Reverse engineered part

After fiddling around with the part from the previous article, I think I might have a reverse engineered technical diagram. I still don't know enough about early 20th century mechanical design techniques to know if this is what they would have done, but it should be enough to at least remanufacture this part.

I also realized that I haven't actually described the part! There are two registers on the typical Monroe calculator, an upper register which indicates operation count (useful for multiplication and division) and a lower register which indicates total. There's a crank which, when turned one way, zeroes out the upper register, and when turned the other way, zeroes out the lower register. The part that I reverse engineered is shown in the original 1920 US patent 1,396,612 by Nelson White, "Zero setting mechanism" in Figure 5. In the patent, the part, 32, is described as follows:


The shaft 60 is normally locked or held against rotation by a rigid arm 32, pivoted upon the shaft 84, and at its free end engaging a peripheral notch 33, of a plate or disk 34, secured to the gear 12...


So the next step might be to make an OpenSCAD file for the part, and put it on Thingiverse so that anyone can recreate the part. It probably can't be 3D-printed at this point, since it really needs to be a metal part. Even Shapeways, which can 3D print metal parts from stainless steel combined with bronze, can only achieve a 1mm detail, and this thing is much more detailed than that.

Full-sized files in various formats: AI | PDF | SVG | PNG

UPDATE: See the thing on Thingiverse.

Carriage pawl reveng

Wooden gear clock plans

Back when I was a kid, there was this kit for a weight-driven clock. I specifically remember that the instructions specified a certain penny-weight of nails for the weights. So my dad and I trekked to the hardware store just to buy those nails. And then I had to count them and stuff them into the plastic casing for the weight. Good times. I think this was the late 70's. Surely the Intarwebz has a picture of everything, but I couldn't find a picture of this thing in several minutes of searching. If anyone finds a picture, please comment and I'll add it to the post.

Anyway, a recent post on BoingBoing reminded me of that. Clayton Boyer Clock Designs designs and sells plans for all sorts of wooden mechanical clocks and orreries. The plans are full-size on paper, which means you can stick them to the wood and cut out the pieces. You can use a CNC, a laser cutter, a jigsaw, a scrollsaw, a router, whatever works. But it's not for everyone: apparently the process is very fiddly to get right, and you have to spend a lot of time making sure the parts are true, and debugging the clock afterwards. Still, it would make a great gift for a high-skilled tinkerer.

(Update Feb 21, 2010) This plastic medieval clock kit from Japan is close, and may have evolved over three decades of being passed from company to company. I do sort of remember the pendulum thing on the top.

This kit is the closest to what I remember, but it's a set of instructions for a wooden kit. The conformation is extremely close to what I remember.

The kit (in plastic) was probably a close copy of this clock from Germany. I also remember it never quite worked right :roll:

A Monroe electromechanical calculator

I know, I didn't give an update this week. I've mostly been lazy this week. I've been playing with an electromechanical Monroe calculator. My dad brought one home when I was, oh I don't know, ten or so. I played with it a while, and then I wanted to see how it worked. I remember opening it up and being confronted with this mass of levers and gears, and I knew that I had absolutely no hope of understanding the thing.

So recently I got one off eBay. It's semi-motorized, has eight columns of buttons, and a 17-digit accumulator, with two other 8-digit registers on top. It can multiply and divide. When I plugged it in, it would turn over sometimes, but more often not. It also smelled like electric burnination, which isn't good. So, like I did way back then, I decided to open it up.

I was so careful, and yet I managed to break off the main knob, the circular thing in the image to the right. It's clear that there weren't any set screws or anything else holding the knob on its shaft, so I pried it loose. Well, apparently prying is the correct thing to do, but unfortunately I must have fatigued the metal shaft because it broke off. Perhaps I'll get lucky and find another one with a good shaft.

Anyway, I opened it up and I was confronted with this mass of levers and gears:

But, armed with decades more experience, and a bazillion tools, and Teh Intarwebz, I knew that I could finally dig into this, and figure out why it wasn't working. I have not yet been able to find the service manual for this thing (an MA4-170, which is one of the many, many Model 1 series Monroe made). However, I was able to dig online into Monroe's patents, and find matching diagrams and descriptions, as shown:

It's not perfect, because the reality is that these things have all sorts of fiddly little adjustments that need to be made. So a service manual would be ideal.