Bronze Hands Lost Wax Project

He's going to get shrink bigtime. We all do it in the beginning. Fat chunky over weight castings. Thinness is a sign of quality.

 

Yeah true, we all we did it haha. Honestly it might not be an issue if the void stays in the middle. Only an issue if it pulls to one wall and messes up the surface.

Here's what you want to do. I tried to show the void that forms. It grows to a certain length and you can either try keep the entire length of the void inside the sprue if it's long enough or if the sprue is too short it will pull into the arm and not be solid, maybe even pulling a void between fingers or touching the surface in one location. Metal contracts a lot when going from liquid to solid and hollow casting reduces this issue a lot, almost eliminating it completely and is also cheaper.



Here is an example of not having a tall enough sprue. You can see the hole in the top photo extending all the way through the sprue into the body of the final piece. This needed tig welding to repair, but without tig to repair it it would have been a scrap piece.

 

Hey guys I'm back after a long weekend.
A few setbacks but i'm still determined and hopeful to get this sucker done!
My rubber mold ended up being too hard to get off and my plaster model broke when i was trying to take it off.
Now that my wax is finally in, I'm going to take your recommendation zap and slush cast the wax model straight in the algenate.
I started to attempt that process yesterday. i had my wax melted and ready to rock, but i accidentally used warm water for my algenate mix and it started setting prematurely before we could get his hands in the mix.
I bought more algenate this morning and if he's available i want to try to get the wax model cast today.

Thanks for the tips zap on casting. can you explain how you'd do a hollow cast? in my mind that feels like it'd be more complicated but then again i don't know how the process works.

 

It becomes hollow only because you build up layers inside the silicone or alginate in wax instead of pouring it solid. Watch my chunk jewel tree modeling video. You'll get the idea.

 

botophucketed..... There is a recent thread over there I'd like to see and EVERY photo is blurred, yet the guy keeps posting them? Wtf?

 

ok i can envision what you're saying about doing it hollow by stopping short in the slush casting process once you have a thick enough layer. any tips on how thick to make the wax shell? and what would spruing look like with a hollow cast?

 

DavidF... have you ever tried to use ultravest without vacuuming it after mixing?

 

Wax shell should be at least 1/4" thick for your first cast. You can do thinner but it takes practice. 1/4 will cast well for you.

Spruing should be a tripod of square sprues over the opening connected to a large pouring cone. The sprues should be at least 30% thicker than the walls of the casting.

You can use it without vacuuming, vibration helps to remove bubbles. If you need to chase them off in metal you'll need to sand blast the arm to even out the texture after you cut them off or it won't look like one uniform surface.

 

Thanks guys! I couldn’t do this without your help!
Wax casting is happening tomorrow afternoon...

 

Curious, what’s the advantage of square sprues
Zap?

 

None.. they are easier to make..

 

Square sprues are used preferentially for bronze because it causes less turbulence/spiraling of metal during a pour than using a circular sprue. Less aeration and less shell damage. This info from a bronze foundry company I visited. Check photos of professional bronze castings they are square for this reason. Could also be bullshit advice.

 

While others in the business say the square corners and edges cause turbulence and disrupt the flow. It's all wank at the end of the day.
What IS fact, sharp edges are prone to blow out, weakness of the shell and difficulty getting adequate coverage on those edges. While I make square sprues, I also take a knife
and whack off the corner lengthwise. It makes less problems when shelling that first couple of layers.

 

I’m not dead. Still working on it guys! Quick question. Will molten silicon bronze stick to solid silicon bronze? I’m wondering if I can cast the hands separately and then join them together with a bronze bridge after they’re cast?

 

Uh....... no.

 

Could you not cast them independently then join them together via TIG, pins, or other method?

 

I’ve decided to mount them independently to a nice wooden base with pins. I think one of the two wax separate hand casts I did today is useable. The second one I had the wax too hot so the slush casting has some cracks and layers. I’ll recast it tomorrow. I’m finding slush casting isn’t working as well as I’d hoped so I’m planning on getting the wax temp as low as I can and solid casting in one go. The decent wax cast I did today was pretty much done that way. Then I’ll core out the wrist/palm to reduce shrinkage during casting.
the good news is that her birthday is in February so if I miss the Christmas deadline I have a more reasonable timeline to work with.
I got a high temp digitally programmable hot air gun that can reach the curing temperature for the ultracast block mold.
and I’ve got my forges coated with a refractory reflective ceramic coating. I also got a steel grate to build my burn out kiln with, and my first welding machine. It’s a trip learning to weld.
Needless to say I’ve been a busy bee but I’m plugging along and getting closer!
Thanks for all the help so far guys.
I’ll keep you posted!

 

Here is some tips to help you. This stuff is written here, but you are kinda short on time. Wax casting never works the first time or even 2 or 3 times. There is something about silicone when casting wax in it. Some pointers. Get your wax HOT... And I mean H O T! Practically SMOKING hot! Shut the heat off. Pour in your mold, sloosh for 10seconds and dump back in the pot. Wait a minute and do it again. Repeat. See what happens is you need your wax pot to be cooling between layers. This will keep you from washing off the previous layer, but hot enough to bond. After you build up a 1/4"-5/16" let it set up for an hour or cool in a bucket of ice water for 5-10mins. Pull your wax model. IF it sucks, melt it and do it again. We haven't identified what it is, but with my silicone, this NEVER works the first time or two. Something else that will help you is preheat your silicone mold with a hair dryer. Don't burn it, but get it hot. Silicone will tolerate molten lead so you can get it pretty hot before it fails. If you've seen the vegoil guy on YT, he throws me a thank you for sharing this procedure with him. He was having the same issues you are. If you get too cold, the layers will not stick to each other. I tell people all the time around here, wax is a mega pain in the ass and you literally have to make peace with it. Once you do, you'll love working with it. But it does take patience, practice and TIME which you do not have much of.

What I didn't understand earlier was the off the wall question about pouring molten bronze on solidified bronze and getting it to stick? You do know you stick your wax hands together at the wax stage and then shell/invest. Before investment, be sure all wax work is exactly as you want it. Parts built, stuff stuck together. It is SOOO much easier to do this in the wax phase and not once it is in metal. If you don't, you'll be trying to learn to tig weld at midnight.