By Jeff Andrews
Calibration can be an issue when doing mobile sharpening. I did mobile sharpening in five states down here in the South before I went strictly mail-in for 15 years. Even though your equipment is solid in your van or trailer, going over bumps, hitting pot holes, and going over railroad tracks does vibrate the calibration off. I would check my calibration weekly on my automated blade machine and the arm position on my scissor-sharpening machines. Most times they were still dead on; sometimes they were off just a couple thousands, but that little variation can cause a scissor to fold at the tips and blades to fail the rub test (explained later on).
In my sharpening shop, the scissor machines never move, but when I roll my two automated blade machines around to clean or when I change the sharpening plate, I check the calibration of the automated arms. Once in a while I have to adjust, but it’s nothing like when I was on the road bouncing around all the time. Bad calibration can really shorten the life of the cutting surface of the blade, because the hollow ground of the blade isn’t centered correctly.
I’ve taught several sharpeners who purchased the same equipment I use about the importance of getting the blade centered on the hollow grind of the plate and not assume the factory marks on the automated arms were correct. Also check the calibration weekly on their automated machine. Bumpy roads can be certain death to an automated blade machine, but taking the time to check calibration will prevent a lot of very angry customers when the blades start to have issues.
Blades don’t have flat surfaces like it seems when you look at them. The cutting surfaces are “pitched” a few thousands so the tips of the cutter teeth and the very rear of cutter touch the blade underneath it. This enables the blade teeth to cut like a tiny pair of scissors as the teeth go back and forth across each other. If they were flat, they would snag in the first inch of hair you tried to cut. Sharpening plates aren’t flat either; they are pitched as well to grind this “hollow ground,” as we call it, to make the blade work. When the blade is put on the plate to be sharpened, the very center of the blade must be in the center of this pitch. If it’s past the center or short of the center, cutting life is shortened. This is where calibration is so important.
Hollow ground is checked by rubbing a freshly sharpened cutter blade on a flat steel plate (test plate). Sharpeners call this “rubbing the blade out.” After you rub it on the plate and turn it over, you can see a small shiny area across the very tips of all the teeth and areas on both sides of the back rail. This shows pretty good hollow ground. If the entire tooth is shiny, it’s out of calibration too far. If the teeth are shiny on each side but not in the middle of the blade, the calibration is too short. Sharpeners who use a manual sharpening machine (one without automated arms) have no calibration to check. Creating a good hollow ground depends on holding the blade in their hand with a magnet and going back and forth across the plate, trying to keep the blade as straight as they can. With a manual machine, every blade is sharpened differently, and the variation can be enormous.
Here is a question to ask the sharpener you’re currently using: “When was the last time you checked the calibration of your equipment?” “Do you rub blades out to check the hollow ground?” If you get a “no” for either of these questions, that sharpener has no idea what kind of work they are putting out. The blades may cut well now, but for how long? Another reason to rub blades out is to check if the machine is indeed grinding a hollow ground blade. Sharpening too many blades on a sharpening plate will decrease the hollow ground capability of it, and the blades will be sharpened flat and will not work long if they work at all. If a sharpener rubs out blades religiously and sees the shiny area on the tips of the cutter teeth start to come down the tooth, it’s a signal to change that sharpening plate.
I know this was kind of long, but I’m hoping to have some sharpeners as well as interested groomers as part of my audience. It may actually let a few sharpeners reevaluate what they are doing to ensure they are putting out good work for their customers. Those that are doing this already know what I’m talking about and will agree that “it’s better for you to catch a potential problem and not let your customer catch it for you.” Calibration is an important part of the sharpening process, and the customer perspective of our work is something we never want to get tarnished.
Jeff Andrews is a World Class Sharpener and owner of Northern Tails Sharpening, Inc. He is an author and pioneer of many equipment maintenance videos and how-to articles that are appreciated by groomers worldwide at no cost. Jeff is a member of NDGAA, IPG, and NAPCG, and still grooms at his shop in Mobile, AL. 251-232-5353 www.northerntails.com