Pruning Trees. And how to remove investment plaster from castings.

by John

The investment plaster is is what the mold is made from when parts are cast in bronze and aluminium.

It is incredibly fine dust until mixed with water, and these need to be in precisely measured weights.

The mixture is poured into the casting cylinder in which the parts are attached to a wax or PLA “tree”. (see yesterday’s post for a photo of a tree).

After casting, much of the investment plaster is blown out of the cylinder when the still hot cylinder and its contents are plunged into cold water. The steam which forms acts like a steam cleaner.

But the parts are still covered with a tenacious layer of investment plaster. More can be scraped off with a screwdriver, wire brush, pressure hose etc. etc. but there remains a lot of plaster in the nooks and crannies, joins and holes.

And it is a fair pain to get it all out.

Yesterday’s castings looked like this after I had sawed the 34 pieces off the trees.

and after more sawing and use of a thin disk abrasive wheel…

there is still investment in the grooves and crevices.

Then most of the unwanted bronze branches were machined and sanded off…

still the investment powder clings on….
then the investment powder all disappeared!

It happened serendipitously. I placed the parts in a gemstone tumbler with sharp stainless steel shot, to take off the sharp edges. And hallelujah! The remnants of the investment powder were also removed. The curved arms in the photo are stainless steel and brass, bent around a mandrel. I have not yet decided which to use.

In future I will use the gemstone tumbler at an earlier stage, to get rid of the investment as soon as possible.

And here is another stage of the pruning of the trees…..

I wonder if holding the angle grinder in a vise, and holding the trigger with a spring clip, will void the warranty?