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August 19, 2012

Blacksmithing: Year 3

For the third year running, I spent a week in the blacksmithing shop at the John C. Campbell Folk School in North Carolina.  Following the trend I set during my last two visits, I continued working on cool but useless mechanical things.  This time around, I made gears.  

Because the gears were so time consuming to make, the final piece doesn't include the puzzle-like assembly or end goal (ringing the bell) of the gizmo I made last year.  The gears started out as a 3" long, 1.5" x 3/8" bar of mild steel.  Using the shop's 55 ton hydraulic press and a 7/16" square punch, I punched a hole every inch along the center of the bar.  I split the bar down the center with a bandsaw, to make two square toothed rack gears.  The rack gear bars were then heated in a coal forge and bent around circular forms.  The gear's hubs were made from 3/4" flat bar of the same thickness, reworked to remove the sharp edges, and with holes drifted in their centers.  The hubs were MIG welded in place.  Getting the gears to run smoothly was an extremely long process of finding the ideal distance between the gears, beveling the gear teeth with a bench grinder, and filing down high and low spots around the circumference of the large gear to prevent teeth from sticking.  Lots of help with the gears, including the idea of punching and bending flat bar to make them, came from Lucas House, the class's instructor.

I drifted a square hole in the center of the drive gear, so it would interface with with the hand crank.

The handle was forged from a 1" pipe, and it spins freely on the crank.

I built a ratcheting mechanism into the crank, so that the gears cannot be back-driven.  The spring was made from the bristle of a heavy-duty wirebrush. 

Here's the frist gear I made.  I ended up not using it, because the teeth stretched too far apart when I bent the gear into a circle.  For the small gear I ended up using, I halved difference between the outer and inner diameters of the gear (minus the teeth), so that the metal would stretch less when I bent it.  The edges were smoothed and given a worn look by wire brushing them with an angle grinder.

In a little bit of extra time I had, I ground this useless but nicely shaped knife blade out of a scrap of rusted tool steel lying around the shop.  Once the rust was ground away, it left a nice pitted surface finish.

Here's some of the interior fo the shop:

A circle of power hammers:

Here's the forge where I worked:

The old shop.  It still has a few forges in it, but it's mostly used for grinding, welding and cutting.

The exterior of the old part of the shop:

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