Thursday, July 30, 2009

Layout methods

Beyond the selection of the type of gauge to use to get the angle you want (dealt with moons ago in this entry) there is the greater issue of laying out the tails and pins on the boards. The first question is whether to do a formal layout at all. Frank Klaus just eye-balls the angle and placing. It certainly works for him.

For those of us who want to do a formal layout we have a couple of options - either the ruler or the dividers. I have seen articles and videos suggesting that the way to lay out dovetails is to decide how many tails you want (3, in this example), add one to this number (to get 4), set a ruler diagonally on the piece of wood such that it spans some multiple of the number that you're looking for (in this case 4", but it could be 8", 12cm, 400mm, whatever you want that is divisible by, in this case, 4), then mark the divisions and use a square to run the lines to the end of the board (hoping that the end of the board is nice and square so you end up where you think you'll end up... otherwise you have to use a marking gauge of some sort to run the lines down to the end). At this point you will now have the centers of your prospective tails marked, so you use the ruler again to mark the width of the tails and now, at least, you know where the tails are, so you can get your gauge and mark the profiles. And if you have any energy left after all of that then you might be able to saw one or two.

There is an alternative, thankfully.

I learned about this method from a Rob Cosman video, and he attributes it to Alan Peters, and from an interview with Peters it seems that he originated it, though certainly it might have been independently discovered by someone else at some point. Regardless, it's a wonderful method and here it is:
Take two pairs of dividers. Set one pair to be the width you want for your half-pins (about half the thickness of the material, is common). Mark the width of your half pins (one on each side). If you cut tails first then you'll be marking the end-grain of the piece. If you cut tails first (like me) then you'll be marking on the outside face of the piece.

This is one of those things that is really simple, but hard to explain without showing it.
Now we set the second pair of dividers to an arbitrary value that represents the pitch of the joint. The pitch is the width of a tail plus the width of a pin. We lightly step the dividers across the piece, starting in the half-pin mark on one side, and the number of steps that the dividers take between the half-pin marks is the number of tails you would have, and the amount that the dividers over-steps the half-pin mark on the other side is the exposed width of the pin when the joint is assembled. If you're one of those skinny-pin people then you want this space to be tight.
Above we see a picture that probably should have been zoomed in more. Anyway, the dividers took two steps and then over-shot the right hand half-pin mark by about 1/4". That's a good pin size for my tastes, so I'll walk the dividers over again and push down to leave marks. I'll step it from the left hand half-pin mark, and then from the right hand half-pin mark, so that it leaves two sets of steps as shown below:

That set of marks establishes the layout for the pins (or tails if you had marked the end-grain).

I hope that makes sense. I might need to rewrite this with better pictures.

I just added the following picture that hopefully adds some sense to the above.

What comes first? The pins or the tails?

The first 'religious' discussion for this batch of postings is whether to cut the pins first or the tails first.

There is a reason to cut tails first in a production environment - you can stack half a dozen boards in the vise and cut the tails on all of the boards at once. This, arguably, saves you a bit of time. Not a lot of time, as the time spent cutting is not great compared to the time spent chopping, but in a production environment a bit of time saved can be important.
Rob Cosman - arguably the most influential of the current crop of dovetail gurus - tells us to cut the tails first.

Looks like there is plenty of reason to cut the tails first, eh?

Well... maybe not.

There is a drawback to cutting the tails first. A big one. That drawback is that you need to scribe the tails onto the end-grain of the pin board. There are three problems involved in scribing from tails to the pinboard. The first is that you are scribing onto end-grain, so it's much harder to see the resulting line even if the end-grain of the pin-board has been planed to perfection. The second is that you are trying to scribe inside a small cavity where there is not enough room for a pencil or even an awl, so you have to use a blade, and that leads us to the third problem. The third problem is that you have to use a thin blade to scribe, and that can be hard to do without taking a slice from your tail or taking the wrong angle, as the blade wants to follow the path its on whether that path is the right one or not.

If, however, you cut the pins first and use them to scribe the tails then you are marking onto face grain, and you have plenty of room to use a pencil or an awl.

I always get better results when I cut the pins first, and Frank Klaus, the Godfather of Dovetailing, says to do the pins first. So did Tage Frid, before his unfortunate passing.

For me my preference is, and will always be, to cut the pins first.

Thoughts on Dovetails. Again.

After a bit of a hiatus I find myself with some time on my hands, so I'm back, and thinking about dovetails.

What is it about hand-cut dovetails that plagues the thoughts of the hobby woodworker? It seems you can't swing a dead cat without hitting a blog or two agonizing about the nuances of hand-cutting dovetails. Are we sheep that need to follow the herd? It seems so, and now it's my turn. Ba-a-a-a-a-a. :)

The following topics will be covered in the next few entries-
- Pins first or tails first?
- Layout methods
- Cut-to-line or pare-to-line?
- How do you chisel to the line?
- Best type of chisel for dovetailing?