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.

.

 

[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.

.

 

[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.

.

 

[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.

.

 

[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.

.

 

[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.

.

 

[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).

.

 

[GreenTwin]

From the Navy Foundry Manual; the "False Cope Method", where an irregular part is rough molded to make a temporary cope, then a permanent drag mold is made, and finally a permanent cope mold made.
Good for irregular shapes, broken parts that are used for patterns, etc.

.

 

[gbritnell]

There are 3 methods for patterns and casting. One is a split pattern. Another is a loose pattern and the third is using a follow board with the one piece pattern. The follow board replicates what would be the parting surface on a normal cope and drag type pattern. The pattern is inserted into the close fitting follow board and one half of the sand mold is made. The flask is rotated and the follow board is removed. Parting powder is applied to the mold and then the other half of the mold is made/tamped. The molds are separated and the pattern is removed. At this point ingates, risers and sprue holes can be scrapped in

 

[Jasonb]

As I said in the other thread unles syou have a 3D printer there will be a lot of work making a follower for this part. The actual pattern is very simple in wood but to get a good fitting follower will be much more work.

The ring and it's web can be turned from two flat pieces of wood glued together with a sheet of copy paper between. Then bore 9 radial holes and glue in your round pieces which can again be turned as a long length with paper on the split line and then cut to length. Bondo the fillets and once sanded just split it apart along the paper line.

If you want a load more work then make a follower by carving this out of wood, I've not shown the radii needed to clear the fillets on the pattern.

To me for a one off it is a wast of time making a follower unless you can print it, even then is there any point?

 

[Jasonb]

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.

You need to get some more pattern making experience, I've probably done more single piece patterns than split and if you also had a few casting kits under your belt you would have handled plenty of castings from single piece patterns. For example the engine I'm currently making from commercial casting kit has 12 castings, 7 of which are from one piece patterns

 

[Fidlstyks]

I mainly used loose patterns, I have a box of wedges and shims that work like follow boards. I have some follow boards too. It saves the time of cutting the sand back. Some I did the follow in CO2 core sand, that was easy.
A CW Amen book shows a skeleton pattern where one parts off and packs in green sand to act as casting wall that supports a green sand core. This allows a core to be rammed green. Usually when casting storm drain pipes.
I have a few split patterns with negative draft, or have loose peices, to use, one flips the mold back over to leave a green core or pull a loose piece of a pattern. I maybe will start a thread on molding some day. The age of digital cameras allows me to take, store and post pictures easily.

 

[GreenTwin]

You need to get some more pattern making experience, I've probably done more single piece patterns than split and if you also had a few casting kits under your belt you would have handled plenty of castings from single piece patterns. For example the engine I'm currently making from commercial casting kit has 12 castings, 7 of which are from one piece patterns

It is really not easy to walk into a foundry these days to see how things are done.
It is almost impossible to walk into any industrial site these days; they are locked down tighter than fort knox.
And the modern foundries uses methods that can be radically different, such as 3D printed sand molds.

How it was, and how it is now are two different things entirely, unless you are some sort of small custom foundry, like the Amish operate.
I would have to guess the Amish use old-school methods, and greensand, but I have seen some of them wip out a smart phone and start talking, and they generally don't do that.

The foundry I would like to visit in the States is the one that Kory Anderson bought, and the one he used to cast his 150 hp Case tractor.
I have chatted with him, and he has invited me, but I just don't have time to travel at the moment.
He does ductile iron, as well as regular gray iron castings, and probably anything inbetween.
He is a great resource for foundry information.
Photo from his website.
It that a boss-hog tractor or what ?
.

 

[GreenTwin]

The Soule steam engine foundry/factory/museum has a lot of their old patterns, and the Speedy Twin patterns are made up into matchplates.
You can make a matchplate by ramming a pattern in a mold, removing the pattern, inserting a dam inside the two mold halves to separate them, and then pouring the matchplate.

I don't recall seeing any two-piece patterns at Soule.

In the hobby/backyard foundry world, which is where I started learning in 2011, two-piece patterns are very common, and for a while I thought of every pattern in "two-piece pattern think".
In 2011, I had zero knowledge of anything foundry, except that I had actually visited an International Harvester foundry that was located in town, and seen them casting truck parts. At the time all I knew was that molten metal was being poured into sand molds.

As I mentioned, most of my 3D printed patterns these days will be 2-piece, just because that lends itself to the flat side being on the printer bed.
About the only problem I have had with 2-piece patterns is flywheel spokes breaking, since that area can get very thin with a 2-piece pattern.
Other than that, there is little reason to 3D print one-piece patterns, in my opinion.

It is very simple and fast to make a follower using bound and, and the follower does not have to be mold-quality, it is just a temporary support.
Sodium silicate binder is cheap and readily available.

If you use greensand only, the Navy Foundry Manual method seems to be a good way to do it without making a follower.

Some photos of Soule Speedy Twin matchplates.
Of all the matchplates shown below, only the one for the eccentric strap could possibly use a two-piece pattern, and maybe the cylinder head matchplate.

I have done plenty of pattern work, and my wife said I don't think I need anything else under my belt, due to my current weight.
Pattern style is a matter of personal preference, and a matter of using what tools the person has, and what works for their foundry setup.
I consider pattern work the least critical aspect of making a good casting.

What is a lot more important than the pattern style is the sprue, runners, gating, spin traps, risers, etc., because that is what makes the difference between a good casting with no defects or hard spots, and a casting full of inclusions, voids, and chills.
"Show me the casting quality" is far more important than "show me your pattern work".
You can make the worst of castings from the very finest patterns.
.

 

[Richard Hed]

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.

.

Some patterns are amenable to one-piece, others are not.

 

[Jasonb]

Exactly what Richard says, why go to the trouble of making a two piece when a single will do.

Here are a few examples, the engine I'm working on now. As these parts will be machined all over and there are no feature sthat require a split its better to use a single that applies to doing it at hole or having it cast commercially. A piston with chucking piece, eccentric strap and two small bearing caps cast as one. I've machined the other single sides ones.

Some other ones I did the patterns for, I'll have to go and photograph the castings if that is what really matters.

Stick of 4 Flanges, bearing caps and an eccentric

Crankcase side cover again no need for it to be split, just a bit of draft around the edge

Other parts were from split patterns

Two different bearing caps again no need for a split

Another one piece, did require a corebox but the pattern is one piece & one piece bearing caps again.

casting

So plenty of cases where you don't need a split pattern or even a follow board/plate as many items only have or need draft on one side

 

[GreenTwin]

Its an ohhh.......ahhhhhh moment when I see flywheel patterns like this.
Maple spokes ?

Very nice indeed.

.

 

[Jasonb]

Mostly beech though as I was using up offcuts there are a couple of maple ones in there.

16" flywheel and about 20lbs of iron

 

[GreenTwin]

That is an outstanding iron casting to say the least !
.