How to Make and Use One-Piece Patterns

[GreenTwin]

I always thought that patterns were generally two-piece, or more, split-pattern type, until I visited Bob Pearson's shop and saw the original Cretors patterns.

All of the Cretors patterns for the popcorn engines, and popcorn wagon cast parts are one-piece.
The cretors patterns appear to be made from bronze, and soldered together, probably with soft solder.
Some of the Cretors patterns would be quite thin if made in two piece, such as the spokes on a #1 flywheel.

It made me question why Cretors used all one-piece patterns for all of their commercial work, if 2-piece patterns are so good ?

I think it boils down to two things.
1. It is much easier to make a pattern in one piece, even if it is pieces of patterns, such as a flywheel spoke.
2. One-piece patterns are very durable, and if made of bronze, you won't easily bend, break, or otherwise damage one even after thousands of uses.
3. One-piece patterns don't have loose pieces that get lost.

The fact that the Cretors patterns survive perfectly intact to this day is testament to the one-piece method.

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[GreenTwin]

I have toyed around with making larger scaled up replicas of Cretors engines, and made a pattern for an enlarged Cretors No.01 flywheel.
I have probably posted this previously somewhere here.

The method I used to make the follower was to fill a shallow flask half with sodium-silicate sand, press the one-piece flywheel pattern down into the sand, scrape off the excess sand down to the parting line, which is half way down the pattern, and then let the sand set (used CO2 actually to set the sand).

After the follower is made from sodium silicate sand, then molds can be made by placing the pattern in the follower, molding the cope, remove the follower and flip the mold, and ram the drag.

The follower does not have to be particuarly accurate as far as getting perfect contact with the pattern, as you would want if making a sand mold.
If there are gaps/holes in the follower, it does not matter, since the follower just holds the pattern in place.

You can place a piece of plastic wrap over the pattern to keep it from sticking the the follower sand, or use traditional parting compound.

I have also used bondo to make a follower, and that makes for a more durable follower.
You can paint a sand follower in thinned epoxy to strengthen it.

The follower system is pretty easy to use, but I seldom see anyone using it.

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[GreenTwin]

Casting the individual spokes.

The single wood spoke pattern was cut from a flat sheet of birch plywood, and then hand carved using a Demel with a long straight bit in it.
The spoke blank had a centerline around the entire piece, and I just worked 1/4 of the piece at a time, down to the centerline.

All of the small round molds were sodium-silicate-bound.

I found that little pot in a 2nd hand store for about $5.00, and the woman at checkout said "You going to cook some sauces?", and I said "Yes, 'sauces' so to speak.............".
It is hard to explain to folks what I do with the stuff that I buy and repurpose.

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[GreenTwin]

In the cast of this flywheel, looking at my photos, it looks like I actually made half the mold just by pressing the pattern down into the sand, and so I did not make a follower.
But this is how you make a follower.

This was sodium silicate bound sand.

I needed some risers on the rim to avoid shrinkage, but this was strickly a proof-of-concept test, and I did not intend for this to be a final usable flywheel.

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[GreenTwin]

Here is my oversized Cretors-replica flywheel casting, compared with an original Cretors No.02 flywheel, and also compared to a Cretors No.01 flywheel.

This was just a proof-of-concept thing, to see if this method would work, and I did not expect to see any sort of quality in the resulting casting.
I was a bit surprised that it actually did work, and it worked far better than I thought it would.
If you are into hand-making patterns, this is a viable way to do it.

This is how Cretors make their flywheel patterns, except they used bronze for everything.

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[GreenTwin]

3D printed patterns lend themselves to a two-piece pattern, since that gives you a way to start the pattern with a flat side.

I have pretty much transitioned 100% to 3D printed patterns, but I do know how to manually make patterns too.

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[GreenTwin]

The flywheel rim was turned from several glued layers of birch plywood, cut round on the bandsaw.
I used a router mounted on the lathe toolbit holder, and turned the lathe chuck by hand.
This prevents a flywheel snag/explosion when you try to rotate a wood piece normally in the lathe chuck.

I use various bits in the router, with a straight bit to get the tapered surfaces on the flywheel rim, and a bullnose bit to get the bead on the inside of the rim.

This was before I went to 3D printed patterns.
Hand turning the pattern in the lathe chuck prevents a disaster (don't ask me how I learned that flywheel patterns can snag and fly out of the lathe chuck.......I have a disaster photo somewhere).

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