Testing Designs with 3D Printing

Some parts on my model Armstrong cannon could not be made until measurements were checked on the assembled model.

The projectile loader was one such group of parts.

The 80lb projectile obviously sits on the cradle. The carriage is at the top end of the chassis, with the barrel angled down by 17ยบ. The arm with the cradle swings around and meets up fairly precisely with the muzzle of the barrel. I am not sure if the projectile is placed on the cradle before or after it swings around. (does anyone know?)

I had these photos, and a few measurements of the loader assembly from the Port Fairy cannons, so I drew them up in 3D.

The components of the loader are fairly simple, and can be machined rather than cast. But I printed the components in PLA so I could test the design before I started to cut metal.

3 components. The bracket bolts to the chassis, the curved arm, and the cradle.

But, when I positioned the PLA assembly on the cannon, it was clearly incorrect. It did not line up with the muzzle of the barrel.

The only way that I could make the cradle line up with the barrel was to lift the arm out of its bracket by 13mm! I am glad that I did not waste time and material making a metal version to these dimensions! Not sure how this error crept in. But I will redraw the arm with an extra 13mm height.

I have not yet decided whether to machine the parts or cast them in bronze. Both processes are a lot of fun. I will reprint the curved arm in either case.

Watch this space!