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Been doing a bit of silverwork which is starting to take off with orders coming in but the problem is the time taken to burnish and polish the rough castings and the pressure on the hands means it limits possible production,a method of mass finishing is needed.
A relatively new machine on the jewellery manufacturing market is a magnetic tumbler/burnisher which uses 2 pairs of magnets in a disc which spins dragging around small 5mm x .3 /.4/.5 mm stainless pins submerged shallowly along with the castings in water in a container placed above but close as possible to the spinning disc.
To begin construction the four n52 20mm x25mm rare earth magnets are drilled and gorilla glued into a double layer ply disc, did buy a hunk of 150mm dia alloy to turn one up but that was too over the top and alloy disc slated to become a master lap, one pair poles are set close to centre opposing each other and other pair opposite poles set further away so as the water drag slows the pins they alternately move inward and outwards each aligned with the field and impact the surface of the nonmagnetic item to be burnished.
Turned up a hub out of a bit of scrap brass to mount disc onto the hubs axle using a thinned down axle nut as a a lock nut
The casework is all cut from some 2nd hand unused polycarbonate sheets to avoid heating of metal structure by eddy currents being induced by the spinning rare earth magnets. Has been a real problem others have found out.
Being a tight arse the cheapest way i could find for making an arbor for the magnet disc and drive pulley was a brand new Shimano front wheel hub cheaper than a set of small bearings even including delivery to NZ and just needed a few spoke holes drilled and tapped for m3 mounting cap screws.
The base for mounting hub was turned on the faceplate to be a snug fit on the hub so little screws only hold hub in hole
A second hand but powerful variable high speed sewing machine motor provides the drive originally destined for an auxiliary motor for a cross slide milling attachment ,have since picked up another.
A cheap varispeed unit along with timer ,switched and fused IEC type plugs, suitable drive belts in varying lengths ,so could select best length one when assembled, along with magnets all sourced ultra cheaply on ebay.
Pulley for shaft was turned from a block of free machining alloy I had to hand ignoring the belts teeth ,needed by motor pulley because of the small diameter but the vee on the larger pulley drives well with friction alone and can slip before smashing something if it turns to custard.
Cutting the perspex has been a little tricky but using finest blade to hand and cleaning up with a cabinet makers scraper makes a good clean joint.(didnt find that out till nearly finished)
Just getting back into finishing this project ,needing something to tinker with after shoulder operation while recuperating so need to source some glue arrange a cover for electrics and seating for the tub on top.
in use it taps down the bead blasted surface removing 70-80% of scratches but being careful not to run it too long as can cause blurring and/or removal of surface detail. On more complicated castings I can spend up to 1 1/2 hrs manually burnishing a single part but this machine will perform 80% of the job on up to 20 pieces in 15 min
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