Sunday, March 01, 2009


My wife teaches violin. This becomes important to this story later. She asked me if it was possible to make longer screws into shorter screws. "Sure", i said. But later it wasn't so clear.

In the mean time, the head board on the bed had come unglued, and the wood screws were stripped. Apparently, it had come apart before, stripping at least two of the screws, and it was put back together with glue and screws. One of the four didn't match the others. Clearly a substitution had been made. Now, two were stripped, and one of those two was bent. I did what i always do. I looked around the house for something that might work. In this case, it was a scrounge through my old wood screw collection. I found two screws that were slightly larger diameter. One was too long, and would poke through the other side of the head board. So i got out a hack saw and unceremoniously cut it shorter. With four screws that should work, i put it back together. It held for a couple days.

Clearly, what was needed was some sort of positive structure. Countersunk wood screws weren't going to do it. I went to the hardware store, bought four 2 inch 1/4-20 carriage bolts with nuts, for about $5. Now, 2 inch bolts are way too long. But the hardware store doesn't sell bolts exactly the length i need. So, i rummaged around the house for a way to cut them to length. I don't have a vice that will do it for me. I have a vice, but i don't really have a work bench. So i cobbled together this contraption. The idea is to cut them with the hack saw. There's a little overhang on the kitchen counter. A scrap 2x4 that i use as a back for drilling was clamped to it to keep the saw away from the counter. Vice grips could hold the screw. A big C clamp i use to fix wooden chairs holds this stack together.

I'm pictured here sawing with my left hand, and holding the end of the screw with my right. I'm right handed, so this doesn't really work. But what did work is to start sawing with my right hand on the saw, and as the screw is nearly cut through, i reach around with my left hand to keep the remaining bit of the screw straight. There's no way to get a picture of this. I should also note that the vice grip is clamped onto the little bit of the screw that i'm throwing out. The vice grip totally mashes the threads. It's very important that the final threads aren't mashed. And that's why my right hand had to do the saw. It's not that my right hand is oh-so-much better coordinated. It's that despite pushups and curls carefully matched for both arms for years, my right arm is stronger. When the saw catches, my right arm keeps moving, where my left doesn't.

After the screw is cut, there's a jagged end to it. I'm holding a file on the block of wood so it won't move, and moving the screw up and down the file. This de-burrs the screw, but also makes it so a nut can thread onto the end. And the result for the head board is that on the outside, the metal caps show. On the inside, the bolts barely stick out from the nuts. They have no way of sticking into the mattress.

Now, you might think that all this cutting and filing will heat up the screw, and possibly even burn your hand. Iron conducts heat quickly, right? But stainless steel does not. And oddly, i didn't learn this in Materials Science in school. I learned it from my brother the welder.

Back to the violin teacher. She gave me a bag of screws, with one dark one. "Could you cut these screws down to the length of the dark one?" So i used the contraption from the head board job. And now there's a bag of smaller screws. But an hour's worth of work was able to take a cheap bag of screws and make them into the custom screws that were desired. They're low quality because they're not very uniform. The heads are a little different than the master. The lengths are a little shorter or a little longer. But they may be good enough. And who knows where one might get the real McCoy?

But good enough for what? These are tuning screws. You screw them down, and they push a lever, which pulls on the violin string. There are tuning pegs that hold the other end of each string. And you use them to get the pitch of the string close. But they're not good enough to get the vibration frequency close enough. The tuning screws are what you use to get the frequency to that last few cents (hundredths of a half tone). And this exercise is all about having the sense to save a few cents.

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