PATTERNMAKING

PATTERNMAKING

This is going to be the difficult page to put together, as it covers such a broad range of subjects. A pattern can be anything that leaves a cavity in the sand. It really depends on what you want to use the casting process for. You can use existing parts for making duplicates or start form scratch. I'm going to gear this page to the latter. I'm also an industrial patternmaker, so I can't help to much on jewelry. But that is something I'm currently looking into. So I'll be talking about what is required to build and layout working pattern. I'm also only going to deal with wood patterns for now. So I might as well start with the layout.

Layout Tools

Obviously not all the tools in the above picture are for layout, but the necessary tools are there. I'm assuming that most people reading this would have the basic power tools, table or radial arm saw, drill press, some sort of rigid disk or belt sander. When laying out or marking a line use a layout knife. When a line is cut into the wood you will know right away when you've sanded to the line, you will need to lay your pattern out to a shrink factor. I try to break the pattern down to simple shapes then glue the pieces together, your complexity is limited by your imagination. You'll need to add draft, there are no set rules for drafting a pattern. Look at the application and it should be somewhat obvious. If an area is machined you can add more draft, if an area is critical but as cast reduce the amount of draft, 2 degrees is a good starting point. For core prints and gating I use 10 degrees draft. The finish on the pattern and the depth of the draw from the mold will also determine the amount of draft required. Another concern would be clearance on a core print. As time permits I'll start taking pictures and making drawings of what I'm talking about.

So looking at the picture you have a layout knife, already talked about, dividers, rigid and flexible rule, square, center finder, protractor, triangle and panel gage. These are the basics, with those tools you can layout any type of pattern no matter how complex. The sliding bevel, depth gage, inside and outside calipers and digital calipers will let you check your work in progress. Such as draft angles and core clearances. What is really needed is a class in geometry, all industrial type patterns can be made with simple geometric shapes, if you know how to do the layout your most of the way to being a patternmaker, if you don't know how to layout the basic shapes the some more training is needed. The rest of patternmaking is how to brake down any job into those shapes how to assemble them and how to use all the tools to effectively build any pattern required. Oh yeah, did I mention it's a 5 year apprenticeship to become a journeyman patternmaker, and another 5 to gain enough confidence to be able of walk into any shop and know you can build any pattern they can throw at you. But that doesn't mean you can't build a good pattern, it just takes practice.

Pattern Details

Every pattern needs some kind of identifying mark. You can buy all the letters you want from pattern supply houses, at a cost. But if you have access to a CNC mill, friend or self, you can make any font, logo or graphic that you need. A typical font can be typed in just about any software package. Mirror the letters or graphic, apply the tool path and your ready to go. The tool I used was the wrong one, 60 deg included angle. you should use a 90 deg included angle. That way the letters can be mounted on a surface that is close to 45 degrees. The nice part of building this home pattern shop and foundry is the fact that I need all the tools. Including a small CNC mill. Now if I require a special font or logo I can create it. Using cam software, Rhino in my case, and pictures I can now add any graphic to casting, in a detail that could not be carved.

Pattern Construction

Since this whole thing started with a Stirling engine, I figure I'll use this page to describe how I build the patterns for this project. These won't be in any particular order, but I'll try to cover as many different ways to build patterns as I can. Again the is the way I do things and is not the only way to do things. One thing I will assume, which is always a bad thing, is that most people will have a working knowledge of woodworking and metal working tools. Just watch the fingers and eyes and whatever else is precious to you. So here I go.
This is about 2 step into the process. The layout for the spokes is the critical part, if you want a balanced
flywheel. I used 6 spokes because it's easy and it's a small, 4 1/2" flywheel. For layout pick any point on
the circle and start scribing the radius around the circle. As the radius is not exactly 1/6th of a circle work
both ways of the start point. There are 4 pieces to the pattern and these are pinned together before cutting
them out.

Parts are pinned through all pieces, don't fill the holes until mounted. Once all the part are cut and sanded, glue
with whatever your comfortable with. The spokes and inside of the rings don't need draft, they will have a full
radius , do not sand the outside until all the work is done on the inside.

All sanded, body putty fillets and ready for lacquer. Draft on the outside should be 3deg or more, as it is machined
the draft won't matter much. The finish at this point should be 180 grit sandpaper. As you work keep the part as
smooth as you can get it, makes the final finish much easer. At this point I'll put one coat of lacquer to keep the
moisture out of the wood. Now I'm ready to mount the pattern.

Figure out where the pattern needs to go and how your going to gate the pattern. Leave enough room for sand
around the pattern so you don't have a runout, 1/2 to 1" depending on the depth of the casting. Glue, nail, screw
or in some way fasten the drag to the snap board. Drill alignment holes and mount the cope pattern.

This shows the drag runner. I use a 1 1/4" square basin and a 3/4" runner, tapering from 3/8" to 1/4", the basin
helps stop the metal from creating turbulence, and the tapered runner slows the metal before entering the ingate.

The cope pattern has a 1/2" diameter riser at the hub, a 3/4" down sprue. I located the ingates in the cope to
reduce the amount of crud entering the casting. Putting a fillet on the intersections of the runner and ingates allows
the metal to flow without washing the sand.

And the completed casting, not too much work left. Cut off the gating and machine. Cool one part just about
done. Well not really this one has some gas pockets and was a test anyway.... wrong alloy. Take a look at
the FOUNDRY page and I'll tell you how I made the casting.

Some things that might help before building any pattern might be, the shrinkage of the metal to be cast, the type of wood the pattern is to be made of and the weight of the pattern relative the metal to be cast. A shrink table will tell you the typical shrinkage of metals. This can also be converted to percents of a foot so common rule dimensions can be converted without the use of a shrink rule. Although anything can be used to make patterns out of knowing in advance the type of wood used will give you an idea of how may castings you could expect to make off of that pattern without repair. Knowing the weight of a pattern in relation to the casting is useful for calulating the amount of metal that will need to be melted. Of course one thing that will help the most for building a wood pattern would be an accurate 2-3 view layout of the pattern that includes shrinkage, coreprints, machined surfaces and loose pieces. I'll try to cover this on a separate page on pattern layout.

Power Tools

Earlier I gave some information on the hand tools, so now I'll talk a little about power tools. Over and above the cost of your small home foundry this could be the most expensive part of this hobby. Depending on how much actual pattern work you want to do and how accurate you want to make it, will determine how much effort you will extend to you pattern shop. your equipment doesn't have to be the best or the biggest, just reliable. I'll put the tool list in the order as to what I consider the most important to the least. One thing to consider is that all power tools have the ability to make a mess out of human flesh, always know where the cutting edge is and don't let anyone distract you while working with any power equipment.
Bandsaw: this is one machine that you don't want to skimp on. It does straight cuts, circles, contours
and angle cuts. With a little sand paper you can make complete patterns and core boxes. A 14" bandsaw
is what I would consider the minimum, but get the best you can afford. Some options that come with the
newer bandsaws will probably not be worth much such and the resaw fence and the fence rails and any
circle cutters. Instead make yourself a wood angle block for resawing and learn to rely on your eyes and
skill to make the required cuts.

Disk sander: add the disk sander to your tool box and now you can flatten your wood, make it parallel
sand the circles you made on the bandsaw. In general it saves you a whole lot of hand sanding. A 12" disk
is minimum a 18" even better. Which ever one you get try to get one that is reversible, may not be possible
in a 12" sander, if you can still find one, mine is a 12" double ender, so I don't need it to be reversible.

Spindle sander: with this machine you've just completed every required power tool to make accurate patterns.
All patterns require a way to cut the wood and sand it smooth, with these 3 machines you can make any type
of pattern you want, the rest of the machines will just make some things easer.

Drill press: how much is your budget and how big is your patternmaking goals. You can get a bench top and
just drill alignment pins or you can get a drill press with a drawbar and use your drill press to plane small pieces
of your work flat, use it as an overhead router or add options to make it into a small milling machine. I have
seen a drill press that doubles as a oscillating spindle sander, this may save you some shop space.

Jointer: a nice machine for making lumber flat without having to hand plane the piece. a real time saver when
used with a planer. One mistake is to think you can joint both sides of a few pieces of wood then glue them
together, the problem being, the pieces of lumber will not be the same thickness and when glued together you'll
just glue in tension, then every time you cut that piece it will warp. Minimum would be 6" blades for a real small
shop, 12" for a mid sized shop and if you want to go pro a 16" is real nice.

Planer: use this to make jointed lumber parallel, this is a good thing when gluing a stack of lumber. With a good
machine you can get the pieces of lumber to the proper thickness without having to sand it. I have one like this
that has been restored. It's quit solid but only has maximum thickness of four inches .

Grinder/buffer: All hand tools you need will need to be sharpened. This can be done by hand, but a grinder/buffer
will make things so much easier. How much you spend is up to you, I've had a cheap grinder for years, but it does
have a slight wobble to it. So I guess you get what you pay for.

Lathe: this machine is a ways down the list, which some may argue with, but unless you plan on doing a lot of hand
turned patterns it's not really something that I would consider for a hobby foundry. All the things a lathe can do
you can do with other machines. This is one of those that make some things easer, such as a bell. A lot would depend
on your wood working skills and what kind of pattern shop you want.

Table saw: you can use this machine for so much it's hard to describe. It's way down on this list because a hobby
foundry won't use it for much more than reducing larger pieces to smaller pieces, plywood lumber, etc. In reality this
machine would take a book to describe all the things it can be used for, all would be used in a actual pattern shop.
My table saw looks similar to this one, with a one horse motor on it, it will cut about anything.

Milling machine: this is a machine that can make life a lot easer. You now have a drill press, overhead router and a
mill all in one package and with a little creativity you have a metal lathe. The only reason it's this far down on the
list, it's not a high priority tool, until your patternmaking requires a higher degree of accuracy. Add tapered end mills
and a complete pattern can milled without any other tools.

Although I have a version of all of the above, sometimes it would be nice to have some of the machines shown, just don't have the room. I'll include some tips later, on some things each machine can do.

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2006-2008

	This is about 2 step into the process. The layout for the spokes is the critical part, if you want a balanced flywheel. I used 6 spokes because it's easy and it's a small, 4 1/2" flywheel. For layout pick any point on the circle and start scribing the radius around the circle. As the radius is not exactly 1/6th of a circle work both ways of the start point. There are 4 pieces to the pattern and these are pinned together before cutting them out.
	Parts are pinned through all pieces, don't fill the holes until mounted. Once all the part are cut and sanded, glue with whatever your comfortable with. The spokes and inside of the rings don't need draft, they will have a full radius , do not sand the outside until all the work is done on the inside.
	All sanded, body putty fillets and ready for lacquer. Draft on the outside should be 3deg or more, as it is machined the draft won't matter much. The finish at this point should be 180 grit sandpaper. As you work keep the part as smooth as you can get it, makes the final finish much easer. At this point I'll put one coat of lacquer to keep the moisture out of the wood. Now I'm ready to mount the pattern.
	Figure out where the pattern needs to go and how your going to gate the pattern. Leave enough room for sand around the pattern so you don't have a runout, 1/2 to 1" depending on the depth of the casting. Glue, nail, screw or in some way fasten the drag to the snap board. Drill alignment holes and mount the cope pattern.
	This shows the drag runner. I use a 1 1/4" square basin and a 3/4" runner, tapering from 3/8" to 1/4", the basin helps stop the metal from creating turbulence, and the tapered runner slows the metal before entering the ingate.
	The cope pattern has a 1/2" diameter riser at the hub, a 3/4" down sprue. I located the ingates in the cope to reduce the amount of crud entering the casting. Putting a fillet on the intersections of the runner and ingates allows the metal to flow without washing the sand.
	And the completed casting, not too much work left. Cut off the gating and machine. Cool one part just about done. Well not really this one has some gas pockets and was a test anyway.... wrong alloy. Take a look at the FOUNDRY page and I'll tell you how I made the casting.

	Bandsaw: this is one machine that you don't want to skimp on. It does straight cuts, circles, contours and angle cuts. With a little sand paper you can make complete patterns and core boxes. A 14" bandsaw is what I would consider the minimum, but get the best you can afford. Some options that come with the newer bandsaws will probably not be worth much such and the resaw fence and the fence rails and any circle cutters. Instead make yourself a wood angle block for resawing and learn to rely on your eyes and skill to make the required cuts.
	Disk sander: add the disk sander to your tool box and now you can flatten your wood, make it parallel sand the circles you made on the bandsaw. In general it saves you a whole lot of hand sanding. A 12" disk is minimum a 18" even better. Which ever one you get try to get one that is reversible, may not be possible in a 12" sander, if you can still find one, mine is a 12" double ender, so I don't need it to be reversible.
	Spindle sander: with this machine you've just completed every required power tool to make accurate patterns. All patterns require a way to cut the wood and sand it smooth, with these 3 machines you can make any type of pattern you want, the rest of the machines will just make some things easer.
	Drill press: how much is your budget and how big is your patternmaking goals. You can get a bench top and just drill alignment pins or you can get a drill press with a drawbar and use your drill press to plane small pieces of your work flat, use it as an overhead router or add options to make it into a small milling machine. I have seen a drill press that doubles as a oscillating spindle sander, this may save you some shop space.
	Jointer: a nice machine for making lumber flat without having to hand plane the piece. a real time saver when used with a planer. One mistake is to think you can joint both sides of a few pieces of wood then glue them together, the problem being, the pieces of lumber will not be the same thickness and when glued together you'll just glue in tension, then every time you cut that piece it will warp. Minimum would be 6" blades for a real small shop, 12" for a mid sized shop and if you want to go pro a 16" is real nice.
	Planer: use this to make jointed lumber parallel, this is a good thing when gluing a stack of lumber. With a good machine you can get the pieces of lumber to the proper thickness without having to sand it. I have one like this that has been restored. It's quit solid but only has maximum thickness of four inches .
	Grinder/buffer: All hand tools you need will need to be sharpened. This can be done by hand, but a grinder/buffer will make things so much easier. How much you spend is up to you, I've had a cheap grinder for years, but it does have a slight wobble to it. So I guess you get what you pay for.
	Lathe: this machine is a ways down the list, which some may argue with, but unless you plan on doing a lot of hand turned patterns it's not really something that I would consider for a hobby foundry. All the things a lathe can do you can do with other machines. This is one of those that make some things easer, such as a bell. A lot would depend on your wood working skills and what kind of pattern shop you want.
	Table saw: you can use this machine for so much it's hard to describe. It's way down on this list because a hobby foundry won't use it for much more than reducing larger pieces to smaller pieces, plywood lumber, etc. In reality this machine would take a book to describe all the things it can be used for, all would be used in a actual pattern shop. My table saw looks similar to this one, with a one horse motor on it, it will cut about anything.
	Milling machine: this is a machine that can make life a lot easer. You now have a drill press, overhead router and a mill all in one package and with a little creativity you have a metal lathe. The only reason it's this far down on the list, it's not a high priority tool, until your patternmaking requires a higher degree of accuracy. Add tapered end mills and a complete pattern can milled without any other tools.