Did I sharpen my knife correctly?

[matt6150]

Hello, I am new to this whole knife making & sharpening deal and i was wondering if I sharpened my Gerber Bear Grylls Ultimate Folding Knife correctly. Although its not an expensive knife, I am a bit worried because it was a Christmas gift. I sharpened it with a metal grinder, sandpaper, and the bottom of a coffee mug. I will post the link of a video with its paper test performance and some pictures at the end. Please give me some feedback so I can stop my worrying. Thanks!

https://www.youtube.com/watch?v=FlYFiQRX5D4

 

[bpeezer]

Is it sharper than it was before?

 

[Blade-fiend]

If its sharp then yes you sharpened it right I guess but using a grinder is very risky as you can wreck the heat treat quickly if you are inexperienced. Sharpening by hand is much safer and will not ruin a heat treat. If the heat treat has been ruined then the knife just will not hold that sharpness for any amount of time. Just something to watch out for in the future.

 

[marcinek]

Is it sharper than it was before?

bpeezer is right. Does your knife cut the stuff you want it to cut? (Apparently the stuff is paper...) If so, you sharpened it correctly. That is the only "rule."

And welcome, by the way.

 

[matt6150]

Yes it is sharper than before. Since I've sharpened it i have been whittling stick and other stuff and it has kept its edge. So, I guess i didn't ruin the heat treatment too much. Thanks for the feedback guys!

 

[22-rimfire]

I would not use a bench grinder. My Dad used to sharpen knives that way and he would essentially wear away the blade completely and that is not even taking into account the heat treat on a blade. You can sharpen a blade even if the heat treat is ruined, the sharpening will often not last as long in most cases when you use it. If it gets dull rapidly with use, know the likely cause.

 

[bpeezer]

Matt, I hope you don't mind but I took a screenshot from your video to make it a little easier for us to get a look at your edge. It looks to me like you actually did a pretty good job of reaching the apex (sharpening all the way out to the edge), but it looks a little rough. What kind of sandpaper did you use, and what kind of backing did you have for the sandpaper?

Here is the edge from your video:

To give you an example of something with a little cleaner looking edge, here is the knife I have in my pocket right now:

And here's a test with the same knife, showing you that the cleaner bevel gives some improvements in sharpness
[video=youtube;LWlS96rHKjA]http://www.youtube.com/watch?v=LWlS96rHKjA[/video]

I hope this helps!

 

[cncpro11]

If its sharp then yes you sharpened it right I guess but using a grinder is very risky as you can wreck the heat treat quickly if you are inexperienced. Sharpening by hand is much safer and will not ruin a heat treat. If the heat treat has been ruined then the knife just will not hold that sharpness for any amount of time. Just something to watch out for in the future.

Not trying to be a wise guy, but aren't most knives finish ground after heat treat?

I do know that putting a convex edge on a blade can get it pretty hot as well and have never seen the h/t being ruined.

Of course I could be wrong but that has been my experience.

 

[eKretz]

Indeed they are finish ground after heat treatment. But most factories doing mass production use coolant flooded grinding wheels and the grinding is done by machine. The guys making handmade knives use lower belt/wheel speeds quite often and always keep a large can of cool water nearby to dip the blade in after every grind so heat doesn't build up. They use a very light touch also and hardly any pressure. If you ever see your blade turn any color at all you've altered the temper of the blade and with it the hardness. The only steel that won't be harmed by this is High Speed Steel, which by design is able to hold its temper at red heat. The danger with HSS however is if you quench the blade into water while it's anywhere near this heat it's liable to form micro-fractures.

 

[cncpro11]

Thank you.
I have modified a few blades with a bench grinder and my experience has been that there is so little material at the cutting edge that it is removed long before it has a chance to get hot and change colors.
Of course I finish it so it doesn't look mangled but have never noticed a change in edge holding or cutting performance.

 

[matt6150]

Matt, I hope you don't mind but I took a screenshot from your video to make it a little easier for us to get a look at your edge. It looks to me like you actually did a pretty good job of reaching the apex (sharpening all the way out to the edge), but it looks a little rough. What kind of sandpaper did you use, and what kind of backing did you have for the sandpaper?

I hope this helps!

Thanks for the feedback bpeezer! I think the sandpaper was 200 grit and I just sanded it by hand which probably wasn't too smart. (I'll check the paper grit later to be sure.) What grit do you recommend?

 

[bpeezer]

Thanks for the feedback bpeezer! I think the sandpaper was 200 grit and I just sanded it by hand which probably wasn't too smart. (I'll check the paper grit later to be sure.) What grit do you recommend?

More importantly than grit, don't sand by hand. I would suggest putting the paper on a hard backing, like a book. Use it like a sharpening stone, it will be a cheap way to learn freehand sharpening and it will make things much more consistent. Avoid using edge leading strokes (cutting into the paper). Once you get good at that, you can start using higher grit sandpapers to refine your edge with the same technique. The sandpaper grits I have used are 320, 600, 1000 (might be 1200, not completely sure), and 2000.

 

[A Justice]

I just saw the video of the knife slashing through paper quickly, couldn't tell much from it.

I don't think a blade needs to whittle hair - at least not if you use it often. Depending on which knife it is, how I use it, what I use it for, every knife has a different edge with a different level of finish. I use my finger nail, visually observing the edge, and paper to test all of them though. My main concern is that everything is consistent - if I only put a 600-800 grit edge on it, I want the whole edge to have the same finish, be a consistent width, and be free of burrs. Slide your finger nail along a blade that has been used heavily - it will be rough in spots. Now slide it along a good blade that is freshly sharpened - it will be very smooth. Now that you see where the rough spots on a blade are, cut the paper slowly drawing the blade through the paper. You will feel those same rough spots on the paper. If the blade is long you may have to make as many as 3 cuts to check the entire edge.

In my experience, this is about the extent of what printing paper will tell you. I have handled very few knives that will not cut paper (excluding knives that have been worn out from cutting or extremely cheap steels), but I often cut paper to check blade performance. Like other people said; if the knife is performing to your expectations, it is sharp enough, but a lot of people try and push that to its limit. It isn't always necessary to spend 3 hours sharpening knives though - a toothy edge will cut some material just as good as a refined polished edge, and at the end of the day the knives can be in the same shape (the refined edge will degrade much faster). It gets to a point where there are diminishing returns, at least if you are using the knife daily.

 

[Jason B.]

The first edge photo in the video shows a large burr on the edge and a edge that looks rather distorted from random grind marks. Using some proper tools would probably help, I would recommend a good stone.