Half Blind Dovetails

[mrdovey]

Jay Mack sent me some pix of some CNC-produced dovetails and got me thinking (re-thinking, actually).

I ended up writing a pair of programs that allow specification of angle, height, maximum tail width, and displacement from the bottom of the board - and which are capable of producing common, half-blind, and full-blind dovetail joints using only a straight bit.

I thought I'd share a photo of the first test result:


10867.jpg

[stickman]

Morris,

I knew if I could get you started thinking on it. Something would come about. Did you do these both flat, or have one upright in your jig. I haven't had time to take the info you gave me and work on it much. But I plan to later on.

Looks good...

Jay

[mrdovey]

Jay...

Tails flat and pins upright (in the jig). I used a 1/8" center cutting end mill.

Thanks for the inspiration!

...Morris

[paco]

Hey guys!

I assume there's radius... and they are matching...?

[mrdovey]

Paco...

Of course there's a radius - and yes, wherever there's a radius in one part, there's a matching radius in the other part. :-)

The trick is to make the radius small relative to the size of the tail. The 1/16" radius in these parts isn't very visible; and I guarantee that if I'd cut the parts with a 1/32" bit, you'd never be able to distinguish the 1/64" radius from a sharp edge.

What's fun is that only six ShopBot commands are needed to cut the outline (external) of a tail or (internal) of a pin gap! The space between pins takes a few more M2 commands to do the area clearing, but since this area won't be visible in the assembled joint, a large stepover can be used.

...Morris

[mikejohn]

Morris
You say "Tails flat and pins upright "
I can see how the joint can be made pins flat and tails upright, but I am at a loss how to do it the other way around. I am assuming the pin is on top in your picture.
............Mike

[gerald_d]

Mike, the top part looks the nearest to a dove's tail, so I thought that was the tail and the other part the "pins"?¿?

Some ideas for round cutting tools.....link

[mrdovey]

Mike...

My understanding is the same as Gerald's - but I could have it backward.

To remove ambiguity, here's a photo of what I've been calling the "pins" side still in the 'Bot jig:


10883.jpg

...Morris

[mikejohn]

Morris and Gerald
You are right.
If you imagine through dovetails, then cut off the tail at its base, the cross section will be rectangular. Cut off a pin it will be trapezoid at its base. Note when you cut them off, they both have the same shape!

Do you cut full depth with a 1/8" (3mm) bit?
............Mike

[drodda]

Morris,
Looks great. Do you allow some clearance so that they will go together after a day or so laying in the shop or do you have to assemble them immeadiatly?

Dave