Re: Machining car end?


destorzek@...
 




---In STMFC@..., <grangerroads@...> wrote :

Vector CAD/CAM. It has a 3D module, but at the time I bought the package I didn't buy that.

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So, all you have to work with is a 2-1/2D CAM package.

SIDE NOTE: 2-1/2D describes the ability to move 2 axes concurrently, but only move the third while the other two are stopped. You can cut a circle with 2-1/2D, driving the tool around the curved perimeter in the XY plane, then increment the Z down while the other two are stopped. To cut a hemisphere, you need full 3D; all axes moving simultaneously.

It should be possible to cut a Dreadnaught end with 2-1/2D software. A number of years ago we had a machine control that was only capable of 2-1/2D motion, but we could select which two axes were active together. To do this end, I would build the solid model and orient laying on the flat back, then section it crosswise (across the width of the car) in small increments, then toolpath the mill to cut each profile in the ZX plane, incrementing in the Y to begin the next profile. You will need to finish with a ball nose tool as small or smaller than the smallest radius in the part. A .015" ball nose end mill should do, as a quick look at some drawings shows 7/8" to be the smallest radius, which is just a tad less than .0075" in TT scale, which is the radius of a .015" diameter tool. A .012 or .014 diameter tool would be better, but .015 is much more available. To get a smooth finish you likely want to increment over only .001 at a time. It's a lot of cuts, but you'll get there eventually. From experience, the "cusp", the ridges between each toolpath, will likely show the most in the fillets where each "wale" and "dart" blends to the basic shape of the end, and some contour toolpaths that follow the fillets around in the XY plane may be needed to smooth them out.

That begs the question of where to get the information to program the 3D model. NONE of the drawings published in the normal places have enough information. Drawings in hobby magazines are worthless, and the Car Builder's Cyclopedias only have what are called General Arrangement drawings. The purpose of these drawings is to show how the parts fit together into the whole. You need the drawings that actually define the parts, in this case typically called "End Detail" drawings. These drawings typically show the two end sheets separately, so the details of the lap seam can be seen, and have numerous sectional views, both horizontal and vertical. Here is an example of the type of drawing you need:

NWHS NW-E48980-NW Mech Dwg

 

Unfortunately, the N&W H.S. archives does not have much on reefers.


Dennis Storzek



 
 

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