Explanation of patterns assembled in photograph below pattern timbers.

Reading from Left to Right.

Nos 01 and 04:

       
                 Alder Pattern Timber.       

          
                         Honduras Mahogany.

        
               Maple Pattern Timber.        

       
                 Pine Pattern Timber.

        
      David  Patterson: Hand Crafted Foundry Patterns.       See notes at left.       s.

         
                Knowledge Is Power.  
                        

Feature Article.

Following is a list of the typical timbers or woods used to construct foundry pattern No pattern shop I've work in has ever used Philippine mahogany, because of its properties. (See below)
 
The thing that people should understand and know about working with timber, is that most wood dust if inhaled as fine particles will remain in your lungs. Pine is the only one that may dissipate over time. I didn't mention cedar because more than any of the other timbers it has been known to cause cancer, and because of that it's not widely used in the commercial pattern shop any more.

MDF(Medium Density Fibreboard) is not one I'd recommend either, just take look at the MSDS and you'll know why. At home, pattern making is more dangerous than doing it for a living because of the lack of safety precautions. (eg dust extraction systems) If you are sanding timber in an enclosed area a good quality face mask should be worn at all times.  
 
The following timbers are what I've used while working in some of the pattern shops in the Washington USA area. The timbers we will discuss are common through out most North American pattern engineering shops. What it really comes down to, is that any wood can be used to make a pattern. At home I've used everything from alder to some scrap Zebra wood. I like Alder for home use because of it's stability and ease of working. My patterns are small so it's not that expensive. Regardless of the type of wood you use, the pattern will only be as good as the finish you give it. If you have an ultra smooth finish on the pattern it will pull from the moulding sand with greater ease, and wont snag the sand in any way.
  
  Timber Pattern Materials:
 
Most Common Types:

Sugar Pine:
Pine is probably the most widely used pattern material today. It's stable, closed grain and is shaped easily. Pine holds up well for short run patterns, fifty or fewer moulds. This wood is pitchy (full of resin) and will gum up a sander. It takes a finish well, either lacquer or shellac, but will require at least three coats. You can get more moulds if the pattern is maintained and stored in a properly ventilated area. If the pattern is stored in a damp area, the wood will most likely swell and possibly even suffer from split glue joints regardless of the quality and type of finish applied to the pattern.
 
Mahogany:
Honduras mahogany is used to produce a better quality pattern, or one that might be used
to make fifty or more sand moulds. It is an open grain wood, but the grain is tight enough that when given three to four coats of some type of finish it will seal well. It's red in colour and is a hardwood. The timber also leaves a purple stain on your fingers, a properly maintained pattern can last through several hundred mould impressions with out any problems. There is another mahogany, Philippine mahogany; this is not a good choice. It's a very open grain wood that is unstable and can contain a lot of slash grain. It will work for one off casting but the pattern will not store well. It is generally considered NOT to be a good pattern timber.
 
Maple:
Maple works for close tolerance patterns. It's stable, and is probably best suited for machined patterns.It is a closed grain wood that will only require two coats of finish. It will last a little longer than Honduras mahogany in normal foundry use.
 
Less common pattern timbers:
 
Jelutang:
This wood has many of the same characteristics as pine. Jelutang is a uniform, open grain
wood that is a little less stable but easer to carve than pine.
 
Poplar:
Poplar is a hard wood, but not as hard as maple, nor will it last as long in the foundry as mahogany. Compared to other hard woods it's less expensive. But is a good cross between maple and pine. It's a little fuzzy when sanded on a disk sander, but the fuzzy nap will disappear after the first finish coat has been sanded. Stability of the timber is quite ok, but it can move quite a bit when cutting.
 

Alder:
This is the type of timber I like. Similar to maple, but not as hard. It lasts about as long as
mahogany in the foundry. It has a closed grain and is very stable, finishes well within two to three coats. All these woods can be machined, but this one seems to have the best overall characteristics for a light CNC machine.
 
MDF board:
I have to admit I haven't used this one much, haven't wanted to. It's dusty, it stinks and
makes me itch. It does machine well because it's completely grain less. The few times I
have used it, I've noticed it's not very stable in a damp climate; it has a tendency to swell.
Once the pattern was finish sanded it took several coats of lacquer to seal it.
Reading MSDS on this material, I won't use it any more. So if you are using this timber
for patterns, you need to take all safety precautions to prevent inhalation of MDF dust particles or fibers.

THE DYING TRADE. By David Patterson.

One of the best days of my life was walking out of a pattern shop with the knowledge that I had a job the following Monday. It was early summer 1973, I was age twenty-four, and almost too old to become an apprentice. The cut off age was twenty-five. Monday came and I wondered what the hell I had got myself into, for the first two weeks on the job I spent cleaning a 1/4" coating of pigeon dung out of some large foundry core-boxes. A great start that was!

I had to finish a six-month probation or trial period, and then I was on my way. Five years later, I finished and became a card-carrying certificate holding journeyman pattern maker. At the end of the apprenticeship program I had to make a decision. The boss said. "You can stay where you're at, or quit and move on to increase your skills". I chose to quit; my employer wasn't too happy but understood, his grandfather and
father were pattern makers. Things were good because I knew I could get a job in a pattern shop any where in the country, even though I didn't, but I could.

But there was a change coming; the industry was undergoing a transformation in the way things were done. I decided to come back to the pattern shop where I started. There standing on the shop floor were two NC mills in the machine shop, and the machinist was starting to cut simple patterns. They failed big time, ha!

A couple of years later some guy came in and was talking about lasers and plastic, for a small investment of $10,000, we could have invested in something called stereo lithography. This was about 1984, the year before I got my first computer. One change was that my original "Home" pattern shop where I started no longer had an apprentice, and none had been trained since the time I had left the shop. By 1987 the union was also gone in this area. Which was too bad, as the Pattern makers League of North
America was 100 years old. And was actually one of the first trade unions in this country.

In 1994 I started taking CAD classes at a local community college. What a change that was, not only could I build anything out of whatever I wanted too, I could now just do it on a computer. Realizing that the patterns I made by hand can now be cut on a machine, with better accuracy. I saw MY career change from hands of skill in creating a pattern to one of simply hand sanding the product that the machine had cut.  So by 1997 I left the trade to design machine parts and castings on the computer.

Between 1997 and now, I've been back to the pattern-shops for total of two years, as a CNC programmer.  I'm a CMM programmer and Cad designer the rest of the time.

Being a Pattern maker is something you either are or your not. I still miss the smell of pine and lacquer, and the simple patterns I build at home don't quite make up for the thrill of laying out the offsets and building the rudder hub for a 600-foot tanker, or arranging the close tolerance tooling for a 15" midrange speaker horn. The pattern making trade is dying, or changing, but either way the traditional pattern making knowledge of old will eventually be lost for good.  
 
David R. Patterson.

Now that you have read Davids article, why not pop over to his web site to learn more.
http://home.comcast.net/~oddkins/foundry_home.html

Editors Note:

We are most appreciative to Dave for passing on his pattern making experience and for writing this article. What ever country you live in, there is a good chance that several native timbers will be quite suitable for pattern making, but you may have to do some research to find which ones are the best.
If you contact a timber merchant who may carry solid exotic timber's for the furniture trade,  ask for a good quality carving timber, as this type will also generally be suitable for foundry patterns.

Pattern timbers obtainable in Australia.
There are several suppliers around Australia.
Pattern Making Timbers Available In Australia..
Sugar Pine. Huon Pine.Yellow Pine. Perfect Plank (Laminated Sugar Pine )
Jelutong. Damar Minyak. Honduras Mahogany. Pulai. Obech.
http://www.afttimbers.com/home.htm.
351 Plummer Street. Port Melbourne. 03 9646 1081. Fax: 03 9646 4734.

OS GIKEN TWIN CAMS.

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