Opinions vary on this next part. Some will argue that reamers should made to run perfectly true in the toolholder using a dial indicator and a few gentle nudges with a plastic mallet or piece of brass, which is good advice for any rotary tool. Others suggest that the reamer's going to follow the hole regardless, so a floating toolholder should be used, which allows the reamer to "go its own way.” Kennametal's recommendation is to use a floating holder where misalignment is present, but to select a high-quality collet chuck, shrink-fit, or hydraulic toolholder for minimal runout in all other cases. Don't use a drill chuck or side-lock holder.
Opinions also vary when it comes to cutting fluid, but whether your shop uses neat oil, synthetic, or water-soluble emulsion, it should be clean and well-maintained. For those with through-the-tool capabilities, by all means use it, even though this might mean upgrading to a solid carbide or modular-style reamer. That statement holds true for high-pressure coolant (HPC) as well, which can spell the difference between success and failure in many machining applications, reaming included.
There's also the programming to consider. CNC machinists using FANUC or compatible controls (which is most of them) have several options. For CNC lathes, a simple G01 command is all that's needed, feeding into the workpiece at the recommended rate and then retracting with a G00 rapid traverse command or an accelerated feedrate. CNC machining centers can use this same approach, although the G85 or G86 boring cycles are another option. The latter of these stops the spindle when the tool reaches full depth and then rapids out, while G85 feeds in and out at the same feedrate. Experiment with each and see what provides the best results for your application, but in no case should you peck the reamer as you would a non-coolant fed drill.
In no particular order, here are a few other factors to think about when preparing for or troubleshooting your next reaming operation:
- Reamers with a left-hand helix tend to push the chips forward during machining. These should be used on through-holes or where generous chip space exists. For all else, select a tool with straight flutes (for short chipping materials like brass and cast iron) or a right-hand helix (for stringy materials) to avoid chip packing in the bottom of the hole.
- More flutes mean a faster feedrate can be used but with less room for chips. If packing is a concern, select a reamer with a lower flute count. Also, reamers tend to cut slightly larger than nominal, so it's a good idea to choose one at the bottom of the hole's tolerance band. If available, adjustable reamers with brazed carbide tips are also a great choice (albeit with a higher price tag).
- Speaking of carbide, if your shop is still using the HSS chucking reamers that date back to the Brown and Sharpe screw machine days, consider upgrading to a solid carbide or even a modular reamer (check out Kennametal’s RHM-E series as an example). Both boast advanced coatings and micrograin carbide for maximum tool life and increased productivity.
There’s more. Modifying the reamer’s chamfer amount and angle can help address challenging hole conditions and materials, although this must be done in a precise manner using specialized tool grinding equipment. Similarly, it’s important to inspect reamers before use. Check for chipping and wear, and replace the tool sooner rather than later. And if you run into trouble, don’t hesitate to reach out for help. Kennametal has dozens of metal removal experts available, ready to lend a hand with this and other machining applications.