Rules of Swiss-Type Machining: Micro-Reaming

The number-one rule of Swiss-type machining – the process is the product. Swiss-type machinists work smart. Less effort, less machine time, longer tool life and maximum repeatability. Producing the most precise pieces while achieving quicker turnaround times with improved tool life is the ultimate goal for any manufacturing shop.

This week, we discuss micro-reaming. So, what is micro-reaming? Let’s break it down…

Reaming, boring and drilling are all processes to make or modify a hole in a workpiece, but reaming is not boring, boring is not drilling and all three present both benefits and challenges to machinists manufacturing parts for optimal repeatability.?So, what’s the difference?

Drilling: A process in which a drill bit is used to cut an approximate hole size into a workpiece.

Boring: A process in which a single point tool enlarges an existing hole in the workpiece to help give the hole a more cylindrical diameter through the hole's length.

Reaming: A process in which one or more cutting elements is used for enlarging to size and to contour a previously formed hole. Its principal support during the cutting action is obtained from the workpiece (Machinery's Handbook 27th Edition).?

Allowance: The difference between the drill diameter and the reamer diameter when the workpiece’s initial hole is drilled

So, to create a hole, you must drill. To enlarge and round out a hole, you must bore. To finish the interior walls of a hole to be more cylindrical, and to a more precise size, you must ream. If there was any confusion around those three processes, it should now be cleared.

This old educational film produced near the end of World War II for the U.S. office of education is a blast from the past! Courtesy of the Museum of Our Industrial Heritage, this fun bit of history details drilling, boring and reaming operations in basic manufacturing. While the equipment and some of the processes are outdated, this is a great way to visualize the concepts.

You might be thinking, “Well, I can just drill to size, can’t I? Why do I need to ream at all?”

It is true that for many applications a modern twist drill can be very accurate when drilling a hole to size, but it can’t reach the level of size accuracy and smoothness of surface finish that the reaming process can. That means reaming is essential in industries that require the most precise accuracy and repeatability, and turnaround times. These industries include aerospace, medical, automotive, and more. Micro-reamers are exactly what Swiss-type machinists need when producing very small and complex holes that need tolerances that border perfection.

There are ten main types of reamers, including the hand reamer, adjustable hand reamer, chucking reamer, straight reamer, machine reamer, rose reamer, shell reamer, tapered reamer, Morse taper reamer, and combination reamer. Now, we could break down the different types of reamers and the way that they can be used, but that’s already been done by various folks across the Internet. For our purposes, we are only going to highlight the workings and best practices of micro-reaming for Swiss-type machining. Let's start off by dipping into the science behind reamer edges.

According to the article Right Reamers featured in Cutting Tool Engineering, most multiple-edge reamers have four to six cutting edges, with larger diameter tools having eight to 12. More cutting edges means more penetration and rounder finished holes, but...

“More edges make smaller chips,” said Josh Lynberg, president of Monster Tool Co., a manufacturer of solid carbide cutting tools, in the article. “However, there is a limitation. You do not want so many flutes that chip evacuation becomes a problem. Most reamers are grouped in size ranges, with numbers of teeth matched to that particular size range.”

James Gosselin, president of Genevieve Swiss Industries, Inc., a leader in high precision tools and accessories for Swiss-type CNC machines and small parts manufacturing, said that reamer geometry varies, and choosing the proper geometry for the job is essential in producing the desired results.

“It depends on whether the reamer’s flutes are straight, left-hand or right-hand spiral. The spiral flutes may provide improved surface finish and better ability to clear out chips,” said Gosselin.?

(From Chapter 23: Drilling and Related Hole-Making Process in DeGarmo’s Materials and Processes in Manufacturing)

Through-holes should be reamed with left-hand spiral reamer because the helix of the flute rotates counterclockwise, and the reamer pushes chips through the hole as it cuts. For blind holes, a right-hand spiral reamer should be used because the helix of the flute goes clockwise and forces the chip to expel out of the hole. He also noted that a straight flute could be used for either depending on the material and purpose of the workpiece.

“Care must be taken when reaming blind holes,” Lynberg said. “Proper chip evacuation must be considered to prevent the chips from marring the hole. You never want to cut a chip twice. This is when a chip that has been cut gets pinched between the reamer and the hole, and the reamer forces the chip between the finished hole and the reamer. This results in poor hole quality or even an out-of-tolerance hole.”

Straight flutes create less chips during a reaming operation, so less needs to be removed, the article states. While using a straight flute, the chips are propelled by the pressure of the coolant and are expelled in the direction of its flow. Some metals, like certain aluminum alloys, should use a straight flute because a spiral flute can compromise the material.??

When you are servicing orders across leading industries, the stakes are high, and getting noticed is as important as being remembered for the right reasons. Giving your clients exactly what they want each and every time that they ask is paramount to your success.

“You have to remember the customer always wants to decrease cycle time,” said Donato Pigno, former product specialist and key-account manager for Komet, a leader in manufacturing dental rotary instruments, in the article Getting Reaming Right featured in Cutting Tool Engineering. “He’ll typically use a roughing tool and a finishing tool.”

While micro-reaming can achieve top quality holes with the highest rate of repeatability in your workpieces, it can also present some specific problems due to the fine nature of the tools and the high level of precision that they need to meet. While working on the microscale, issues with tools alignment are often persistent, specifically during the reaming process.?

“Parts that require tiny holes with precise roundness include micro valves and components for pneumatics and fuel delivery systems. For these and related applications, Genevieve Swiss, a manufacturer of tools and accessories for small-parts machining, offers carbide micro reamers in diameters as small as 0.0236 inch. The company says a floating holder should be used for such small reamers to compensate for machine positioning inaccuracies. A small amount of float helps the reamer follow a hole’s path should that path deviate from the centerline slightly. It also prevents the reamer from tapering or ‘bell-mouthing’ the hole,” said Derek Korn, executive editor of Modern Machine Shop, in his piece The Importance of Float During Micro Reaming.

??“The orbitally floating holder from Genevieve Swiss allows for as much as 0.009 inch of off-center float as a reamer follows a drilled hole. A proprietary bearing design returns the reamer to the center position upon completing each reaming operation, ensuring part-to-part consistency. In addition, float sensitivity is adjustable to accommodate reamers of different diameters.”

Orbitally floating micro-reamer holders are a great solution to solving problems with positioning accuracy encountered in micro-reaming jobs. Designed with a "True Orbital Float" feature in the front and back axis, they ensure extreme precision while creating small holes because their precision bearing design allows the tool to return to the center position after the reaming operation is completed. This self-centering floating holder helps ensure consistency workpiece-over-workpiece.

GenSwiss micro-reamers are made of K15 carbide. They have a left-hand helical flute with a right-hand cutting geometry and include various coating options. Float sensitivity is adjustable to accommodate different diameter reamers with a diameter tolerance of +0.00 to -0.00012 inch.

When it comes to surface finishing and reducing inaccuracies for precision, many believe that reaming can’t be beat.

“It is dangerous to say you just want to use a drill with a reaming quality,” said Pigno. “You will never get the same result.”

For certain jobs, a core drill can be a good option for creating a surface finish within a hole that is adequate. The core drill is a hybrid reamer and drill. It can remove more material than the reaming process while eliminating the need for boring. When it comes to course corrections with faster turnaround times, the core drill could be the right tool for the cut, but it won’t match the extreme precision and ultra-high quality of the reaming process. This is especially true while working in the microscale, making micro-reaming an essential step in manufacturing the highest-quality pieces.

In summary, the main goal of reaming is to bring the hole to finished size and smoothen the interior walls of any existing hole. Whereas boring enlarges the hole, and drilling creates it in the first place. Drilling a smaller diameter hole to be finished with reaming will produce more accurate results with a smoother surface finish. An orbitally floating micro-reamer holder provides ultimate precision when aligning the reamer with the hole to craft a perfectly round interior at the correct size.

For the best results while micro-reaming, always remember to choose the right reamer for the workpiece’s material, use a sharp reamer with coolant-thru capability (meaning your cutting oil is in contact with the cutting edge), maintain the correct cutting speed and angle, and keep obstructions clear and out of your working environment.?

Check out GenSwiss' line of floating micro-reamer holders and reaming tools today!

You can learn more about the basics of reaming on the microscale, macroscale and everywhere in between, as well as when each operation is best used, from this video by Stuart de Haro.?

Want even more Rules of Swiss-Type Machining? Check out our last installment covering Thread Whirling.

More about GenSwiss…

Genevieve Swiss Industries, Inc. brings to market unique high precision tools and accessories, advancing small parts manufacturing and enhancing Swiss-type machine processes. Our high quality product line of cutting tools, machine tool holders, and live spindles are imported from three of Switzerland’s primarily world-class manufacturers:?PCM Willen SA,?UTILIS AG, and?Louis Belet SA.?

With more than 35-years of experience in the industry, GenSwiss aims to improve distribution efficiencies and increase manufacturing productivity. We strive to deliver products which meet or exceeds customer expectations, providing a reliable service with application solutions for YOUR critical small parts manufacturing.

Our own GenSwiss designed and manufactured?Signature Series?products are becoming a favorite among CNC Swiss-style machinists.?These products include high quality rotary?broach tools,?Ti-Loc? extensions?and?saw arbors,?high precision straight shank saw arbors,?compact straddle knurl holders, and?many more.