Making of the PzIII/Iv Cupola

[Brian Leach]

Hello everyone!

I thought i would share with you the trials and tribulations of casting the PzIII/IV cupola.

I going to cast this in magnesium brass. This is strong, easily machinable, and can be soldered/braised.

It has a nice silvery color.

These are the first parts I am going to make



The process is to make a silicone mould, than make wax castings (patterns) from that , than cast plaster (or investment) around that. The wax pattern is than melted/burned out of the plaster after which metal is poured into the voids creating the part you want. (And there are more steps in the process in order to get therre!)

So, first i made a model of the cupola


I than printed out the parts on my 3-D printer (which is very cool!)








These parts are than cast in silicone





Here I would like to assure you that the casting part numbers are very nicely cast in the relevant parts
(pictures to follow)















The next step is to make the wax patterns.

Unfortunately , because of the storm last week here in the NW USA, I have not yet received this so we will need to wait.

So until next time,

Have a good day!

[Steve Lewington]

Hi Brian

What a fantastic post thank you so looking forward to the next one.

Kind Regards

Steve.

[Jim Fowler]

WOW! The work looks excellent, and very impressive. And, I am envious of your talent!

I look forward to seeing more, and an opportunity to buy them!


Best Wishes,

[Brian Leach]

Thanks everyone for the nice comments.

I wasn't very happy with the first set of silicone moulds that I made so i made a new set.



These are a bit easier to inject with wax, which I tested out today

Getting the temperature right is tricky. The wax wants to flow at 69-71C, but once it begins flowing it cools, so you need to bump up the temp or pressure. Bumping up the pressure causes the wax to get between the mould halves, bumping up the temp takes time, a lot of time.

So here are some of the waxies I made today











Today I took the parts for the vacuum chamber over to the welders.



The part sticking out of the top is the flask which holds the investment into which the molten metal is poured. It is not welded to the vacuum chamber. It is slipped into the chamber filled with the investment. A vacuum is applied to the chamber which helps the metal to fill the mould voids.

I pick the chamber up tomorrow
I will also make the waxies I need for this weeks pour.

I hope this is not going too slow.

But, until tomorrow, "keep your stick on the ice"

[Jim Fowler]

Brian,

It's exciting to see this work - I very much enjoy these posts! And, I know I can't thank you enough for making this effort and sharing it and the parts with all of us!

(I actually brought my laptop to the hospital this time to follow this....they have WiFi now!)

Best Wishes,

[Brian Leach]

Hi Everyone!

I made a little progress this week. I made the first wax trees today. These will become the voids where the brass is poured into the flasks, creating the parts we want...











I have two wax trees ready to invest. Once that is done the investment will sit for a couple of hours and harden. I will then invert it over a steamer to melt out as much wax as I can (recovering it for later use). Once that is done I will begin the twelve hour wax burn-out process that removes the last of the wax from the form. Then will we cast the brass, fianlly. I am only doing two flasks now to be sure it will work as I want. If all is well I will begin producing cupolas next week.

Here are a couple of the vacuum chamber I had made last week. The flask sitting on top in the first picture will have the investment form from which the brass castings are made. A vacuum is put on the flast to draw the gasses out of the investment while pouring the brass, producing a more detailed part.

Does anyone know why the wax tree is on the scale?





Have a good day!

[Jim Fowler]

This is very exciting! Can't wait for the next post!

I assume you weigh the wax tree to determine the total amount of wax use to judge the recovery of it later - to ensure the core is empty for the pour?

[Brian Leach]

Jim,

Thanks!

Good guess :

Actually using the weight of the wax I can calculate the volume of wax used. I than subtract that from the volume of the flask which gives me the volume of investment I need to mix up reducing waste.

We are planning the pour for Sunday morning so tomorrow night we will be busy for a while. Pictures will follow.

Have a good day!

[simon_manning]

interesting and great to follow on this thread, enjoying it a lot, well done brian, regards simon manning.

[Paul. Fowler-Smith]

wow, so near! Its much more complicated/interesting than I had imagined, thanks for sharing the process.

Paul

[Brian Leach]

Hi

I had expected to post pictures on todays castings, but I made a small (but significant) mistake which caused me to loose my waxes, and I broke my camera in a seperate incident.

Monday we will redo the waxes and castings, pictures to follow.

Sorry for the wait

[Jim Fowler]

Brian,

Its a process, mistakes are how folks learn the process. Just take your time and be careful.

Best Wishes.

[Robert E Morey]

Brian,
Great play by play on the casting process. You have made a lot of progress, and looking forward to seeing the first cast parts. You are keeping us in stitches waiting to see the results!
Best regards,
Bob

[Brian Leach]

Hello everyone!

Yesterday I finally got a test pour in. It went well though not as planned (does it ever?).

My furnace had trouble coming up to the temp needed for brass, so I poured aluminum instead.

I had had a long day of it with the problems with the furnace, so I didn't bother to degass or flux the aluminum. This led to impurities getting into the casting, and having a porious surface. I also poured the aluminum too hot which contributed to the porosity. That being said, I think the casting went well. Now I need to "tune-up" my patterns and do a large pour and begin making the cupolas.


This is the setup. The paint pots are used as a large vacuum resivoir for the vacuum chamber




This is the flask ready for investment and vacuum degassing


Bottom of flask with investment


Top of same



Flask in oven. This goes through a series of temperatures up to 1150F. It took about 16 hours to "cook". in this picture the flask is upside down to let the wax run out as it melts. I recover that in water under the flast. After two hours of this I removed the pan, inverted the flask and started some serious burn out starting at 750F...


The furnace


Crucible with melted aluminum. Note: this was too hot (noted by color)


Flask after pour


Flask after being immersed in cold water. The investment instantly shatters allowing easy removal from the flask


And here are the castings. As noted earlier, they are not perfect. This was kind of a "proof of comcept" run






I hope you enjoyed. If you have questions I'll try and to answer them

Have a good day!

[Brian Leach]

Hello everyone!

It has been a couple of weeks since I last posted.

If you remember, I had trouble with my foundry melting brass. I decided that I needed a new burner. The burner I had was not well designed and did not burn completely or well hence the dramatic flames out of the top. Trying to save time I purchased a new burner. I had considered a forced air burner, but found a naturally asperated burner and decided to use that, keeping the system a little simpler. Well, I have not yet received my burner (nor have I received word other than payment hase been accepted, is this an oops on my part? ). I had consdered making a burner of my own, but I wanted to save time. I could have had it made by now. I may do that yet. Mine will be forced air, propane (LP).

Waiting, I decided to build a new foundry. I have not constructed it yet (waiting for the burner) but
I may start Tuesday if I do not hear from the burner guy. I am concerned about getting the burner hole the correct size.

The foundry will be a composit of fire brick and mortor with a sheet metal skin. The design was, done on SolidWorks (over kill). I cut the bricks on a table saw. It was easily done and as you can see, very nice results. This foundry has much thicker walls than most I have seen in the internet, though the few pros I have conversed with have foundrys more like mine (I copied). The other foundrys I have used lost an incredable amount of energy through their walls and were extremely hot, untouchable after they began to heat up. Brass having a higher melting point needs more energy to melt. The extra insulation saves energy, of course, making the melting easier and faster. The section in the pictures is 9 inches high, a diameter of 16 inches, with a 7 inch central diameter. The topp and bottom will add about 6 inches to the overall hight.

So, here are a few pictures for you. Regardless, this week I will be building the foundry so we can get this project going.
This is a bit frustrating for me too at times I am hoping to post a video comparing the burners (if I ever get tthe new one)













As I said earlier, the design dimensions were to be 16" OD, 7" ID. After cutting the brick the ID and OD were within 1/8" of design. I was amazed. Done very well, but purely by accident. I wish fabracating always worked out so well!
Have a nice day!