Interesting joint

[Dave Anthony]

I recently purchased a Japanes abacus on ebay. It arrived today and I found the corners are miter joints with hand cut dovetails. It's pictured here along with a Chinese abacus, a suan pan. The suan pan, shown on top was invented in China during the 11th century, and it can used to calculate in hexadecimal. The suan pan shown here has rods made of bamboo. There are 2 beads on each top rod, called heaven beads, and 5 earth beads on the bottom rods. Each heaven bead is worth 5, and each earth bead counts as one. Sucessive rods represent the digits of a number. The Chinese abacus was introduced to Japan around the 15th century, where it is known as the soroban. Around 1850 one of the heaven beads was removed from the top rod, and around 1930 one of the earth beads was removed. A modern soroban has 1 heaven bead on each top rod and 4 earth beads on each lower rod. That dates the soroban here as being made sometime between 1850 - 1930. For an 80+ year old item, I'd say it's held up rather well. It also has a sliding dovetail holding the base on. While the corner joints are certainly not perfect, there is no way I would attempt to cut them.

[Peter Pedisich]

Wow, that is fascinating. Very sophisticated minds back then.
As for me, I'd have better luck cutting those joints with a worm drive saw...outside...in January...on Mount Washington...in a t-shirt, than figuring out how to use an Abacus.

[Darnell Hagen]

I'm with Peter,the joint is easy compared to the abacus.

http://i152.photobucket.com/albums/s168/DarnellHagen/P1490954.jpg

[Van Huskey]

Very cool, thanks for the pics and history!

[Dave Anthony]

How does one cut such a joint? I've cut dovetails with a jig & a router that look great, and hand cut dovetails that look, well, not so great, but at least I understand how someone could create such a thing. In this case because the joint is not tight I can look into it and see it is a 45 degree miter joint with a pin on one side and a tail on the other. Do you cut the dovetail then the 45? Part of what impresses me about this thing is that it has an impression of utility about it - turn out a large number of these each day, it's a functional item & a functional joint - nothing special here.

[Anthony Whitesell]

I can see in my head how to cut the tail (cut the 45 miter then cut/chisel the tail), but the pin is another story. I couldn't help notice that it is a single pin/tail which would make it much easier.