The Shop > Metal Stuff
Lost Foam Casting: a Crankcase in Zinc Alloy
Eugene:
Andrew,
Two reasons ...... first I never thought of it :( and second I had the PC power supply to hand anyway. Steve, at the bottom of my "thingies box" I've got a 220V dimmer switch which I can press into service if I need it. When I've done the immediate casting that I need, I have a cunning plan for the ATX unit, so again I'll be recycling the already recycled! I've got a DC motor with a 2 rpm reduction gear not unlike a windscreen wiper motor that the unit drives a treat ..... it might very well do for a fine feed on my wee Myford.
Eug
vtsteam:
Eugene you can't use an AC light dimmer on the input of a regulated computer power supply!!! Don't do it.
It can be used on an older transformer type AC or bridge rectified DC supply, like a "dumb" unregulated automotive battery charger. Or even on a transformer alone for AC output (as long as it's output is safely under say 25 volts or so.
However, The DC LED Dimmer can be used with your supply -- it is five dollars and change postpaid --or equivalent more or less in your money. It goes on the Output of your PS, not the input.
Andrew -- hot cutting wires can be run on either DC or AC as you probably have guessed -- just a resistance wire. A computer power supply is fine as long as it has enough current capability, and you do DC power adjustment on its output (not its input)
awemawson:
Steve, I don't think Eugene, and certainly I am not, suggesting that you use one of these devices on a DC power supply.
The suggestion is to use them on the mains feeding a low voltage transformer (this is how the current is controlled on many welders of a certain vintage)
vtsteam:
No I didn't think you were, Andrew, but I thought Eugene was considering it. Apologies if I misunderstood.
I've run all three for cutting wires:
A 25V transformer and dimmer on the AC side with 24V AC output to the wire
An old style auto battery charger with a router speed controller on the AC side with 12V DC output
A computer power supply with the 12V DC side feeding a DC LED light dimmer like the one I've shown.
vtsteam:
This morning with the sun coming in low through a window it was possible to highlight the difference in surface finish and detail fidelity of the second casting and the third (last) one.
On the left we can see the zinc separated from the mold walls by layers of molten polystyrene. The drywall compound was not absorptive and the plastic stayed inside the mold.
On the right the you can see that the actual texture of the foam has been recorded and transferred to the metal. Polystyrene was pulled out of the mold by absorptive plaster of Paris allowing the metal to cool against the mold sides and record the very fine detail of the foam texture. And a blob of hot glue which was used to attach the sprue to the pattern is also preserved in perfect detail on the left
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