Silver Pistol Butt Cap

[davec2]

I have a pair of rosewood stocked pistols that I started when I was a Midshipman at the Naval Academy many years ago.  I stopped working on them when I figured out that I didn't know enough to complete them the way I wanted them to turn out.  I recently figured out that if I wait much longer to get good at this, I will be dead and the pistols will remain unfinished.  At any rate, I have a silver butt cap that I wanted to copy and modify for this pair of pistols.  I didn't want to try to carve a matching pair by hand so I made the following mold of the original and pumped a few waxes.  I will modify one the way I want it, cast it in silver, and then make a second mold to duplicate it.  Here is the start:

Original:



Original cut from mold:



Getting ready to pump a wax pattern



Pumped wax:



A few spare wax patterns:



More to follow when I cast the first one.

[Paddlefoot]

Nice pieces. Lets see some pistols.

[KLMoors]

Cool stuff. How do you know where to cut the yellow material to get the original out, without damaging the pattern that is molded into the yellow material?

It looks like you cut it so as to just barely skim in behind the original part.

[Tim Crosby]

  The process just fascinates me, I look forward to seeing the next step.

     Tim C.

[Acer Saccharum]

Cool stuff. How do you know where to cut the yellow material to get the original out, without damaging the pattern that is molded into the yellow material?

It looks like you cut it so as to just barely skim in behind the original part.

Dave has a sixth sense where the part is underneath all the yellow. I use clear silicone, because I don't have that super-vision.

[davec2]

KLMoors,

I use a surgical scalpel and follow the spru into the part.  I know from a mark I make on the outside of the mold where I want the part orientation to be when I start, so I know where the mold lines will end up.  Other than that, just follow the part and pull the rubber away as you cut so you don't mark up the original.

[Acer Saccharum]

Yes, the pulling while cutting works well. A series of photos BEFORE you encapsulate in rubber helps a lot, too. I forget what and where things are. 

[docone]

Tom, you can put strips of paper, and use magic marker on the mold. You do this prior to vulcanizing.
Use the sprue to start, and pull the rubber as you cut.
Just wait untill you make a mold of a pin set hollow back ring.
Use a sharp blade, and water to lube while cutting.

[davec2]

I have made a mold (using room temperature cured silicone rubber, not a hot vulcanized rubber mold) by running some Scotch tape around the edges of the pattern and cutting to find the tape.  The only detriment is that the part will come out with a flashing that replicates the tape, but, in most circumstances, this can easily be trimmed away in the wax and the technique allows the mold to be cut without getting too close to the original pattern.  I have used this on a trigger guard where I wanted the parting line right at the edge and was lazy enough not to want to chase it that closely with the scalpel.

[Paddlefoot]

Dave, is your setup able to cast brass as well as silver? Just wondering what is really required to do this type of work. Most pictures of brass casting seem to look really industrial rather than the way this looks more like a jewelry oriented process.

[whetrock]

Dave, can you briefly explain how you inject the wax? Maybe show the tools/setup used for that step? Thanks.

[docone]

I do not prefer this type, but for one offs it will work.
http://www.riogrande.com/Product/Rio-Mini-Hand-Wax-Injector-with-Thermostat/700043?Pos=268
I have one, and I reccoment keeping a bag over it when it is at rest. Dust will clog the filter of the pump.
I get good detail though. I prefer the pink hard/flexible wax for mold release.

[whetrock]

Thanks, Docone.
So, by looking at the pump on your link, and looking at the sprue on Dave's cap, I presume that you hold the mold over the pump, just using hand pressure to keep it in place. (I presume that the mold goes back in the little cup, so that everything holds shape) and that the pump then squirts the hot wax up into the mold.  (It is not poured in, but is rather pumped in from the bottom.) Is that right?

I also noticed a small sprue-like tab on the tip of one of the extensions on the cap. Is that what I'm seeing? I assume that you have to make a small escape hole in the mold at the end of each of the extensions so as to let air out as the wax goes in.   (Is there a hole in the cup? Do you use the cup to hold the mold when injecting the wax?)

I am I on target here?

[Acer Saccharum]

Rio Grande sells all the equipment needed for investment wax casting. Gesswein does, too. Better be sitting down when you start looking at prices. That's why many people make their own stuff.

Have you checked out Paul Hamler's work? He's got an amazing array of lost wax casting equipment that he made. He and Jerry Huddleston are genius inventors and experimenters.

[davec2]

Whetrock,

The wax pump I use is much like the one shown in Docone's post except that the hot wax is sealed in the pot by a lid and the pot is kept at about 15 psi with air pressure.  For most of my smaller molds, the air trapped inside can escape via the parting line of the mold as the wax is injected.  For these larger molds held closed by the retention cylinder, there are some very fine holes I put in place at various points in the mold to let the air out ahead on the incoming wax.

Acer is correct, new equipment is fairly pricey, but I bought the wax pump I have off Craig's list for less than $100.  It looks much like some of these:

http://www.ebay.com/bhp/wax-injector

[whetrock]

Thanks, guys. Your explanations are helpful.
I also read the wikipedia page on investment casting. It provides a helpful overview.
http://en.wikipedia.org/wiki/Investment_casting
Also reviewed Hamler's work (thanks, Acer) and links he had in this thread: http://americanlongrifles.org/forum/index.php?topic=18462.0

I look forward to seeing the rest of the process!

[KLMoors]

Dave, thanks for your explanation. It still seems like black magic to me!

It is one of those things that make me very glad that there are other people that know how to do it.

[Rolf]

Beautiful work!!!Can you fill a wax mold without a pump?

best regards

Rolf

[Acer Saccharum]

You need wax under pressure to fill a mold. Not just random pressure, but CONSISTENT and CONTROLLABLE pressure. Without those two attributes, you'll be completely frustrated in trying to fill a long cavity, like a trigger guard, or small detailed parts. The pressure also pushes the air out of the mold. Rubber molds tend to trap air. Gravity feeding is not going to work with rubber molds.

You might be able to gravity feed into a plaster multi-piece mold. Plaster has to be damp, or the wax will stick to it.