Dovetail Cutter Design

[asallwey]

I'm toying with making a 1" dovetail cutter using a carbide insert. I found a number of 'builds' on the internet, most of which look very similar to comercial cutters. Typically they have the insert's top surface on centerline with the cutting edges and tip extending beyond the body just a little. I have seen one or two where the insert extends inward past the center point of the holder. I'm wondering if this would be a problem? Most I have seen seem to reach the centerpoint at the most.

I have some TCMT32.51 inserts with a side length of ~.623". Would this be a problem since it would go past the center point? I was considering getting some TCMT21.51 which have a length of ~.410".

Alex

PS Is it me or is it hard to find the length of an edge for a given insert? Doesn't seem to be a common dimension. What am I missing?

[Mark Rand]

PS Is it me or is it hard to find the length of an edge for a given insert? Doesn't seem to be a common dimension. What am I missing?

US insert specs go by inscribed circle, European insert specs go by edge length usually for identical inserts. it can be worth looking for equivalent numbers on your search engine of choice.

[Toolguy]

Inserts are measured by "inscribed circle". That means that an insert with a 1/2" inscribed circle insert the 1/2" circle would touch all the flat sides. This makes a same size square insert different than a triangle insert and different than a diamond insert. Right on size for a round one though.

You need a positive rake insert if you want to do that. If you put a negative rake insert (straight sides) with the cutting edge on the cutter centerline, it will have major interference behind the cutting edge. If the cutting edge of a positive rake insert is on or just behind the centerline of the cutting tool then the ends can overlap in the middle. If the ends overlap you can only have a 2 insert cutter.

If they don't overlap you can have a 3, 4, 5, etc. insert cutting tool. You want to make the insert pockets so the insert is .003 to .005 higher in the middle than at the edge. You want to make the holes for mounting screws .003 inward towards the inside corner from nominal so they pull the insert into the pocket when tightened.

[Lu47Dan]

Here are four videos on making a dovetail cutter.
Video 1
Video 2
Video 3
Video 4
I have not started on my copy as of yet.
Dan.

[asallwey]

Toolguy,
I've seen the data on inscribed circle. I just don't know how it translates to length of a side.

So if I tip the center up slightly, what happens to the 60* angle? This is starting to sound rather tricky!

Dan,
I've looked at the first video before, and frankely I have a hard time spending the time on him. He has good info, but the baggage that comes with it kind of overwhelms me. It's sad that some folks can't stick to the topic.

Alex

[Toolguy]

If you tip it up slightly the angle will be off that much. It depends on the application whether it's a problem or not.

There are trig tables to show you how to calculate the length of sides from the inscribed circle size. The corner radius will affect the length a little.

That series of vids could have been done in 15 or 20 minutes. It just isn't that hard.

[Lew Hartswick]

I've looked at the first video before, and frankely I have a hard time spending the time on him. He has good info, but the baggage that comes with it kind of overwhelms me. It's sad that some folks can't stick to the topic.

Alex

Yep! I start a vid. and if the first thing I see is a dog in the back of atruck I delete the thread. :-( This was
SUPPOSED to be about making a tool . :-(
...lew...

[DR]

Most commercially available HSS dovetail cutters are not positive rake so don't cut freely.

The same probably applies to most insert cutters.

I believe Dorian Tool offers positive rake dovetail cutters, 60 degree, using a TDEX insert. TDEX have high edge clearance. Maybe with high clearance the insert can be tilted slightly in a couple planes without distorting the 60 degre edge. I'd like to see one to figure how they get positive rake with a triangular insert.

[John Stevenson]

Yawn,

Sorry must have fell asleep, has the video finished ?

[asallwey]

DR, I've seen the TDEX insert on other dovetail cutters. I believe it has a 15* rake.

But what does the X stand for? My copy of MH (25th) doesn't have it, and a couple of charts don't either.

I'm not a math wiz, but I did try to calculate the edge length from the inscribed circle. Since the od is given, that forms one leg of a right triangle. Since the insert is a triangle (equilateral), the corners are 60*, so the angle of the right triangle would be 30*. Using this formula in excel: tan(radians(30))*2 gives the length. But the value seems to be a bit longer than what I measured for a TCMT321, 0.623" measured and 0.650" formula. I suppose this could be attributed to the rounded nose or radius (at each end)? Just wondering if my math approach is right.

Alex
Alex

[oldtiffie]

Just as an aside, why not use a shaper as shapers are made for making dove-tails.

No need to worry about making a dove-tail cutter or buying one either.

If you don't have a shaper then ask around to see if there is someone here who can/will help out?

[DR]

DR, I've seen the TDEX insert on other dovetail cutters. I believe it has a 15* rake.
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Alex
Alex

The 15 degrees would be the edge clearance.

The rake would be determined by the mounting pocket.

At least that's the way I look at it.

[oldtiffie]

Making a dove-tail cutter is one thing but measuring the dove-tail may be quite another.

https://www.google.com.au/search?q=google&rls=com.microsoft:en-AU:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7IRFC_enAU360&gfe_rd=cr&ei=xg-OVbDSEqHu8wfuoKXwAQ&gws_rd=ssl#q=measuring+metal+dovetails

See Machinery's Hand Book for a comprehensive discussion and guides to making and measuring dove-tails.

[Paul Alciatore]

I made an error in my post and will have to revise it before posting.

[Mcgyver]

Yawn,

Sorry must have fell asleep, has the video finished ?

no kidding....first video is 20 minutes!! I could go get a job at mcdicks, buy 4 hss cutters and be back before the video as over....