by Jeff Andrews, Northern Tails Sharpening
Calibration is affected by mobile sharpening. For 15 years I provided mobile sharpening in 5 states of the South before switching to strictly mail-in services. Even solid equipment in mobile vehicles going over bumps, potholes and railroad tracks is subject to loss of calibration by vibration.
As a mobile sharpener I had to check my calibration on my automated blade machine and the arm position of my scissor sharpening machines no less than weekly. Many times they were dead on accurate but sometimes they were off a couple thousandths. Even such a little variation can cause a scissor to fold at the tips, and blades to fail the rub test.
In my stationary location scissor machines never move. Yet when I roll my two automated blade machines around the shop for cleaning or changing the sharpening plate, I have to recheck the calibration of the automated arms.
Once in a while I have to adjust but it’s nothing compared to when I was working mobile sharpening on the road. 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 using the same equipment the importance of getting the blade centered on the hollow grind of the plate, and not assuming the factory marks on the automated arms were correct. They also need to check the calibration of their automated machine weekly.
Bumpy roads can be certain death to an automated blade machine and the result is very angry customers.
Why is Calibration Critical?
Blades do not have flat surfaces though it may look so. Their cutting surfaces are “pitched” a few thousandths so the tips of the cutter teeth and the very rear of cutter touch the blade underneath. 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 cut. Sharpening plates are not flat either. They are pitched to grind the “hollow ground” to make the blade work.
When placing a blade on a plate for sharpening the its center must be in the center of the pitch. If it is passed or short of the center cutting life is shortened. For this reason calibration is critical.
You check the hollow ground 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 shinny area across the tips of all teeth and areas on both sides of the back rail. In this case you have a pretty good hollow ground. If the entire tooth is shinny it is too far out of calibration. If the teeth are shinny on each side but not in the middle of the blade, the calibration is too short.
Sharpeners using a manual sharpening machine (no automated arms) have no calibration to check. Creating a good hollow ground depends upon holding the blade in their hand with a magnet, and going back and forth across the plate trying to keep the blade as straight. With a manual machine every blade is sharpened differently and the variation can be enormous.
Here is a question to ask the sharpener you are currently using, “When was the last time you checked the calibration of your equipment?” or “Do you rub blades out to check the hollow ground?”
If you get “no” for an answer for either question the sharpener does not have a really good idea of the kind of work they provide. Even if the blades cut good now, how long will the good cut last?
Another reason to rub blades out is to check if the sharpening machine is indeed grinding hollow ground blades. Sharpening too many blades on a sharpening plate decreases its hollow ground capability. Blades will be sharpened flat and not work long if they work at all. If a sharpener rubs out blades consistently and observes shiny areas on the tips of the cutter teeth starting to come down the teeth, it is a signal to change sharpening plates.
I am hoping to add more sharpeners to my readers as well as interested groomers. We may actually get more sharpeners reevaluate their services and insure they are putting out the best sharpening their customers. Those that are doing this already know what I am talking about and are likely to agree that it is better for the sharpener to catch potential problems and not let their customers catch them instead.
Calibration is an important part of the sharpening process, and the customer perspective of our work at Northern Tails Sharpening is something we never want to tarnish.
Now everyone knows what I do about calibration. It is good to know as a groomer what it takes to ensure your blades are sharpened correctly. Knowledge is power!
Have a great day grooming, and read those labels. ♦