Warbird Information Exchange

Hi

Cool project!! In sand casting you use your original part as what you phrase as a buck. A two piece steel frame called a cope and drag or upper and lower halves of the box are filled one at a time with casting sand, which is hand packed with a ram compressing the sand very tightly around your part making a perfect impression or mold of your part in one side of the box. You flip it over and cut your parting lines[ were the seam would be] Cover it in talcum powder as a mold release agent, then put the top part of the box on fill it with sand and do the same hand packing as before. Now you have a two part mold, you carefully seperate the top and the bottom to reveal your original part. You now remove the original part an have a 3-d mold almost ready to pour. In the top half you cut a fill and vent hole with a small troff that lets the molten aluminum flow through and fill the cavity that will soon be your new part. You pour in the melted aluminum in one hole until it comes out the other hole let it cool then you knock all of the sand loose and there is your new part. Each part you cast you has to go through the same process and you destroy the mold to get out the new part. The sand is used over and over again so you do not have a permanent mold that makes several of the same part, that is called die casting. Sand casting requires a new mold for each part made. After youve done it a few times you realize how much back breaking work it takes to make just one raw casting then comes the machine work. So that gives you a little idea on why it costs so much to make new castings and as mentioned before as it cools the aluminum shrinks about 3% the bigger the casting the more it will shrink.

Thanks Mike

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IF YOU CAN FIND IT WE CAN FIX IT

Mike,

Thanks for the info on the sand casting technique. I kind of had a basic idea of how the casting process worked but always assumed the sand cast mold could be used over an over again...I guess not. I now see why it's so darn expensive to have these made!

If it comes down to having recastings made of the shell parts I'll probably go in with Bill and the guys working on the B-17 "Desert Rat" in Marengo, IL. I guess the remains of their turret is pretty smashed which means they'll be in need of shell pieces as well. The bigger the production run the cheaper the cost!

John

I never said is was really easy, but with a little study and work someone could have fun doing the casting.

15 years ago we were designing a long range fuel system for the Cessna 185. We had to make a new cast part for the fuel bowl. Sure it was not as big as what needs to be cast for the ball turret, but we built up all the equipment we needed, cast the parts and were able to do all of the prototype parts we needed.

Production parts were done in a house that specialized in that work, but we saved a ton of money doing the first run conforming parts ourselves.

It is quite fun stuff to do, and not THAT hard in the end. Unless you have some type of time line you are working against.

We have done several prototype parts since then, and usually having to teach someone how to do it as the last guy has moved on.

Read about it and don't pass it off as too difficult. If everyone did that, then Gary would not be where he is now.

You are right about that. Taigh has the coolest toys. Here is a picture I took of the unit.

I agree...Taigh Ramey must love going to work every day surrounded by so many "goodies". Is it true the Stockton museum also has an operational B-29 remote turret system? That would be impressive to see! These WWII gunsights and firing systems always continue to amaze me. The gunsights are like early computers the way they factored in air speed, azimuth, elevation, and distance to target so the gunner could accurately hit the target without having to lead it.

John

Yes it is true, in fact there was a post the other day with a video of that system. Taigh has been collecting this stuff since he was a kid and has made a very cool museum there in Stockton. He also has a nearly complete B-29 forward fuselage section in the museum. He is a stickler for making everything absolutely original and having all of the original equipment function. You should see his SNB-5P, it is just absolutely original truly the coolest twin Beech flying although I have a feeling his AT-11 project will the end all of original twin Beech restorations.