Valve gear – a complex OnShape part

The valve gear for #622 will be printed as a single part.  As with most of the parts, the original drawing needed to be redone.

The first time around, I thought I was very clever by using a minimum of sketches.  I chose parts of the sketches to extrude to different depths, but hard-coded the extrusions.

This time I think I’m even more cunning: rather than hard-coding the depths, I used a second sketch, on a plane perpendicular to the elevation sketch to fix all the depths.  Then I proceeded to extrude up to vertices in the sketch.  Working with the elevation sketch in the foreground, I then extruded the furthest elements of the part first, and worked back toward the elevation.

I remember the first version of this part taking a long time to draft, and being a real mind-bender to figure out the offsets.  However, with the sectional sketch fixing the depths of the extrusions, it was trivial.  Sectional sketches are a big productivity boost!

valvegearSketches

Another change that I’ve been making with the 3D printed parts this time around is to bake the minimum wall thickness into the dimensions using the max function.  I define both the scale and minimum wall thickness as variables in the part studio.  Then the dimension equation for 1 inch go like this:

max( 1/#scale in, #minWallThickness)

While I have no intention of scaling this locomotive “kit” up or down, if I did, this approach should enable the part to be the scale thickness if the part gets scaled up to S scale.  On the other hand, if the part gets scaled down to N scale, it would still be printable.

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2 thoughts on “Valve gear – a complex OnShape part

    1. Maybe in version 2. Right now, I am (trying to) optimize for getting something built as quickly as I can. I know it doesn’t seem that way, but that’s what I’m doing!

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