What angle for 1:6 dovetails?

[Bob]

Cant seem to figure this out as I am new to dovetails. What angle would a 1:6 ratio be? I am a math idiot.

Bob

[Morris Dovey]

Seems like it'd be arctan(1/6) = 9.462322208025617391140070541742º

[Bill Rogers]

9 1/2 degrees.

It is a measure of the tangent of the angle.

On your calculator press these keys:

1 / 6 = inv tan

...and you should see 9.46. Rounded will give the above. Don't forget to press the = key after 1 / 6.

Make sure your calculator is set to use use Degrees, not Radians or Grads. It should be there by default.

Bill.

[John Grossbohlin]

If you are laying out handcut dovetails why bother with an angle measure? Draw a right triangle with 1" and 6" legs and set a bevel gauge to hit the ends of the legs along the hypotenuse with base of the gauge against the short leg... Or use a framing square and adjust the bevel gauge to hit the

1" and 6" marks on the inside edges. Of just set the bevel gauge by eye and use it! If it's in the ballpark that is all that matters as you should lay out the tails from the pins (of the pins from the tails depending on which you cut first).

John

[Fred the Red Shirt]

Indeed, it is surely more accurate, and more importantly more precise (e.g. reproducible) to lay out the linear dimensions than to try to read/mark 9.5 degrees with a protractor.

What really counts is the match between the pins and their mating tails which is why you should always cut the pins fist and use them as a guide to mark the tails, unless you are a heretic who cuts the tails first and uses them as a guide to lay out the pins.

BTW those doevetail marking guages built like saddle squares the Lee Valley sells are sweet.

[Andy Dingley]

Too tapered, mainly. I'd go with 1:8 instead. 1:6 is used for softwoods, but if you're just learning to cut these, you're better doing it on some decent timber (ash or beech are good). Getting them tightly cut in squishy timber is a thankless job.

To set the bevel, lay out the measurements on the straight edge of a scrap of timber - 4" in, and 1/2" off to the side. Then set your bevel to this line.

And remember Tage Frid's approach - saw them accurately the first time. If you can't do this right, practice the sawing until you can (and a decent rip-sharpened saw helps). Don't fool around trying to "chisel them to accurate shape".

[B a r r y]

Or get or make some of these:

Barry

[Bill Rogers]

I won't argue the distinct advantages of layout [usually based upon firm mathematical principles] over calculation when applicable. However, you really don't need to be *that* concerned here about accuracy and precision.

Also, the carpenter's square is a bit unweildly for non-construction type work, and that's my argument here, unless you are building a barn. I own an adjustable drafting triangle marked clearly to the nearest half-degree, and can guesstimate between those if necessary. That's set in a jiffy, and for transfer I'd lay across an adjustable bevel, as you suggest, and use that to mark the dovetails. Fast, simple, and accurate ...but first I'd calculate the angle, again simple and quick on the calculator. Continued use of the same bevel gives precision in either instance.

As a balance, I'd suggest possible use of graph paper, and use the grid lines to get your angle. Go along one and up six, or along two and up twelve ...and so on. Carefully fold the paper, and use it as is if necessary for a small amount of work.

Bill.

[Phisherman]

tan a = 1/6 a = 9.4623 degrees

I'd set my bevel gauge to 99.5 degrees or 80.5 degrees. A 1:6 ratio should be used for soft woods, 1:8 ratio for hardwoods.

[Fred the Red Shirt]

Franz Klaus marks the depth of cut with a marking gauge then cuts the pins freehand, spacing and angling them by eye. He then uses the pins to layout the tails and here I think he uses a small square to draw a perpendicular line accross the endgrain of the board. I tried it just like he does it and it is surprisingly easy to get, oh, 3 out of four fitted tightly. But his all looked balanced, the same size, shape and spacing.

[Gordon Airporte]

Bah. Freehand them you wimps. People should KNOW you didn't use a router ;-)

[B a r r y]

Right!

Close enough is good, as long as the pins and tails match.

Barry

[patriarch]

B a r r y wrote in news: [e-mail]:

And fill the gaps with epoxy! ;-)

Patriarch

[Larry Jaques]

On 9 Jul 2004 02:43:03 -0700, [e-mail] (Andy Dingley) calmly ranted:

I cut some pristine doveys in some birdseye SPF this morning for S&G. Well, OK, they weren't pristine and it was vertical grained doug fir. What angle? "Oh, that looks about right." I'd post a JPG but don't want to scare anybody.

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[Australopithecus scobis]

Right. I was flummoxed for a while working on a drawer recently: Purely be serendipity -- not innate skill! -- two sets of pins and tails matched each other exactly. Dry fit one side, OK, dry fit the other, OK, ... and the drawer was inside out! The immediate "Oh, Sh*t" eventually turned to an "Aha!" Drawer is now right-side-out and functioning almost perfectly -- it's just too small for all the cruft I stuffed into it...and it's the overflow drawer!

[Larry Jaques]

On Fri, 09 Jul 2004 16:44:29 -0400, Gordon Airporte calmly ranted:

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[B a r r y]

Right at that moment, I would have run out and purchased lottery tickets!

Barry

[U-CDK_CHARLES\Charles]

For 1:6 dovetails, I set the angle to . .um . . 1:6?