In December last year, I shared with you my designs for a set of Bachmann Mainline Replacement wheel centers, you can find the post here.  This week I received the first test prints, so I want to show you how they came out.

I printed them in Shapeways Smooth Fine Detail Plastic as this material is very accurate and cost-effective.  They were printed on a sprue, and as they are transparent, you can see the circles on the far side where the sprue was cut off.

Initially, I was very happy with them, although they still need to be cleaned ready for painting, they looked perfectly round, and all the detail, such as the raised counterweight edge and rounded spokes, have come out well.  But I’d made a mistake; the offset hole which fits over the connecting rod fixing peg didn’t fit.  Looking at the wheel below you can see this fixing peg has two diameters.  The wheel center fits over the larger section and I measured the smaller.

Consequently, as you can see below, the hole in the 3D printed wheel center was too small.

But I still needed to see if the wheel center fitted in the actual wheel, so I used a drill in a pin vice to open out the hole.

This didn’t go so well.    The Smooth Fine Detail Plastic, unlike the original flexible injection-molded plastic, is hard and therefore brittle so the wheel center cracked as the drill went through.  To be fair the material was very thin at this point and was never designed to be drilled out.  But this did allow me to test fit it in the wheel, and it fitted perfectly.

I also wanted to test the wheel center with the smaller counterweight, although it should be the same size.  This time, to make the hole for the side rod peg larger I used a round needle file.

I just about managed to keep the wheel center in one piece; I had to file it down so it was only 0.3mm thick.  Again the wheel fitted, so once the hole is increased these will work.

I’ve now modified the 3D computer model to allow for the larger pin.  I also added a small radius to the rear edge to ensure any discrepancy in the wheel inside corner would not affect the wheel center.

I’ll do another test print to ensure these modifications work. This material, although it doesn’t always respond well to being drilled or filed, is perfect when the design is right. That’s the beauty of test prints, it allows me to perfect the design so the material is never compromised.  I can then spray them a flat black and permanently fit them into the wheels, ready for reassembly of the locomotive.