How would you core this?

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Adirondack
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How would you core this?

Post by Adirondack »

2 1/2” scale switch stand. I’ll probably laser cut the target bar in steel.

I plan on pouring these in 353 aluminum.

Thanks

Chris
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jscarmozza
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Re: How would you core this?

Post by jscarmozza »

That's a beautiful piece of work Chris, was that done with a 3D printer? I would make a split pattern and instead of the open interior, I would make it solid and raised as a core print,then create the open area in the mold with cores. Keep in mind that you can stack cores, file, sand, drill and saw them to get the shapes you need. Curious to know how you decide to make the mold and how they turn out. John
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Re: How would you core this?

Post by Adirondack »

jscarmozza wrote: Sat Jan 22, 2022 8:58 pm That's a beautiful piece of work Chris, was that done with a 3D printer? I would make a split pattern and instead of the open interior, I would make it solid and raised as a core print,then create the open area in the mold with cores. Keep in mind that you can stack cores, file, sand, drill and saw them to get the shapes you need. Curious to know how you decide to make the mold and how they turn out. John
Yes, printed on my FDM machine as the resin printers were full.

Makes sense. I'd like them to be as ready to run as possible. I have to add a few details before I call them done. I'll post photos, as I'm an attention whore. LOL

Thanks

Chris
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RONALD
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Re: How would you core this?

Post by RONALD »

I would use a different approach, Lost Foam.

I have been working for decades with Lost Foam.

If I needed just maybe a dozen of the switch stands, I would construct them from Styro-Foam.

The foam pattern would then have added gating and a sprue, waxed on the surface, and then invested in Sodium Silicate treated sand.

The photos attached show some of these.

In the 2nd photo, I'm hardening the sand using Carbon Dioxide gas.

In the 4th photo, I used a ceramic slurry to coat three bearing journals, but for various reasons, unless you are in production, ceramic slurry is too expensive and not that easy for a hobbyist.

I might try doing Lost Wax, but that is a little more involved.

The last photo is of the various parts to making a Lost Wax casting, did not have a 3D Printer, pattern was carved by hand.
Lost Foam044.jpg
DSCN8804.jpg
Lost Foam047.jpg
DSCN8235.JPG
DSC_0552.JPG
jscarmozza
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Re: How would you core this?

Post by jscarmozza »

Ronald, a few questions; what type of styrofoam do you use and what tool do you use to cut it, would a thin coat of plaster of Paris work in place of the ceramic slurry, would green sand work or is the sodium silicate hardened sand necessary?
All of my lost foam castings (white styrofoam) have come out with very rough finishes, your truck and wheel castings are fantastic, I would like to be able to turn out work of that caliber. John
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Re: How would you core this?

Post by Adirondack »

jscarmozza wrote: Mon Jan 24, 2022 5:42 pm Ronald, a few questions; what type of styrofoam do you use and what tool do you use to cut it, would a thin coat of plaster of Paris work in place of the ceramic slurry, would green sand work or is the sodium silicate hardened sand necessary?
All of my lost foam castings (white styrofoam) have come out with very rough finishes, your truck and wheel castings are fantastic, I would like to be able to turn out work of that caliber. John
Hey John. I know that the extruded (blue or pink) stuff works best for this operation.

Chris
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Re: How would you core this?

Post by Adirondack »

RONALD wrote: Mon Jan 24, 2022 12:37 pm I would use a different approach, Lost Foam.

I have been working for decades with Lost Foam.
Hi Ronald. You pose an interesting alternative. While I don't think foam is the right choice for me given the size of my production runs, the process itself is a good idea. There are special filaments available for my 3D printer so I could print out multiples of such a large piece accurately with little to no hand-working.

I can then burn them out in the traditional investment casting process, or use the "lost" process with sand such as you suggest. I think it's time for some experimentation to see which produces the best results consistently, with the least amount of input on my part.

Thanks

Chris

PS-Any particular reason you went with white brass for your rerailer? Just curious...
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Re: How would you core this?

Post by jscarmozza »

Thanks Chris, I'm also going to do some experimenting with lost foam.
Do you know of any 3D printing foam medium that would be suitable for lost foam casting? One of my live steam buddies is a 3D printer and we may be able to collaborate on a few things.
John
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Re: How would you core this?

Post by Adirondack »

jscarmozza wrote: Tue Jan 25, 2022 1:30 pm Thanks Chris, I'm also going to do some experimenting with lost foam.
Do you know of any 3D printing foam medium that would be suitable for lost foam casting? One of my live steam buddies is a 3D printer and we may be able to collaborate on a few things.
John
https://us.polymaker.com/products/polycast
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Re: How would you core this?

Post by jscarmozza »

Thanks Chris.
RONALD
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Re: How would you core this?

Post by RONALD »

Lost Foam has now been around so long that there is a lot of info available on the internet.

When my article on what was then called "Full Mold" was published in the November 1984 Live Steam Magazine, very few, mainly large castings, were made that way.

I bought my ten sheets of 4'x8'x2inch foam from an outfit called White Pines Pattern Lumber, still have three sheets left.

If your not into worrying about time or an occasional failure, then most of the foam available can be treid.

If you must, find a company that has pattern lumber and ask about foam for patterns.That foam will form less ash.

Anything in the mold has to be turned into a gas by the hot metal, so having a foam that will burn up correctly is what you want.

Some manufactuerers use unexpended beads into aluminum molds to make patterns, but that is beyond a hobbyist.

For cutting foam, just look at what the HO or O Gaugers use to cut their foam to make scenery, plenty of tools available.

As far as coating for a smoother surface finish, I use a wax coating from Blehm Plastics that I purchased decades ago, below is info on the company.

They may have a minimum order amount?

It is certainly not necessary to harden the sand, you can just put dry sand around the pattern and pour, but in that case I would use some kind of vibrator to compact the sand while you pour.

I have also done castings with dry loose sand in a five gallon bucket, with a vacuum cleaner pulling thru a fine screen near the bottom, and a piece of plastic wrap covering the top. One must quickly poor into that, but it does work.

Stay away from Plaster of Paris. Moisture may cause it to spit the metal back at you, the investment used in the Lost Wax process is heated to a very high temperature, with Ceramic Slurry, the mold is coated many times and then heated to red hot.

https://interviewmania.com/discussion/8 ... cellaneous

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jscarmozza
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Re: How would you core this?

Post by jscarmozza »

Thanks Ronald, I'm going to make up a small pattern and give this a try. Thanks again,John
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