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This project started in 1997 as a learning exercise for the purpose of teaching myself AutoCAD.  Somehow the CAD exercise slowly evolved into a series of incomplete CAD models that culminated in the (also incomplete) SolidWorks CAD model seen above and the assortment of real-world parts seen below.  While it's been a wonderful learning experience, I'm still not sure I will find time to finish it.  In the interest of reducing the time commitment of finishing this model, I have given serious thought to revising the design to incorporate oscillating cylinders. Regardless of the outcome, I can say it has been thoroughly enjoyable to research, interpret, document, design, and fabricate the components you see here.

Various processes have been employed in the fabrication of the parts.  The plate frames and some of the valve gear components were laser cut by one of my students from AutoCAD files I generated.  The frame stretcher was milled from the solid using the vertical slide accessory on my 25 year old Taig lathe.  It was then shaped, as was the buffer beam, by my own hand with a jeweler's saw and needle files.  While I am fascinated and pleased by the laser cut parts, I am more proud of the "hand hewn" ones.  I have developed a real appreciation for cutting metal with hand tools.  The wheels were turned on my Atlas 6" lathe from castings made by Locosteam in the U.K.  They are the only commercially available parts on this model.  I removed more material from the backs of the wheels than is usual.  This was done to give the impression of older style wheels that were generally of lighter construction.  Because no no original drawings exist, some of the details and dimensions are plausible reconstructions (based on research of better documented Crampton types).  Some license has been taken in certain areas in the interest of operability. Overall though, the proportions and major dimensions are faithful to the first batch of Cramptons built by Tulk and Ley in 1846 -1847.

For those of you that have asked when it will be finished, I must confess that there has been no progress made in over seven years.  At least, not on the real model.  I have, however, made progress on the CAD model and have honed my skills on SolidWorks in the process.

The chassis is complete, save a few modifications to the center axleboxes.  I don't want any weight resting on the center axle and am going to allow it to "float".

This eccentric rod is finished and therefore, not flat like the others.  I silver brazed a "doubler" on the small end and then cut the notch with a small cutter in my Taig lathe.  The ogee-like curve on the back of the forked end was produced by hand with a needle file.

I learned 3D CAD modeling with this project.  The image above is of a 90% complete AutoCAD R14 model.  While AutoCAD has some great 3D capabilities, it has substantial limitations when changes to the models and the related drawings are required.

crampton osc-5-06-333.jpg (47820 bytes)

Above is a design study of the oscillating cylinder version.  (click image to enlarge)

 

The earliest CAD work on this project was done in 2D and was slow and painful.   (... I meant to say very educational.)  Mechanical design is an iterative process and while 2D CAD facilitates changes better than the paper based paradigm it replaced, it still leaves much to be desired.

Modern parametric CAD tools such as SolidWorks, Pro-Engineer, and Inventor allow for incredible design flexibility.  In part, this is done by placing the emphasis on the creation of geometry and function.  Modern CAD tools have evolved from simple documentation tools, to indispensable engineering tools where many possible solutions may be quickly and accurately compared and analyzed prior to making the first actual prototype.  In the above model, I was able to check for interference and confirm the accuracy and timing of the valve events.
I would encourage anyone that has not yet tried their hand at cutting metal to jump in.  A jeweler's saw (with lots of high quality spare blades) and a set of quality needle files is a relatively small investment.  (A small stock of Band-Aids is equally useful in the beginning...)  Try your hand at cutting some scraps of 16 gauge brass or steel sheet.  You'll never know where this might lead you unless you try.  The potential rewards are many and varied.  Don't let the lack of a "complete" machine shop stop you from getting underway.  I had convinced myself that I needed better tools to be able to start the projects I was interested in.  One book in particular helped me to transcend the "armchair engineer" phase.  It was J. E. Minns'  "Model Railway Engines".  In this book are many fine examples of beautiful work performed with simple tools by mere mortals like us.  The most impressive part is that many of the most beautiful models featured in the book were created in the latter part of the 19th century!  Desktop CNC equipment was still over a century away.  No more excuses, start cutting metal!

Michael Martin - January, 2007

PS  If you find the CAD part of the process interesting, check out your local community college for courses.

 


All content 1997-2007, Michael Martin.  All Rights Reserved.

Direct corrections, questions, or comments to: mike@panyo.com      -     Visit Modern Steam Online
Last updated Wednesday, January 10, 2007