Easy Reprofiling

[davek14]

I have a number of knives I made years ago from knife files.
I actually had an easy way to differentially temper the spines leaving the edges as hard as the (old style Nicholson, not case hardened) files.

As I get older, I'm finding a home for much of my collection in the hopes that things I've accomplished or accumulated will outlive me. I have reams more knives than I would use in the unlikely event that I live 30 more years.
Anyway, these knives are blunter than butter knives. They need reprofiling behind the edge and are harder than woodpecker lips there.
I have a few that I use that I have tediously reprofiled by hand and they hold an edge like a champ.
So, I would like to reprofile the rest and give them to younger friends and family.

What's the best power tool for reprofiling which will not heat the edge? Something relatively inexpensive or useful for other work once I'm done with this project.
Inexpensive would be best since I will likely downsize and not have a garage to work in in 10 years or so.

 

[kwackster]

You don't need a power tool for that, a 10 dollar coarse Chinese diamond file will reprofile the hardest steel easily and will also not overheat the edge.
I own 120 grit, 180 grit, and 300 grit, and use all three quite often, mostly with a light coating of WD40.

Recently i even reground an old Buck/Strider 881 tanto blade in BG42 steel into a convex shape with the 300 grit diamond file, currently busy refining the surfaces on a vitrified green SiC stone with again WD40 oil.

 

[Obsessed with Edges]

I used an 8" x 3" DMT Duo-Sharp bench hone to reprofile the edge on a ZDP-189 blade (Kershaw Leek). Those are hardened well into the 60s HRC, at least as hard as most quality files would be. And the ZDP-189 has an awful lot of chromium carbide lending extra wear-resistance as well. All that said, the bench-size DMT (Coarse side) ate the steel easily. Took about 45 minutes to finish that job at a relaxed pace.

With the same blade, coincidentally, I used a 3" x 21" grinding belt in 50-grit Zirconia-alumina, cut at the seam and glued flat to a board, to grind down the spine near the tip. I'd done this to fix the tip after it broke off (ZDP-189 is brittle at such hardness). This method also ate the steel easily, and I finished that job in about 30 minutes or so. The 'before', with broken tip, and 'after', with the spine re-ground to a pointy, new tip are shown below. The edge bevel seen is what I'd done on the 8" x 3" DMT C/F Duo-Sharp with an Aligner guide clamp for a clean & flat bevel:

As hard as good files are, if the appropriate abrasive is selected for the job, the files won't be nearly as hard as the abrasive. Maybe 1/2 as hard, at best. So it can still be a relatively easy task.

 

[davek14]

Do diamond files cut any better than DMT hones? Can you press hard to hog without knocking the diamond off?

Dave: I used to reprofile with emery cloth a fair amount when I worked in machining. They would throw away a lot of it slightly used. I got a roll of double sided tape and would tape it to a plate.
Since I had plenty to work with, it went quickly changing it often. That's still usually what I use, but I do have 5 or 10 knives to do and I don't have those resources laying around.

I did see that a Chinese diamond file can indeed be had for about 10 bucks on the big river and might give that a try.

What do you think of those variable speed grinders you can get at that discount harbor for about 30-40 bucks?

 

[Obsessed with Edges]

Regarding using diamond for reprofiling, there's little need (or none, actually) to press hard. The diamond will cut deeply at moderate-to-light pressure and pressing harder won't make it work any more aggressively. Plated diamond hones will only cut to the depth of the exposed abrasive layer on the plating, which is very shallow. And it'll cut to that depth easily, with only light or moderate pressure. What really speeds things up is the working surface area & length of the hone used. And making sure the hone stays lubricated will also keep it working more aggressively without loading up. I like to use a back & forth scrubbing motion to reprofile, doing so with just enough pressure to maintain control of the angle. It should be comfortable doing it this way - if your hands are getting tired too fast, or getting sore, it's likely that too much pressure is being applied.

Another option would be a coarse SiC oil stone in a benchstone-sized format. Decent ones can be found for maybe $25 or so. ACE Hardware used to carry an 8" x 2" bench stone (2-sided C/F) in SiC, but I don't know if they still do - they more often sold those stones in aluminum oxide instead (still decent, though not as aggressive as SiC). Those were pretty good stones and were priced in that $25 ballpark when I found mine. And Norton's Crystolon stones kind of set the standard for SiC oil stones. I don't think they're much more expensive in an 8" x 2" format. They do make them in even larger formats as well, up to about 11" x 2-1/2", if I recall correctly.

 

[cudgee]

I used an 8" x 3" DMT Duo-Sharp bench hone to reprofile the edge on a ZDP-189 blade (Kershaw Leek). Those are hardened well into the 60s HRC, at least as hard as most quality files would be. And the ZDP-189 has an awful lot of chromium carbide lending extra wear-resistance as well. All that said, the bench-size DMT (Coarse side) ate the steel easily. Took about 45 minutes to finish that job at a relaxed pace.

With the same blade, coincidentally, I used a 3" x 21" grinding belt in 50-grit Zirconia-alumina, cut at the seam and glued flat to a board, to grind down the spine near the tip. I'd done this to fix the tip after it broke off (ZDP-189 is brittle at such hardness). This method also ate the steel easily, and I finished that job in about 30 minutes or so. The 'before', with broken tip, and 'after', with the spine re-ground to a pointy, new tip are shown below. The edge bevel seen is what I'd done on the 8" x 3" DMT C/F Duo-Sharp with an Aligner guide clamp for a clean & flat bevel:

As hard as good files are, if the appropriate abrasive is selected for the job, the files won't be nearly as hard as the abrasive. Maybe 1/2 as hard, at best. So it can still be a relatively easy task.

Fantastic work.

 

[davek14]

Regarding using diamond for reprofiling, there's little need (or none, actually) to press hard. The diamond will cut deeply at moderate-to-light pressure and pressing harder won't make it work any more aggressively. Plated diamond hones will only cut to the depth of the exposed abrasive layer on the plating, which is very shallow. And it'll cut to that depth easily, with only light or moderate pressure. What really speeds things up is the working surface area & length of the hone used. And making sure the hone stays lubricated will also keep it working more aggressively without loading up. I like to use a back & forth scrubbing motion to reprofile, doing so with just enough pressure to maintain control of the angle. It should be comfortable doing it this way - if your hands are getting tired too fast, or getting sore, it's likely that too much pressure is being applied.

Another option would be a coarse SiC oil stone in a benchstone-sized format. Decent ones can be found for maybe $25 or so. ACE Hardware used to carry an 8" x 2" bench stone (2-sided C/F) in SiC, but I don't know if they still do - they more often sold those stones in aluminum oxide instead (still decent, though not as aggressive as SiC). Those were pretty good stones and were priced in that $25 ballpark when I found mine. And Norton's Crystolon stones kind of set the standard for SiC oil stones. I don't think they're much more expensive in an 8" x 2" format. They do make them in even larger formats as well, up to about 11" x 2-1/2", if I recall correctly.

Thanks guy. Good tips. I have been using smaller hones. What do you use to lubricate?

 

[Obsessed with Edges]

Thanks guy. Good tips. I have been using smaller hones. What do you use to lubricate?

I use a light & thin mineral oil, like Norton's Sharpening Stone Oil. Apply just enough for a thin 'sheen' on the surface of the hone, which is all that's needed to keep swarf from clinging to the hone. Part of my preference to use oil is due to issues I've noticed with using water (or water & dish soap). The climate is very dry where I live, and water evaporates too fast from the surface of the hone. So the oil keeps the surface wetted much more reliably. When it gets dirty with a lot of swarf, I wipe it off with a microfiber towel and reapply another light sheen of oil.

On the SiC oil stones I mentioned, such as the ones I found at ACE - those can be pretty thirsty and will soak up a lot of oil. For those, I've used a less expensive laxative-grade mineral oil found for cheap at the grocery store or pharmacy. I've actually stored some of my oil stones in a vat of that mineral oil to keep them saturated. Can also melt some petroleum jelly into the pores of the stone, which makes it much less thirsty and easier to use with less oil overall. Norton's SiC stones ('Crystolon') are already filled with a grease of sorts, so they won't be nearly as thirsty for oil.

 

[FK]

+1 on the Norton Sharpening Stone Oil, DMT recommends using dry,,,, they do load up and slow down without a lubrication on the hone. The Norton is very light compared to grocery store mineral oil and will go a long way to improving your diamond hone performance. I also use it on ceramic hones from Spyderco, really helps them to keep cutting and not load up which will only burnish the steel.

Regards,
FK

 

[eveled]

I use a hand held carpenters belt sander. Sometimes i mount it in my machinist bench vise. Go slow let the blade cool. Dont try to do it all in one sitting. Or switch from one knife to another letting them cool in between.

 

[nevertakeadayoff]

I love sharpening my knives. I hate wasting time.

I would always spend at least 45min getting a mirror edge using an EdgePro/Hapstone system. And because it took so much of my precious time, I would be selective with how and when I used it after I was done.

Now, with the Tormek, I no longer hesitate to use the blade because it's only 5 minutes on the Jap stone to get the edge back. Reprofiling a blade with the other stone is about 5 minutes, too. It's sickening to think about reprofiling a blade on the Hapstone. I hate wasting time. If you do, too, get something like the Tormek.

 

[3D Anvil]

I have a KME, but it’s the same deal; reprofiling is incredibly tedious. I really need to get me a Tormek.

Often I’ll do most of the reprofiling on the Ken Onion grinder or stones, and then finish on the KME.

 

[davek14]

I love sharpening my knives. I hate wasting time.

I would always spend at least 45min getting a mirror edge using an EdgePro/Hapstone system. And because it took so much of my precious time, I would be selective with how and when I used it after I was done.

Now, with the Tormek, I no longer hesitate to use the blade because it's only 5 minutes on the Jap stone to get the edge back. Reprofiling a blade with the other stone is about 5 minutes, too. It's sickening to think about reprofiling a blade on the Hapstone. I hate wasting time. If you do, too, get something like the Tormek.

Thanks for that. I just looked at the Tormek. That thing's pretty sweet, a bit pricy.
Yeah, with 5-10 knives to do, 45 minutes per knife is a bit daunting.
I've been looking at variable speed grinders for about $45. If I'm careful and have the speed turned way down, that might work well.

 

[nevertakeadayoff]

Thanks for that. I just looked at the Tormek. That thing's pretty sweet, a bit pricy.
Yeah, with 5-10 knives to do, 45 minutes per knife is a bit daunting.
I've been looking at variable speed grinders for about $45. If I'm careful and have the speed turned way down, that might work well.

Ya, Tormeks are overpriced a bit. I bought the T4 because I didn't want to spend $500 on the Jap stone.

There are alternatives. Grizzly, Rikon and other wet grinders for ~$200.

The variable speed grinders will probably help. However, I imagine you'll still have some reprofiling to do with your stones.

 

[davek14]

There are alternatives. Grizzly, Rikon and other wet grinders for ~$200.

The variable speed grinders will probably help. However, I imagine you'll still have some reprofiling to do with your stones.

To flatten it out and take off any high spots? Yeah. I'd expect that. I'd ask what speed would be good, but I imagine that would depend on the stone diameter.

 

[rm41400]

I have the Tormek t-8 and it’s very safe to use relative to an adjustable speed grinder.

The speed difference is huge between the two and then you also have the water to prevent overheating.

I still on occasion will use an adjustable speed harbor/Hercules bench grinder but rarely on anything really nice that I’m worried about messing up

 

[davek14]

I have the Tormek t-8 and it’s very safe to use relative to an adjustable speed grinder.

The speed difference is huge between the two and then you also have the water to prevent overheating.

I still on occasion will use an adjustable speed harbor/Hercules bench grinder but rarely on anything really nice that I’m worried about messing up

Hmmm. Gotcha. Good answer.
So the Harbor stuff is too fast?

 

[rm41400]

Hmmm. Gotcha. Good answer.
So the Harbor stuff is too fast?

yeah I’m gonna say it’s probably not your answer… 2000-3400 is it’s range with no water vs I don’t know maybe 200 rpm on the Tormek. Some alternatives to the Tormek might be worth looking at as mentioned above if you want to save$.

maybe others are more skilled with the bench grinder than I am but it’s not my go to for finished heat treated knives/ straight razors.

Another option is a dremmel. I did some rough work on some kamisori and regular straight razors and it was a nice balance between speed and finesse.

I was eyeballing a cheap harbor bench grinder with the dremmel attachment today. The slim profile of the handle would really allow you to work the length of the blade better.

 

[Jason B.]

Belt sanders and power tools in general will remove metal quickly which leads to over ground and under ground sections so I would not recommend it at all. Even if you were to send them to someone like me for machine sharpening I would expect you to understand that its a machine process done by hand and eye, and even with a skilled hand the grind lines can be good but never as good as hand ground on a stone. On high speed belt grinders care needs to be taken with harder steel, they will burn faster, just an fyi.

Waterstone type grinders that run at slow speed are GREAT for this task and eliminate all worries of heat build-up. I have yet to use a Tormek but have used Japanese style flat and angled waterstone grinders and they do a wonderful job but again it takes good grinding skills to use, things can go from "this is great" to "how do I fix this" real quick. Tormek's guide system can help but one pass on a slow wheel is still like 100 on a stone.

Regardless of the route you take I think abrasive choice will play a larger role if the blades are as hard as you say they are (64-66HRc). This means grinding will be unforgiving and any sort of hard bonded wheel is going to glaze over quickly. Softer waterstone type wheels will wear quickly and also glaze if containing an inferior abrasive (cheap wheels).

For hand sharpening a cheap diamond plate like the CKTG 140 grit diamond plate for $30 will rip through hard steel and is something I use often for very damaged bevels. If diamond stones are not your thing then a Shapton Glass 120 is one of the fastest and cleanest cutting waterstones on the market, PITA to keep flat but a monster on hard steels. I mention clean cutting because most waterstones of coarse grit get sandy or too muddy and wash out grind lines and tbh, are not made for that type of grinding.

 

[nevertakeadayoff]

Ah, I didn't put much thought into what he referred to as "variable speed grinders". Thank you guys for correcting my bad advice.

I don't find the stone wearing to be an issue on the Tormek's standard stone (SG200). I just even it out with a diamond stone when I detect a dip in the middle. Same with the Jap polishing stone, which is what I use the most. Honestly, I was going to buy the diamond stones they just released for the T4, but I don't know how to flatten out a diamond stone!

Back on the subject here. I don't think he's going to reduce his time with the knives unless he spends some money.