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For the first time in months, I got a chance to get back into my shop over the weekend. Boy was it nice. I had a piece to build for a customer, a piece that was promised some time back. (Thank you very much for patient, understanding customers.)
I selected the rough lumber for my project, chopped the piece into workable sizes and rolled the cart to the jointer. As I pushed my first piece over the three-knife cutterhead, I was amazed at how loud the operation sounded. I was caught off guard and wondered if the machine was not properly tuned to work.
Then I realized that the sound was loud because over the past few months, all my woodworking has been in the shop at Popular Woodworking. The magazine’s jointer has a helical head. It seems noticeably quieter.
Is that why both Jet and Powermatic added helical cutterheads to a few new machines? I went back to watch the videos from our AWFS Coverage page. Powermatic installed this type of cutterhead on many of its new jointers and planers (click to watch the video), while Jet added a helical cutterhead on the jointer/planer combination machine (click to watch the video). Now my curiosity was piqued and I decided to see if helical cutterheads were best.
The loud sound is what garnered my attention. I decided to start there. The next day I grabbed the sound-level meter and took two readings at the 12″ Bridgewood jointer in the PW shop. While running idle, the reading reached 86dBAs on the meter. The next reading was while cutting a piece of 4/4 mahogany. That number was 94dBAs. The difference between running idle and at full work with a helical cutterhead equipped machine was only 8dBA.
After work I loaded the meter and the mahogany board into the truck and headed straight to my shop. There I have a 12″ Delta jointer. I repeated the same tests. This time the three-knife head moved the sound level meter to 89dBAs. That’s only a difference of three decibels over the helical head, big deal. But when I jointed that piece of mahogany, that’s when the difference appeared , big time. While cutting the 4/4 material, the decibels jumped to 112dBAs. That’s a significant increase. A helical cutterhead is quieter.
The surface that’s jointed is the telltale sign of a good set of knives. I studied each jointed surface under a magnifying-glass light only to discover no significant difference between the two resulting cuts. Yes the three-knife head left small almost indiscernible ridges in the surface that are easily sanded smooth. But the helical knives left ridges as well. They also were very small and easily smoothed with a sander.
So far, the only difference I’ve found is the sound level. And with hearing protection, is that an issue? On Wednesday, I’ll look into the costs differences , we know going in that out-of-pocket expenses are higher for the helical , and reveal if I found that one cutterhead is better than the other. (Care to make a guess?)
If you’re interested in reading more about the Jet Jointer/Planer Combination or the Powermatic Thickness Planer shown in the picture above, click on the PDFs listed below.
,Glen D. Huey
JET 12 in Jointer-Planer.pdf (27.63 KB)
PM 22-in Planer.pdf (27.63 KB)
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One major feature of the helical knife in the picture, as well as some of the after market replacements, is the use of "indexable" or "index" cutters. On the unit in your photo it appears as though each of the individual cutters has four usable cutting sides. Meaning that when one side is dull you simply loosen the screw, rotate the cutter 90 degrees and your back in business… assuming the head assembly was made with some level of accuracy. Contrast this with conventional jointer knives that are truly a pain to replace and must be sent out to resharpen.
"The difference between running idle and at full work with a helical cutterhead equipped machine was only 8dB."
Just to clarify, sound measurements made in dB are done on a logarithmic scale. A change of 3 dB is equivalent to a doubling of sound intensity, so if the Delta is 3 dB louder at idle than the Jet jointer, that means that it’s twice as loud. A change of 8 dB between idle and a cutting operation is close to 8 times an increase in sound.
Now clearly, this is better than the 23 dB jump on the Delta jointer, but it’s still a significant increase in sound level.
It’s also good to keep in mind that hearing damage begins at 85 dB, which is less than either machine running at idle.