Modular reamers are widely used in high volume automotive work, but are equally applicable for low volume repeat jobs.  Image: IscarClick image to enlargeby Kip Hanson

Put away your chucking reamers; it’s time for a modular approach to hole finishing 

High speed steel chucking reamers have long been the go to tool for hole finishing. They’re readily available in practically any size, and like their cousin the Jobbers drill, they’re inexpensive. Setting one up isn’t terribly difficult—just stick it in a collet or floating holder and get reaming. 

There’s just one problem: as with any HSS cutting tool, they’re slow. And because there’s no way to flood the hole with generous amounts of cutting fluid, tool life and chip control can be problematic, especially on deep or blind holes. Nor are chucking reamers terribly accurate, not compared to boring or burnishing, anyway—assuming you have a relatively generous hole tolerance and the surface finish callout isn’t overly fussy, have at it. As long as you’ve drilled the hole to the right size and it’s fairly straight, chucking reamers do a decent job. 

Solid carbide and carbide tipped reamers are a better alternative, yet these are typically custom order, so you’d better plan ahead. 

As any machinist knows, carbide cutting tools achieve cutting speeds several times faster than their HSS cousins, although carbide reamers face the same challenges with cutting fluid starvation—unless you can find one that’s coolant-fed (not impossible, just difficult), it’s going to be tough to keep the hole clear of swarf. 

Tales from the field
Dispirited over all this reaming negativity? Don’t be. There are several solutions, albeit ones that require additional planning and a higher initial investment. They’re called modular reamers, and if you’re not yet using them—particularly on repeat or high volume jobs—you’re missing out on some significant improvements to your hole finishing operations. 

Since it does an excellent job of lubricating the tool and flushing chips out of the work area, through-the-tool coolant should always be used when reaming.image: Horn USAClick image to enlargeShane Schirmer, application and sales engineer at Horn USA Inc., has first hand experience. 

“One of my customers produces the same part four times a year in lots of 1,000 pieces, and they were actually scrapping more parts than they were making,” says Schirmer. “By moving them to our DR style reamer, we eliminated all of the scrap and sped up cycle time significantly.”

Fellow application and sales engineer Ryan Schaefer has seen similar results. 

“The hole quality is great, but the productivity increases are even more dramatic,” he says. “I was at a shop the other day and the operator was actually afraid to push the cycle start button, the reamer was moving so fast. And another came back and told us their customer was complaining because the surface finish was too good. We actually had to kick up the feedrate a little bit to make the hole rougher.” 

How do they work?
Each of the companies interviewed for this article has its own series of modular reamers, each with its own mounting styles, size ranges, and unique geometries and coatings, but all share some similarities.

As you might have guessed from the name, modular reamers are equipped with a replaceable head. Once the reamer has been mounted in the turret or toolholder, changing heads literally takes seconds.

Many modular reamers are made with a variable pitch geometry, eliminating vibration and chatter, particularly at the start of the hole. 

Because they’re carbide, cutting speeds are typically four to six times higher than high speed. 

Since modular reamers are often engineered to order for the specific material and application, feedrates are similarly increased. Ditto tool life. 

Through the tool coolant is a given with modular reamers. Part quality is better, chip evacuation and process
stability assured. 

Unless your desired hole size matches one of the standard offerings (1 mm increments are fairly common), you’re going to wait six to eight weeks for delivery. Plan ahead. 

As with standard reamers, left hand flutes are available for through holes, and right hand flutes for blind holes. Be sure to use the correct style for your application, or chip control can be a problem. 

A wide variety of cutting tool materials and coatings are available with modular reamers, including carbide, cermet, PCBN, and PCD.image: CeratizitClick image to enlargeThe downside to all this is cost. Comparing a modular reamer to a chucking reamer is like comparing a bicycle to a sports car. The results, however, are well worth the investment. 

This final point is the roadblock for many shops—why spend several hundred dollars or more for a modular reamer when a twenty dollar chucking reamer will get the job done? 

“Our Bayo T-Ream is targeted at high volume manufacturers such as automotive, or in the aerospace market on difficult materials,” says David Vetrecin, holemaking product manager at Iscar Tools Inc. 

“Performance and process stability are the main drivers in these segments, far more so than tool cost. That said, a job shop using a modular reamer to make a handful of parts can easily justify the investment based on the tool’s higher performance level, provided it can be amortized over repeat jobs or common hole sizes.” 

Ready, set, go
Setup and usage recommendations are also fairly standard across brands. Eliminating runout is job one in any reaming application, modular or no. A shrink-fit or hydraulic toolholder is the best way to achieve this. If spindle or turret alignment is a concern, a “steerable” holder or adjustable sleeve should be used. Do not use a collet. 

Most manufacturers offer reamer reconditioning services. Modular heads can usually be re-sharpened several times without compromising size or hole quality, provided the tool isn’t pushed beyond the point of no return. CBN, PCD, and cermet tips are available, as are multiple coating options and carbide grades. 

Some manufacturers recommend boring a small section at the beginning of the hole to get the reamer started, others suggest taking a quick pass with a boring bar down the length of the hole, especially if drill walk exists. Depending on the desired accuracy and straightness, however, it’s often possible to skip this step and ream the hole immediately after the drilling operation. Check with your provider for their specific recommendations. 

Michael Hunter, product manager for holemaking at Ceratizit Chicago, says the Komet brand of  modular reamers offer both simplicity and performance. “Reduced cycle time is a huge advantage,” he says. “Application-specific geometry is built into each tool for maximum performance; there are no adjustments, which compared to boring the hole to size is a huge benefit. This also means lower scrap rate—since reaming is often one of the final operations on many parts, a modular reamer might prevent scrapping out a $20,000 workpiece. They make a huge difference in the right application.” SMT

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