hollow ground clipper blades

E

elementfe

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I'm not sure this is the correct forum for this, but here goes:

I'm starting a sharpening service and would like to work with salons and pet groomers. A lot of their clippers are hollow ground, and I want to make sure to understand how the hollow works. Is it front to back or side to side, and what is the radius on the grind?
I have some large radius grinding equipment but sure don't want to experiment on somebody's favorite very expensive clipper!

Thanks for any ideas, tips or pointers!

Andy Gladish
Guemes Island, WA
 
I sharpened a pair once for a friend and if I remember correctly they were hollow ground down the center (think single bevel Japanese knife). When I sharpened them I just flattened my waterstones and laid the back side with hollow flat on the stone and worked through the grits. Do not strop on the sharpening side as that will radius the edge and that will not work, strop the outside.
Hope this helps.
 
Thanks, Chris, that makes a lot more sense than the crown being end to end, but it's been challenging to work out just how the dedicated machines are made- I'm beginning to suspect that, as in many cases, the fact that it's not that complex leads people to talk about it like it's rocket science/juju! :)
As far as I can work out, they use a very slightly cone shaped rotary disk and lay the blade on the disk with the cutting edge aligned to the c.l. of the disk. Not a particularly precise way to hollow grind, since the radius is slightly different from outside to inside of the disk, but obviously good enough.

Looking forward to understanding this better!
 
I am saying do not worry about the hollow. It is there just as a relief. When you sharpen a straight razor you lay the spine on the stone to set your angle. This is the same principle as the shears. You are going to remove the material from around the hollow. The goal is to have them FLAT. That is where the cutting action comes from because there is no set to the blades.
 
Thanks, Chris!
They do ask for hollow grind sharpening, but it stands to reason that it wouldn't be neccesary for each sharpening.
I would think you'd get a better cutting action in any case by at least finishing on a flat surface, as you describe.
 
Maybe this may help. I shear sheep and grind my own cutters and combs. They are ground with a slight hollow across the middle of the comb and cutter. The disc used is 14" and has about a 1 degree taper falling from center to outside. The grit paper is glued to the disc and then clamped to a plate that is tapered to keep the taper correct for grinding. The disc is mounted in the vertical position and the comb or cutter is held to a pendulum that is centered on the disc, then the unit is moved back and forth across the disc with the pendulum hanging from a hook. This produces a slight hollow so when tension is placed on the cutter against the comb the cutting edges rub as well as the thin heel of the cutter and not the whole cutter and comb. There are some people that grind flat but if it isn't perfect the comb and cutter may not run with the proper tension just on the cutting edges and will load up with wool under the cutter and not work properly. This method is usually finished on a lapping table to insure the comb and cutter are flat. If you use the tapered discs lapping is unnecessary. Hope this helps.
 
One other thing, the combs are ground on a 40 grit disk and cutters on an 80 grit disk.
 
Thanks, this is very helpful!
My 1deg disk isn't that big, just 9", but since the radius is most pronounced near the center of a beveled disk I should be able to get the same effect if not a squeak more.
I wonder if just a touch on a lapping surface might not be a good idea anyway, as long as it's just on the teeth and heel.
 
I realize that the clippers you are sharpening are finer and smaller than what I use but the burr left by the coarse grit cuts faster and longer than a fine edge but I deal with dirt and vegetation that is hell in equipment. Also you are sharpening to cut hair which is much finer also. I would see how the lapping works out, it might work better and pull less hair also.
 
That's one I'm still coming to terms with: that a rough edge would cut better than a polished one.
Currently my main quest in seeking to understand the world of edges and sharpening.
For instance, the serrated part of a hybrid knife won't cut as well as the plain part if it's just been sharpened, but in the real world people don't keep their knives particularly sharp, so the serrations actually cut better.
My Great Grandma's bread knife still goes through crusty bread like crazy without serrations, but it's very thin and very keen.

I certainly won't argue with what you observe, and I accept that it's true, but I won't rest until I feel I really understand how that can be true- perhaps, as you say, in certain applications where the edge is going to get beat up anyway, it's like a serrated knife and does the job longer because it's toothy.
 
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