Pattern Making For The Hobby Foundry Worker.
Success or failure in the hobby foundry will depend to a large degree on the skills & ability to create timber patterns that work, i.e. patterns that are easy to mould, lift or separate from the sand mould.
Patterns with incorrect draft on vertical surfaces, badly finished corner fillets, or a pattern that has not been finished to an ultra smooth finish will be difficult to mould & remove with green sand. Pattern making is a special skill and art in itself, most apprentices spend several years to learn the trade. But the average hobby foundry worker most likely won’t have the time, or the patience to get involved with the art of pattern making to that extent.
But some basic skills are worth the time & effort to learn, for without the skills to produce patterns, you wont have the success you
desire with your hobby foundry work, unless you PAY to have patterns made for you, but that would take all of the fun out of it, and also cost you a sizeable amount of money. Professional pattern making costs can vary from a few hundred dollars for simple patterns, right up to several thousand dollars for complicated pattern designs.
Recently I happened to overhear a pattern maker who designs and builds patterns & core boxes for alloy & cast iron cylinder heads, there was mentioned of pattern tooling costs to be around $20,000.00 AU, before you even think about melting & pouring any metal.
If you were a former student of the old tech school system from the sixties & seventies, there is a good chance that you still remember skills required to operate basic woodwork hand tools. Some of the finest patterns have been made from timber using very basic hand tools.
More than likely you still have a chisel set tucked away in a drawer, or perhaps a spoke shave, wood plane & handsaws, plus a host of other tools that could be used to make excellent patterns in the home hobby shop.
It doesn’t matter if they happen to be a little rusty, take them out of the tool chest and bring them back to life again, re-grind the cutting edges and hone the cutting edge with an oil stone, very soon you will have some useful tools to work with.
Remember sharp tools give the best results.
Do the same with the wood plane and any other tools, such as a small set of carving chisels which can be used to carve intricate shapes into wood. You’ll need some good pattern timber or lumber as it’s called in the states… doesn’t matter, it’s all wood isn’t it.
There are many types of timber suitable for pattern making, but, you’ll probably be limited to what’s available in your area or region. Quality pattern timber is expensive to buy, so ask for off cuts at the local timber merchant, which you may get for a considerable discount. You’ll be looking for a soft timber that doesn’t splinter, has a straight grain, is easy to work or carve, and finishes to an ultra smooth finish.
One of the easiest timbers to use is jelutong, this timber comes from the Philippines, I don’t know whether it is from plantation timber, or old growth forests, but it is great to turn on a lathe, and easy to shape and carve with sharp hand tools. Other pattern timbers in use are cherry wood, mahogany, maple, white pine, and many others.
Quite often a master pattern can be made from timber, and then a replica mould is made using RTV 585 silicone, a quick method to remake replica production patterns. The replica patterns can then be mounted onto a match plate along with the runners & gates, this method will enable you to mould & cast multiple parts at the same time.
With a little practise you will soon know enough to make reasonable quality patterns that create good sand moulds.
There is one important pattern making tool that will make you wince when you purchase, but it is an important tool to have if you want to make accurate patterns where shrinkage rates are concerned.
The tool is the “Pattern Makers Rule”, this is a ruler about 500mm (20″) long. Made by Rabone Of England. No B5.
And the graduations are marked as: 1/30-1/40- 1/60-1/80,
The graduations represent the amount of shrinkage allowance for different types of metals. The pattern makers ruler provides a built in shrinkage percentage, which means you don’t have to calculate the final measurement or size of your pattern, you simply take your measurement direct from your shrink rule, and transfer the measurement to the pattern being made.
The system is quite clever in the way it’s all been calculated.
For a quick example, the 1/30 scale measurement seems to give the correct result with patterns used to cast items in aluminium.
Machining allowance on specific parts of a given pattern may also need to be considered, generally your own judgement can be used to judge that.
Pattern making can be quite a challenge for the hobby foundry worker, but once you learn the basics and develop your skills, with a little practice your patterns will get better and so will the overall casting quality.
If you intention is to make many patterns, the investment in a shrink rule is well worth the money.
Once you have the hand tools required you may want to purchase a good book about pattern making using traditional wood work tools, pattern making deserves a study all on it’s own, but it forms an integral part of foundry work. You are the boss of your own workshop, now you have to be prepared to wear the hat of the pattern maker & that of the sand moulder & founder.
If that sounds like a lot of work, it isn’t really, you’ll soon learn what will work best for you. Spend the time to learn all you can, and you’ll be rewarded with encouraging pattern making results, which in turn will provide good quality metal castings.
So that’s a good run down on hand made patterns with simple wood working tools. But technology has moved on, even for the hobby worker, we now have low cost 3D printers made in China. I have witnessed some remarkably complicated plastic patterns made on a cheap 3D printer… it is, I believe where the future of pattern making is heading… even for the hobby worker.
You could do worse than to put a bit of time and effort into learning about 3D pattern printing, you may even find that you can service other hobby foundry workers with small pattern making jobs… Definitely worth thinking about.
We have a video a short video that illustrates the making of production patterns from an original 3D printed pattern.