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By custard
#1225766
Mitred dovetails got mentioned in a recent thread, they're a useful joint for certain applications so I thought I'd do a short WIP in case anyone's inspired to have a go. They aren't difficult, but it's best to follow a proven process pretty closely.

Step one is to get out some stock and mark it up.

Mitred-Dovetails-01.jpg


Whenever I'm dovetailing, even on a test piece, I like to use the standard markings used all across the English speaking world for drawer components. The tail boards (drawer sides) each have a quadrant in the lower front corner on the outside, the pin board (drawer front) has a semi-circle on the bottom edge on the outside. If you were making drawer and had a back as well then that would also have a semi circle on the outside lower edge, but this time with a vertical line through it. The advantage of these markings is that you'll never get confused regarding the orientation of dovetailed components. If you're making a piece with multiple drawers then it's common to add a number to each of the symbols.

Even for a quick test piece like this you must have straight, flat, and true components,

Dovetailing-True-Stock-01.jpg


Dovetailing-True-Stock-02.jpg


Unless your boards are completely true you'll get into a right mess with mitred dovetails. Unfortunately many hobbyists embark on projects with boards that look more like this, and to be clear, these simply aren't true enough,

Dovetailing-True-Stock-03.jpg


Dovetailing-True-Stock-04.jpg


This doesn't get spoken about as much as it deserves. Accurately and efficiently truing stock with hand tools requires quite a lot of effort and practise; but unless you have access to good quality machinery there's just no alternative to acquiring those skills if you want to make clean, professional looking furniture with gap free joinery.

I guess anyone making mitred dovetails will have already cracked basic dovetailing, so I'll skip through some of the basic stuff. I normally work tails first for dovetails, but for some reason I prefer to work pins first on thicker stock or with mitred dovetails. These boards are 30mm thick so I'll work pins first. Mark up the pin board using your normal preferred method, mark the waste, and then do all the vertical cuts exactly the same as for a normal through dovetail. I saw straight to the line, I don't want to faff around with paring if it's not necessary and personally I think paring on through dovetails is simply less accurate than aiming to do the job straight from the saw. I appreciate that paring the pin board on lapped or half-blind dovetails is appropriate, just not on through dovetails.
Mitred-Dovetails-02.jpg


Incidentally, I'm using a 1:7 slope, but you can obviously use whatever you want. So you should now have something like this,
Mitred-Dovetails-03.jpg


So the next stage is to hog out the majority of the waste down to about 1 or 2mm away from the scribe line. I use a fret saw but again, use whatever method you're most comfortable with,
Mitred-Dovetails-04.jpg


Mitred-Dovetails-05.jpg


Mitred-Dovetails-06.jpg


I think I've reached the limit for number of photos in a single post so I'll pause here and pick up the story in the next post.
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By custard
#1225768
We're now left with chiseling away that last remaining 1 or 2mm of waste to get down to the scribe line,
Mitred-Dovetails-07.jpg


I prefer to work down half way from each side, and work back in small stages until there's a fairly thin, even line of waste that can be comfortably removed with a single chisel stroke,
Mitred-Dovetails-08.jpg


Mitred-Dovetails-09.jpg


Mitred-Dovetails-10.jpg


If you look closely you'll see I didn't quite make it as even as I'd like on this one, some of those final chisel cuts will be thicker than others. This risks the chisel being pushed back and compressing the scribe line. I'm sure I'll get away with it here, but when I find myself doing inferior work like this I treat it as a red warning light to slow down and pay more attention. This is often a good time to take a short break and re-sharpen the chisel!

After taking those final cuts you should always check the accuracy of your work with a square, you need to be absolutely confident that the "floor" of the dovetail is either dead flat or slightly hollow. Any evidence of a bump will guarantee that the joint won't close up.
Mitred-Dovetails-11.jpg


Once you're sure the pin board is absolutely as you'd want it then it's time to do a normal, pins first transfer on to the tail board.
Mitred-Dovetails-14.jpg


Up to now everything has been exactly the same process for both normal through dovetails and for mitred dovetails. But once the transfer is completed you encounter your first departure from the normal through dovetail process.

You now need to mark a 45 degree line on both the outside edges of the pin board. This should run from the bottom outside corner to the inside scribe line. Check the photos of the finished job at the end of this thread to be absolutely sure you've got this line in the correct orientation and you've marked on the right side for the waste!
Mitred-Dovetails-12.jpg


Now, having marked the cut line go back and check everything one more time. If you haven't marked out correctly there's no recovery after cutting, it's either right or the piece needs to be processed through the wood burner! Once you're totally sure then make your saw cut, but here's the thing, stay about 0.5-1.0mm outside the marked line. In other words, having said previously I like to finish straight from the saw I'm now making an exception. You will deliberately leave excess material that will have to be pared away later.
Mitred-Dovetails-13.jpg


That's your pin board nearly complete. It's time to take another break and then we'll move on to the tail board.
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By custard
#1225772
Having previously completed the transfer, from the pin board to the tail board, we put the tail board in the vice and carry the markings across the end of the board and do all the saw cuts, exactly as you normally would, except don't make the two outermost cuts. So your tail board should look like this,
Mitred-Dovetails-15.jpg


As you can see, I've made six saw cuts that are absolutely as normal for a tail board. But the two outermost cuts haven't been made.

This is now the second area where the process departs from normal, through dovetail, practise.

You should mark another 45 degree line on both the outside edges of the tail board, like this,
Mitred-Dovetails-16.jpg


Now, take your saw and make a cut. But instead of cutting straight across as you normally would you'll cut at 45 degrees, from a whisker above the scribe line to a whisker away from the far corner, like this,
Mitred-Dovetails-17.jpg


In effect this is a compound angled saw cut, because you're both following the 1:7 dovetail angle slope and you're also cutting at 45 degrees. Said like that it sounds impossibly difficult. It's not. It requires a reasonable degree of hand saw proficiency, and a great deal of close attention, but believe me it's perfectly do-able. If you've already mastered regular dovetailing then there's no question that you're fully ready for this challenge.

As before, you then complete the cut on the marked 45 degree line, about 1mm into the waste. This is what the completed cut looks like from a couple of different angles,
Mitred-Dovetails-19.jpg


Mitred-Dovetails-20.jpg


You're now ready to start fitting the pin board and tail board together. If you've cut accurately they should go together fairly smoothly with just some light hammer blows. But because we made those 45 degree mitre cuts well on the waste side we're not expecting the joint to fully close. All we're really doing at this stage is checking the dovetails themselves are accurate,
Mitred-Dovetails-21.jpg


Mitred-Dovetails-22.jpg


Mitred-Dovetails-23.jpg


That looks promising. The dovetails are coming together cleanly, but we'll have to do some more work on the mitres to get a tight, gap free joint.
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By custard
#1225774
Because the 45 degree mitre cuts were made cautiously on the waste side we'll have to pare them back. Which begs the question, why faff around, why not cut straight to the line? The answer is because it's actually very difficult to be 100% confident about where that 45 degree mitre should actually be, and unless it's placed precisely, I mean far better than +/- 0.1mm, probably something like +/- 0.001", you'll end up with a gap somewhere. So the safe thing is to saw outside the mitre line, then pare back in stages with three or four interim test assemblies until you hit the perfect fit.

For this you need a paring block, something like this,
Mitred-Dovetails-24.jpg


There are several different ways of making a paring block. I usually cut them on a sliding compound mitre saw (SCMS), the negative hook geometry of a sharp SCMS saw blade produces an almost polished surface. But if you haven't got access to a really good SCMS then you can use a disc sander, a table saw, a shooting board, or if you're reasonably proficient with a bench plane you can do the entire job by hand. I used to do that all the time and it's a good exercise in improving your bench plane skills.

I've heard it said that the paring block should be at least twice as thick as the workpiece. I've gotten away in the past with less but it's a sensible rule of thumb. The problem is that the paring block plus the workpiece may be too long for normal chisels. Here you can see the ferrule is catching,
Mitred-Dovetails-25.jpg


In this case the answer is a dedicating paring chisel. This happens to be a Japanese paring chisel, but the longer blades of western ones will also overcome this problem.
Mitred-Dovetails-26.jpg


I suspect that before the first world war paring blocks were used much more widely, which is why you find so many older paring chisels. If you do buy one though it's worth checking the back is perfectly flat for it's full length, you're basically referencing from that back so any hint of banana shape will prevent accurate work. You can see here that with care a paring block and a good paring chisel will produce immaculate work,
Mitred-Dovetails-27.jpg


I bumped the paring block back in tiny stages, working sequentially around all four mitres. After the third round of paring it all came good; with tight, gap free results throughout the job. This isn't glued up, but I did make a couple of plane strokes to clean up the layout lines and remove the symbols,
Mitred-Dovetails-28.jpg


So, where would we use a mitred dovetail? It's not impossible, but you're unlikely to use it in a drawer. IMO drawers are best dealt with using normal through and lapped/half blind dovetails. But if you dovetailed together a solid carcase for cabinetry work it's a nice, quality touch to use mitred dovetails, at least at the front of the carcase as it avoids that slightly crude, "butt joint" look of normal through dovetails.

Another application can be imagined from this photo,
Mitred-Dovetails-29.jpg


I'll sometimes make up benches or coffee tables from a single board of dramatically figured timber, arranged in the above configuration. Mitred dovetails just look better in this application, and an added bonus is they allow for the grain to flow unbroken around the corner, at least at the edges, which is another sign of quality.

One final point, gluing these up, especially in thicker timbers, requires some care. You'll get better results with some intelligently applied cramps, and for a really critical job I'll temporarily attach cramping blocks to apply cramping pressure perpendicular to the mitre glue line. It's more work but it's generally worth it.

Anyhow, I hope someone finds this useful. Once you've cracked normal dovetailing then mitred dovetailing is a realistic and appropriate next step up the skills ladder.

Good luck!
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By thetyreman
#1225779
thanks custard, you have convinced me to give it a go, I think I'm going to use it on a pair of bookends and hopefully it'll look even classier than regular dovetails, you also have me seriously lusting for some holdfasts now, they come into their own for this, still haven't got any but that may change soon!
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By thetyreman
#1227658
couple of questions custard if you don't mind? why do you start with the pins first if it's above a certain thickness? and secondly, do you pare away the inside corners of the pins like your would normally for a through dovetail to help ease it in? also once this joint is achieved, would a 'next level joint' be a secret mitred dovetail, have you ever used it?
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By custard
#1227672
thetyreman wrote:couple of questions custard if you don't mind? why do you start with the pins first if it's above a certain thickness? and secondly, do you pare away the inside corners of the pins like your would normally for a through dovetail to help ease it in? also once this joint is achieved, would a 'next level joint' be a secret mitred dovetail, have you ever used it?


To be honest the choice between pins first or tails first is pretty random so I'm not going to try and justify the decision, all this is just personal preference rather than any attempt to claim best practise.

With a thicker workpiece I find it easier to balance the pin board precisely on the tail board for the transfer. Furthermore, with thicker boards you can't get away any longer with a slightly tight "compression fit", I use a couple of little tricks to consistently achieve a compression fit on drawer sides, they in turn benefit from a tails first approach, but in the absence of that it opens the door to pins first and easier transfers.

Yes, I'll sometimes very slightly undercut the inside corners on the tail board to ease a fit. But I don't do it nearly as extensively as other people. For one thing I tend to judge the quality of dovetails as much on the inside of the joint as on the outside, I really dislike any dark tell lines telegraphing the layout on the inside. But again, that's just personal choice and not necessarily right for everyone, if I was racing the clock on piece work believe me, I'd be undercutting like a demented beaver!

Regarding secret mitre dovetails. I have cut them, but only as a training exercise. I've never had a job where it might make commercial sense to incorporate them into a piece of furniture...and I probably never will! To sink a great deal of time into making something that's deliberately obscured from the client doesn't sit well with the parlous financial reality of custom furniture making.
By Roxie
#1227823
Thank you Custard for your informative mitre/dovetail workshop. It inspired me to have a go, albeit using a piece of pine, I know "worst wood you could use", but it turned out better than I thought it would. Not too difficult to make if you check and re-check and get all edges and faces square. I make boxes and will try to incorporate these just for the hell of it.

Thanks again
John