johnsmachines

Yesterday I made some cast aluminium parts for the model 1:10 Armstrong RML cannon. It was the first time I had done lost PLA casting, and seeing the castings emerg from the investment mixture was thrilling.

Today I had a closer look at the parts, band sawed them from the trees, and tidied them up with some belt sanding and filing.

There were 3 central columns.  In each case the vertical side flanges came out almost perfectly, but the bases contained some voids.

The undersides of the bases shows that the voids match the internal structure of the original 3D print.  This indicates to me that the fault arises from the 3D print, not from the molten metal pour.  Those columns were among the first 3D printing that I had done, and I remember that the surface layers were only 3 layers thick.  Since then I print substantially thicker surface layers, which I believe are more water tight, and less likely to let the investment material leak into the structure of the print.

Although they look very ordinary, I will fill these voids with JB Weld, then paint them with automotive filler primer, then the final paint coat(s).   If they are still substandard I will start again with new 3D prints,

I also poured 6 wheel forks.  2 were so bad that I have melted them down into ingots for re-use.  The other 4 looked resurrectable.  Unfortunately I had a mishap when bandsawing the parts from the tree.  The tree was flung across the workshop, and one of the forks snapped.  Of course it was the best one.

So 3 of the 6 forks were put into the re-melt, and I did some tidying up on the other 3.

This lot was remelted into an ingot for future re-use.

The 3 on the left after some tidying.  Same problem with the voids in one base, but structurally OK and can be fixed.  I scrapped the one on the right.   I might eventually remake them all.

So, although I ended up with 6 use-able parts out of 9 made, and most of those require filling, I am still reasonably happy with this first attempt.  I think that the 3D prints were the weak link in the chain, and with that assessment I will try another casting run in a few days.

Meanwhile, back home I printed a Tyrannosaurus Rex.  I think that it is my best 3D print so far.  It is 250mm long, and the level of detail is excellent, even the vestigial arms are intact.

About the colour.  No one has any idea what the original T Rex skin colour was.  So even this red is possible (but unlikely).   Nor do the scientists know what noises the T Rex made.  Could have been a reptilian hiss, or a roar, or a porcine grunt.   Whatever, I am glad to never hear it.

The print took over 24 hours.