Get reaming right: Testing & Quality Assurance

At its best, reaming can be a grand finale, leaving high-precision holes with excellent surface finish. But the final act of the holemaking process might be spoiled by bad actors playing roles that result in scrapped parts and broken tools.

To prevent horror shows like this, as well as lesser disappointments, during reaming, machine shops and their toolmakers can take a variety of steps to help ensure that the process doesn’t deliver an unpleasant surprise ending.

According to experts, one of the main culprits for reaming gone wrong is runout. And it doesn’t take much runout to throw a reaming process off-track, said Patrick Cline, national product manager for holemaking at Iscar USA, a cutting tool supplier in Arlington, Texas.

“After 0.0003″,” he said, “especially in high-speed reaming, you’re going to see problems start to show up.”

Cline explained that runout-related troubles, such as chatter and rough surface finish, are caused by unbalanced cutting forces that make tools oscillate.

And reaming, he said, “is a very high-force process because there’s a lot of friction (caused by) a lot of contact between the reamer and the part. That’s why it’s important to have the same amount of cutting pressure all the way around.”

A key to preventing problems resulting from runout is the choice of toolholders. Instead of standard collets, shops engaged in reaming should opt for holders that minimize runout, said Robert Tennant, engineering manager for round tools at Star Cutter Co. in Farmington Hills, Michigan.

Cline said almost all cutting tool companies sell toolholders that can be adjusted to reduce runout. As an example, he pointed to Iscar’s Finefit product, which is adjustable both radially and axially.

Another adjustable offering from Iscar is its Bayo T-Ream high-speed reaming system. He explained that Bayo T-Ream features three adjustment screws that can be tightened in turn to move the reamer enough to eliminate runout.

“It’s a simple solution and very cost-effective as opposed to buying a specific adjustable holder like Finefit,” Cline said.

Users of the Bayo T-Ream system can eliminate runout using adjustment rings that fit onto the body of the reamer. Image courtesy of Iscar

In addition to runout, chatter during reaming can be caused by the feed rate, said Steve Pilger, North American product manager for holemaking at YG-1 Tool (USA) Co., a cutting tool supplier in Vernon Hills, Illinois.

“Typically,” he said, “I found that increasing the feed rate slowly and finding a sweet spot will eliminate that chatter. We call it feeding past the chatter.”

Taking Stock

Chatter is just one of the problems that can be caused by the stock left for the reamer to remove. The right amount of stock for a particular application depends on the tool and the material being machined.

Chatter and poor surface finish might be the result if too little stock is left for reaming, said Cline, who ties the problems to how a tool removes material in these cases.

“You want to cut that material as opposed to rubbing it off,” he said. “Every cutting edge has a certain amount of edge prep that you need to get past. And if you don’t leave enough material, then you’re never really cutting. You’re just rubbing, which (produces) a lot of pressure and heat.”

On the other hand, excessive amounts of stock also can cause reaming troubles.

“If there’s more stock than what’s recommended, we have to make sure the tool is sharpened on the end to clear that amount,” said Jamie Dunneback, Star’s sales manager for round tools. “Let’s say somebody’s leaving 2 mm a side to ream and my tool’s not sharpened to machine 2 mm. That tool’s going to hit where it’s not sharpened, and you’re going to chip it or break it.”

He pointed out that the suggested stock removal amounts for different materials don’t vary much. A general rule, he said, is to leave about half a millimeter per side for a reaming operation.

Cline said recommended stock amounts range from 0.002″ to 0.008″ per side, depending on the material hardness and the size of the reamer. He added that reducing unneeded stock by relatively small amounts can give a big boost to tool life.

Longer Life

Dunneback said tool life during reaming also can be extended by running at the feeds and speeds recommended for the material being machined and the number of cutting teeth on the tool.

Reamers offer much higher penetration rates than single-point boring bars. Image courtesy of YG-1 Tool (USA)

In addition, reamer life depends in part on the job done by the roughing tool before reaming.