Friday, September 4, 2009

New Kid on the Block: Carving with Plaster of Paris

New Kid on the Block: Plaster of Paris
I've had this block of plaster of paris sitting on my work bench for a few weeks already. Haven't gotten around to working with it yet. In one of my previous posts I wrote that I accidentally broke the main fuselage of the Macross Lancer II SF-3A project that I was working on.

I use plaster of paris as my work material when carving because it is cheap and easy to form and mostly because that was what those local figurine carvers told me they were using. Other materials they told me that they were using were Styrofoam boards (glued together or as a block and wood). Plaster of Paris can also be easily mended, based from my experience.

Searching around the web and touching base with other modelers, I've found that professional modelers use modelling boards and putty when carving models. Modelling board is sturdy enough for it to be machined in a lathe or a milling machine. I think I've found a local variant here in my country, known as a polyurethane board but I'm not keen on using it because of its price. For a 2 inch, 4 ft by 3 ft board, it will cost me about $25.

Other good scratch building materials for carving I've heard about was thick cardboard, used in picture frames. There was also the rubberized tiles. Then I've also heard of people carving out putty used in automobile body work repair. Based from my experience, that putty is indeed workable and dries up very fast after mixing of the hardening catalyst. I've read that diluting the automotive putty in acetone reduces its thickness so that it can used in model kits.

I first make a block of my workpiece by not using the standard 2:1 ratio between water and plaster of paris. I usually put a little bit more plaster over water because I want my work material a little bit harder. Salt works as an accelerant in the hardening of plaster of paris, but I refrain from using that. One time while mixing up a batch, my plaster of paris hardened within 10 minutes without me putting in any salt. I could only assume that it could have been my salty sweat dropping into the mixture to have caused that. Touching the plaster with your salty hands also has this effect of accelerating the hardening process.

I also bake the plaster of paris out in the sun for a few hours to remove any excess moisture. I've found out that baking it in the oven for a few minutes at 150'C has the same effect.

When carving the plaster of paris I usually stay outside the house. The reason for this is because it really kicks up a dust storm. I made the mistake of carving in my room once, boy did I have a hell of a time cleaning up afterwards. The material data sheet of plaster of paris states that it is a safe material to work with, despite that I still use a mask. I still have to upgrade my mask though to a filter type used in automobile painting to be more safe.

Below is a shot of some the tools that I use (Mask, Caliper, metal ruler and Leather Man pocket knife with file):
New Kid on the Block: Tools for working with plaster of paris

When making the pattern to follow when carving on the block, I first print out a 1:1 image of the item that I am working on. Using the caliper against that, I can then easily transpose the measurements to the block using a cutter and metal ruler. I prefer the metal ruler because it can't get damaged by the cutter and because it can flex a little bit against the work piece.

New Kid on the Block: Carving with Plaster of Paris

When carving I use your typical wood carving set found in the hardware shop as well as an electric router and a cutter. When shaping the form to the pattern however, I prefer to use the file found in my Leatherman knife. I have a few other files that I bought but I found out that the leatherman knife has the perfect handle that my hands feel comfortable with. In the end that's what matters I guess, that you feel the most comfortable when working.

I'm not sure what sanding grade it has but most likely its a 100 in one side and a 400 in the other. I can change the grade further however with the use of sanding paper that I wrap around the file.

If everything goes according to plan and if there are no major interruptions, I might be able to whittle that rectangular block down to this.

New Kid on the Block: Carving with Plaster of Paris

This time I'm thinking of trying out some wet sanding techniques that I've read up about. The benefit of wet sanding they say is that it gives a smoother finish and won't wear down the sandpaper or file as much. After trying it out a bit I've also found out that it doesn't kick up as much dust either. You end up consuming a lot more oil though, because the water will end up rusting up your files.

I guess one other thing that should be mentioned as being needed in any scratch building project, is the "intangible" material known as determination and relentlessness. The determination to relentlessly carry this project to finish even when you end up breaking your work piece... hehehe. Of course there is also the required curiosity to try and seek out new materials for figure making and scratch building.