Any old textbook that details sand casting of engines?

[99Panhard]

As a point of reference, these are the pattern and core box for the pistons shown above that John O made. You can see how much draft there was to get the piston out of the sand. The core boxes have a piece attached at the bottom only because the molder at the foundry preferred to make the cores in two pieces and past them together. They could have been made in one piece but I didn't think it expedient to disagree with the guy who was doing the job.

 

[johnoder]

! Many thanks for posting those Joe!!

 

[johnoder]

Comment on the pattern

 

[Shipp]

Also, if you can get a good model of it and have a friend with a 3D printer, you can print it oversize for your appropriate shrinkage and sand cast it. They make printer filament specifically for casting. Haven't tried it myself, but it's on the project list.

 

[stephen thomas]

The core boxes have a piece attached at the bottom only because the molder at the foundry preferred to make the cores in two pieces and past them together. They could have been made in one piece but I didn't think it expedient to disagree with the guy who was doing the job.

That's (flange) is so the core can't float &/or tilt.
Especially since it is only supported from one end.
With something thin-wall like a piston, uniformity of section is worth locking in.

Also, note the re-entrant section that will yield a flange, presumably for strength (in the piston?) With that, a one-piece box is ruled out. For whatever reason, probably related to baking them, single formed cores seem to have been rare even when there were no re-entrant shapes and the core was short, stout, and plenty of draft. It surprised me when i started making patterns. For shell cores, which are blown in one piece, 2-piece boxes are necessary so the cores can be extracted.

smt

 

[Peter from Holland]

I did cast a CI piston once
About 5'' in diam
I used the old worn out piston as a core box Split it in half
Then wrapped something around it to make it thicker for machining allowence
Then some longer sheetmetal wrapped around that to create a core print
The mould was just a piece of round wood
Came out perfectly the second time

Peter

 

[rustyironism]

As a point of reference, these are the pattern and core box for the pistons shown above that John O made. You can see how much draft there was to get the piston out of the sand. The core boxes have a piece attached at the bottom only because the molder at the foundry preferred to make the cores in two pieces and past them together. They could have been made in one piece but I didn't think it expedient to disagree with the guy who was doing the job.

View attachment 367061

I am by no means a professional pattern maker, but if I am reading this right, I would say that the added plywood at the base is so that each side of the box could be filled and swiped to make the half-line flat, where they can be glued together.
With that much detail in the core, filling from the top to make a one piece core would possibly miss a lot of the details.
Here are some pictures of core boxes to explain my thinking.
The small one could be rammed from the top and completely fill the box, while the larger one has details that could only be filled by making two halves.

I hesitate to make it look like I know what I am doing as both of those are at the foundry now and I can only hope they work!

Foundry work has become easier with resin-bonded sand reducing the talent needed for pounding green sand, but it is still challenging.

I have been ramming petro-bonded sand for my small model and experimental furnace for aluminum and bronze, but I leave the iron for the Big Boys.

My brother is making a core out of 3d printed plastic that we will try to melt out of the mold with the molten metal later this year.

The Big guys are 3d printing sand cores with no need for draft to remove from a box and even have undercuts!

Fascinating stuff!

Mike

 

[99Panhard]

I wasn't there when the cores were made but that is what I understood to be the case. He didn't say why he wanted to do it that way but this makes a lot of sense.