Grading or Evaluating Hand cut Dovetails

[Erik Johanson]

Not sure if this would be the right place for this but I thought I would give it a try any how. I am a Technology Education teacher at a high school where among other subjects I teach a few woods courses. I have recent assigned my students to cut a set of Hand-cut Dovetails. Teaching them about how to lay them out, how to cut them out, etc. The idea was to give them some real practice using a chisel, hand saw, and various other hand tools. I am getting near the end of the project, The joints don't look terrible....some of them any way, and I am having difficulty creating a rubric (a teaching tool used to help evaluate a students work based on a specific set of criteria). I was wondering if maybe if some of you guys could help guide me in the right direction.

My question is this: If you were evaluating someones work who had made hand-cut dovetails, what would you look for? What qualities do you feel are most important in a good quality dovetail joint?

Any opinions would be greatly appreciated.

[bob blakeborough]

It depends whether or not you are grading on a cosmetic or function... In the old days, dovetail were purely functional and were not usually used in places they would be seen so they were not concerned with the cosmetics as much as just fitting tight. Nowadays people use them for cosmetic appeal more often than not, and that is completely different.

[Jim Koepke]

It may be necessary to create a few different grading criteria.

Fit - least gaps.

Visual appeal, this could even include proud pins & tails that are lightly paired to have a more tactile feel to the joint.

Straightness/cleanlyness of saw & chisel work

Best for each style if some are using the thin tailed "London" style as opposed to ones made for equal sized pins & tails. Maybe some students will select the most contrasting woods or other considerations.

jtk

[David Weaver]

Proportions and fit.

No clue how to tell you to measure them, other than subjectively. Maybe you could put together some feelers of various thicknesses and aggregate the total of the 3 largest gaps, and give them a visual standard for proportions and do that subjectively.

[Brandon Craig]

Among the others mentioned, I'll add: Consistency of angles. Checking for saw marks beyond the line. Presence/absence of tear out from the chisel.

[Christian Thompson]

If the joints are loose you might be able to measure the play in the joint angle (i.e. try to make the joint angle acute by pushing the ends together, measure it, then try to make it obtuse by pushing the ends away from each other, measure again, and then calculate the difference). If the joint is tight and there is no play, test for square.

More subjectively look for gaps at baseline, gaps between tails and pins, etc...

Christian

[Matt Radtke]

This is one big old "it depends."

I would give high marks to anyone that can glue up their box, with everything be nice and square, and not need to use clamps.

Then I would stress test the box. Pass/Fail is the wood surrounding the joint failing before the actual joint.

If you pull off those two, I figure that's worth 90%. The last 10% could be for beauty.

[Chris Friesen]

I think it's sort of unfair to come up with grading criteria after the fact. If I were your student I would have wanted to know what the important criteria were *before* starting the project, that way I'd know what to pay attention to.

Sometimes cutting below the baseline is fine, sometimes not. Sometimes cosmetics matter, sometimes not. Sometimes variation in angle is considered a mark of "hand-cut", sometimes it's undesirable.

If you're going for function over form, have them dovetail an "L" joint, glue it up, clamp the vertical board, then start stacking weight onto the horizontal board. They get marked on how much weight it holds before failing.

[Roderick Gentry]

I think you can create a rubric, that doesn't have to be the basis for their mark.

I can think of four frameworks: The aesthetic, the execution, the efficiency, and structure.

On aesthetic I would probably poach the drywall finish standard which is like 6 levels of finish, so you could maybe start with actual application of finish, where and how appropriate, you could have the form and layout as appropriate to the piece being made, the degree to which the dovetail is clean and tight, form and neatness and execution of part and random toolmarks. But the general idea is to have standards at different levels that build to the end result. This makes a lot of sense with drywall where each level is a trip to the site or discrete step, and they can all be the endpoint. That is somewhat true here where the base of the pyramid level might be appropriate for a packing case, or the underpinnings of a piece of studio furniture, but they each go through those base steps. Different projects proceed to various cumulative levels.

Execution is the same kind of scale, but you could simply look at it as a parts manufacturing exercise, not necessarily pyramidal, where you look for flaws. Each bruise, overrun saw cut, etc... is a point to the negative, each tight joint line, etc... is a plus.

Efficiency is a how the kid did it, how many parts he went through, speedy skills he mastered, in accordance with how you taught the lesson.

Structural evaluation would be some kind of destruction test (many of those are very misleading), or other standard for evaluating the physical integrity of the joint.

[Don Dorn]

I'm in that business too - don't worry about the subjectivity as it is a real world criteria. In this case, I agree with the poster who said to lay out the basic requirements ahead of time. Layout, consistency of angle, gaps, offset fitting and ability to fix minor issues are just those that come to mind. Try to keep it simple.

Lastly - you should be lauded for teaching such a skill in today's educational system. Many of your students will hopefully catch the bug, but even those that don't will someday talk about how their teacher taught to them to hand cut a dovetail joint. Fantastic - and keep it up.

[Erik Johanson]

Thank you guys so much this has been very helpful. I agree with you that it would be helpful to have given them this ahead of time, I definitely dropped the ball on this one.

@Don - Thanks for the praise... I am sadden to inform you that this will be the last year for some time to come for these classes at my school. Due to budget cuts they are cutting the program in half and not offering the majority of the materials courses at the high school. I am trying to impart as much knowledge as I can on the few that I have left before I am moved to another building.

[Bob Lang]

At Woodworking in America, they stuck playing cards in the gaps, then deducted points for each card that would stick. To me, where the joint is located in the finished piece makes a difference, and what's acceptable varies based on the visibility of the location. If you look at old pieces, there are a lot of joints that look bad that have held together for a couple hundred years. Without making the criteria clear going in, it's hard to judge.

Bob Lang

[john brenton]

Gaps and spacing. Perhaps you'd want to give the kids a xeroxed example, as well as bring a live example to have in the class that they can study. Other than that, it's too subjective so maybe it would be better to have the students grade each other's work.

[Jim Matthews]

+1 on gap testing.

Given that these are likely first timers - that's the only part they can genuinely control, and can be definitively measured.
Get a set of feeler gauges if you want to quantify things. Better still, have them make boxes and put them over a bright light source to check for leaks.

I would have a second round if that results in a draw - using air pressure to test tightness of fit.

[Don Dorn]

I respectfully disagree with expecting too much perfection from students doing this the first time. They should be encouraged for giving it a whirl and short of looking like hens teeth, it's a good day. If they are judged to harshly, they'll take the message that they are incapable and many won't ever bother again. To those that find it a positive experience, it most likely won't be their last and then the teacher has truly acheved sucess in my opinion.

I'm not an "everybody" wins a trophy person, but if we all look back to our actual first set, I doubt they resembled anything done by Klausz or Cosman.