Cutting dovetails-Machinery's Handbook and video

[Janderso]

Ok, so here's the trick.


FIRST, pick a 'width' for your dovetail, inner-point to inner-point on the 'female' part of the dovetail. Center your spindle, and "know" the width of your cutter.

Say, you chose a 1.250 'width' for the inner points on the female part, and a .750 'cutter' width. Cut down the center (or, more likely, have cleared it out with your roughing mill) and set your depth (lets say, .200" for this), and cut until the 'points' hit their size, just like if you were trying to cut with a normal straight cutter. In this case, 1.250" wide, -.750" cutter, is .500. .500" / 2 (for each side!) is .250", so you cut until your DRO reads .250" and -.250".


NOW to do the 'male' part, you do the reverse when you 'cut', you cut the 'width' of the 'inner points' PLUS 1/2 your cutter width. Calculating the inner point is as easy as just doing the trig.

The inner 'corner' is 60 degrees thanks to your dovetail cutter. You want to find the 'adjacent', so open your favorite right-triangle calc (like this one!) https://www.calculator.net/right-triangle-calculator.html

"Alpha" is 60 degrees. 'a' is .200" (the depth we decided above). We're looking for 'b' here, which ends up being 0.11547. Which means the 'narrow' points on the female dovetail are 1.250" - (.11547 *2), or 1.01906. (1.250" because that was the 'inner width' we chose above, *2 because there are two triangles created by the dovetail cutter, 1 on each side).

SO now you want to cut the 'male' side. Target 'inner point to inner point' is 1.01906" (plus perhaps a touch for a running fit!). Cutter is still .750. Set the cut 'depth' on your part right to the .200" we decided on above. Then, with the DRO centered, cut the 'outside' of the part until the DRO reads DOWN to (1.01906 + .750)/2 (cutter size!), or 0.88453.

At this point, your dovetails should be just about right-on, as long as your DRO was. No measuring over pins, just good-new DRO + a small amount of trig

I’ll work on this today.
Thanks for your time with this!

 

[Janderso]

The upper Rogue is one of our favorite rivers. We have stayed many times at a little resort just up the road from Prospect, toward the cutoff to Crater Lake national park. It's rustic but close to a lot of pretty country to explore.

You may have gone down the Avenue of Boulders trail there at Prospect. Pretty impressive, too. We love all the Madrone trees along the trail.

The Rogue river comes from a very large spring inside the park, called Boundary Springs. It goes from nothing to a good-sized creek in just a few hundred yards.

Yes, that's the place. There is a small cafe there. Great comfort food and homemade pies.

 

[homebrewed]

Yes, that's the place. There is a small cafe there. Great comfort food and homemade pies.

Beckie's Cafe. I think it's named after the original owner's family name, Beckemeyer or something similar. We've eaten there many times over the years. Huckleberry pie, yum!

 

[Janderso]

Beckie's Cafe. I think it's named after the original owner's family name, Beckemeyer or something similar. We've eaten there many times over the years. Huckleberry pie, yum!

YES. That's it. Wonderful place.
Unexpected considering the location is out in the sticks. The town of prospect is down the road a piece. Not much there either.

Oregon is known for all the berries that grow there.
Huckleberry,
Blueberry,
Strawberry
Marion berry
Rasberry
Blackberry,
Dingle berry

 

[Janderso]

Well shoot.
I'm too ashamed of myself to show my work. The dovetail project came out terrible.
I think I can salvage it but I am going back to the drawing board.
I think I may be over my head here.

 

[homebrewed]

I'm working on a version of this clamp system, too. I have cut pieces for two of them, plus a "jaw" I can mount directly on my mill table. I mean, why is it necessary to make two of them just to clamp stock (the second one is for a different purpose). The fixed "jaw" will be much easier to make so that looks like a no-brainer to me. It also should be easier to tram if necessary.

They will be drilled/tapped so I can attach sacrificial jaws when I need to machine thinner stock all the way to the edges. I'm not going to harden them since I'm not sure just how often I will use them; and that way a cutter _might_ not be damaged if it inadvertently encounters the steel portion of the clamp.

The other thing: I'm not going to machine dovetails. Don't see the point since a slot will work equally well for restricting horizontal motion, the main thing is to achieve a reasonably decent fit between the two pieces.. They just will have slots and matching bosses.

My work on this is prompted by yet another project that would benefit from having some of these available. I hope.....

 

[Janderso]

Got it
My first go round had me pulling out my fingernails when I had two more passes to go but the dovetail cutter and the ER40 collett had other ideas.
I scrapped the male part and started over. Lesson learned.
I put the cutter in an NT30 end mill holder. Rock solid with great results. My neighbor helped me with the trigonometry.

I am so happy I could dance. Never mind, that was a bad idea.
Next step, drill and counterbore for the hold down screws.
Then, these parts go in for heat treatment.

 

[jmkasunich]

Ok, so here's the trick.


FIRST, pick a 'width' for your dovetail, inner-point to inner-point on the 'female' part of the dovetail. Center your spindle, and "know" the width of your cutter.

Say, you chose a 1.250 'width' for the inner points on the female part, and a .750 'cutter' width. Cut down the center (or, more likely, have cleared it out with your roughing mill) and set your depth (lets say, .200" for this), and cut until the 'points' hit their size, just like if you were trying to cut with a normal straight cutter. In this case, 1.250" wide, -.750" cutter, is .500. .500" / 2 (for each side!) is .250", so you cut until your DRO reads .250" and -.250".

Just one "gotcha" to keep in mind when doing things "point-to-point" on a dovetail: your cutter probably doesn't have perfect points. And your mail dovetail probably loses its points when you debur/chamfer the sharp edges. So measuring the points can be tricky. Even a few thousandths of rounding on the points of the cutter or the male dovetail will be enough to throw off the fit. The idea behind the "measure over dowels" method is that the dowels touch the angled sides of the dovetail somewhere around the middle rather than at the points.

 

[ErichKeane]

Just one "gotcha" to keep in mind when doing things "point-to-point" on a dovetail: your cutter probably doesn't have perfect points. And your mail dovetail probably loses its points when you debur/chamfer the sharp edges. So measuring the points can be tricky. Even a few thousandths of rounding on the points of the cutter or the male dovetail will be enough to throw off the fit. The idea behind the "measure over dowels" method is that the dowels touch the angled sides of the dovetail somewhere around the middle rather than at the points.

In my case, there IS no measuring, since you're cutting both sides. While the dovetail cutter doesn't have perfect points, the deburring makes up for it and rounds over the male part.

 

[Janderso]

Next step,
I’m waiting for a small roll (12’ x 10”) of stainless wrap. MSC had it.
Then I can heat treat and temper before the final grind.