Saturday, April 11, 2015


While helping out at a scouting event, planting trees, I ran across metal straps used to hold bundles of stakes together.  They seemed springy, and likely steel, so I thought, "spring steel!"  Well, they're not, but they did give me the opportunity to try to make spiral springs.  Here's one of the straps:

I started by annealing the strap, bit-by-bit in the flame of the blowtorch.  Then, I wound the spring with needlenose pliers.  In the picture below, one end of the spring is gripped in the vice while the other is in the pliers.  As the pliers are turned, the spring tightens.

It was initially quite kinked, so I wound the spring very tight to ensure even, round coils.  Since it was annealed, the spring seemed to basically stay put.  I then held the whole spring in the flame -- which mostly worked since the spring was small -- and brought it to bright red hot.

Unfortunately, I had a lot of trouble keeping heat on the outer coil, so it didn't get as hot.  In any event, when I was satisfied with the temperature, I quenched the spring in a can of water.

It took quite a bit longer to cool than I expected, so I stirred the spring in the water to ensure even cooling.  Here's the finished spring.

It's clearly uneven and imperfect.  I also forgot to drill any mounting holes, but I was also unsure of how it would turn out.  However, the spring rings when plucked, and moves pretty easily.

It seemed that when I pulled the spring very tight before quenching, the spring's shape was better.  However, the coils rubbed against one another (oil helped a bit).  That's why I ended up with the looser shape shown above.  It seems like the spring can take about half a turn in either direction without taking a bend that sets, which is pretty good given the fact that this is just some steel strap I found.

Sunday, April 5, 2015

Drive pulley adjustments

To keep the drive mechanism on my clock simple, it has a drive weight on one side and a counterweight on the other.  The two weights are hung on either end of a nylon cord, which passes over the drive pulley.  The idea is that the counterweight applies friction on the pulley so that the drive weight turns the pulley.  However, the drive pulley on my clock is fairly slippery.  I've been wrapping the weight cord three times around the pulley to get enough friction to prevent slipping.  This isn't a good arrangement because the cord tends to overwrap itself on the pulley and then jam.  This makes winding the clock (lifting the drive weight while taking up the slack with the counterweight) difficult, and also seems to stop the clock occasionally.

So to improve the situation, I mounted the drive pulley back in the lathe and turned a narrow groove that's just shy of the diameter of the cord.

After cutting the groove, I roughed it by gouging with an old small screwdriver that I tapped with a light hammer.

The groove is mostly centered in the pulley, but leaves enough clearance so that the cord clears the cheeks of the pulley (and everything else) on its way out of the clock.  The cord sits tightly in the groove, held in place by friction.