I work part time at a small foundry. I come in once or twice a week as an independent contractor to maintain the machines, repair equipment and fabricate things as need be. At one point I was asked to build a few flasks- frames to hold patterns.
They typically buy their flasks from a specialty supplier, but they needed these in a hurry. I built these in my own shop, and quickly arrived at an acceptable, if crude, production setup.
The photos show the finished pieces, of course. Other photos show the finger joints being machined: clamped two at a time to a sled, and cut with a dado set on the radial arm saw. The sled is elevated in steps to achieve successive tenons. Sets of end pieces are mated with sets of side pieces to make a flask.
In a production shop, a ganged cutter or other expensive, single purpose apparatus would make all the cuts at once, ensuring fast, consistent cuts. Well, I’ll have none of that nonsense in my shop, thank, you.
One challenge was arriving at a dimension that would allow one setup to cut both end and side pieces, solved with a combination of math and experimentation. The other challenge was coordinating the thickness of the dado blade with the blocks used to raise the sled to arrive at good fitting joints. All that required was a good caliper, a variety of shim stock, and patience. Obviously, it all had to be done efficiently enough to be cost effective. All in all, it was a satisfying task.
The final photo in the series shows the project that followed this one- a steel rack to hold flasks- two shelves, twelve feet long, and tall enough to walk under. The legs are bolted on after delivery. After fussing with shims and calipers, this was a nice change of pace.