Dovetail layout calculator

So all this recent talk about dividers got me to thinking about laying out dovetails. Some folks go for the Frank Klausz "lay 'em out by eye" method, and that certainly works. For the more OCD set (myself included :)) who prefer a more symmetrical layout, Rob Cosman's divider layout method works nicely. The only problem is this method requires some "guess and check" fiddling. For the really obsessive compulsive woodworker, I put together an Excel spreadsheet to calculate your divider settings.

Attachment 180248

It's more or less self-explanatory, with a few caveats. You input W, a, b, c, and n. The calculator takes care of the rest. Note that when entering the dovetail slope, you just enter the "run" (i.e. for 1:7 dovetails, you'd enter 7). By default, it assumes that the full-pin-width, pn is exactly half the half-pin-width, b. Change the formula as necessary to suit your taste.

Check to make sure your chisels will fit for removing the waste (tn and pn), set your dividers to b for the half-pin and d to walk off the pins and tails, and go to town! Feel free to share this with anyone who may benefit from it, and let me know what you think.

Share and enjoy,
Jon

Wow that just made my head hurt a little... jk, looks good.

However I generally sit there with a ruler and marking knife and lay it out to look right. This helps on drawer backs with open slots where I want hole pins.
either that or I have drawn them out on paper when designing the piece. I have a tendency to have spacings that are a little wider here then there and such. I also don't do the 1:7 deal, usually my pins are 10* or there about. I find it easier to set with a protractor.

For drawers and smallish boxes, laying them out by eye works pretty well for me. For larger case work, it gets a little tougher. And like I said, I'm a little OCD about symmetric dovetails. :)

As for the slope, the calculator takes a 1:x ratio entry, since that's how many dovetails markers are made. The angle in degrees is calculated over in the metric measurement column. If you prefer to specify the angle, just overwrite the formula in that cell with your angle of choice.

I felt a breeze as I was reading your post, and as I opened the document I felt a mighty gust of wind through my hair. Way over my head.

I still don't understand the two divider walk about either. And please don't try to explain it to me...I won't get it.

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Originally Posted by Jon Toebbe

So all this recent talk about dividers got me to thinking about laying out dovetails. Some folks go for the Frank Klausz "lay 'em out by eye" method, and that certainly works. For the more OCD set (myself included :)) who prefer a more symmetrical layout, Rob Cosman's divider layout method works nicely. The only problem is this method requires some "guess and check" fiddling. For the really obsessive compulsive woodworker, I put together an Excel spreadsheet to calculate your divider settings. ...

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OK, not to diminish your work, quite nice actually; but I strongly dispute that the laid out freehand dovetails are less symmetrical than those produced by some more formal layout method. It's just too easy to bisect a line, bordering on the trivial.

Pam, who doesn't call it the Klausz method because she started doing this after her first dovetails 30 years ago, before she had ever heard of Klausz

Since you admit you are OCD there is a reason to your method. Ron Herman says he is CDO(he alphabetized it). I must admit it seems way to much work for me. I work by eye and would probably be done cutting the dovetails before I figured out the spread sheet. This is supposed to be fun so I assume that you enjoy that part of the process or at least it's result.
Right now I am coming from the opposite end of the spectrum. I am preparing for a dovetail demonstration so I am experimenting with cutting dovetails with a hacksaw with a 12 ppi blade, a block of wood with a screw in it for a marking gauge, a sharpened screwdriver for a chisel, a block of 2 x 4 for a mallet and a pencil. I was fairly pleased with the results, laid out by eye of course.
The results of laying out by eye improve over time. Try seeing how close you can get by placing tick marks on your wood with a pencil where the dovetails will go. Then layout using your dividers and spreadsheet and compare the results. With time you may find that you don't need the added help.
Mike

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Originally Posted by john brenton

I felt a breeze as I was reading your post, and as I opened the document I felt a mighty gust of wind through my hair. Way over my head.

I still don't understand the two divider walk about either. And please don't try to explain it to me...I won't get it.

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I can show you sometime.... Or I can loan you the video and see it for yourself.

Jon,

That is a great use of modern technology.

I once did a spread sheet to scale adirondack chairs from adult size to kid size and even doll sized.

For dovetails I use an old fashioned method kind of spread sheet. This is mostly because it is a short hike from the shop to the computer and back.

My old fashioned method is a story stick.

First a piece of wood was chosen that is long enough to cover the biggest item on which I am likely to use dovetails to join. Then a dovetail was drawn on a piece of scrap stock to accommodate the chisels to be used. In this case it was a 1/2 & 3/4" group. This was also a joint for strength more than show. The pins and tails are about the same mass size of wood. The story stick is about 2' long. It can actually be used on stock down to about 1-1/2" just by setting a tail in the middle of the stock and having the outside be the pins.

This is a picture of a previous one I made.

Attachment 180308

My thoughts are drifting to the idea of using a square profiled story stick to do layouts for different profile dovetails. Need to put in a note to look for another one of them round tuits.

jtk

Thanks John! I was actually being a little facetious, although I have never used the two divider method. I use one divider and my dovetail marker just to make the pins the same size, not for spacing. If I ever were to do fine work I would use the two dividers, and probably need that tutorial.

I'll still take you up on a visit sometime. We'll have to get together once things slow down for me around here. I should have had you over when the wife and kids were out of town. We could have been smoking and drinking and not worried about dragging shavings onto the carpet!

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Originally Posted by Jim Koepke

My thoughts are drifting to the idea of using a square profiled story stick to do layouts for different profile dovetails. Need to put in a note to look for another one of them round tuits.

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That's a clever idea for any story stick. Especially if the projects they marked out were somehow related. Table and chairs, rocker and footstool, etc. Less to lose track of, as long as each edge was prominently marked with which project it went to... a side chair whose seat was level with the tabletop might cause problems. :)

Jon

Thanks for the excel calculator. I appreciate the time and effort it took to make it. Some folks would be happy laying things out with a stick and a string. Don't get me wrong the Egyptians built some amazing things with that method. So I am not knocking it. If that is how one chooses to do their work and they can make quality projects that way then great. I wish them plentiful hours of personal satisfaction in their work.
But others like myself are comfortable with accuracy. Perhaps it is because I am a machinist by trade and the width of a human hair is enough to scrap a $20,000 part. If you work with tight tolerances every day then using that ability in the wood shop is not that big of a deal. Some people are comfortable with it some aren't there isn't just one right way.
I do woodworking with a set of 6" calipers in my pocket because that is what I know and I am as quick with them as the guy that has been using his favorite stick and string for the last 20 years. When I told a guy at the local woodworking store that I used dial calipers he scoffed and said wood moves to much to be that accurate. I decided to test that theory. I took my electron powered rotating rip saw device along with a cast-iron fixture designed especially for cutting tenons. After fettling it in with a dial indicator and calipers I was capable of cutting a perfectly centered tenon .250 in width in scrap of poplar. On the day I made the tenon it measured .250 I left the wood untreated in my garage that is not heated or air conditioned so it would be exposed to humidity and temperature changes. At various times over a year I would pick up that tenon and measure it again to see just how much it moved. The max I have seen it move was .248 to .252. That is .004 of an inch which happens to be the thickness of the average human hair. Heck aluminum and copper move that much or more depending on temperature. So if the guy at the wood store is correct in his theory then using calipers on aluminum and copper is crazy because it moves to much.
With all that said I am inclined to believe that if you have the capability to be that accurate and you don't find it bothersome then by all means do your work the way that brings you the most personal satisfaction. Use the spread sheet, set the dividers and walk them across your work because you know that if the math is right the balance will be there also. I like line from an old John Wayne movie. It goes like this "it ain't bragging if ya can do it". So if you can do the math and be that accurate go for it. Incorporate accuracy into your work because the good Lord knows there is plenty of so called hand crafted stuff out there that a guy could show lacked accurate measurements using a stick and a string.

Ed

Thanks Very Much........

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... there isn't just one right way...

... by all means do your work the way that brings you the most personal satisfaction.

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Isn't that what it is all about?

jtk

I am a railroader, which means you may or may not understand my schedule.... but drop me a p.m. sometime. We can set something up sometime or another.