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Jefferson Bookcases #8: Cleaning up a dovetail

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Blog entry by Dave Polaschek posted 08-12-2020 07:06 PM 417 reads 0 times favorited 11 comments Add to Favorites Watch
« Part 7: Smoothing and prep for shellac Part 8 of Jefferson Bookcases series Part 9: First shellac »

A couple years ago, when I was new to woodworking, I read about how to cut dovetails by hand, and how to clean them up. But a lot of it was mysterious. How close can I saw to the line? What happens if the dovetail is too tight to go together when I test fit it? What if it’s too loose?

So in order to write down some of the things I’ve learned over the years, here’s a look at one dovetail on the pin-board, from after I’ve made the vertical cuts to until the tail board fits over it well enough to glue it together.

First up is cutting out the waste between the pins. I do this with a turning saw because the fine blade from Gramercy Tools leaves a pretty good finish, plus the 12” long blade cuts through the waste between pins in just a few strokes (maybe six) if I’m cutting full-length strokes, plus I’ve never had good luck chopping out the waste with a chisel, especially in pine and poplar.

So after the first cut, I end up with something like this.

I slid the blade to about a quarter inch from the bottom of the cut, and started cutting out the waste. I angled down until I was less than a millimeter from my line (probably a little too far) and then started turning horizontally. I overshot a little, so angled back up, and then when I got close to the line, I worried about finishing up with the back side of the cut about on the line.

So that’ll need some cleanup. But I still have to cut from left to right. Left to right or right to left first doesn’t really matter, but it’s a lot easier if you’re consistent. I always cut right to left first, then left to right. I start on the rightmost bit of waste first, too, so I’m moving right to left, then moving back left to right. Not sure why, that’s just the way I’ve settled on.

So cut left to right. I concentrate on getting the back end of the blade to the line, and sort of let the front follow, trying to level everything out. And this is what I get.

Not too bad. If everything is going well, I’ll have just a hint of my original pencil line left. In this case, not so much, but it’s just missing, so I’m not sunk. I’ll take a fairly fine rasp and try to hold it level from to back and side to side and just knock off anything sticking up above the line. And avoid dinging the walls on the left or right with the edges of the rasp if possible. Maybe a dozen strokes if I’ve got a pretty messy cut. I’m not trying to get it perfect, just close enough that it’ll go together. So this is what I got to.

I cleaned off a couple high spots on the near side, and generally cleaned up the back side, removing a lot of the fuzz left from sawing.

Next up is test fitting the tail board in. In this case, the pin to the left was a little tight. After putting the pieces together and pulling them apart, I could see a burnished bit on the pine (it’s why I enjoy cutting dovetails in pine: close is plenty good, because the wood will compress a little). So I took the rasp and smoothed off just a little on the wall of the pin to the left, where the red circle is, and then down to the bottom of the pin (which was so tight it didn’t even get burnished because I couldn’t close the joint up).

And with that (plus similar cleanups on the other pins), the joint went together. Tight enough that the glue will hold, and loose enough that nothing will crack when I drive it together with a mallet. I don’t even really need a mallet, and can push the joint together by hand if I want. But I’ll probably give it a whack just to be sure, because, as Chris Schwarz says, IQs drop about 50 points as soon as the cap comes off the glue bottle. Hammer good! Bang!

-- Dave - Santa Fe



11 comments so far

View Arlin Eastman's profile

Arlin Eastman

4529 posts in 3409 days


#1 posted 08-12-2020 07:21 PM

Dave

I have never liked the small saws to finish up the cuts. I rather using chisels to finish it off that way everything is nice and straight, however I still go way over the line or under the line in trying to clean things up. :(

-- It is always the right time, to do the right thing.

View Dave Polaschek's profile

Dave Polaschek

5841 posts in 1430 days


#2 posted 08-12-2020 07:59 PM

I’ve never had good luck with chisels for chopping out waste, Arlin. Far too often I end up with major blowout because I tried to take too big of a bite with too dull of a chisel. And I’ve gotten pretty good with my turning saw, so it works for me.

-- Dave - Santa Fe

View Oldtool's profile

Oldtool

3026 posts in 3039 days


#3 posted 08-12-2020 08:14 PM

Whatever works to your satisfaction is the way to go, and you seemed to have nailed it.

One suggestion that occured to me however, since you clean up with rasp and/or file anyway, have you tried just cutting out the waste in two quick X cuts first, avoiding having to turn the coping or turning saw? Just a thought.

-- "I am a firm believer in the people. If given the truth, they can be depended upon to meet any national crisis. The point is to bring them the real facts." - Abraham Lincoln

View Dave Polaschek's profile

Dave Polaschek

5841 posts in 1430 days


#4 posted 08-12-2020 08:42 PM

In a perfect world, I wouldn’t clean up with a rasp at all, Tom. I’d be done with the second saw cut. Lot cheaper and easier to resharpen a saw or buy a new turning saw blade than to buy a new rasp because I’ve worn one out (and I have almost used up the Gramercy Tools rasp I’ve been using to clean up dovetails for the past three years. I don’t think it’ll survive past the last of these cases…

-- Dave - Santa Fe

View duckmilk's profile

duckmilk

4331 posts in 2172 days


#5 posted 08-12-2020 09:00 PM

I do the same as you except after the rasp, I will use a chisel with slicing cuts to finish. Pine is a pain though. By its nature it is designed to be cut with a skill saw.

-- "Duck and Bob would be out doin some farming with funny hats on." chrisstef

View theoldfart's profile

theoldfart

11998 posts in 3299 days


#6 posted 08-12-2020 09:23 PM

Dave, I use a long throat fret saw. Turns easily in a saw kerf and because it’s lightweight much easier for me to hold level.

-- "With every tool obtained, there is another that is needed" DonW ( Kevin )

View Dave Polaschek's profile

Dave Polaschek

5841 posts in 1430 days


#7 posted 08-12-2020 09:24 PM

I like just about everything about pine but trying to slice end grain with a chisel, Duck. It’s easy to plane smooth (as long as I avoid the long cathedral grain that wants to pop loose and make a real painful splinter), and I’ve even gotten reasonably good at planing the end grain of dovetails off with a block plane.

Most of my joinery before this has been in poplar, though. That’s just darned well-behaved, as long as you don’t mind the green…

Kevin, I have two turning saws, but use the smaller (lighter) one almost exclusively. Lighter is better. But for me the problem isn’t so much holding level as being level. I seem to be able to cut to a line pretty well with the turning saw. It’s just that I always think it can turn tighter than it actually can, and then I end up overshooting my mark a little.

I suspect it’s just a matter of more practice, so I guess I’ll get there.

-- Dave - Santa Fe

View Dave Polaschek's profile

Dave Polaschek

5841 posts in 1430 days


#8 posted 08-13-2020 02:56 AM

Thinking about this, I should see if I can clean up the dovetails with a float. Floats cost about the same as rasps, but I know how to sharpen a float. And if I wear it completely out, the remnant of blade would probably make a fair knife.

Hmm! I’ll have to try that on the set of pins I’ll be cutting tomorrow.

-- Dave - Santa Fe

View theoldfart's profile

theoldfart

11998 posts in 3299 days


#9 posted 08-13-2020 04:35 AM

Watch out for the corners!

-- "With every tool obtained, there is another that is needed" DonW ( Kevin )

View Dave Polaschek's profile

Dave Polaschek

5841 posts in 1430 days


#10 posted 08-13-2020 12:29 PM

Good point, Kevin. If a float works, I may end up grinding tapered edges on one of mine to make it a dovetail-specific tool.

-- Dave - Santa Fe

View Dave Polaschek's profile

Dave Polaschek

5841 posts in 1430 days


#11 posted 08-14-2020 06:51 PM

Haven’t tried the float yet. There’s always something…

But I did have a miter that was pretty bad. Here’s my fix:

I stuffed it with some shavings, then soaked them with CA glue. Once that dried, I planed it smooth, then filled the remaining gaps with sawdust and more CA glue. It ain’t pretty, but it looks better than a big gap.

-- Dave - Santa Fe

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