Computer Numeric Controlled (CNC) machining allows engine builders to achieve almost unbelievable levels of accuracy and consistency. The programmability of a digital computer not only automates the operation of the equipment but also provides a level of repeatability that can’t be matched by manual equipment. That’s why CNC has been the backbone of virtually all manufacturing for the past 40 years.
CNC-controlled lathes, mills and machining centers can be used to machine a wide variety of industrial and automotive parts. Most engine builders who have CNC equipment, however, use it primarily for engine block and cylinder head machining. Even so, the possibilities don’t end there. Some engine builders are using the capabilities of their CNC machining equipment to do all kinds of things, including engraving valve covers and other parts, making carburetor adapter plates, custom engine parts, motorcycle parts, even industrial parts.
“If you can dream it, you can machine it,” said one CNC equipment supplier. In other words, if you can design, map and program a part for a CNC machine, figure out a way to fixture it and acquire the right machine tools to cut it, the only limitations on what you can do are the physical dimensions of the part you want to machine and the size limitations of your CNC equipment. A full featured 5-axis CNC machining center obviously offers the widest range of capabilities, but 3-axis and 4-axis machines are also able to do many jobs.
Although most of the automotive CNC equipment that’s being sold today is geared for automotive head and block work, there’s no reason why this same equipment can’t be used to expand your business in new directions. When the economy went into recession and the demand for engine building took a big hit, some engine builders who had CNC capabilities began taking on custom CNC machining projects to offset the drop in their automotive work.
The move to diversify the kind of work they were doing not only helped them weather the recession but to strengthen and expand their customer base. Up to 50 percent or more of the work that some of these shops are doing today is non-traditional CNC machining. This includes making custom automotive and non-automotive parts, machining various types of castings and other components, and even doing custom CNC programming for others.
Tom Nichols of Automotive Machine & Supply in Ft. Worth, TX, says his shop specializes in high end import engines and Harley Davidson motorcycle engines, but that nearly half of his business is now custom CNC work. Nichols owns six CNC machines, including a 5-axis machining center that he originally bought to do cylinder head porting. His equipment also has a digitizing probe which he uses to copy and import parts dimensions into his MasterCAM CAD/CAM software.
The software digitizes the dimensions of parts that will be copied, and determines the machining strategy and tool paths to make the part. The information is then exported into G-Code, which is used to run the CNC machining equipment.
One of the custom jobs he did was to make a set of velocity stacks for an alcohol fuel dragster. A pattern for the velocity stacks was first hand shaped out of wood on a lathe, then flow bench tested and reshaped until the desired flow characteristics were achieved.The wooden stack was then digitized using the CNC probe and imported into the CAD/CAM software to make the parts on the CNC equipment.
Nichols said the digitizing probe allowed him to accurately locate and mill the flats on the stack so when it was installed on the injection manifold, it fit perfectly. “That would have been a long manual job to machine, but the CNC software and equipment made it fallin’ down easy.”
Some of the custom CNC jobs Nichols has done recently include machining Hemi connecting rods, idler bushings for a BMW supercharger kit, making parts for his own block boring machines, brake caliper adapter brackets, engine adapters for mating Isuzu diesel engines to GM pickup transmission housings, steering bushings for 928 Porsches, a set of custom oversized Pony emblems for a Mustang, Yahama luggage racks and metal replacement taillamp mounts for Harley motorcycles that were originally made out of plastic and prone to cracking.
Some of his non-automotive jobs have included machining heads for industrial compressors, making custom 10-inch multi-groove pulleys for gas well compressors, parts for aircraft maintenance work, flare holders used by parachutists during exhibition jumps (US Army Golden Knights), and even custom sport knives.
Making custom CNC parts requires not only a highly capable 5-axis CNC machine with good CAD/CAM software, said Nichols, but also all of the related equipment that may be needed to support and do the R&D that’s required to develop and make custom parts. For automotive work, this might include a flow bench, balancer and so on.
Nichols said he can do small CNC batch work from one to 200 pieces at a time, or just the CAD/CAM programming if a customer wants to do his own production. “There’s quite a learning curve with CAD/CAM software if you’ve never done it before. You can get the basics down in a couple of weeks, but it can take six months to a year to really learn everything the software can do.”
Nichols said entry-level CNC equipment is not that expensive and can be learned fairly quickly. “For $10,000 plus maybe $3,000 for tooling and fixturing you can get yourself a small hobby CNC machine for low production custom parts. It’s a good way to learn CNC before you move up to larger, more expensive and capable CNC equipment.”
“CNC allows you to do more work with fewer people. We used to have 6 to 7 people working in our shop. Now we do the same amount of work with just two people. The CNC machines do most of the labor that we used to do manually, but it does take longer to set up a CNC job initially. Some jobs can take one to two hours to set up the programming and fixturing. But once that’s been done, the CNC equipment does everything else,” said Nichols.
Gordon Schiffelet of Performance Automotive in Bethalto, IL, bought a 4-axis CNC machine for blueprinting blocks and heads. He says his equipment is absolutely vital for the kind of work his shop does, but that it also allows him to take on some custom CNC jobs, too. “We do custom valve cover engraving, make manifold spacers, modify main caps and other engine parts, and have even made parts for a local tool & die shop that makes big castings.”
Monty Crawford of Arrowhead Speed & Machine in El Dorado, AR, is another engine builder who is using his CNC equipment for a lot of custom work. “Last month, I’d say about half of the jobs we did was something other than traditional head and block work.”
Crawford said that sometimes a customer will bring him a rough sketch or drawing of what they want him to make. He then has to program the part, a task which he says comes naturally since his background is a tool design engineer. Based on experience, he can usually quote a price for a job that includes any required development time, programming, handling and cutting time on the CNC equipment. “We use the same shop labor rates for custom CNC work as we do for traditional automotive work.”
Crawford said one non-automotive project he’s undertaken recently is machining lower receivers for AR15 assault rifles. “The gun market has gone crazy recently, and it’s hard to get finished parts for many guns. I have a source for the AR15 receiver forgings so I can machine them myself.” Crawford said the AR15 gun parts he is making is more of a hobby, but if they sell well it could open up a whole new niche for his business.
Pat McCready of Nyes Automotive in Muncie, IN, currently has two CNC machines for doing automotive work. “Our CNC machines are busy all the time, so I haven’t had much opportunity to look into doing custom jobs. But when I bought the machines, I was thinking that at some point down the road I’d like to branch out into some custom CNC work. I’m not there yet but hope to develop some new opportunities at some point.”
Thinking of Buying a CNC Machine?
Anyone who is considering buying CNC equipment should have basic machining skills and experience. Most suppliers of automotive CNC equipment include basic training to get you up and running, and most of the machines come with basic software for cutting and milling parts.
The software may also include an engraving program for machining valve covers, plaques, plates and other flat surfaces – a feature that has proven to be very popular with a lot of CNC users for making signs and trinkets to promote their own business.
For copying parts, a digital probe is a must for tracing the dimensions and contours of parts with complex shapes. You’ll also need some type of CAD/CAM software to create a digital blueprint of the part and to create the G-code to run your CNC equipment.
Depending on what type of CNC equipment and software package you end up with, you can make anything from custom billet crankshafts and camshafts to complete cylinder heads and engine blocks. And once a project has been mapped and programmed, it can be stored for future projects so you don’t have to redo everything from scratch.
Although many engine builders have bought their CNC equipment only to machine automotive cylinder heads and blocks, you also need to think about all of the other possibilities this type of equipment can open up for your business. As once CNC equipment suppler told us, “Don’t limit your thinking to the kinds of jobs you are doing today.
Think about the kind of jobs you might be doing three to five years from now. Think about the work you are currently farming out to somebody else and how your CNC equipment might allow you to do the same work in-house. Think about all of the other custom CNC machining opportunities that may be available in your local area.”
What is CNC?
CNC is simply a means of automating the feed rate, cutting speed, location and angle of the machine tooling. The hand controls on a machine are replaced by servos that are operated by a computer. You tell the machine what you want it to do by typing on a keyboard or using a touch screen (such as bore the block, cut the upper and/or lower O-ring seats for the cylinder liners, align bore the block, resurface the block, etc.).
You also enter the necessary parameters that tell the machine how much metal to remove. The part is then fixtured and located manually or automatically with respect to the tooling, and the computer takes over to run the equipment and perform the desired processes.
What happens if you screw up and enter the wrong coding that controls the machine? If the CNC equipment has built-in software safeguards that can detect obvious input errors, or tooling travel or positioning errors, it should stop the machine and/or ask for corrections before proceeding. If the software lacks such capabilities, however, you may end up with an expensive hunk of junk in the machine, or broken tooling. Accuracy is essential so the machine doesn’t drill a hole in the wrong place or too deep, or mill off too much metal from the surface of a part.
Programming is the key to CNC machining. That’s the part that intimidates many people who might otherwise want to get into CNC but are reluctant to do so. As we said earlier, most CNC equipment suppliers will provide basic training to get you to the point where you can perform basic machining. Additional hand-holding and tech support may be provided as needed so you’ll be happy with your equipment. It takes time to gain confidence, but with each job you accumulate more and more experience until eventually you can do just about anything.
CNC requires input commands that tell the controls how to move the tooling. In a 3-axis machine, the X, Y and Z coordinates correspond to in and out, left and right, and up and down. That’s basically all you need for basic engine machining. If you want to automatically repeat the same process for both banks of cylinders on a V6 or V8, or a complex work piece that has more than one surface, you need a 4-axis machine (the 4th axis is the rotation of the workpiece).
For porting cylinder heads and making complex 3D components, the workpiece and tooling head both have to move so the tooling can follow complex curves and circular motions. This requires a 5-axis CNC machine (the 5th axis being the circular movement of the tooling), and software that can program the intricate movements.
CNC machines can be programmed manually using G-code or M-code commands entered on a keyboard or touch screen. The code commands correspond to various tooling movements in the X, Y and Z planes. Each line of code tells the tooling where to move, how quickly to move and at what angle so metal is removed where it is supposed to be removed. G-code and M-code training classes are offered by many trade schools and online.
Easier to use software allows “conversational programming,” so you don’t have to know G-code or M-code. You just enter dimensional answers to basic questions about where you want metal cut, milled or drilled. Some CNC control screens will even show you a 3D map of how the tooling will move as it machines the part. Most machinists can be up and running with conversational programming fairly quickly with minimal training. They won’t be doing any custom machining, but they will be doing boring, surfacing and similar jobs. The ability to do custom work will come as they gain experience with CNC.
Once a CNC machine has been programmed, the work piece is mounted and fixtured in the machine. Its position must then be zeroed relative to the machine tooling before you press the GO button. From that point on, CNC takes over and does everything else. You don’t need an operator to run the equipment or to babysit it. And if you are performing the same job over and over again on a run of similar parts, CNC will do each job exactly the same every time.
The adaptation of CNC machining in the engine rebuilding market continues to grow – especially among those who would classify themselves as high-end or specialty engine builders. Most would agree that CNC has become a “must have” tool for their shops. Many have also found that having CNC capabilities in-house not only allows them to make their own custom automotive parts but to also make all kinds of different parts for a much broader range of customers. It’s all about making the most of what you have and making good money while you’re doing it!