The Amana church bench is a time-tested design.
Amana Church Bench – FineWoodworking
I don’t understand why the plank seat doesn’t split. front and rear legs are mortised into a sliding dovetail cleat which is pinned to the plank seat going the other way. Why doesn’t this cross grain restraint split the plank with seasonal movement? You’d think that the leg should only mortise into the cleat, rather than going all the way through both materials. That accounting for wood movement doesn’t seem to be required in this case.
What’s the difference between this cross grain restraint and one that might lead to cracking over time?
Replies
It would appear to me there is enough movement allowed on both sides of the mortised legs to prevent a split. Also, it should be considered in aligning the leg grain with the seat grain.
The seasonal change in the 6" between the legs in pine would be about 1/10 of an inch... well within "squish range" for a softwood. If it gets loose as a result the tapered mortises will just settle down and tighten with use. I wouldn't be surprised if the leg tenons poke out a bit on older benches.
1. handn't thought of how much of a triangular section this is -- puts more forces on the plank seat when multiple people get up and sit down at the same time. the cross-batten is as much to give a deeper socket for the leg as to keep the seat flat. subtle.
2. I am thinking about replicating in cherry, so not sure if that's close to the limits of "squish." one way to find out...
Have a look here:
https://woodbin.com/calcs/shrinkulator/
I imagine that some did split, and that yours might.
The ones that survived do not necessarily equal 100% of the ones that were built that way.
The ones that split were simply discarded, and the ones that didn't became the 'archetype.' This phenomenon can easily result in a logical error, as you most likely can see now that it has been pointed out.
The form and proportions are lovely. And this is what matters. Don't alter them. If you see a better way to build it to prevent a potentially split seat, then by all means do.
Shakers were not infallible.
Don't let a "shrinkage table" entice you into a construction that raises the hair on your neck. Those things are just a suggestion as to what might happen and imply a precision that does not exist in actual practice. They are popular with certain professions who take up woodworking as a hobby. A time-value-of-money table is dead nuts on to several decimal places, a shrinkage table is not. It cannot be reduced to a mathematical formula, and is not a substitute for your own judgment. Your furniture will live in a completely different environment than Shaker furniture did, and you will not be building it with the stock they had available to them.