# Wax casting



## Burl (Jan 2, 2008)

As many of you know, a couple years ago, I started making couplers in brass. The process was to design it in Sketchup, have one (a pattern) made by Shapeways in brass, and send that to a foundry. There, a rubber mold was made, which was used to generate wax copies for the investment casting process.

Recently, I started clandestinely researching wax casting on my own. I figured with the experience I had in RTV mold making & resin casting, I should be able to make the jump to wax casting.

I experimented by melting jewelry wax in a crock pot, and injecting it with a syringe. It almost worked, but I couldn't get consistent results. The more I experimented, the more I saw that heat & pressure had to be finely controlled. That led me to buying a wax injection machine:










I decided to try it out on a coupler/draft gear pattern that was more prototypical, so I designed these parts & had them printed in FUD (Frosted Ultra Detail):










I found the wax injection process to be a new learning curve. Unlike resin, wax has to be injected under pressure. The tin-cure RTV (MoldMax series) I normally use, was too soft. Platinum-cure RTV offered a wider range of durometer ratings, and after some experimentation, I settled on Smooth-sil 950. 

Learning to cut the molds was also a new experience to me. In wax casting, all molds are glove molds. That means the pattern is mounted on a sprue, and completely enveloped in RTV. After the RTV sets, the pattern is carefully cut out, making a two part mold (sometimes more than two parts). I quickly realized this was an art. I watched video after video on YouTube on cutting rubber jewelry molds, and butchered a couple of my own, before I got the hang of it.

Anyway, here are the wax patterns I was able to make:










These will go off to the foundry next week, and I'll find out in a couple weeks if he can cast them or not.

In case you're wondering why I'm doing this, this puts the burden of inventory control on me. Slight revisions are easier for me to keep up with than the foundry. There is also an up-front cost to having them make the rubber molds (starts at $50 for the smallest molds), so I'm hoping this will let me lower my end costs.


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## Tomahawk & Western RR (Sep 22, 2015)

but burl, how much does that sci-fi lookin contaption ya got there cost??


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## Burl (Jan 2, 2008)

Costs about as much as I was paying for one run of 100+ parts from the foundry.


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## SD90WLMT (Feb 16, 2010)

Guys... This is purely Our hobby.. Costs! Is that an issue when compared to the pleasure derived from all this sci-fi fun? Yet.. Where will it lead to in the future!
Burls work is flat out awesome. I've followed his efforts for years, along with Brians amazing work... I'm just hoping to get back to hobby work on my model building this year and get a little closer to Burls detailed efforts here!
Press on.. We know not where this will lead. Spock .. Out!

Good to see your consistent results now Burl! Press on Buddy!
SD


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## MJSavage (Dec 27, 2007)

Those turned out great Burl!


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## ewarhol (Mar 3, 2014)

Dang Burl. How cool! In just getting a grip on 3D designing, but still have lots to learn. Keep it up our hobby needs people like you. You gonna offer your parts in 1:29 and 1:32? Others


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## CliffyJ (Apr 29, 2009)

I'm jealous as always, Burl, haha! 

Seriously, it's really neat to see your progression on making such fine parts. Looking forward to seeing your castings.


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## Burl (Jan 2, 2008)

Eric: I hadn’t thought about it, but I suppose I could. I’ll have to wait & see how these turn out before I get serious about it. I would probably only do 1:32. I don’t know enough about the other scales (most of which seem to be narrow gauge) to know if these would be appropriate.


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## fockewulf37 (Mar 26, 2012)

Why are you not making 2 piece molds instead of having to cut them out?

ty


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## Burl (Jan 2, 2008)

Two part molds are a lot more work, and they are unnecessary with this process.

Watch this video, and maybe it will make sense:


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## fockewulf37 (Mar 26, 2012)

I was not complaining. I just think 2 part molds make much cleaner parts when casting alot of parts. I do alot of casting and just have not been happy with the results cut apart molds. 

Your doing great work and by no means am I knocking anything here..

ty


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## Burl (Jan 2, 2008)

I didn't think you were, and I apologize if something I said implied that.

In making the transition to wax, I have discovered the harder mold rubbers work better with glove molds. And if they're cut correctly, the cut itself becomes the registration mark. Wax also leaves surprisingly little flash (compared to resin).

Tell me more about your process. Myself, I usually get better results by cutting a mold, than making in in multiple pours.


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## Scott (Jan 29, 2008)

Mate. I hear you. One of my projects was to cast in wax masters for moulding a door latch assembly for the Rn wagon. As an effort to speed the build and keep costs down, the wax casting was good. However I wasn't satisfied with the hand made masters and the glove mould. The experience was worth more than money, and will see improved masters in future.


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## Burl (Jan 2, 2008)

Scott: were you making your own waxes & shipping them out? Did you run into any problems with packaging, or shipping conditions?


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## Bryan14 (Oct 12, 2012)

What foundry do you use?


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## Scott (Jan 29, 2008)

I was originally looking at home casting in white metal. Due to limited funds I was exploring cheaper options of producing items quickly and at a much reduced cost. Figuring inhouse production would be both time and cost effective. John Dersch offers casting at good rates with high quality production in Sydney so I went with him.

I actually considered sending wax masters, encased either in a rtv glove mold or investment cast to protect the integrity of the wax item to a caster in Sydney. With the Australian climate and the unsurety of how our postal service treats items I couldn't risk it if I posted to the other side of the country. The thought of losing items (it's happened) via post or damage was a fiscal deterrent, so I ended up sending a master over and he did all the production at a reasonable cost with superfast turnaround.

I have been researching the possibility of home casting more, a local guy does his own whitemetal items - so looking to pick his brain and see how he does it.


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## fockewulf37 (Mar 26, 2012)

I have a question. Why are you not casting the parts in Resin. Is it that it won't hold up over time? The parts look substantial enough. 

Thanks Ty


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## Burl (Jan 2, 2008)

If I can use resin, I do. But couplers have a lot of stress on them, and resin can't handle it.


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## Tomahawk & Western RR (Sep 22, 2015)

burl, but wont the wax melt?


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## Burl (Jan 2, 2008)

The wax isn't the final product. The wax is used to make an investment (plaster) mold, which is then cast with brass.


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## Ironton (Jan 2, 2008)

This used to be called "the lost wax process". The wax is made as close to the finished product as possible and then imbeded in mold material with extra material added to allow the final product material to be poured in. Then the mold is heated to melt the wax which is poured out. Next the material you want to use is melted and poured into the mold. When cooled the mold is broken up (yes, a one time use mold) and the final product is available for finishing.
The upside is a very high quality final casting. The down side is you do two molds, one for the wax master and again for the final product. This is done for each final product.
Hope this helps you understand Nate.


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## David Leech (Dec 9, 2008)

Another issue is a little shrinkage each step, so one normally makes the original a little larger than the finished part.
All the best,
David Leech, Delta, Canada


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## Burl (Jan 2, 2008)

Got my stuff back from the foundry today. Of course, I had to stop everything I was doing to put one together:


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## Dave Meashey (Jan 2, 2008)

Burl;

Way back in 1978, I heard the regular operations folks for N&W refer to those draft gear boxes as a "bell mouth."

Regards,
David Meashey


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## Burl (Jan 2, 2008)

Any idea why?


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## Dave Meashey (Jan 2, 2008)

Some of them were more flared at the opening. Those were usually used on long cars such as TOFC and auto racks. But I noticed the term tended to get applied to all of those large draft gear housings.

That is my best guess,
David Meashey


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