Ream on: Drilling Performance

My machining education was quite different from most. Circumstances forced me to learn a lot on the fly, so broken tools, bloody fingers and scrapped parts were common on my journey.

Learning to ream a good hole was one of the more difficult matters that I struggled with, and I learned much about what not to do. Fortunately, I was exposed to skilled people, and I managed to get short but effective lessons. With a little guidance from experienced toolmakers, I overcame the difficulties, and reaming high-quality holes became easy.

My first mistake was thinking that reaming a hole was as simple as “drill the hole, ream the hole, and you’re done.” Generating the right-size hole with a reamer is more than simply sticking it in the hole. Several variables need to be considered before putting the reamer in the hole.

Like all machining operations, tool quality is important. Buy a cheap reamer, and you will regret it. Go ahead and purchase a high-quality reamer from a reputable manufacturer. In general, reamers manufactured in Germany, Japan or the United States are best.

Consider the tolerance of the hole, and buy the right size of reamer for the job. Reamers rarely cut undersize holes, so plan to ream a hole larger than the diameter of the reamer. It always is a good idea to buy one reamer sized to the lower limit of the tolerance band and one reamer sized to the nominal dimension. Starting with the smaller reamer is a good way to limit the risk of making a hole that can’t be corrected.

An old guy once told me that a reamer was running too fast if I could not count the flutes as it spun.

Having the best-quality tool that is sized perfectly doesn’t ensure a good hole. Oversize holes are overwhelmingly the biggest problem with quality when reaming, and radial runout is the primary contributor to oversize holes. Eliminating runout can be done in a couple of ways, beginning with making sure the reamer is held in the best method possible. In some cases, this means using a good collet. In other cases, this might necessitate a high-quality chuck. No matter how it is held, if the reamer wobbles when it spins, you likely will end up with an oversize hole. One of the more creative solutions I have seen for combating runout is holding the reamer in a boring head so the reamer can be “dialed in.”