Friday, August 26, 2011

Thoughts about materials

I’m old enough and had an interest long enough in things wheeled both petrol driven and calorie propelled to have experienced and read a great deal.  I have read books and available magazines for years.  Found and read obscure books of metal fabrication, manufacturing techniques and vehicle design books and articles.
So as regarding my project of the Overland and how all of the basic bits will be hung together to actually be the Overland TT privateer racer these are some of my thoughts.
For my purpose cycle parts are all of those things other than the engine, drive line and wheels.  And as I ‘m very cheap but hide that behind wanting to be green and recycle and reuse when possible most of the Overland cycle parts will be adapted from other bits and pieces of things.  The fenders will be cut down from beat up alloy trials fenders.  The fuel tank and probably the oil tank will be panel beat from old Land Rover Birmabright alloy.  The headlight and tail will be fabricated from and old SU fuel bowl and an SU carb cover.  The thumb throttle will be made one of two ways; fabricated from the bronze cam lever of an old AC fuel pump or modified from and old alloy choke lever.
The frame and fork to provide something to hang all this stuff from will be of my own design.  I’m not a design genius.  I just research really well and don’t have any probably borrowing an idea here and there from the design genius’ I come across.
The frame will be gas welded using new aircraft grade normalized 4130 chromoly steel seamless tube.  I have looked at all of the pro and cons of gas welding the frame; done the due diligence research and for my application and wanting to do it myself in a cost effective manner, gas welding is the way to go.  I figure if you can build an aerobatic airframe gas welding the tubes and have the FAA approve it as airworthy then it will be fine for my Overland.
The basic idea will be a hard tail frame using the gear box and engine as stressed frame members.  Then create as many properly triangulated frame structures around the first main frame triangle, I should come up with a strong and rigid frame at a very minimum weight.  I will be using a great deal of ideas from the motorcycle racing community and the mountain bike community for the overall geometry of the frame. 
What I want for this frame is it will be light weight, rigid and mechanically strong.  Will have handling which the engine will not be able to outperform and be better than I am as a rider.  Stability at low and high speeds will also be a consideration.  I don’t like twitchy mountain bikes or motorcycles.
Of all things I have mentioned the welding will take the longest to complete.  Because I can’t say I’m a gas welder.  I also have never successfully welded Birmabright.  Both 4130 welding and alloy welding are what I will be learning.  An upside to this lack of skill is a good deal of off-cuts and panel trims to use while learning.  So I will be burning through alloy and tube over the next few months. 
The quality control on the frame tube welding will be checked by a good friend who is a vintage aircraft restorer and has many years of experience with both motorcycle frames and airframes.  He thinks I’m nuts to want to use gas rather than MIG/TIG because of how much faster MIG/TIG are.  Unlike him I don’t have to justify hours of work to the customer because I am the customer and I’m not charging myself for labor
The reason for using 4130 needs some explanation of a sort.  In all my reading and research some of the lightest and most competitive motorcycle specials used Reynolds 531 tubes.  The same goes for mountain bikes.  Of course time has moved on and that today is not true because of the increased use of aluminum, titanium, carbon fiber and high tech steel.  But I have never been accused of being overly concerned about what is current or new or hot.  I can’t afford real Reynolds tube.  But I can afford 4130 which is in reality just a hair breath away from having the same metallurgical mix as 531.    
In this entire project one thing that is always in mind is safety.  As a result of several life experiences with the military and just living in general, I don’t particularly fear death anymore but I also am a chicken and don’t handle pain very well.  So I really want to be able to enjoy the fruits of my labor rather than have it kill me by my own stupidity.  So safety in the garage and safe design and construction methods are always at the top of my list.

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