compound angle dovetail layout help

[Daniel Rode]

I'm looking to make a project that will feature dovetails on a compound angle.

Sort of like this:
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I'm not quite sure how to layout the dovetail angles. If it matters, my sides will splay out about 15 degrees. Any pointers would be helpful. This is a practice project for me. I've never made anything except square dovetails. Should I look to try something simpler first. Having only 2 sides angle out, for example?

Thanks in advance!

[Jim Koepke]

As with so many things we humans tend to over think the path to finishing a project.

The depth of the pins and tails will run on an angle parallel to the finished end grain edge.

If you cut tails first the end grain line will have to be off of 90º by the amount of tilt. Same for the pins.

This is from my thought process and not from experience so it could be all wrong.

You might want to try this on a piece of scrap first. It is also my suggestion to cut all the pieces to length ganged together as much as possible so all the angles match as much as possible. Of course if you have a table saw this may be unnecessary.

jtk

[David Weaver]

Cut tails first and mark the angle of splay on the tail board across the end grain (so that the cuts on the tails are parallel to the base when the board is sitting splayed). Use tails to mark pin boards and cut, and you're done.

[Daniel Rode]

Do I need to do anything special laying out the pin angles. They are at 75 degrees rather than 90.

[Cody Kemble]

This video helped me visualize how to set up the angles. I found it easier this way than trying to do all the math. The math wasn't the problem, my ability to perfectly cut was.
http://www.youtube.com/watch?v=e9h9maJNFAc

[David Weaver]

whatever angle you need to have to mark the tails across the end grain, you'll need to do the same thing with the pins. If you use a bevel gauge to mark across the tail board, just use the same one to mark the pin board.

[Daniel Rode]

Thanks everyone. I *think* I know what I need to do now.

When either the pin or the tail boards are angled, it seems fairly simple (relatively speaking). It gets more complicated when they are both angled but not too bad. The video Cody posted really helps visualize it. I don't have 3 bevel gauges but I think I can do what I need with just 1 :)

I suspect the first couple attempts are going to be firewood.

[Warren Mickley]

I made hundreds of dovetailed trays with sloped sides back around 1987. It is complicated because it doesn't quite lend itself to two dimensional drawings; I will try to give some help.

First of all there is the slope of the bottom edge. This is how much the sides lean from vertical. The bottom usually rests on a flat plane.

The second angle is the slope of the side edges relative to the bottom edge. This angle is larger than the first because it has to meet the leaning of the adjacent side.

The third angle is close to 90 degrees, maybe around 94; it is the angle of the side edge relative to the face of the board. If you make this exactly 90 degrees then your box will not close up nicely. You will have to force it together and there will be gaps on the baseline.

When I made these I did the math, trigonometry in three dimensions, which is work. I knew all three angles for several different slopes in my head. What I would recommend however is getting a block 2x4x6 or so and cutting the sloping angles on two or four sides and using this model to set up your bevel gauge for each of the three angles.

I cut the tails first. If your side edge angles 15 degrees and you use a 10 degree bevel angle for dovetails, then each tail has one side that is 5 degrees from the straight grain, and the other that is 25 degrees from the grain. This makes for short grain on one side and a weak dovetail. Instead what we do is have each cut 10 degrees from the grain direction. 15+ 10 =25 and 15 -10 =5. This is stronger and more handsome. The pins are marked from the tails and the other cuts are parallel to the bottom. One of my friends used to say "Everything is worked off the bottom."

Do make a solid block for reference and do some practice (all four sides) with scrap.

[Daniel Rode]

Thanks Warren! I think I understand but I can quite visualize it yet. I'm going to need to read this through a couple of times and try to mock it up before it clicks. It's definitely more complicated than I initially thought.

I made hundreds of dovetailed trays with sloped sides back around 1987. It is complicated because it doesn't quite lend itself to two dimensional drawings; I will try to give some help.

First of all there is the slope of the bottom edge. This is how much the sides lean from vertical. The bottom usually rests on a flat plane.

The second angle is the slope of the side edges relative to the bottom edge. This angle is larger than the first because it has to meet the leaning of the adjacent side.

The third angle is close to 90 degrees, maybe around 84; it is the angle of the side edge relative to the face of the board. If you make this exactly 90 degrees then your box will not close up nicely. You will have to force it together and there will be gaps on the baseline.

When I made these I did the math, trigonometry in three dimensions, which is work. I knew all three angles for several different slopes in my head. What I would recommend however is getting a block 2x4x6 or so and cutting the sloping angles on two or four sides and using this model to set up your bevel gauge for each of the three angles.

I cut the tails first. If your side edge angles 15 degrees and you use a 10 degree bevel angle for dovetails, then each tail has one side that is 5 degrees from the straight grain, and the other that is 25 degrees from the grain. This makes for short grain on one side and a weak dovetail. Instead what we do is have each cut 10 degrees from the grain direction. 15+ 10 =25 and 15 -10 =5. This is stronger and more handsome. The pins are marked from the tails and the other cuts are parallel to the bottom. One of my friends used to say "Everything is worked off the bottom."

Do make a solid block for reference and do some practice (all four sides) with scrap.

[Daniel Rode]

I hacked this up in about 30 minutes. It's pretty rough but better than I expected for the fist time out.

The angles need to line up precisely before the pins will slide in. It might have fit together OK if I had left it alone after sawing. Instead I rushed into paring the pins when it didn't go together quickly. I set the angles for the tails by eye. Just a wild guess. I'll focus on Warren's advice for the next one.

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