Semi-monocoque Sprint Car rolling chassis. www.engineeringnews.co.nz 23 is so unpleasant with the heat, the noise, the smell and the oil fumes – we try to get it all over and done with at once. So we do 10 or 15 engines in a week. The neighbours are very good and don’t complain too much about the noise.” Nelson is in the process of making his own 3-D printer. He bought one from the US, but it didn’t work very well, so rather than shop around until he found one that suited his purposes he decided to make one. In the one that he bought, all the parts that moved were heavy and all the parts that didn’t, weren’t – so the reverse became the main design criteria. The prototype is now in production and already printing production parts. The main use for the printer is induction manifolds and trumpets, which need to be made from materials resistant to petroleum liquids. 3-D printing is also ideal for the shapes involved. The overall sizing of the machine is conditioned to accommodate a V8 inlet manifold. And also to be able to print plugs and patterns for casting. The printer has two heads so that he can print the support structure at the same time as the final component. “Some Nylons can resist 130°C and acetone, methanol, ethanol and gasoline, so I don’t have any problems with it melting from temperature or chemical attack,” says Nelson. “It’s also machinable and tapable, so I can machine holes for inserts and if I rough it up, I don’t see why I can’t put two or three layers of carbon fibre on top, to give it some stiffness. For one or two parts it’s way cheaper than modelling it, generating tool paths and machining the final component from solid. Also for testing something on the dyno, it’s very much quicker.” Nelson prefers to be able to start a project and go from start to finish in one operation, rather than get distracted. “I really like working with large assemblies in SolidWorks and when you see that it all fits together, it’s really satisfying,” says Nelson. “I’ve developed a series of routines for the 5 axis machine to level things up and to identify the orientation and start point for the machining, so it’s very easy to set up any machining process. It gives feedback in terms of how out of line or level the component is and makes adjustments accordingly. With the motorised beds and fixtures, once an engine block is located it can be machined from either side without doing further setup. The Centroid 5 axis machine is designed for machining large automotive components.” Once an engine block has been probed and the required bore size calculated the machine goes through and machines all the cylinders to match. “Because of the requirement of about 30 of each line of engines per season, I would typically machine 10 at a time and bulk order all the other components,” says Nelson. “Unfortunately these $55,000 motors are going into Superstocks, which routinely drive into each other, which can write off these expensive engines in seconds.” Another typical job – a customer has some blank forged pistons and wants a particular profile machined into the top, again because either the component is unavailable or it would take too long to get. In this particular case the job consists of probing the sample piston on the 5 axis machine, using the data to generate a solid model, develop tool paths to the model and then machine the blank piston. “A couple of hours work,” says Nelson. “You have to do things fast, because otherwise you don’t get paid enough. We’re often doing a million-dollar job for $100 budget. And a lot of the time we’re doing something that nobody else can do.” EN
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