LFMC11 - Plaster Dip

LFMC 11 - Plaster Dip

Perfecting the Plaque...

I took this shot in early to mid October (2003) after the wife took me to the Mall er' I mean "Land-Fill" in search of treasure...

I was stunned to read on http://www.backyardmetalcasting.com/ 's forum about a tank that let loose and resulted in some very serious injuries.

In contrast to the usual jawing about beer-swilling good-times and running on the edge... this picture is kind of eerie.

Tanks are pressurized vessels and are probably best left alone, or handled with an added measure of caution.

As I was all out of stock, I had to get some scrap ready for this session of casting. On the left is your basic Briggs & Stratton 3.5 HP Lawnmower motor, which really didn't have has much metal as I thought it might. The Outboard is a 1950's Viking that was OEM'd by the Sears company in the days that everything came from a catalogue.

The Viking 2 cylinder 2-stroke was removed, leaving a Vintage drive assembly that will be "Electrified" in the future. The castings were so impressive that I was in awe at the fact they were made 50 years ago. Stripping both engines had a calming effect as I liberated the metal for a higher purpose.

So, with a source of Aluminum, stripped down and busted-up with the wood splitter, I'm ready to rip into the next phase of casting.

The idea is to try and approach a repeatable consistent finish, and stream-line the production process. My reference for surface finish has been Dave Kush's Plaster Dip Process.

Since I'm interested specifically in Plaque Manufacture, there has been some modification, as a straight dip doesn't quite work.

The plaster of paris is mixed to the consistency of sour cream and laid into the surface of the plaque. The mixture is squeegee'd over the surface a few times to ensure that as much material is worked into the smallest openings.

Air Bubbles appear to be a non issue at this point, and the items are left for a week to dry. I doubt that a week is needed, but the last chance I had to work on this was the week prior.

Of the 4 (four) plaques, this had an interesting flaw (pictured on the left) where a small hole in the bottom of the "g" in Lodge sprung a leak that filled an air pocket between the surface of the Plaster and the sand. The point of the plaster is to allow the foam mold to be positioned with the lettering faced down, to get maximum effect of the metal filling the void left by the foam.

The image on the right is proof that some progress is being made, as the surface is the smoothest that I've achieved to date.

There is a minor amount of distortion, but the challenge in this image is more on the milling of the foam than how it poured out.

The match stick offers a point of scale and helps illustrate the quality of the surface. Of the 4 plaques this is the only one that had all 4 digits of the year intact, the other three had minor variations in the "filling in" of the loop in the 9 and/or 6.

The choice is to thin the mix even more or try using a tooth-pick to release trapped air pockets in the tighter spots. My inclination is to try and avoid too much fiddling and fine detail touchup as the plaster is laid in, so thinner will be the next step

Here are the results from the NOVA grill emblem, again a huge step forward, but still not good enough to consider a success, the 4 flaws are the loop in the "9", the top inner vertex of the "V", center of the "A" and a line cut through the second "S" in the SS logo.

The last flaw was me running the wrong Gcode after the foam was done... Now that was due to talking with a beer and not paying attention.

In closing, if you're into "Hobby Casting", invest in yourself and follow a few forums that have a good cross section of casters to learn from, and watch for posting that could save your skin or even your life.

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