Shop Days

The last couple of days at work have been Shop Days, with a fair bit of time spent in the department’s machine shop making holes in a metal box. This would, I’m sure, be the occasion of much hilarity among my old junior high shop teachers, as my ineptitude in both metal and wood shop was pretty impressive, back in the seventh and eighth grades. I’ve gotten considerably more coordinated since those exceptionally gawky days, though, and I can use a drill press or a mill without too much trouble now, though no-one will ever mistake me for a machinist.

In a certain sense, Shop Days are among the most satisfying days I have at work. There’s a real feeling of accomplishment at the end of the day, as there’s a concrete Thing in the lab that wasn’t there when I came in in the morning. It’s something I can point to, and say “What did I accomplish today? I made that.”

Granted, that doesn’t sound like much, but it beats spending eight hours re-aligning optics.

Details of the recent Shop Days are below the fold.

As alluded to in a recent post, my main laser suffered some damage with the arrival of humid summer weather. As fixing the problem was going to take the laser off-line for a few days anyway, I decided to bite the bullet, and put it into a proper air-tight box (previously, the laser was out on the table, and covered with a cardboard box to keep air currents off, because putting it in a box was too time-consuming). That way, I can seal it up and add some desiccant, and hopefully keep the worst of the condensation problem at bay.

This required several steps: first, the purchase of a suitable box (from Newark Electronics, whose web catalog is appalling, but who are really very easy to deal with if you have a print edition). Second, the drilling of nine holes of various sizes, then the installation of electrical connectors, and finally, soldering the appropriate wires to the appropriate connectors.

Six of the nine holes were absolutely trivial– relatively small through holes for connectors or mounting screws. Two more were easy to drill, but needed to be tapped to take 1/4″-20 screws– the hardest part of that was finding the tap in the shop (the machinist is away on vacation this week, so I was on my own today). The final hole was 7/8″ in diameter, for the output beam, which was trickier– I drilled a pilot hole first, but the big drill still got caught, and yanked the box out of the vise. This happens about every third time I need to drill a large hole in something, and isn’t really a problem as long as you can suppress the urge to grab at the (now rapidly spinning) box when it comes loose.

The most annoying part of the process, for me, is always the soldering of wires to connectors. I’m pretty terrible with a soldering iron, mostly because I’m big. Not only am I somewhat lacking in the “delicate touch” department, but my hands are pretty large, which means I have a tough time getting things into position in a compact box, just because I can’t quite fit my hands in to push things where they need to be.

If you’ve never done it, the essence of soldering is this: you put two pieces of metal that you’d like to join together in contact with one another, and you bring a hot soldering iron in contact with both of them. When they’re both sufficiently hot, you touch a piece of solder (a soft mix of tin and lead) to the metal parts, where it melts and flows into the gaps between them. Then you remove the soldering iron, and the solder cools and solidifies, forming a strong joint between the two.

It sounds really simple in principle, and looks easy on spiffy how-to sites, but as always, there are a bunch of things that can go wrong with the execution. Wires never seem to want to stay where they’re put, so it’s really easy to have two wires pop apart just at the point where they get hot enough to melt the solder. And, of course, they’ll stay hot just long enough to burn your fingers when you try to twist them back together.

It’s also critical to make sure to heat both objects equally. Failure to do so will create the dreaded “cold solder joint” which looks like it’s connected, but will pop loose give the slightest opportunity. This can be a problem when one of the two objects is pretty sizeable– two wires of comparable size will heat evenly, but attaching one wire to a big metal connector is a real pain. Banana plug connectors are about my least favorite things to solder to, because they consist of an inch-long metal plug with a tiny little tab on the back, and connecting a small wire to the tab requires getting the entire damn plug to the same temperature as the tab. And, again, that big metal plug will remain at finger-burning temperature for a surprisingly long time.

Also– and the importance of this message cannot be overstated– the soldering iron itself is really freaking hot. Don’t touch it with your finger, you moron.

(I burn myself with the soldering iron about every third time I have to make connections inside a box. It’s the big hands thing again, and you know what they say about guys with big hands. That’s right, they’re always burning themselves when trying to solder things in tight spaces.)

By the end of the day Wednesday, I had successfully completed the box, and also glued a microscope slide over the big hole, as a makeshift window (it’s close enough for government work). I put BNC connectors onto a couple of the cables that I had to cut to move the laser into the box, connected the others to screw posts, and hooked everything up. Even though I know I’m not actually an idiot, I was somewhat surprised, as always, to find that everything worked fine. The laser turned on, the beam made it out through the center of the window, as planned, the temperature controller successfully controlled the temperature.

I installed the box back on the table where the laser had been previously, and took a minute to admire my work. It was, as always, pretty satisfying to see a new Thing in the lab, and know that I made it myself.

Of course, the beam is now an eight on an inch higher than it was this morning, which means it doesn’t pass through any of the optics any more. Guess what I’m doing Thursday?