johnsmachines

My model Armstrong cannon has some components which will be difficult to machine, and would involve silver soldering many tiny pieces.

For example, the steel brackets in which the wheels are supported, and the centre column.

There are 4 trolleys like this.  Each one has 2 or 3  wheels.  It is a Z shaped profile with 3 gussets visible and 2 more inside.

The centre column.  It could be fabricated.  

But being basically lazy and always looking for the easy way out, I have decided to investigate the possibility of casting these parts.  And some others.

So I have printed them in PLA filament, with a view to a “lost wax” type of casting process.  It will be “lost PLA” of course.  Maybe doing the casting myself.  But also checking the possibility of having it done professionally.

The PLA printed parts which will be melted and burned away in the casting process, have to be as well finished as possible.  So I have been experimenting with various settings in 3D printing.  One problem is that the molten plastic thread has to be supported.  Overhangs up to 45º or even 60º can self support.  And even horizontal overhangs can self support if the gap is not too big.

But this gap, about 20mm, proved to be too big…

The threads are partly bridging the gap…

Horrible.  It is the underside, but even out of sight, it is unusable.

So, I am printing up some supported versions, even as I type this.  And I am going to look at some casting equipment which I might be able to borrow.  Apparently the gas furnace is very noisy, and it needs a home with no close neighbours.   List…. a furnace capable of melting bronze, a crucible, investment casting powder,  protective gloves, helmet or face mask, leather apron, tongs, slag ladle, a casting box.   There are many YouTube videos on the subject of lost PLA casting.    Watch this space.  But if the quote for professional casting from my printed molds is not too fierce, I will probably take that path.