Clean Lines on Flat Grind - How Hard Can it Be On Thin Material??

C

Cushing H.

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Jun 3, 2019
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From your experience - is it generally more difficult to get a nice clean line on at flat grind at the transition from the grind to the blade flat at the spine for thin material as opposed to thicker material?? (I am not sure if this end-of-grind line has a name??) the videos giving tutorials on this show a nice clean line without a lot of fuss. I have tried this on three knives so far ... and all looks pretty good until I get down much closer to the end of the grind ... then things fall apart (fail to keep the line). On the other hand, I am working on pretty thin stock (0.08" O1), and am trying for a pretty low angle ... typically a grind distance of about .7" . Is this still just a matter or practice, or is it just plain more difficult with thin stock? (or easier with better equipment? - right now I am stuck using a Harbor Freight 1x30 belt sander - no flames please - am trying to work up the courage to order a real grinder.....)
 
It is harder for me on thinner stock. Are you grinding post heat treat? That helps. Also the harbor freight 1x30 doesn't have the most rigid platen in the world. When I was using one of those I made a thicker platen out of heat treated steel. That helps but then you struggle with bogging it down.
 
The material is in annealed state. Its easier on hardened material? I would have thought the other way around... yeah -it does bog down .. moreso on profiling though. Makes me wonder if i am not using enough pressure when flat grinding??
 
here is a technique that can help.

Grind to about 1/8" from the spine.

Slow the grinder down a lot and then use a new 120 belt and with very light passes work that up to about 1/16" away from the spine. Be sure to get all previous scratches out.

Then put on a new 220 belt and make a pass, look, make a pass, look, make a pass, look until it is where you want it then move along to 400.

At 400 you are not looking to move any lines just remove scratches.

Using the grinder on SLOW and checking each pass really will improve that top line.
 
A grinding clamp helps to keep the plunges strait and crisp. With your setup, I would file a starting line in the plunge, it makes the belt run in the right spot; if you match this with a good belt you can get better results. If you get to purchasing a new 2 X 72 machine, PM me, I can help you improve your grinds and do it faster.

Enjoy the learning, Fred
 
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Sharp belts are a must. I've chased and chased lines and then put a fresh belt on to get a good crisp line in 1 pass.

I also like to rest the blade on a rest and pull the blade across the belt will a finger controlling the pressure
 
Yes, it is harder because the angles are usually shallower and the material moves around more due to heat and grinding stress. Saber grinds on thin material are TRICKY. I'd suggest going FFG instead.
 
A couple of the responses did not make sense to me (some of the later ones did as well) ... but just to be sure - a picture is worth a thousand words (in this case two pictures). Attached (hopefully immediately below) is a hand sketch.... I am talking about the clean line (hopefully) parallel to the edge. In this case, consider the grind is 1" wide, and the total blade is 2" wide at widest. (I am NOT talking about the plunge line - for kitchen knives they drive me crazy because they get in the way of later sharpening). I have been able to get about 1/2 way through the grind ... then things go bad - because as one person commented, the angles become so small, even a small change in angle against the belt destroys the clean line (as one person commented ... I just "converted" them to FFG :) . However, this CAN be done on thin stock. Second photo is my pro-made Nakiri with Kurouchi finish (to make the grind line clear). Blade thickness is 2mm, and they held a pretty darn clean line (I have a non-Kurouchi Gyuto with the same basic idea of a clean grind line on a 2mm thick stock). CAN it be done on our equipment? or should I just drop the expectation until I develop a very,very steady hand (and a 2x72 grinder :) ). (sorry ... I do not know how to insert photos in-line....)Clean_grind_line0002.jpg IMG_0505.JPG Clean_grind_line0002.jpg
 
To get that 1" bevel you need to dye chem your blade, take a caliper and place it on the edge and draw it over the blade to copy the profile of the edge to the blade.

Always when grinding start the edge on the belt then lay it down onto the flat, it is kinda like landing an airplane.

Do not try to lay it flat onto the belt or you will screw up the grind.

if you can follow the edge on the grinder and little by little decrease the angle to climb toward the scribed line. If you are off the dye chem will show where you are off.
Once you establish the grind then gentle pressure toward the spine will walk the grind line up toward the line you marked as the goal.

Only use sharp belts and make a pass and look what it did , then continue to make a pass and look again. Do this until it is even and approaches the line.

Think light pressure, sharp belt, 1 pass, repeat again and again.
 
This one is 1.5mm , hollow grind :)
Qn0lSTV.jpg
 
N Natlek hollow grinds are much easier to get a 1" grind then a flat grind.
Once you establish the hollow you simply ride it up.

Flat grinds do not have the luxury and if you blink wrong the grind is off track.
 
AVigil said:
To get that 1" bevel you need to dye chem your blade, take a caliper and place it on the edge and draw it over the blade to copy the profile of the edge to the blade.
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You can get it without that, but layout will probably help

My advice is lots of practice. sometimes using sandpaper or stones will help. If you can't get it to look good, just turn it into a convex grind and you will still have a usable knife :p
 
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Alex Topfer Alex Topfer of course you can get it without that, but you will get it if you do that and skip all the unnecessary stone and hand sanding
 
AVigil AVigil IMO, while you're developing the muscle coordination for the grinding hand tools will still be necessary if you want a good result. We can leave it to C Cushing H. to work out how they want to do it.
 
Alex Topfer said:
AVigil AVigil IMO, while you're developing the muscle coordination for the grinding hand tools will still be necessary if you want a good result. We can leave it to C Cushing H. to work out how they want to do it.
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Maybe, but I have taught several people how to grind and upon following instructions they never needed to use a file or hand sand to take a grind to completion.

Sure you can use files and sand paper to make up for the lack of grinding experience, or a person can slow down follow instructions and learn how to grind properly.

Proper technique comes first, then grinding becomes second nature. A person can have zero knife grinding "muscle memory" but if they follow proper technique they will successfully grind a blade every time.
 
AVigil said:
Always when grinding start the edge on the belt then lay it down onto the flat, it is kinda like landing an airplane.
Click to expand...
This might have been my downfall - i did try going right to the flat. Ill have to try this technique next time. I do have one more piece of O1 i can use to practice on before i send all off to JT for heat treat. Rather long one though - destined to be a 240mm Wa-Sujihiki - though that might be foolhardy given warpage risk (it is 0.08” stock)
 
Cushing H. said:
This might have been my downfall - i did try going right to the flat. Ill have to try this technique next time. I do have one more piece of O1 i can use to practice on before i send all off to JT for heat treat. Rather long one though - destined to be a 240mm Wa-Sujihiki - though that might be foolhardy given warpage risk (it is 0.08” stock)
Click to expand...

Just barely touch it at a steeper angle at the edge, not enough to grind but enough you can feel the belt. Then gently gently lower the blade down onto the established flat.

Just like landing and airplane.

This will really help buggering up that top grind.
 
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