Gear Work

  Well, I could not stand it any longer and I had to start the gears today.  Before I describe the process, some basic information about the gear that I am working on.  This gear is called the great wheel on the going train.  What's so great about it?  It really just means it's the largest gear on that side of the clock.  It has a 12" diameter with 96 teeth.  That comes out to about 3 teeth per inch.

  To start off, I need someway to forge the circle as perfectly as possible.  This is where the layout table comes into play.  This is what the table looks like.  You will notice too circles.  One circle has an outer diameter of 12" and an inner diameter of 9 1/2".  Also in the picture is a piece of 1 1/4" x 3/8" stock that is 34" long.  If you do your basic math you may think that that is not enough (12" x pi = 37.7").  However, the forging process stretches the metal on the outside and compresses it on the inside of the circle.  This means you actual want to use the midpoints between the outside and inside diameter when determining how much metal you need.

p.s. (Thank you Francis Whitaker for sharing this tidbit of knowledge.)

  Anyway, here is the layout table.  You can just make out the circles.  (Click on any of the images to see larger).



So, to make the circle, a portion of the bar is heated and bent using a twisting fork.



  After each heating, the bar is compared to the layout table to make sure it is staying true.  Here are some progression pictures.  I used a technique described by Francis Whitaker in which 1/4 of the circle is made on one end then you switch and work on the other end.  Not quite sure why this is but I think its to help with the tendency of the metal to twist in your hand if there is too much metal out to one side.  Anyway, here are the series of pictures.



 


Oops!  When I closed the circle, I had too much material.  The overlap is about 1 3/4" too much.



I reopened the circle a bit, cut off some material.  The circle was closed back up and welded.  The bulge of the weld can still be seen as this is prior to cleanup.  What is nice is that all around the circle it is only off by at most 1/32" of an inch.  Woo hoo!



  The only minor issue is that during the welding, I accidentally burned a small amount of steel from the edge.  It is a small amount and I think I may try to cut the gear so that a gap between teeth will be where the small amount of metal was lost.

  I next decided to start on the spokes.  This involves taking a rectangular piece of metal, splitting it down the middle on both ends.  These are opened up and draw out.  These work photos give the idea.  (Notice the punched holes, these help with the split being nice and clean.)









  I ran out of time and daylight so I had to stop before I was really done with the spokes.  However, I laid the rough version of the spokes onto the gear just to give an idea.



  So, making some real progress and I hope to start on the arbor soon.  Once the arbor is done, then I can cut the teeth.