The Home Machinist!

After working toward this for the last few years I have had success!!!
Attached are pictures of the first two castings for my Pacific Coast Shay 1.6"/foot I have under construction. These are lost wax castings of silicon bronze. I made the wax molds from acrylic as it is easy to machine and repair; wax was then injected into the mold by a home made air pressure wax injector. The burn out was done in a converted kiln which my dad acquired from somewhere. My vacuum chamber is a old propane tank which I cut the top off of ( after purging it completely)and welded a flange to the top edge to place a seal so that the plate that holds the flask during casting will seal to the tank. All of the holes were cast in and only needed slight clean up before tapping. I picked probably two of the most difficult parts to mold figuring if I can do these the rest will not be too bad (famous last words). I did the casting on new Years day and am still so excited I can't stand it. Just had to show them off to everyone.

Rick,
Absolutely beautiful work! I can certainly understand why you are so pleased. I've worked with commercial investment castings in the past, none of which would have been any better than those you've shown. You've obviously done your homework.

How do you feel about talking about some of your processes? I'd be interested in knowing if you used a CNC for the molds, or did them the hard way. Having mentioned acrylic, I got the impression they were machined from stock. I've machined a fair amount of acrylic, but have never attempted a repair. Would you mind sharing how you do that? How are you melting your bronze?

Please tell us as much as you'd like to share. It's not every day that one finds such professional results from home shops.

Harold

Thanks for the compliments Harold!!

I would be happy to share everything I have learned and the processes I have used.
I used a combination of CNC and manual machining for the molds (maybe I can post some pictures of the molds and my little CNC machine along with the wax injector etc. in a day or so) What I have in my home shop is a old stepper gantry type machine that we used at work to do some experimenting with on the machining of composites before we got our first VMC at work. The machine was made by Techno-isel (spelling) and originally had a Porter Cable router attached to it for a spindle. I have upgraded its drives / screws and controls to use Flashcut CNC. I also fitted a Sherline spindle, modified to run about 8000 rpm, and use their end mill holders so that a tool change can be programmed in and is easy to do although manual. I do my design in Keycreator (formally Cadkey) I have used this software at work since the old DOS days of the early 90’s and everything is done in solids. Keycreator has a cam package built into it that works directly on solids making G code generation a snap.
I machine the molds from acrylic, mainly 1” thick sheet that is solvent bonded together to make thicker blocks, as far as repair I am just talking about fixing by gluing or filling with epoxy. I use acrylic because my “light duty” machine can handle it without much problem and it is one of the less expensive rigid plastics, I do have in my collection a couple of "practice" molds.
I am doing my melt in a furnace I bought back in the mid 70’s, it was made by (and I am not sure of the name anymore) Pyramid products it takes a #4 crucible. I run it off of propane (tapped into the 500 gal tank beside the house).
The stack saddle was from the second attempt (didn’t get the investment into the flask fast enough on the first attempt and it thickened up), the stack itself was also a second attempt. The first attempt I did not have any support built into the bottom of the flash for the investment, so when I pulled a vacuum just before the pour the investment was sucked out of the bottom of the flask. So I have learned a little bit every time and that is what makes it fun.

Rick

Rick,
That is some great looking stuff. I would like to add my voice to the chorus that will beg for more information on your processes.

Best regards,
Greg B.

Rick,

Nice castings, congrats on your results!

I find doing my own foundry work to be a very satisfying endevor. Opening a flask after pouring is better than opening Christmas presents, imho! I have been working on castings for a 70 ton Willamette, and an 80 ton Climax using the lost wax process, so understand what you are dealing with.

Keep posting the images!

Doug E.

Excellent idea! I can't imagine anyone net benefiting from your efforts. I'm particularly interested in the injector you mentioned.

Thanks for your comments on the repair of acrylic. Makes sense. I've made a few patterns in my day-----and have used almost anything that works. I've used Bondo for filet work----looks funny on the pattern, but doesn't transfer to the casting. We have to be somewhat creative unless we have an endless supply of money. I don't have.



Way cool! I recall seeing them displayed at a show some time ago. From all appearances, you're getting some nice brass out of the furnace. Are you using recycled stuff, or buying new material? Do you de-gas? Using a pyrometer?



Yep-----and there's not much chance of avoiding the learning curve. Looks like you've shortened yours about as short as one might reasonably expect, though.

I'm quite impressed with your vacuum setup.

I trust you're using investment similar to that used in the jewelry industry?

Be certain to keep all of us informed of your progress, and share more pics with us.

Harold

Here are a few pictures of the molds and the wax injector.

Harold,

I do use jewelers type investment and used "new" metal. I did not degas the metal nor use a pyrometer. Just used a little borax flux.

A few more pictures

I will be glad to answer any questions or explain in more detail about anything anyone has interest in

Rick

Rick,
Thanks, once again, for posting such informative pics and comments. Your dedication to your project is quite inspirational.

Does it take long for the wax to cool in the molds? Looks to me like it would be slow cooling, but would avoid cold flows as a benefit. Have you had any problems in that regard?

It was very interesting seeing the mill, and helps me understand your logic in machining plastic. I was thinking of the difficulty of forming the radius on the stack saddle mold------a daunting task by any other means. In all probability, you'd have had to make the mold in multiple pieces had you not had the CNC. Very nice setup.

Regards the injector--------looks like a person could use an old pressure cooker to build one. What are your thoughts on that idea?

Can you tell me more about the heater you chose? Are you using a thermostat?

When burning out, are you trying to recover any of the wax, or are you burning it off?

Harold

Harold asked



I typically leave the wax in the mold for about 10-15 minutes this is mainly due to the runners taking a bit to cool. I haven’t had any cold flow problems. I have had best results with a room temperature mold when I shoot the wax. The stack mold due to the thin section and length took some experimenting to get right. I tried different waxes at different temperatures. The best wax I have found so far is Castaldo Gold injection wax. I get it from Lacy West Jewelers Tools and Supplies (they have a web site) I inject the wax at about 15 psi until the mold fills then up the pressure to about 70 psi and hold until I see the wax start to pull away from the sides of the mold and then just let it sit there with pressure on it for a few more minutes. This is one great thing about clear molds is that you can see what is happing inside the cavity. I wish I had this feature on some of the injection molds I have build over the years. I tried injecting at 70 psi right off but what happens is that the wax inside the pressure pot does not flow fast enough and the air will end up blowing thru wax and into and into the mold.





A pressure cooker might be a possibility. What I found out is that temperature control is very important. I am using a band type heater at around 1200 watts. I first tried the cheapest way of control and used a light dimmer, this worked ok but I could not maintain a temperature close enough plus I had trouble with over heating the wax near the sides. I then scrounged up a temperature controller and thermocouple. This set up works great. I have the thermocouple reading the side of the pot not the wax. Since wax is a pretty good insulator if you stick the thermocouple in the wax you will overheat the wax right next to the walls of the pot. The only downfall to this is that it takes a few hours to bring a pot of wax up to temp. I did install two risers in the bottom of the pot to help transfer heat to the wax; this made a significant improvement on wax temperature consistency. The injector is made out of a piece of alum pipe 6” ID with ¼ wall; I welded a bottom in to it and turned a top out of plate.




At this point in time I have not tried to recover any wax. I am burning out in a kiln that I added a process temp controller to. With the controller I have the soak and ramp times are programmed in so it is just a matter of turning it on a waiting for the burn out to complete. I have the kiln mounted on a furniture dolly so I Wait until I am sure there will not be any rain and roll the kiln outside and start it up. I have become comfortable enough in the controller and kiln set up that I will start it up in the early evening so I can pour the next day around lunch time.

I am impressed with your results. kudos on the development. I had not thought of using a hard mold for wax.
Why so much pressure after the wax is put in? Does it tend to ball or shrink badly? Apparently you are using a topped pot and pressuring with air to inject? Not a rod pump or some such injector?
I have only manual machines for my work. But I can copy almost anything as a master intead of all the teadious machining of the cavity.
De-airing my waxes have not been a problem, as the natural heating of the bubbles make them lighter in the wax and they float out. I had thought of an acrylic top to a metal pot, and using the shop vac to raise and lower the pot pressure several times on the liquid wax for de-airing, but this did not seem necessary yet.
I am using simple rtv type molds that are blocked and cut, the rubber melted inone of those fryer type home counter crockpot lookin things, but a croky-pot wont get the output for temperature.
I use the american brown casting wax, and a simple dipper to flow it in. So far the wax melter is just a light bulb under a coffee can. Too much room for operator error dufing football games, so it will get to be a crock pot with a temp control too, probably a water heater type to get all the functions together.
So far limited attempts have been good. but I need to build more equipment. I might use the lp tank idea for the wax melter, that would allow a simple plug to accept a water heater control, all very cheep.
I am experimenting with Ceramic slip and dipping it in aerated sand for a shell that I can burnout and put in a drysand bucket for backup. This seems to be a good way to produce a lot of complete molds cheeply with small material loss, and cost. I plan to roast off the wax and collect what I can in a catch tray that drains into a plastic bucket below the oven. I have an electric oven, that is being didsassembled for parts to build a baking oven forpowder coating. It will serve as a melt out oven as well, but I dont know if it will attain enough temperature to bake all the wax. Seems about 700 will be tops. Oven construction will be double wall steel with a two inch ciramic fiber core. 14 guage spangle galvanized, brake formed lips to sheet-screw together for the box. Legged up to about 3 foot for easy access.
One warning about waxes, they can burn like diesel fuel, so take normal prcautions on fire safty. I would enjoy hearing about your reasoning in your development of your system. thanks for sharing.

Steamin10

The reason for the pressure is to help prevent sinks and shrinkage, it seems to help. More pressure and hold time is a cure for sink marks and excessive shrink in plastic injection molding and that is where my experiece and direction comes from. Yes I am using a topped pot with air pressure for injection.
I do not de-air my wax, only the investment.

Rick

Rick,

Incredible work. You are a credit to the hobby and to lost wax foundry work. I like your idea for the clear wax injection molds so one can see what is going on inside. I am sure that has been one of your best teachers in regards to wax pressure.

Speaking of wax injection pressure, You mention starting with 15 psi before uppping to 70 psi. To achieve this pressure change, do you just give the regulator a turn or two to jack the pressure up at the correct moment of wax injection? I see what appears to be a pressure regulator on the back side of your wax injection pot.

I believe I have had too high a pressure in the past with some wax injection events but could not see inside the mold. I may try to make a composite mold the next time with a acrylic base plate covering the mold cavity to see what is happening.

Have you ever had moisture problems with the compressed air source? I have read where the air should be completely dry if being used for air pressure wax injection. as even small amounts of moisture can give trouble.

How long do you heat the wax before injection?

Keep up the impressive work.

Rwilliams wrote



Yes there is a regulator and once the mold fills I just crank it up, the smaller saddle mold fills at 15 psi with no need to turn the pressure up. The stack has a fairly thin section and need the extra pressure to prevent sink and excessive shrink.



I haven’t seen any issues do to moisture in the air. I do not keep the pot closed and pressurized except when I am ready to inject. I use as much a visual reference as temperature to determine when the wax is ready in inject. If the wax gets to hot then I have problems (sticking in the mold and sink issues). So I run the wax a bare minimum temperature just below the published injection temp of 175 degress.





It takes my pot a few hours to bring the wax up to temp. I have it set up to heat up slowly to prevent overheating and degrading any of the wax

Rick

I have a small comercial pressure wax injector that I have been using for injecting molds I have made from steel, aluminum, Delrin, and epoxy resins. I use 15lbs pressure and the long hold but I would be afraid to put 70 psi on the pot. That is a lot of pressure with 200 Deg. + hot wax. As long as you provide a long spru for extra wax there are no problems with voids. Temperature control is very important as is having a pot that holds a lot of wax. The one complaint I have with my pot is when you are making a lot of parts you have to stop to add more wax and that means a wait time until it comes back up to temp.

John Buckwalter