Honing/fixing a bent blade (not warped)

[global_dev]

Thank you for sharing. The best way to get people into this is to have good mentors. Anyone who is willing to spend their time sharing their experience should be encourage. But they should also be open for constructive feedback. I am not referring to any of these references, but there is some misleading information out there.

I dont know any of us here who aren’t willing to help once the call goes out. The first step is asking for help early.

and since there are many paths to success in addressing an issue, honers need to make sure they understand what their method will entail and if they are good with that resultant look and feel.

certain members have their own style of finessing an edge into shave readiness, and we all know who’s who for the most part. Pretty much certain we all agree to disagree so homework must be done.

after a decade of successful honing, i’ve never really felt the need to so the method described, is that the wobble test and fix? Just some rolling x strokes or thin hones and the job gets done.

 

[JPO]

I dont know any of us here who aren’t willing to help once the call goes out. The first step is asking for help early.

and since there are many paths to success in addressing an issue, honers need to make sure they understand what their method will entail and if they are good with that resultant look and feel.

certain members have their own style of finessing an edge into shave readiness, and we all know who’s who for the most part. Pretty much certain we all agree to disagree so homework must be done.

after a decade of successful honing, i’ve never really felt the need to so the method described, is that the wobble test and fix? Just some rolling x strokes or thin hones and the job gets done.

Yes i am referring to the wobble test. The picture in the post is after some correction was done to the spine etc. So it was pretty bad when i started. I was able to hone it as you describe with the geometry shown. I guess it is a common problem, especially with those dovo best quality razors. When it was new even a narrow hone struggled to make contact on the concave side. The other side is not an issue, you just use an rolling x stroke.

 

[Steve56]

All properly made smiling blades will wobble on a flat plate. If the bevel is an even width, toe to heel and the razor smiles, that means that the spine is thinner at the toe and heel where the width is narrower, and thicker in the middle where the razor is wider. so it wobbles.

You can grind the spine flat and re-set the bevel and you will lose a lot of width and ruin your razor.

 

[global_dev]

When it was new even a narrow hone struggled to make contact on the concave side.

Talking 1” or so wide stone? and the contact was not happening at all?

 

[Steve56]

 

[JPO]

Talking 1” or so wide stone? and the contact was not happening at all?

Yes it was riding on the edges. The edge never worked any good. A little correction on the spine helped.

 

[global_dev]

Maybe time to consider a rounded edge hone from your other post or convex to address some thing like that?

 

[Darth Scandalous]

Maybe Dovo should change their name to D'Ovo to highlight the egg-shaped curve they seem to be famous for.

 

[2bit_collie]

I have a bent Greaves - I dealt with it with a variant of the narrow hone. I bought a round hard ark file from Dans (I think 1/4” diameter by 4” long). Not too expensive. I used the file to set the bevel in the bottom of the concave section (only about 1/2” of edge). Then I wrapped progressively finer grits of W/D sandpaper around the file and used that to refine the edge. As a final step I dug out my Dremel based router kit and cut a 1/4” radius filet on one edge of each of my pasted balsa strops and reapplied paste.

 

[JPO]

Maybe time to consider a rounded edge hone from your other post or convex to address some thing like that?

That is what i ended up using, but it seems like this is a subject reserved for private conversations.
I did shape the bevel with convex Naniwa pro 3k (R=1.5 m), i then used a convex coticule with a larger radius. I finished with tomo slurry on a flat Nakayama asagi. Then you are able to do the last finish by using the corners of the stone, rolling x etc. and get a nice edge. Using an skew angle when shaping the bevel also allowed my to get a little taller bevel. The topic is also covered in a different post, but is also something that is difficult to discuss. The message sometimes seems to be to just learn how to hone
Just do what they did over a hundred years ago. If you show evidence that someone actually did do this over a hundred years ago then what? Fake news probably
Someone makes the subject personal by introducing a plate to shape your stone. The subject is lost in all the drama. It is not that difficult to do it by using simple means. It took my under an hour to shape three stones.

 

[JPO]

Here is how the edge looked like after the coticule, before the jnat. Here you can see how the hollow ground bevel formed. I just thought the intersecting scratches looked interesting.

 

[eKretz]

These razors are not actually bent; that would imply that they were straight at one time and were forced into a crooked shape. These qualify as either warped or ground crooked to begin with. If the steel is fully hardened it will be very difficult to cold bend much without breaking it.

The best solution would probably be to work around the warp by using a very narrow hone, the side of a hone, or a convexed hone.

There is a method that would probably work to straighten these razors but it isn't for the newb. The process would be more likely to make the razor worse or destroy it if attempted by someone not already intimately familiar with this process. If you would like to try it, do it on a razor that is cheap and that you don't care about.

So here is how to do it using a process called flame straightening. Using a torch, (even butane or propane will probably be fine) quickly heat a small spot on the spine (keep the heat well away from the hollow part of the blade and especially the edge - might be good to submerge that part of the blade in water) that is in the center of the convex side, then run cold water on it immediately afterwards to instantly cool it. The length of time the torch should be played on the blade should start very low, like under a second. If you don't have the edge submerged be ready to instantly cool it afterward so if the heat starts to travel down it can be stopped quickly. After every attempt, check the movement of the convexity to see if you're done. Add a little more time to the heating cycle every time until you've got it straight.

There is no danger of the blade becoming harder, the steel should never get above a temperature that turns it blue. This will soften the spine a bit in the heated area but that's a trade-off decision you'll have to make for yourself. This is much gentler in terms of stress on the steel than trying to cold bend the blade, but there is still the possibility that the blade could crack. Like I said, best experimented on with a blade that isn't important to you or expensive to make sure you've got your process down. I've not had a razor crack doing this but I've only done it on 5 blades.

I learned to do this on large weldmenta and even steel shafts that were slightly bent. You'd be amazed at what can be done with a little judiciously placed heat. This process basically quickly expands the steel in the heated section but it is constrained from expansion by the cooler steel around it, which creates a plastic deformation situation. Once this deformation takes place, the steel is cooled and contracts to a smaller dimension than it had before. So heat should be applied to the "longer" side or outer convex side of the radius that you want to shrink.

 

[JPO]

These razors are not actually bent; that would imply that they were straight at one time and were forced into a crooked shape. These qualify as either warped or ground crooked to begin with. If the steel is fully hardened it will be very difficult to cold bend much without breaking it.

The best solution would probably be to work around the warp by using a very narrow hone, the side of a hone, or a convexed hone.

There is a method that would probably work to straighten these razors but it isn't for the newb. The process would be more likely to make the razor worse or destroy it if attempted by someone not already intimately familiar with this process. If you would like to try it, do it on a razor that is cheap and that you don't care about.

So here is how to do it using a process called flame straightening. Using a torch, (even butane or propane will probably be fine) quickly heat a small spot on the spine (keep the heat well away from the hollow part of the blade and especially the edge - might be good to submerge that part of the blade in water) that is in the center of the convex side, then run cold water on it immediately afterwards to instantly cool it. The length of time the torch should be played on the blade should start very low, like under a second. If you don't have the edge submerged be ready to instantly cool it afterward so if the heat starts to travel down it can be stopped quickly. After every attempt, check the movement of the convexity to see if you're done. Add a little more time to the heating cycle every time until you've got it straight.

There is no danger of the blade becoming harder, the steel should never get above a temperature that turns it blue. This will soften the spine a bit in the heated area but that's a trade-off decision you'll have to make for yourself. This is much gentler in terms of stress on the steel than trying to cold bend the blade, but there is still the possibility that the blade could crack. Like I said, best experimented on with a blade that isn't important to you or expensive to make sure you've got your process down. I've not had a razor crack doing this but I've only done it on 5 blades.

I learned to do this on large weldmenta and even steel shafts that were slightly bent. You'd be amazed at what can be done with a little judiciously placed heat. This process basically quickly expands the steel in the heated section but it is constrained from expansion by the cooler steel around it, which creates a plastic deformation situation. Once this deformation takes place, the steel is cooled and contracts to a smaller dimension than it had before. So heat should be applied to the "longer" side or outer convex side of the radius that you want to shrink.

This would be a fun experiment, just to develop some sort of process.
I would lean more towards an force method. The edge on a straight razor is more or less in the neutral axis of the section, so bending the spine should not effect the edge. If i knew the yield limit and the elastic modulus of the hardened steel i can calculate the force needed to create a permanent deformation. I guess this type of information is not available, so a trial and error method would be needed.
Have someone documented something like this?
Will it breake
It is probably

 

[eKretz]

It will probably break if you move it very far at all. The trouble with trying to straighten hardened steel cold by bending is that hardening the steel raises the necessary deformation of the object before it will yield. So in other words, if you had an unhardened steel bar and a heat treated one, you'd actually have to flex the hardened bar way farther than the soft one to get it to bend and stay bent, which makes it a lot more likely to break. If you do try the cold bend method, I'd advise trying to make many small little bends/tweaks at different places along the spine rather than trying to do it in one go at the center. Spreading it out like that will decrease (but not eliminate) the chance of breakage.

You can find the yield strength relatively easily with a Google search. Simply look at a similar steel (1095 or something) at probably 58-60Rc hardness level. Elastic modulus does not appreciably change with hardness. It won't be as easy as you imply to calculate as the cross sectional shape of the razor is not a very standard geometric shape, but you can probably just approximate that and be close enough. Also pay close attention to how close the yield strength and the ultimate tensile strength are to each other.

 

[JPO]

The story would probably end with me saying don’t do what i just did. Either it gets bent worse then it started out or it breaks.
If you bend your hardened steel bar when it is fully supported in both end, what we call membrane stress develops. You are then able to get some permanent deformation without bending it to much. The down side is you may end up with a worse shape then you started.
I did manage to hone it, so it is in a good place now, but i have an Ralf Aust with the same issue. Two out of three Solingen blades have had the same shape.
I have only one new TI razor, which have a bad reputation, mine is close to perfect. I might just be lucky with this one.

 

[JPO]

It will probably break if you move it very far at all. The trouble with trying to straighten hardened steel cold by bending is that hardening the steel raises the necessary deformation of the object before it will yield. So in other words, if you had an unhardened steel bar and a heat treated one, you'd actually have to flex the hardened bar way farther than the soft one to get it to bend and stay bent, which makes it a lot more likely to break. If you do try the cold bend method, I'd advise trying to make many small little bends/tweaks at different places along the spine rather than trying to do it in one go at the center. Spreading it out like that will decrease (but not eliminate) the chance of breakage.

You can find the yield strength relatively easily with a Google search. Simply look at a similar steel (1095 or something) at probably 58-60Rc hardness level. Elastic modulus does not appreciably change with hardness. It won't be as easy as you imply to calculate as the cross sectional shape of the razor is not a very standard geometric shape, but you can probably just approximate that and be close enough. Also pay close attention to how close the yield strength and the ultimate tensile strength are to each other.

After some “research“ i think your first suggestion would probably be the best solution. At what temperature does the steel start to loose it’s hardness? I have an adjustable heat gun. If i combine that with some color charts for temperature, it might be one solution.
230 deg c seems to be safe if i am reading this correct.

 

[eKretz]

You won't get good results with a heat gun. A torch is necessary, especially on such a small part. You need to get the heat in FAST, then cool the part down quickly before it spreads. If you heat with a heat gun the heat will spread nearly as fast as the part heats up, and you won't get the differential thermal expansion needed to actually yield the steel. You'll give up a little bit of hardness right where the torch is played on the spine, but that should be the only spot that's altered.

The tempering chart you posted should give you a good idea of what will happen to the hardness as the steel is heated. Observing the color created on the steel by the torch will give you a good general idea of the temperature reached at the surface of the steel, there are temperature/color charts available on Google.

How I have done this for razors is to hold the blade over a deep water reservoir (I used a 5 gallon bucket) with my left hand and the torch in my right. I quickly bring the torch over the spine in a single spot for just a second, don't wave it around, then lower the whole blade into the water and swish it around. You can keep the edge submerged while you heat the spine this way also. Check for movement/straightness, repeat if necessary. The key to this process is sneaking up on the straightness a little at a time until you get it just right. Too much heat too fast and you'll immediately have a bend in the opposite direction.

I will stress again that you'd probably be better off just using a narrow hone, but I understand if you must try it, as I also needed to. Just to see if I could do it.

 

[H Brad Boonshaft]

Rolling X.

How it’s been done for hundreds of years.

 

[LJS]

These razors are not actually bent; that would imply that they were straight at one time and were forced into a crooked shape.

When this topic resurfaces every once and a while I keep wondering why people think the razors have been “bent” or just how that would happen without snapping that hard steel Like trying to bend a good file……snap. I can’t imagine anyone out there annealing razors to bend them and then retempering, so just confuses me to think about a razor that got bent. And let’s say they don’t snap like good hard steel……how do you bend a straight razor accidentally? Would take some force more than average drop or neglect - like closing a door on it or running it over.

Unless someone can demonstrate a razor getting bent, I’m still going to believe they are manufactured that way.

If you have enough experience they can be honed just fine. But I admittedly don’t like warped and crooked razors. Have one on the bench right now I am messing with.

 

[JPO]

When this topic resurfaces every once and a while I keep wondering why people think the razors have been “bent” or just how that would happen without snapping that hard steel Like trying to bend a good file……snap. I can’t imagine anyone out there annealing razors to bend them and then retempering, so just confuses me to think about a razor that got bent. And let’s say they don’t snap like good hard steel……how do you bend a straight razor accidentally? Would take some force more than average drop or neglect - like closing a door on it or running it over.

Unless someone can demonstrate a razor getting bent, I’m still going to believe they are manufactured that way.

If you have enough experience they can be honed just fine. But I admittedly don’t like warped and crooked razors. Have one on the bench right now I am messing with.

I am sorry for the confusion. English is not my first language. When i say bent, i do mean there is a curvature in the blade from manufacturing. The blade in question was honed just fine, but i guess when someone starts to talk about open flames and stuff to affect the geometry of a blade, then i guess i got a little exited My engineering mid started spinning. To much time to think (overthink). It is not always about finding the best solution, but to figure out a different solutions.