johnsmachines

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. I read every comment and respond to most.

Tag: metal polishing

POLISHING TINY BRASS PARTS

My model carronade has quite a few very small metal (mostly brass) components.  They are fiddly and a bit difficult to hold while finishing (filing and sanding and polishing).

So I bought a tumbler which is designed for polishing metal jewelry and gemstones, and gave it a go.

 

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It cost just under $300, including a kilo of stainless steel bits, and some polishing compound.  It is designed to run for weeks at a time when polishing rocks, but I find that 30-90 minutes is enough for my brass parts.

 

 

 

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The drum will hold 4lbs of parts.  Shown here are the stainless steel polishing bits.  The drum revolves quite slowly, about 30rpm.  Water is added so that the drum is just under 1/2 full.

 

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The before

 

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after 30 minutes.  It could use another 30-60 minutes of tumbling.  Not all of these bits are for the carronade.

 

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This is the sight for the carronade.  Complex and tiny and has sharp edges.  Ideal for the tumbler.  The CNC program diagram on the screen.

I am still experimenting with the tumbler.  So far I have used only the stainless steel shapes to do the polishing.  I will try some abrasive compounds soon.  Garnet dust seems to be the commonest abrasive.

 

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More bits for the tumbler

 

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A preview.  Almost finished.

 

 

 

 

 

 

 

 

 

 

Cheap Engine Turning

A few posts ago I posted some photos of the Koffiekop Stirling Engine, the top plate of which I had decorated with “engine turning”.  I had borrowed the engine turning tool and it worked well.  But I really wanted the circles to be bigger than the 5mm diameter which the Brownells kit produced.

Today I experimented with disks punched out of metal polishing material, glued to the end of same diameter dowel.  (1/2″ = 12.7mm diameter).    I used Super Glue, and no problems with adhesion.

The dowel was attached to a chuck in a drill press.  Running at about 200-300 rpm, and pressing firmly.  No extra cutting compound ( I imagine that these metal polishing pads already have an imbedded cutting compound).  If I was using washing up Scothbrite  type material, I would expect to have to add a cutting compound.

The steel I was testing had surface rust.

Very happy with the result.  Next time I will use CNC positioning to pattern the circles, and overlap the circles so the crappy rusty steel disappears.

I understand that if engine turned surfaces are oiled, they are relatively rust resistant.  Presumably some oil remains in the microscopic grooves.

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The top tool shows the tool after considerable use. It is a bit worn, but the thinning is mainly compression of the material. Compared with an unused tool below. And the surface rusted steel, which has had the tool applied in a semi random pattern, at the bottom of the snap.   (it is a home made tangential lathe tool sharpening jig).