CNC Bed Mill Provides Speed, Precision For Race Engine Shop

Engine builders know that recreating a winning combustion chamber with a hand die grinder is time consuming and doesn't always produce a 100 percent accurate copy.

Case Study From: 5/15/2003 Modern Machine Shop

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CNC-equipped Millport Rhino 40B bed mill

Tom's Auto uses a Centroid CNC-equipped Millport Rhino 40B bed mill from Millsite Engineering to build and repair custom cylinder heads for drag racing, circle track, hot rod and street rod cars.

Producing exact copies of custom race engine cylinder heads is difficult. Engine builders know that recreating a winning combustion chamber with a hand die grinder is time consuming and doesn’t always produce a 100 percent accurate copy.

With racing of all types growing in popularity and the aftermarket street rodders demanding high performance products, the ability to produce custom cylinder heads in quantity is a necessity.

This is the situation encountered by Tom’s Auto (Clarksburg, Pennsylvania). Tom’s Auto is a full-service race engine shop, building and repairing custom cylinder heads for drag racing, circle track, hot rod and street rod cars. Increased customer orders and the schedule demands of racing made it necessary for Tom Hemphill, the shop’s owner, to find a way to get more high quality engines “out the door.” He needed to find an alternative to hand porting and grinding.

Tom’s Auto creates custom race engine cylinder heads and offers a repair service for damaged heads. New heads are prototyped by starting with an existing casting and drastically modifying the combustion chamber shape and the intake/exhaust ports by using a combination of hand shaping and CNC machining. Once the new head design has proven itself on the dyno and has performed well at the track, CNC copies of the head are made. “To be competitive, we need to make around 2,100 hp,” Mr. Hemphill says. The CNC copies are machined from a solid block of 6061 aluminum. The CNC has made it possible for Tom’s Auto to create new billet CNC heads that will produce the same horsepower of the proven prototype head design.

At the Performance Racing Industrial Show, Mr. Hemphill saw a demonstration of the “copy and cut” digitizing feature on a Centroid (Howard, Pennsylvania) CNC-equipped Millport Rhino 40B bed mill from Millsite Engineering (Ravenswood, West Virginia). Mr. Hemphill knew it was just what he needed.

“It’s cylinder head porting that got me into CNC,” he says. “The porting work we were doing was very time consuming. You have eight intake and eight exhaust ports in a head. The closer you can come to making them the same, the more power you can make. And . . . it’s real labor intensive doing it by hand. We were getting to the point that we were doing more extensive porting. Originally, we started removing 0.06 inch to 0.1 inch of material. Then we got to the point where we were working on heads that we actually had to remove 0.25 inch of material in some places.”

The CNC machine has given Tom’s Auto the ability to produce custom race engine cylinder heads that will exactly match a proven head design in horsepower and performance. Through CNC digitizing and machining, customers are assured that they will receive an exact reproduction of a proven head design.

The shop performs both digitizing and machining with the Millport bed mill. The Millport CNC eliminated the need to buy a dedicated digitizing machine, reducing Mr. Hemphill’s initial investment and reducing the learning curve with only one system to learn. The digitizing interface is in conversational format and integrates with the rest of the control software.

New business the Centroid CNC machine has brought to Tom’s Auto is the ability to do repair work on any brand of high performance cylinder heads. Rather than scrap a favorite cylinder head, a race team can now choose to have the head repaired to the original shape. When an engine blows up, very seldom does the whole head get destroyed.

Mr. Hemphill ordered the Millport CNC machine equipped with the Centroid digitizing package. The Centroid “DP-4 all surface touch probe” is equipped with a standard M3 thread that has allowed Tom’s Auto to create its own custom-shaped probe stylus to match the special “lollypop” carbide cutters used in machining the combustion chambers and ports. These lollypop-shaped styli and cutters allow undercut digitizing and machining. The CNC also came with a built-in hard drive for onboard digitized part G-code storage, which eliminates the need for an extra computer to be hooked up to the control, further simplifying the digitizing process.

Mr. Hemphill uses the same probe to locate part positions that he uses for digitizing. He uses the conversational probing cycles to automatically find centers, edges, corners, part zeros and heights. To locate a new head for machining or digitizing, he selects the probing cycles graphically, follows the instructions on the screen, presses the cycle start button and the part location is automatically set. Mr. Hemphill is constantly tearing down and setting up new jobs, so the amount of time it takes to set up a new fixture or vise is an important factor.

Tom’s Auto used to send lightening work out of the shop until it acquired the new Rhino 40B CNC bed mill. “It would take about 2 weeks just to get a set of pistons lightened,” Mr. Hemphill says. “Now we’ll have a set done in 2 days.” This is significant—by keeping the work in house, the company is able to reduce the cost, increase the quality and decrease the time it takes. “The piston manufacturers only have four or five forgings for a large range of sizes,” Mr. Hemphill says, “so a large diameter piston will have a thick wall that adds weight.” He uses Centroid’s conversational programming, Intercon, to program the lightening operations. He makes use of Intercon’s Teach mode to swing three-point arcs inside the piston so he doesn’t have to calculate any arc endpoints. Once he has swung the arc for the one side, he just mirrors the same arc to machine the other side. “From the underside of the piston, we have written programs and go in there with long end mills with radius corners and lighten the piston anywhere from 70 to 90 grams,” Mr. Hemphill says.

After the pistons have been lightened, he drills a precision 0.040-inch gas port in the oil ring groove, which provides better ring sealing and oil control. “To gas port a set of pistons, it used to take 8 hours by hand,” Mr. Hemphill says. “Now we can do a set of pistons in an hour and be doing something else while the machine does the work!” Tom’s Auto also only breaks about a quarter as many drill bits.

Since the word got out about what Tom’s Auto could do, the company has had plenty of work. Mr. Hemphill says, “It [the new machine] allows us to be a little fussy with the work we pick to do, and we have been able to elevate our customer base.”

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