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Past Projects – Trial and Error

April 7, 2007

Building our house put a lot of my creative outlets on hold for a while, and while there remain a number of responsibilities to complete, I should soon be ready to build my shop, and then in turn get down to business on a lot of overdue projects.   

I took a field trip to a classic car restoration shop Friday afternoon, and that got my juices flowing again.  But working on cars is just one venue for expressing my ideas.   I thought I might recap a few previous and in progress, projects that might be potentially interesting to someone, somewhere out in the blogosphere.    

Leading up to the official start of my house, there was an enormous pile of felled trees,   stumps, and dirt from prior clearing work on the property, including the work on my neighbor’s house, completed first.  This pile was roughly 60 feet in diameter and 10-12 feet high, and had become a hopeless tangle that had to go before the house could begin.   I decided to build a shear to go on the end of my excavator, so that I could sit in the cab and extract trees and stumps, and cut or crush them into smaller pieces for easier chipping or burning.   This project took several months to build, plasma cutting and mig welding together many pieces to form the finished product which weighs around 500-600 lbs.  My neighbor, and project contributor, Rick was a helpful resource, lending manpower, a trailer and generator to allow work “in the field”.

Here are some pictures taken early in the initial trial fit assembly where I was working out the mounting points and the overall geometry.  I work from drawings, guesstimated measurements, and some trial and error as I fit things together and discover interferences, or other trouble spots that weren’t evident on paper.


Here’s another view to give more perspective on the overall dimension.  The jaws are 3 feet in length, and the overall assemble is about 6 feet long,  4 feet wide, and 1 foot in depth.  Note the jaw is a double weldment on one side, and single on the other, with the blade edge meshing between the double serrated members.


Once completed, there were still a number of wrinkles to work through.  Firstly, my initial design was not able to manage the tangential force that would try to twist the blades during use.  While the blades themselves were more than strong enough to manage the120,000 lbs of force applied by the dual hydraulic rams, one per jaw side, the 2″ diameter pivots were not.  I had only considered the shear strength of the 2″ solid steel pin – more than adequate, but had not considered the force that would would try to deflect the blades, one past the other, rather than them staying in plane.  It was a function of the leverage along their length, some 3 feet against, the 3-4 inches in their width where they are mounted.  sandford-son-014.jpg

I applied an “engineering change” of some external bracing  to manage this force.  These 2X3 braces were aplied to both sides of the single blade, while the design of the double jaw (the one on left side with serated teeth) had enough stability inherent in the fact that it was double thick, and therefore had a wider surface to dissipate the load.   This update allowed the shear to work well enough for my purposes, cutting through stumps and tree tunks, however it still fell short of it’s full potential.   I’ve aquired some 4″ diameter heavy wall stock (formerly the hydraulic ram out of an elevator) that I’d like to use to to rework my design a bit.  I plan to use this much heavier bushing material in conjunction with 3″ solid pins and to redesign with double pivots so that it will work like bolt cutters instead of the single pivot design as here.  

After I build my shop…..

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