Tips for flattening bevels?

Case_D

Case_D

Joined
Oct 13, 2019
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89
So I'm having trouble keeping my bevels flat. Coming off the belt grinder there might be some uneven spots or worst-case a small bump near the spine or edge. I've been very careful when grinding not to get off on the angle, but inconsistencies still happen. When on the rougher grits, you can't really see it, but when polishing on higher grits, you can see the low spots not polishing up.
The worst was when using cheap aluminum oxide belts. I think the edges were curving out and gouging the blade. The blade I last made I used a belt progression of 60grit ceramic, 120 grit ceramic, A160 trizact ceramic, A45 trizact, A30 trizact. After that it was much better, but I still had some low spots where they weren't getting completely polished. I have tried going back down in grit to try to flatten it, but it seems any blade coming off the grinder will not be perfect.

So what I'm asking is
What's the best way to keep your bevels flat?

I've seen a few different techniques, such as sandpaper on granite, but I already go through so much sandpaper.
I've also seen in some workshops a horizontal wet grinding wheel, which seems pretty effective. I found one by "Shinko" that I can get for about $150 plus an extra 180 grit stone for another $80. Though I don't know if this machine is reliable or large enough for frequent thinning or flattening bevels. I also have some very rough benchstones on the way, but I've heard that using freehand stones for an entire bevel would take too long, since such a wide area make you lose so much pressure.

Thanks for any help you can give.

Edit.
Essentially what I'm saying is no matter how long I spend polishing a certain grit, I can't get some deep scratches out, meaning there's a low spot. I ground one to 120 grit, then spent about 3 hours handsanding to 220 grit, constantly changing to new paper, and finally lost all the grinder marks.
 
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Have you considered using edm stones? The softer ones that break down faster cut fairly fast. Not light speed, but a decent rate. The flatter you can come off the grinder, the easier it'll be.

Congress Tools, Inc - Categories - Congress Polishing Stones & holders

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I correct my low/high spots by passing the blade on the grinder at an angle.

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All the techniques you mention seem more for finishing. The knife should come off the grinder with flat bevels and no high/low spots. I'm currently hooked on the Tim Hancock method of knife grinding: scribe a center line, grind up to it at 45 degree angle, work the bevel down to the spine using a teflon pushstick. You can see this technique in these videos:



 
Case_D said:
What's the best way to keep your bevels flat?
Click to expand...
Unfortunately, the answer is going to depend on exactly what you're doing. First question I would ask is, are you using fresh belts?
 
i assume you are using a flat platen ? if you have facets or your blade looks like a flintknapped arrowhead, that means you are changing the angle on your wrist, which will grind a different area of the blade. i suggest a fred rowe bubble jig. it will train you to keep your wrist at the same angle.
 
my grinds are still fairly crappy, so I generally move off the machine at 120 or 220, depending on how bad I screw up, and then flatten it all out with a sanding stick and 180 grit paper. I'm sure that will change as I develop some technique, but for now it seems to be doing the job
 
N.W. Gean said:
Have you considered using edm stones? The softer ones that break down faster cut fairly fast. Not light speed, but a decent rate. The flatter you can come off the grinder, the easier it'll be.

Congress Tools, Inc - Categories - Congress Polishing Stones & holders

Congress tools categories - Congress Polishing Stones & holders - Congress Polishing Stones, Stoning Oil, UltraFine Ceramic Stones, Diamond Ultra Stones, Dressing and Roughing Stones, Stone Holders, Norton India & Arkansas Stones, Degussit Ruby Stones
www.congresstools.com
Click to expand...
I've tried using the stones that came with my Edge Pro. Those seemed to load up rather than break down. Might try those EDM stones out.
 
john april said:
i assume you are using a flat platen ? if you have facets or your blade looks like a flintknapped arrowhead, that means you are changing the angle on your wrist, which will grind a different area of the blade. i suggest a fred rowe bubble jig. it will train you to keep your wrist at the same angle.
Click to expand...
I'm using a glass platen. When I'm done, there aren't visible facets. Just deeper scratches that won't come out. It's clear to me that the bevel isn't quite flat, but it's usually not visible.
 
weo said:
Unfortunately, the answer is going to depend on exactly what you're doing. First question I would ask is, are you using fresh belts?
Click to expand...
After I get to the final dimensions of the bevel on 60 grit, I switch to a fresh 120 grit ceramic. After that if I use AlO belts, they're fresh. The trizacts last much longer. I'm doing all of this on a glass platen.
 
So lets get this straight .. you are rough grinding with 60 grit (pretty course)
then 120 grit (still pretty course) and wondering why there are deep scratches ??
why not try some 220/320/400/600/800 belts to see if any of them clear that up for ya ..
A45 is about a 320/400 grit if you still have deep scratches it is what you are doing not the machine.... keep the blade dead flat against the glass platen and let the belt do its job
if it is old/worn use a new one.. only move on after the old scratches are gone.. there are Zero shortcuts to success it takes lots of real work....
 
Pinoy Knife said:
So lets get this straight .. you are rough grinding with 60 grit (pretty course)
then 120 grit (still pretty course) and wondering why there are deep scratches ??
why not try some 220/320/400/600/800 belts to see if any of them clear that up for ya ..
A45 is about a 320/400 grit if you still have deep scratches it is what you are doing not the machine.... keep the blade dead flat against the glass platen and let the belt do its job
if it is old/worn use a new one.. only move on after the old scratches are gone.. there are Zero shortcuts to success it takes lots of real work....
Click to expand...
No, I do use the all those belts. What I'm saying is, I can go through belt after belt after belt on 220 and not get all the scratches out from 120. Ergo, the blade isn't dead-flat, and I'm just burning through higher grit belts. On the 120, I go back and get it as flat as I can, but I can't get it dead flat off the grinder - just close to the eye. So, to keep from destroying too many higher grit belts, I want to know how to get the blade as flat as possible so that it can polish evenly.
 
I am not great at grinding so I find ways to get around it. Since I do full flat plungeless grinds. I bevel the whole blade so I can plate quench it easily. That makes it really easy to grind vertical. Kinda like what's in the picture but I can get at it from any angle. Using a grinding magnet helps a lot as well because you can get some good pressure but keep it flat and not flex it and get low spots. If you have VFD slow it down and use a wet belt and try to keep as much surface area on the belt so you feel the flats and then spread the pressure somehow but use enough to pull off shavings. Leave the blade thick enough so you can correct things and use a stiff belt so it stays nice and flat. It's probably not the right way to do stuff but it's a way get things done until you can develop the skills to do it the right way. You also might find your own way. So long as you can get it done it's all good.
 
Case_D said:
No, I do use the all those belts. What I'm saying is, I can go through belt after belt after belt on 220 and not get all the scratches out from 120. Ergo, the blade isn't dead-flat, and I'm just burning through higher grit belts. On the 120, I go back and get it as flat as I can, but I can't get it dead flat off the grinder - just close to the eye. So, to keep from destroying too many higher grit belts, I want to know how to get the blade as flat as possible so that it can polish evenly.
Click to expand...
ok then it sounds like you are not getting the old scratches out before putting new finer ones in ..
Grinding is 100% about Pressure you apply pushing the blade into the belt. .if you do it uneven well you get big problems to try to resolve... the belt just eats whatever you feed it (and pretty fast)
don't take this wrong but try some "Paint sticks" to get your grinding better.. then move onto steel/blades..
the best way to "Fix" your problems of uneven grinds is Practice.. lots of it (not being Negative) just stating a fact...
 
you mentioned polishing the blade evenly in your last post. your first post talks of a 400 grit finish. are you trying for a mirror finish? i have a suspicion you never got the 60 grit scratches out with the 120 before moving on to the 220. so you might be trying to remove 60 grit scratches with your 220.
 
Lots of good info here. What speed do you grind at? Slower speed can help achieve flatter bevels. I come off at 65 micron belt and then hit the bevel with a course grit diamond stone to check…if I’m good on my grinds, the diamond stone doesn’t really need to do much work to keep everything crisp. After that I hand sand and only increase the grit when the previous scratches are gone.
 
Case_D said:
So I'm having trouble keeping my bevels flat. Coming off the belt grinder there might be some uneven spots or worst-case a small bump near the spine or edge. I've been very careful when grinding not to get off on the angle, but inconsistencies still happen. When on the rougher grits, you can't really see it, but when polishing on higher grits, you can see the low spots not polishing up.
The worst was when using cheap aluminum oxide belts. I think the edges were curving out and gouging the blade. The blade I last made I used a belt progression of 60grit ceramic, 120 grit ceramic, A160 trizact ceramic, A45 trizact, A30 trizact. After that it was much better, but I still had some low spots where they weren't getting completely polished. I have tried going back down in grit to try to flatten it, but it seems any blade coming off the grinder will not be perfect.

So what I'm asking is
What's the best way to keep your bevels flat?

I've seen a few different techniques, such as sandpaper on granite, but I already go through so much sandpaper.
I've also seen in some workshops a horizontal wet grinding wheel, which seems pretty effective. I found one by "Shinko" that I can get for about $150 plus an extra 180 grit stone for another $80. Though I don't know if this machine is reliable or large enough for frequent thinning or flattening bevels. I also have some very rough benchstones on the way, but I've heard that using freehand stones for an entire bevel would take too long, since such a wide area make you lose so much pressure.

Thanks for any help you can give.

Edit.
Essentially what I'm saying is no matter how long I spend polishing a certain grit, I can't get some deep scratches out, meaning there's a low spot. I ground one to 120 grit, then spent about 3 hours handsanding to 220 grit, constantly changing to new paper, and finally lost all the grinder marks.
Click to expand...


One thing that helps is to remember that you aren't removing the scratches you are removing all of the material around the scratches.
 
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