Page 4 – The Frame

Test Print V1

I got to the point I wanted to test print to see where I was at. I like doing this for a couple of reasons – all the planning in the world and I can manage to put something in the wrong place or distance and .. I can determine that I need to rework a part to make it look better or stronger.

supports/Feet

These are not bad but just on the cusp of being too thin. Looking at them I also realized that they may appear too thin to support the machine. We are talking something like 14,000 lbs meaning each of these supports would have to support over a ton.

The V1 design has walls 0.434 mm/0.017″ thick. This is O scale so that translates to 0.82″ full size. I suspect that would be more than adequate – but I am more concerned with getting a good print. Therefore I upped the wall thickness to 0.8 mm/0.031″ – or 1.51″ full sized.

I am just going to “assume” that these are cast iron feet riveted to the I-Beam framing.

Support Beam

The support beam is made to support the casing. It is supposed to fit against the sides of the casting with the five bolts. The problem was that you have to wash the prints in alcohol and this warped that top edge. It straightened in the after processing – drying and curing but looking at it I got to thinking.

This was created originally before I had a 3D printer with the intention of scratchbuilding from plastic. The support beams would have been from Evergreen angle. Now with my printer available I can decide that these need to be strengthened and the ‘shape’ changed from angle iron to iron castings. This will remove the warping problem and just look better.

Shaft Hole size

The shaft hole is shown with a radius of 1.613 mm or 3.226 mm dia. This is 0.127″ which you would think be fine for a 1/8″ rod (shaft). The problem is that this is from the CAD drawing. In reality it printed so the 0.125 aluminum rod could barely be twisted into the start of the hole which tells me that hole shrank 0.002/0.003″ when printed. This is common as the resin always shrinks a bit. To fix this I will change the hole size in the CAD to 0.130″/3.3 mm – this SHOULD take into account that shrinkage.

Supports

The supports completely failed on one side and part of the pad pulled up at one place. This .. I know what the problem is. The way I oriented the frame there are a lot of flat surfaces meaning during printing the pulling of the model from the FEP sheet is more difficult. The common answer to this is to orient the model at 30° or 45. The downside is increased print time – but a quicker print time means nothing if the print fails.

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