MODELING: Simple Tool Solves Problem

np cab end

I have been frustrated with making radial roof ends for various types of cars.   In the past, I have used a large metal divider with sharpened points to cut a curve in styrene.  The problem is that I have not been able to cut a uniform radius on multiple pieces.  I end up spending time sanding the parts to match.

My problem created this solution to make a smooth radius curves.  I made a trammel bar with an Xacto blade on the end.  The simple tool was made from .060″ styrene and a piece of .040″ brass wire.  By locating the pivot point equal to the desired radius I was able to cut a 14′ 3″ radius for a caboose end and a different radius for the cupola roof.   The whole deal is set up to fit on a piece of particle board.

tool back

The hole for the radius is drilled in the .060″ base.  The brass pin clearly shows in the picture above.  I position the part to be cut along a centerline on the particle board.  It is held in place with tape.

tool front

The #11 Xacto blade is held in place with some .020″ styrene strips and a machine screw.   The cutting process is done by moving the base from left to right.  It is better to use several light passes rather than a few heavy cuts.

I am sure that there are other ways to do this but this is my attempt.  The tool does the job for me.

Happy Trails,



11 thoughts on “MODELING: Simple Tool Solves Problem

  1. What a terrific idea, Gene. Thanks for sharing this. I assume you start and finish your cut beyond the width of the car end, and then trim the end to the proper width?

  2. good use of an old technology-I even have some old trammel points-but didn’t extrapolate the thought to a modeling application-you did!
    Thanks again,

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