Hi thesidetalker:
The internal angles of the fixture are relieved so you could put a dead sharp dovetail in there and it will still clamp on the faces and not on the corners.
With this style of moving jaw that uses a flexure, I always make the dovetail on the stock taller than the female dovetail in the fixture, so when it clamps, it butts hard on the floor of the fixture dovetail and not on the tops of the rails.
So the female dovetail is 0.100" high and I will make the male dovetail on the stock 0.125" high.
That way the top corners of the female dovetail in the fixture can be dead sharp and still not hit in the corners of the male dovetail on the stock.
(I buy standard 60 degree Harvey dovetail cutters with a 0.010" corner radius to dovetail my stock, no fancy, expensive Ingersoll 45 degree cutters like 5th Axis sells...I want the cheap ones!)
I do it this way because the moving jaw rolls a tiny bit as it clamps (because of the location of the pivot point).
I don't want the clamp to push the stock out of position when it rolls.
Also, I want to be able to get all 0.100" of those dovetail sides to participate in clamping the stock, so putting a female radius in the bottom corner of the dovetail is counterproductive.
So is cutting down the clamp height by putting a radius on the tops of the dovetail sides.
Even if the top and bottom radii are only 0.010" each, you lose a total of 20% of the clamping height when you don't need to, and by the time you butcher a flat or chamfer onto the dovetail sides of the stock so you're sure to clear the corners in the fixture you can easily lose 50% or more of the clamping area.
So I stone off the sharp corners of the rails so you can't gore yourself but otherwise I leave them alone, and this is why.
Cheers
Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
