Casting Notebook
A Homemade Surface Plate from Plate Glass
I am wanting to make the Gingery Lathe. The problem I encountered was finding a flat surface to reference against. In Dave's book he suggested using the plate steel that was to be the ways as a test standard. The problem with my piece was that it had a slight bow to it. Nothing critical and would be pulled out when bolted to the bed, but in my opinion it would not due as a standard.
In another one of Dave's books (the second or third) he addresses the issue by suggesting the use of normal plate glass as a surface plate. He informs us that plate glass as it stands is close to being flat. And that the smaller imperfections can be fixed by lapping two plates against each other. (Although I am leaning towards three separate plates to do this job more accurately) I decided I would give it a go.
I called my local glass supplier and ordered two pieces of 1/4" x 8" x 30" plate glass, then stopped by a local automotive supply store for a couple tubes of valve grinding compound. I brought the stuff home and laid the glass out on a piece of wood that came with my tool chest to protect the top. Next I coated one piece of glass with a thin coat of grinding compound and then the fun began. (NOTE - You can click on the images for a bit of a larger view)
You could tell the plates were fairly flat, they stuck together like the dickens. As I tried to lap the pieces together, the bottom glass slid all over and the top plate would not budge. My solution if you look at the picture to the left, was to take a piece of rubber shelving material like you would find in the kitchen area at your Walmart store and lay the bottom glass on top of it. My favorite helper (Melissa) held the board still so that I could lap the plates together. I would like to tell you that it was a simple process for me to do but it was work. Even though the bottom glass stays put the plates adhere to each other and did not slide well. Dave instructs us to lap the plates together until they are uniformly frosted (about 200 strokes). Attention to the photo shows the two plates stacked together and the grey stuff between them is the grinding compound. After about 50 strokes (circular movements of the plates) I thought I would slide them apart a bit and see how progress was coming. I smeared some of the compound from the bottom glass and it looked as pristine as when I started. Tonight after going to a function, I will lap some more. Hope my helper holds out! :-)
UPDATE
My plates got knocked to the concrete floor, shattering them, before I had them finished. Needless to say I was rather discouraged. :-( But I did find a free shipping code for a $50 or more order from a company so just bought a granite surface plate.
An attempt to inject wax by hand
Someday I want to be able to cast precious metals like gold and silver as well as other metals with great detail maybe in Pewter or other white metal. A common thing to do in this process is to make a flexible mold either out of rubber or RTV. This mold is then injected with wax to create a master for use in lost wax casting. (An example of this type of mold can be seen elsewhere on this site under the RTV molds in that section of the book). You will find many jewelers that will do this. They have either created the piece themselves or have ordered the mold from somewhere. The procedure usually uses a piece of equipment specifically designed to inject wax. The costs vary depending on what the machine will do. I have seen them cost anywhere from $300 and up. Being on a feeble hobby budget, I decided to try to inject wax by hand to see if it could be done.
Like any other NET-AHOLIC, I searched to see if anyone else before me has tried it and what their success was. My search turned up the following page: www.opalcamp.com (Looks like it may be gone now)
The gist of the article was to clamp your mold in between two aluminum plates, heat the wax and use a syringe to inject it into the mold. My experiment follows:
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· · · MATERIALS
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TEST #1:
Procedure: I placed the pot on the stove with some water in it. Next I took the candle and put it in the glass and placed it in the pot of water and turned the burner on. While the wax was melting I lubricated the plunger of the syringe with some petroleum jelly and clamped my mold together with the "C" clamp. When the wax had fully melted I pulled the syringe full and injected it into the mold.
Result: The mold seemed to mostly fill with only a few places of trapped air. (These could have been caused by a cold mold.) Otherwise the wax seemed to catch a lot of detail. Next I tried to remove the wax model from the mold. Unfortunately the wax broke before I could get the piece extracted.
Conclusion: I would not have called the attempt a complete failure. I was able to inject the wax by hand and get most of the detail. Things working against me were:
- Candle wax may not be the best wax to inject with as it seems brittle on its own.
- The mold I used was originally created to cast pewter. The RTV was fairly stiff and gripped the wax model tightly. Additionally, there were vents cut into the mold that would not allow me to keep pressure on the wax until it solidified.
TEST #2:
Procedure: I decided to try it again with a different mold. Otherwise it was the same procedure as above in test 1. The mold used in this attempt was a mold I made for the Trollhalla coin. The coin is the diameter of a silver dollar and a little thicker.
Result: The mold seemed to mostly fill and capture most of the detail. The only real defects were shrink cavities. I was able to remove the model from the mold without breaking it.
Conclusion: The mold I used this time only had one riser. As a result I was still not able to maintain pressure on the wax. Without the ability to maintain pressure on the wax, it is free to shrink as it solidifies. One reason I think is because there is not enough wax in the sprue to feed the casting to prevent it. I am going on the presumption that wax cools like metal.
Final Thoughts: In order for hand injecting to work, I believe that it is important that you use a mold with only one opening to inject wax into with no external vents. The molds that I have created up to this point are all designed for gravity casting lead or pewter into and as a result have vents and risers cut into the mold. I also think that it is important to keep a steady pressure on the wax as your injecting it from the syringe. The reason is to help prevent shrink cavities. Another thing I would think useful would be to heat the syringe with the water your using to melt the wax to help slow down the cooling effect of the cold syringe. Whether or not that is possible with the plastic syringes I have is unknown and untested by me. I am pretty much set on making my own wax injector and not trying anymore hand injection, I do however have one RTV mold that has not yet been cut with sprue or vents or risers. I may try one more time just to see if it works. If I get around to it I will post it as a follow up to this article.
The Casting Notebook
The notebook contains sections of material that outline experiments or small things that I have tried to do but does not require a section elsewhere. You will find things like My attempt at hand wax injection and making a surface plate from plate glass.
Injecting wax by hand
Making a surface plate from plate glass