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machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment.

Category: metal casting

Bronze Casting -2

When I looked closely at the rifling cutters which I had lasered out of a broken Brobo saw blade, I realised that I had boobooed.  I had measured the thickness of the blade at 2.5mm, which was actually a bit thinner than I wanted, but would have been acceptable. But when I measured the cutters, they were only 2.2mm thick.   Reason?  The saw blade had been hollow ground, and the blade inside the teeth was thinner.   Too thin, I decided.

So after some wailing and teeth gnashing I have ordered some 3mm thick tool steel in the form of planer blades, which I am pretty sure will not be hollow ground, and I will ask the laser cutter to cut me some more blades.  So waiting waiting.

And I am setting up the cannon barrel for rifling.  The CNC rotary table (stepper motor hidden behind) will be bolted to the CNC mill table.  The barrel is held in the jig which is held by the mill quill.  The cutter, (not seen in this photo) will be drawn out of the barrel by the mill X axis, while being rotated in the A axis by the rotary table.   That is the plan anyway.  But still waiting for bits to arrive so I can finish the cutting tool.

P1053658

The Armstrong cannon barrel held to the mill quill, and the rifling cutter will be held by the CNC rotary table.

IMG_8537

The rifling tool which I will not be using because the cutter is too narrow.  The cutting edge just peeping out of the slot will be dragged and twisted through the barrel bore.  The cap screw adjusts the degree of protrusion.

 

BRONZE CASTING

Meanwhile, I am accumulating various bits of gear to do some bronze casting.   An electric furnace with graphite crucible from China, Some jewellery investment material for the moulds, and a second hand pottery kiln for preparation of the moulds, and melting out the PLA 3D printed parts.   I will take some photos when it is all here.

And SWMBO has conscripted me to assemble and install some kitchen cupboards for a property which she is renovating.

P1053684

P1053685

These are flat pack units.  Kaboodle.  Well designed and CNC cut and predrilled.  Not quite finished.  Waiting for the stone bench tops to be made and installed, and for appliances to be wired and plumbed.  Frankly I would prefer to be tidying up my workshop, but hopefully I am gaining some “Brownie Points”.

Bronze Casting. 1.

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.

rear trolley

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.

IMG_8411

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.

print unsupported threads

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

print unsup oblique

The threads are partly bridging the gap…

print unsup end

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.

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