# Casting your own ceramic parts



## samstu (Sep 21, 2019)

Hi All:  I've been lurking here for a while and wanted to share a problem I encountered recently and my solution.  I purchased a Hobart welder generator for 215 bucks which included 100 ft cables, tig setup and 4 ft tall argon bottle.  Long story short, used by milking machine repairman who needed stainless steel repair capabilities.  Fellow died 15 years ago and family was going to scrap.  One of those "it ran" projects.  So it needed everything from valves unstuck, corroded connectors repaired etc.

The object of this post was broken ceramic insulators in the large resistor coil for the welder to adjust welding amps.  There were all cracked, some missing and are no longer available.  This is a characteristic issue for these welders which has ended the service of countless of these units.  These are long u shaped pieces which separate the turns of the resistor and insulate them from the supporting steel bars.

So I made a sample insulator using fusion 360 with some changes such as increasing length so less insulators are used and to decrease interior channel width to add some strength.

Once I confirmed fitment, I made a pla mold.  I chose an open one piece mold with a single bar insert for the channel.  I cast the parts using Rescor 750 (a castable ceramic) from McMaster -listed as shock proof castable ceramic.  When mixed per directions, this is curable at room temp but requires heating to 225 f for 2 hours to strengthen.  Firing to higher temps gives more strength.  Instead of demolding parts, I simply melted the mold off the parts as part of the curing since I didn't design any draft into my mold.  I used a BBQ grill and a thermometer and over 6 hours heated progressively to 500 degrees.  Melted PLA smells surprisingly like a berry pie in the oven.  I subsequently fired the parts to 1100 f in an incinerating toilet (incinolet) since I don't have a kiln.  The finished parts fit correctly and the welder has been returned to service.  These parts are good to 2700 degrees per instructions.  If I had access to a kiln and fired to 2200 degrees, the parts would have been even stronger.  

For what it's worth, the mold is posted on my thingaverse page.  

Picture 1 is broken insulators  Picture 2 is PLA mold.  Picture 3 is after melting off mold.  Picture 4 is assembled ballast resistor.


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## mikey (Sep 21, 2019)

Pretty cool! Never would have occurred to me to try that. I'm now a fan!


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## C-Bag (Sep 22, 2019)

I love it when somebody fixes an obvious manufacture fault. Good job and thanks for posting.


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## Ulma Doctor (Sep 22, 2019)

excellent save!
the world of 3d printing makes just about anything possible!

berry pie you say????
i'm totally into anything resembling pie (or cobbler for that matter) 

i'm impressed by the repair, you did well my friend.


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## jwmelvin (Sep 22, 2019)

Awesome stuff. I used the same method to cast a ribbon burner for my forge with 122x 3 mm holes in a ceramic block. Worked great.


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## Norseman C.B. (Sep 22, 2019)

I would like to see your ribbon burner and the build if possible, I am building a vertical forge as time permits
for forge welding Damascus billets seems to me that ceramic would be a much better and longer lasting 
medium than cast Mizzou refractory..............


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## plunger (Sep 22, 2019)

Do you think this would work making ceramic pistons for a pressure washer that cnnot be obtained. They would need to be highly accurate and smooth and hard. Diameter 18mm by 38mm long with an internal hole of 9mm.


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## samstu (Sep 22, 2019)

Pressure washer parts:  
What I did, I can say NO.  My parts are not hard enough due to lack of high temperature firing and use of a shock resistant compound.  Also no where near same accuracy as machined parts.  The same company sells other products with a higher density.  The product I used is produced by cotronics.  If you look at their website, they do sell machinable ceramics which could probably work for some period of time.  However, I have no experience with these products and I think new pressure washer pumps are relatively cheap.  Castable and machinable ceramics are not cheap.


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## larry4406 (Sep 23, 2019)

Very clever solution!


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## brino (Sep 23, 2019)

Great tip. 
I was unaware of those materials, so thanks for sharing this!
-brino


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