anvilfire logo (c) 1998 by Patrick Dempsey
anvilfire! News
Reporting LIVE! from Asheville, NC - June 1998!
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JYH-1  JYH-2  JYH-3  JYH-4  JYH-5  JYH-6
JYH Scale Drawing
Before building something with this many parts and relationships you should make a scale drawing. The one above was proceeded by a number of sketches and a lot of measuring. The critical dimensions were stroke and shock travel. Once determined the scale layout was necessary to determine the length of the columns. Click image for details.
Design is an iterative process. The guide design above was suggested to me by Josh Greenwood. Originally it was to use a piece of railroad rail, the flange becoming the slide and the cap the ram. Luckily I was unable to obtain the 150# rail I wanted. After examining the rail I had, I realized that the center of gravity (mass) is near the center of the web. I wanted more of the mass to be out in the ram and I wanted more throat depth. So I decided to use a short section of 6# x 25 pound wide flange beam, cut off one flange and weld on a piece of shafting for the ram. While laying out the beam to be cut I realized that I could leave the center and cut off two strips thereby gaining about 3/4" more throat depth. The strips cut from the sides could become guide spacers (requiring shims).

Good plan I thought, and proceeded to make the above drawing. While making the drawing I made another realization. I was going to cut off part of the flange and then weld a piece back in the same place (within 1/4")! So, the plan changes again! This will save finding, cutting and welding one part AND will produce better results.

This area of the design has required quite a bit of thought. Ideally the lifting point on the ram is on a axis through the center of gravity. However, in this design the center of gravity does not line up with were the load is applied at the dies. So I have compromised and attached the linkage between the center of gravity and the point of applied load.

I have also had to back away from my original plan of designing so that the shock could not possibly be over extended. The problem is, if I designed in this narrow range it left no room for hand held tooling and dies. It also assumed that the design premiss of the shock absorber was going to fail. I decided I could not design with a defeatist attitude. If it didn't work I'd have to replace the shock with another linkage and the point became moot. Since making this decision I ran a test, lifting and droping a weight with the shock absorber as quickly as I could. The shock only extended a very small amount (1/4"). This is what I expected. The rest of the dynamics are still a question that only a working model will prove.
East Coast JYH photos NEXT! East Coast JYH! p.4

May 19th, 1998
Copyright ©1998 Jock Dempsey