Basic Pattern development In The Hobby Foundry

Success or otherwise in your hobby foundry will depend to a large degree on your skills & capability to create easy patterns, i.e.
Patterns that are easy to mould, lift or cut off from the sand
mould after a diplomatic rap.

A pattern that has incorrect draft on vertical surfaces, badly complete angle fillets, or a pattern that has not been complete to an ultra plane stop will be difficult to work with.

Carpentry Framing

Pattern manufacture is an art in itself, pattern making
apprenticeships take around three or four years to complete, before you are given your "Trade Ticket".

The median hobby foundry employee most likely won't have the time, or the patience to get complex with the art of pattern manufacture to that extent.

But the basic skills are worth the effort to learn, because
without them you wont get far with your hobby foundrywork, unless you Pay to have all of your patterns made for you, but that would take all of the fun out of it, and also cost you a sizeable whole of money.

Construction costs of pro pattern manufacture can vary from a few hundred dollars for easy patterns, up to some thousand dollars for complex pattern designs.

I happen to a know a pattern maker who designs and builds patterns & core boxes to make alloy & cast iron cylinder heads, it is not unusual for pattern & core costs to be around ,000.00 Au before you even think about melting & pouring any metal.

If you are a patrimony of the old tech school law of the sixties
& seventies, there is a good opportunity that you still remember how to skilfully use woodwork hand tools.

Some of the finest foundry patterns were made using basic hand tools. More than likely you still have a chisel set tucked away in a drawer, or a spoke shave, wood plane & handsaw, plus
a host of other tools that could be used to make exquisite patterns in the home hobby shop.

And if they happen to be a bit rusty, then get them out again and bring them back to life, re-grind the cutting edges and hone
them with an oil stone.

Remember what your trade instructor always told you; "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 you could use to carve intricate shapes in 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 favorable for pattern making, but, you'll probably be slight 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 important discount

You'll be seeing for a soft timber that doesn't splinter, has a straight grain, is easy to work or carve, and finishes to an ultra plane finish.

One of the easiest timbers to use is jelutong, this timber comes from the Philippines, I don't know either it is from plantation timber, or old growth forests, but it is great to turn on a lathe, or shape and carve with sharp hand tools.

Some of the other pattern timbers in use are cherry wood, mahogany, maple, white pine, and many others.

Quite often a specialist pattern can be made from timber, and then a replica mould is made using Rtv 585 silicone, this is a quick recipe to remake replica yield patterns.The replica patterns can then be mounted onto a match plate along with the runners & gates, this recipe will enable you to mould & cast multiple parts at the same time.

With a slight practise you will soon know enough to make inexpensive capability patterns that create good sand moulds.

There is one foremost pattern manufacture tool that will make you wince when you purchase, but it is an foremost tool to have if you want to make correct 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 report the whole of shrinkage discount for distinct types of metals. The pattern makers ruler provides a built in shrinkage percentage, which means you don't have to hypothesize the final measurement or size of your pattern, you simply take your measurement from your shrink rule, and replacement the measurement to the pattern being made.

The law 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 ensue with patterns used for cast aluminium items.

Machining discount on exact parts of a given pattern may also need to be considered, commonly your own judgement can be used to judge that.

Pattern manufacture can be quite a challenge for the hobby foundry worker, but once you learn the basics and create your skills, with a slight institution your patterns will get best and so will the whole casting quality.

If you intend on manufacture lots of patterns, the investment in a shrink rule is well worth the money.

And while you're at it buy a good book on pattern making, it deserves a study all on it's own, but it forms an integral part of foundry work, and because you're the boss of your own workshop, you have to learn to wear the hat of the pattern maker & that of the sand moulder & founder.

Sounds like a whole lot of work doesn't it, but 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 results.

Col Croucher.