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For this post I define "spine side" and "edge side" as it relates to grinding a knife blade. 

If the abrasive (flap disk or belt sander) is moving from the spine toward the cutting edge, I would call this "spine side"

If the abrasive (flap disk or belt sander) is moving from the cutting edge  toward the spine, I would call this "edge side".

In my opinion the "spine side" is safer because it's almost impossible for the abrasive to bite into or grab the blade and throw it at high speed. 

In the "edge side" mode, too much pressure or wrong angle of attack could force the blade to cut into or grab the abrasive belt of flap disk with unpredictable/dangerous results. 

 

 

 

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Good topic of discussion Dick but there is an established terminology for what you're calling spine side and edge side. I suggest you use the established terminology to help mitigate confusion. 

My Father the machinist metal spinner, taught me his terminology as "dragging or pushing" the edge but I've heard others. Dad was mostly concerned with sharpening lathe cutters, drill bits, chisels, etc. We used the same terminology to mitigate the same  wire edge effect sharpening knives, wood chisels, planer blades, etc. 

Hopefully one of the master bladesmiths authors will speak up and provide a more universal term. 

One of my "Things" is trying to encourage everybody to use the same jargon so we don't spend so much time explaining what we mean. There are really good reasons for specialized trade / craft languages, "jargon", especially in emergencies. For example imagine you're sailing a 3 masted clipper ship and you need to tell the men in the rigging to "Bundle up the highest big cloth thing on the second mast from the front." You'd have the whole crew stop what they're doing to try to decide if you're talking to them. Yes? A short command that leaves no doubt what you mean and who to makes a lot more sense. No? Okay, the sailers are going to laugh or shout but that's okay. "Furl the fore main top gallant!" Short concise and unmistakable, there is ONLY ONE sail by that name and ONE group of crew manning it. Nobody else on the crew is going to think they're being given a command and stop their job and the crew in the rigging know exactly what's wanted and how to perform the task.

Sorry for the long winded reply, I'm not beating up on you I, not at all. I think you're starting a good discussion especially because of the safety factors. I had a friend who was way TOO CASUAL kill himself when a blade he was grinding was snagged by his grinder and was thrown through his heart. He was dead before he hit the floor. So, please believe me I'm all in favor of your topic.

I'm just making my case for using a common jargon to discuss it.

I'll express my opinion of using flap disks for any kind of precision grinding later in the discussion. . . <SHUDDER>

Frosty The Lucky.

 

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There is no more risk in sharpening edge grabbing onto the moving force of the belt, any more than the spine doing it.  That is nonsense.  I use edge up so I can see the edge thickness, and keep it even. so edge into the belt, since running the belt the other direction would just throw the metal dust into your face :D

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Ahhh, good to see you Steve! I believe Dick was referring to the direction of the blade, not the grinder. I can't imagine how nasty it'd be with the grinder direction reversed.:o Though how easy it is to let a flap sander snag an edge falls into the :o category.

I requested your input regarding the common term for the orientation of the blade on the grinder. Edge up? Spine up?

Does drag or push the edge make any bladesmith sense? 

Frosty The Lucky.

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Makes sense, the Edge is the subject and could go without saying, Up or Down should be a good term. Down on a wire wheel or buff, not so. Unfortunately I know of guys running both wheels reversed to grinders and for pretty good reasons. Up and Down may not be specific enough to cover all conditions. Hmmm? 

I doubt any "Bladesmith" or "Maker" would use a flap sander or disk but how often do we see aspirants posting? New guy may not have enough knowledge or shop skills to sift good from bad from outright dangerous suggestions. 

I have trouble not thinking about this sort of thing.

Frosty The Lucky.

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If we're talking about grinding bevels I don't see how anyone could reliably get good grinds with the cutting edge down - freehand anyway.  As Steve pointed out you need to be able to look at what will become the cutting edge as you grind to ensure that it's even and ends up at the thickness you desire.  Trying to accomplish that with the cutting edge down would be a constant "stop and check" frustrating endeavor since you'd essentially be grinding blind with regard to the edge thickness and even-ness.  If you were doing a full flat grind it also would be just as likely to catch the edge and throw the blade out of your grasp with cutting edge down or up anyway.

A variable speed grinder is a big help too.  My most recent project is a straight razor. Attempting to get an even grind on a final edge about as thick as card stock with the cutting edge either down or up would be close to impossible at full speed.   It would also easily overheat the edge and destroy the temper.  However, with a fresh belt and low speed you can make small adjustments to the grind with little to no danger of the blade being ripped out of your hand or overheating the blade.

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Posted (edited)
On 8/21/2022 at 10:31 AM, Frosty said:

Good topic of discussion Dick but there is an established terminology for what you're calling spine side and edge side. I suggest you use the established terminology to help mitigate confusion.

 

What is the  "established terminology for what I am calling spine side and edge side."  ?

Edited by Mod30
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Spine and edge are definitive terms. Adding side is like saying the ceiling side and floor side of a room. Not technically incorrect but not recognized terms.

Frosty The Lucky.

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I am still fairly low on the learning curve when it comes to grinding blades, but I will share one thing I have observed.  With relatively low or insufficient belt tension, I think there is a tendency for the belt to bulge ahead of the blade.  If grinding edge side up, there will come a time in blade sharpness where the belt will easily be cut.  This might be more of an issue with woodworking sanders used for metal work.

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