1 - 14 of 14 Posts

Hand cut dovetails usually have a 7° or 8° angle depending on the material.

Dovetail cutters are usually similar angles and the fit depends on the depth you set the cutter at.

Tight fit, lower the cutter slightly.

Loose fit, raise the cutter slightly.

Does material 3/4" thickness require minimum 3/4" long cutting section on the bit??

Does the template determine the bit angle ??

I have a Stotts and his wbsite talks about an 8 Deg. bit but what about 7 or 9 deg.??

Joined

·
12,004 Posts

It depends on whether you want through dovetails or half blind dovetails.zxxer12 said:

Does material 3/4" thickness require minimum 3/4" long cutting section on the bit??

Does the template determine the bit angle ??

I have a Stotts and his wbsite talks about an 8 Deg. bit but what about 7 or 9 deg.??

The angle is personal preverence when hand cutting dovetails.

Router cut dovetails are determined by available cutter angles. So, I think this begs the question, are you going to custom grind dovetail cutters or have them custom gound? Or, are you looking for visual relationships? Perhaps a design manual that talks about proportions would help. Can't help you there. I have a Craftsman Dovetail Jig where all the spacing and angles are fixed. I precut one dovetail, measure the width and angle with a dial caliper, refer to trig tables, move dovetail jig with dial caliper measurements, move router depth with dial caliper measurements, finish cut. It's worked perfectly so far. Good Luck with your search and have fun.

Hi. I'm a brand new member here, and this is an old thread. I don't really see an answer to the original question here. So it seems I have something to offer.

Many decades have passed since my F in shop class, I have 4 college degrees, and I am doing much better now. I am a "re-beginner" at woodworking.

Here is the math. If the explanation below is hard to visualize, please tell me. I can put an illustrated version on my web site.

Draw a sketch of the interface between the two dovetail-joined parts. It should look like a jagged line of opposing trapezoids. I'll try to do that with ascii art here (if you used a fixed-width font, it might work):

----- ----- -----

\ / \ / \ /

----- ----- -----

It doesn't matter whether this is a blind or through dovetail joint. The analysis below focuses only on the geometry of the joint interface. (How that lines up with your workpiece determines what kind of dovetail joint it is.)

Define some variables:

h = depth of cut (distance from top to bottom of my diagram above)

d = diameter of router bit at widest point

p = period of the dovetail pattern (distance from corner of one tail (or pin) to the next tail (or pin)

e = angle of dovetail bit. This is the angle between any of the slanted lines in my diagram and the vertical, and corresponds to the way bit angles are defined in typical bit specifications. (The total angle subtended by the bit, a pin, or a tail is 2e.)

The universal relationship between these variables is

h sin(e) = d - p/2

I just purchased an Incra Incremental Positioning Jig Model 25971. It comes with a couple of templates, one for box joint and another for dovetails. These templates are only good for two particular dovetail bit geometries and a couple of stock thicknesses. Rather than buy more templates, I can use this formula to make my own, for any bit geometry and stock thickness.

The distance between any line and the next in an Incra template is p/2, and the distance between any A line and the next A line or any B line and the next B line is p.

All I have to do is check and maybe calibrate the scaling accuracy of my printer and I can crank out any template for any geometry with a simple computer program. The printer scaling can even be slightly off, and the Incra incremental positioning jig will get it perfect as long as p is an integral multiple of 32nds of an inch.

Joined

·
5,700 Posts

We hope you will elect to participate often, you have much to offer it appears.

Oops! Slight mistake here. That should be a tangent function, not a sine function. That is,h sin(e) = d - p/2

h tan(e) = d - p/2

For the small angles typical of dovetail bits, it doesn't matter too much, because then sin(e), tan(e) and e (if in radians) are all approximately the same. And you're probably going to begin by making a test cut and adjusting the bit height (h) to get a good fit anyway.

Also, while I am splitting hairs, it wouldn't surprise me if the angles given on the bit packages are actually rounded to only 1 significant digit. When I set up to do dovetails on a router, rather that using trig functions, I just use the approximate relations

tan (14) = 1/4

tan (10) = 1/6

tan (9) = 5/32

tan (7) = 1/8

Joined

·
161 Posts

Generally available bits are carbide tipped, so the angles are usually rather clumsy looking. The carbide cutter is brazed to a steel shank, and the resulting profile is thus a dead giveaway that the joint created is machine made.

Handmade dovetails can be quite thin (given the limits of the wood strength) and elegant. One company makes very small angle bits out of HSS. Not as strong or durable as Carbide, but the results are beautiful. Go to The Craftsman Gallery, chipsfly.com. The drawer bits (some as small as 6 °) must be used carefully in hardwoods. They break easily.

Gary Curtis

Joined

·
130 Posts

This is pretty much as I understand it too, info gleaned from others...There are some rules, in fact. Smaller angle dovetails are suitable for hardwoods. In softwood, because the tail might pull out of the pin, or because the wood might actually break, you must use the larger angle dovetail bits.

Dittos, but most of us don't have the time or patience or whatever to make James Krenov style dovetails, but can all appreciate how beautiful they are, and serve as inspiration. Myself, I've only ever done one project, a small bookcase, in hand cut dovetails... just to learn and try. Was inspired by one of Krenovs' books enough give it a go. They turned out pretty good for a first time effort... but let's just say, that you couldn't make a living out of doing them at the speed that those went,Generally available bits are carbide tipped, so the angles are usually rather clumsy looking. The carbide cutter is brazed to a steel shank, and the resulting profile is thus a dead giveaway that the joint created is machine made.

Handmade dovetails can be quite thin (given the limits of the wood strength) and elegant.

Think these are what you're talking about:Handmade dovetails can be quite thin (given the limits of the wood strength) and elegant. One company makes very small angle bits out of HSS. Not as strong or durable as Carbide, but the results are beautiful. Go to The Craftsman Gallery, chipsfly.com. The drawer bits (some as small as 6 °) must be used carefully in hardwoods. They break easily.

Individual Bits: The Craftsman Gallery, chipsfly.com

8-degree 3/16" HSS Dovetail Bit

8-degree 3/16" HSS Dovetail Bit: The Craftsman Gallery, chipsfly.com

I never knew anyone made these... so, thanks!

Joined

·
161 Posts

At the other extreme, this same company makes and sells a 28mm dovetail bit. That's about 1 1/8" in diamter. I made 20 feet of knockdown (no glue) wall benches out of 2x6 and 4x4 douglas fir timbers using sliding dovetails for the legs, aprons and stretchers with this bit. I can stand on the bench tops.

Seeing as the bits are HSS, I made the cuts less aggressive by hogging out an initial trench using a half inch carbide spiral bit and then following up with the dovetail. I sharpen all my HSS bits with a light pass of a diamond paddle and, so far, haven't seen a noticeable reduction in bit diameter. I love HSS because the edge can be honed so fine.

But they won't last forever.

Gary Curtis

1 - 14 of 14 Posts

- This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Router Forums

A forum community dedicated to router and woodworking professionals and enthusiasts. Come join the discussion about different types of routing and routers, shop safety, finishing, woodworking related topics, styles, tools, scales, reviews, accessories, classifieds, and more!

Full Forum Listing
Recommended Communities

Join now to ask and comment!