a window box and I want to use Sliding dovetails in its construction. A little bit about the project. I am using an upper & lower rail with a sliding dovetail slot in each of them to receive the outside panels. Each panel needs to connected with sliding dovetail joinery on the left and right edges but I want to also add a sliding dovetail pin on the top and bottom edges as well. My problem is that the geometry for this joint obstructs each other and I am wondering how to go about making the geometry work. I know how to do it with the wood but sketchup is proving difficult.

I hope that I have explained this clearly enough, TIA

I have placed a Layout PDF file below for some reference.Joinery Question.layout (86.7 KB)

Window Box.skp (93.5 KB)

Ed. are you thinking about this from a practical point of view or just a SketchUp model view? If it’s the latter, select all of the geometry there and run Intersect Faces>With Selection. Then erase the unneeded stuff.

Which way will the grain be running on this part?

Nope I will be making this. The grain will be running top to bottom

So the wood toward the outside of the vertical dovetail socket will be rather delicate. There’s only an 1/8 in. from the point of the dovetail to the edge of the board.

After running Intersect, draw in lines as shown below.

Then erase the unneeded edges. If you lose the top face on the board, trace one of the edges with the Line tool to heal it.

There’s other problems with this joinery. The vertical dovetail socket and dovetail cut on the opposite side intersect which will create a bad spot. Likely to blow out if you cut with a router.

Thanks as always Dave I didn’t realize you could use intersect like that and I actually got a “context option” never saw that before … usually all I get is selection or model options

I generally always use the With Selection option because it gives the best control over what does and what doesn’t get intersected.

Does this look something like what you are expecting?

I recreate the board with the vertical dovetail socket and made it a wee bit longer than the gap between the rails. Then I used Trim from Eneroth Solid tools to trim the vertical piece. Since the trimmed component won’t be a solid due to the intersecting dovetail cuts, I copied the rails, explode the components and made a single component containing their geometry. This component was also solid so it could be used with Trim to make the cuts.

Yep that was exactly what I wanted go idea about thickening the edge of the side dovetail … do you mind if I have that as a skp so I can study it

Here you go. I think the end piece, when it expands will break out the end of the mating piece. Sliding dovetails are cool and all but I’m not sure they are the best choice for a piece that will be outside and wet.

Window Box.skp (58.9 KB)

Someone I know used the joint in a outside pice of furniture and it’s still around !!! I was going to use a T&G but some people said it’s not that strong and would fail quicker !!! What joint would you use??

Thanks again

You could use the dovetail but I think you’d want considerably more meat toward the outside of the joint than the 1/8 in. you’ve got. I’d use a tongue and groove. It would be plenty strong especially if you offset the tongue to the inside. Use an outdoor rated glue such as Resorcinol or expoy. I would also frame it up in the same way a frame and panel door is done with the stiles going by the rails instead of the other way around like you have it. That would help to prevent water getting trapped in the joints. I would expect you’ll have a sort of frame around the top and that will cover the end grain of the stiles.


As a further thought, sliding dovetails are notoriously tricky to fit. If you cut them tight, they are impossible to slide all the way home. And if you cut them loose enough to slide easily they are sloppy. Many people make them tapered so that they snug up only in the last inch or so of the slide. Of course, tapering requires more skill.


I meant to add what Steve wrote about the sliding dovetails. They are fussy to fit and I don’t think they make sense in many situations.

thanks Again I’ll use the locking rabbet in the corner instead of the sliding dovetail and offset it more… but the front panels need to be in the stoles because I need to fit all this wood in tight quarters as I am putting a liner in and my hangers can only for a box no deeper than 7” as it is it will be 8-1/2” deep

Dave do you think it possible to put a sliding dovetail in in one of the long edges and a slot on the back long edge of the board we were working on yesterday while still maintaining a sliding dovetail on the top and bottom

Can you taper them using a router bit in a table if so how??

Probably. I’m not quite following what you want to do.

Yes. You can. Typically the taper is only done along one side of the joint. You put a spacer in against the fence to create a wedge for that tapered cut. The taper doesn’t need to be dramatic so a very thin shim can be used as the spacer.

You need a guide jig that has the taper and use a bit that is smaller than the groove so it cuts one side at a time.

I want to create another type of panel which will be used to create all the panels along the front of the window box … I wanted these panels to slide into each other on the long sides…so we created a board yesterday with a sliding dovetail on the right edge , I want to create a slot to which will mate with the sliding pin on the left side

Sorry I’m not explaining very well…

If only there was a quick modeling program that would let you rough out an idea and get others opinions…

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You can make tongue and groove joints for the panel pieces to slide into grooves in the stiles. Remember, you need to allow some room for the wood to expand and contract with changes in moisture and temperature. If you try to restrain the wood, it’ll tear the box apart.

What are you expecting for the final dimensions of the box?