While there have been too many words written about dovetails, there has been far too little written about using wood compression in the joint.
The only time I hear it discussed is on the woodworking show circuit, when a demonstrator is dovetailing a purpleheart board to accept a white pine one. The demonstrator has a wide margin of error when he assembles the joint because of what Glen D. Huey calls “the mash factor.” You can compress pine – a lot – when it is dovetailed into a stout wood.
In my shop, I use wood compression when cutting dovetails to keep things tight without splitting. Here’s how.
After I cut the first half of the joint I show it to the other half and use a knife to mark the shape of what I want to remove. Then I saw out the joint, but I stand off a tiny wee little itsy bit from the knife line.
How far I stand off depends on the wood. With soft woods, such as white pine, it might be 10 thou or so – I’m just guessing at the measurement. With hard woods, such as cherry or walnut, it’s less. With oak or teak or maple it’s almost nothing. I leave the knife line and the tiniest sliver possible. But I still leave something. Everything compresses.
— Christopher Schwarz
Currently listening to Teenage Fanclub, eh? I couldn’t resist cranking up What You Do To Me after reading that :0)
Chris the first time I heard this it was like an ah ha moment in my dovetailing (insert the V8 head-slap). That little tid bit is worth the price of admission!
I’ve had the ahhh moment, but still a bit short of the AHA!
I’ve learned to only deepen the line enough to be distinct. My saw kept falling into the trench giving sloppy joints every time. Putting my thumbnail into the line and starting the saw against it works…ok for me.
My dovetails still look like crap, but they do hold the wood together (ahem, mostly).
Frank Klausz is my dovetail hero so I have vowed to fake it til I feel it, eschewing dovetail training wheel devices along the way.
So that is the difference between a smidgeon and a hair’s width! Eye balling it right Chris?
Figured this out watching Rob Cosman give a demonstration with walnut and poplar. I went up right after the demo and picked up the piece he had just finished and noticed that the saw cut on the pins board was ever so slightly offset from the line. Lightbulb moment indeed.
Hand cut dovetails intimidate many workers. I think this is why so many line craftsman style furniture. It’s mostly mortise and tenon. I tried a dovetail jig and immediately became confused. So I ignored this form of joinery for several more years. Then I discovered the use of hand tools instead of power tools and popular woodworking magazines videos.
Nuff said
I would argue that a great M&T joint is harder to cut than a great DT joint…but that could be a personal problem…
I think what you say is true. The beauty of a dovetail joint is the ability to lay out one half of the joint directly off the other (superposition, as we engineers would say). The M&T requires much more careful layout. Wedged M&T joints help overcome minor mistakes in that department!
Line =like
Is there any tapering or shaping of the pins or tails? How do begin pounding the joint together when the pins are cut a little “fat”? Does it just go as long as they’re not “obese”? ha
As stated above, I think my dovetails suck. I do, however, relieve the unseen inside edges just a tad. Shaving just that little bit off aids the compression process and prevents (mostly) splintering.
Hence quartered white oak sides. stable, hard and wears well. And yeah, it’lll compress your show wood. A little chamfer on the inside corners, where it won’t show, helps ease it together at the start. Somewhere between a gnat hair and a fleas eyebrow is about right.
Kevin at Glen- Drake tools has developed his offset gauge for just this purpose: http://www.glen-drake.com/. It’s the world of metal mechanics applied to wood. I’ve watched him saw many dovetails at Hand Tool events and they are as good as you’d ever need them to be.
I need a lot more practice with the dovetail saw. Whenever I try to leave a gnat’s hair width from the line, I end up with about a pencil’s width! I then pair down toward the line with a chisel, which is much easier to control. I’ll keep sawing and sawing until the day I learn to control the saw better.
Chris,
I am sure you have answered this before but I can’t find it on you blog anywhere. Can you tell me what kind and where you got the lamp you use on your bench?
Thank you,
Josh
It’s a Luxo — they are available at many office supply stores. Old Luxos are built like tanks. The new ones are lightweight, but still good.
I just cut some oak on oak dovetails in my last project and they did not compress well for me. They did chip and splinter a lot though…..Luckily I was able to re-cut them because of a different screw up. The second round was better.
Oak does not compress much at all. You’ll dial yourself in after a few joints.
Perhaps a.005″ back bevel on marking knife?
“But i’mmuchbetterknow”, GomezAdams