Advice on reshaping a broken tip

[grepper]

I have an 8" chef knife with about 1/2" broken off the tip.  I've read that this should be reshaped from the back side of the knife, forming a nice curve to the tip.

My question is how to approach the wheel?  90 degrees across the width of the wheel using the jig?  Parallel to the wheel?  Into or away from the stone?  I wouldn't want to dig gouges into the wheel if that is even possible.

I'm clueless!  Appreciate any advice.

Thanks,

Mark

[Mike Fairleigh]

Depending on how close you want to match the original blade shape (that's a big hunk of blade gone), you may need to start by re-profiling the whole edge or part of the edge with a file, then sharpen.  A single cut bastard file held at 90* to the edge (with the knife held in a vise) does a very nice (and quick) job of shaping an edge.

To see an example of what I mean (but on an axe), skip to the 21:40 mark on this:

https://www.youtube.com/watch?v=2B7Wy7iskVE&list=FL-LX95Glj7A5fJNhtsnJZ_w&index=14

[grepper]

I found this advice on the 'net.  About 1/2 way down the page it shows making a curve from the top of the blade:
http://www.cheftalk.com/t/64048/tip-of-knife-chipped-off

Of course, others say grind the cutting edge.  What's a noob to do?

Is it better to do this preliminary work with a hand file or maybe a regular bench grinder rather than with the T-7?  I suppose with a bench grinder you would have to be careful not to over heat the blade.  Is the hand file idea so that you don't use the Tormek for removing such a large amount of steel?

[Mike Fairleigh]

Yes.  Tormek grinding that much steel (IMO) would take too long.  If you go that way, at least make a roughing (fast) pass over the stone with the truing tool first.  On the other hand a dry grinder will be too easy to overheat the steel - thin steel overheats so quickly it often happens before you can pull away from the wheel.  Not to say that it can't be done that way, but I wouldn't recommend it.

Another option would be to draw the shape you want onto the blade, then rough out the shape with a cutoff wheel on a Dremel.  Then file & wet grind.

[grepper]

Thanks for the advice KSMike.  Makes sense to me.

Guess it's a 6" not an 8".  Oh well.

Should be an interesting project.  Hopefully it won't turn out looking like a first grader did it.

Here's a picture of the blade:
http://www.screencast.com/t/uzQZrGzHSC3

[Jeff Farris]

Looking at the picture, I would do it in the Tormek, freehand with the wheel turning away from the edge, and do it on the edge side. I would do it just like I was sharpening, turning it over frequently, rather than re-profiling and then sharpening....don't know why, but that's what I would do. 

[grepper]

Interesting.  If you do it from the cutting edge, in order to get a smooth, non-dramatic curve, you would have to start quite a ways back from the tip.  This would change the curve of the blade around the tip appreciatively. Not good or bad, just different.

If you do it from the spine, it's a lot more metal, and the overall thickness around the tip is thinner because the width of the knife is tapered towards the cutting edge.

BTW.  Anyone know the term for the distance from the cutting edge to the spine?  In helicopter blades that would be called the "chord".

Anyway, if you wanted to grind from the spine towards the cutting edge, would you do it holding the knife perpendicular 90 degrees to the wheel, or parallel with the wheel, or just mess around with it and see what works?

[Mike Fairleigh]

Chord's good enough for me. 

Seeing the blade, I agree with Jeff.  That isn't as much of a chunk as I was envisioning.  It's still enough re-shaping that I'd be tempted to run into the blade rather than away, but I'll always defer to Jeff.  I'm pretty impatient.

[Justin]

Looking at the heel on the blade i would say the whole edge needs reshaping. I would see that knife a practice blade personally.

[Rhino]

I dinged the sharp edge of a chef's knife and lost a half dime worth of material on the cutting end near the tip.  I reground the sharp edge, the shape is never the same again.  I enjoy it but it is not the same knife.  It also took all afternoon and the blade still looks funny.  Whenever I sharpen the blade, I try to take more metal off the make the blade shape a little more pleasing but it is slow going.

If this was my knife, I would just grind down the broken edge from the blunt end and turn it into a santoku type blade.  At least that way, you keep the blade to handle angle - although, of course, you are missing the tip.  Since it is a hobby for me and I am not trying to save money, I would buy a grinder to turn it into a santoku blade.  Or borrow a standard bench grinder. 

Don't let the blade get too hot.  Dip it in water often using that bench grinder.  That is just a thought.  I've never used a grinder other than the Tormek in my whole life. 

[Jeff Farris]

Interesting.  If you do it from the cutting edge, in order to get a smooth, non-dramatic curve, you would have to start quite a ways back from the tip.  This would change the curve of the blade around the tip appreciatively. Not good or bad, just different.

If you do it from the spine, it's a lot more metal, and the overall thickness around the tip is thinner because the width of the knife is tapered towards the cutting edge.

BTW.  Anyone know the term for the distance from the cutting edge to the spine?  In helicopter blades that would be called the "chord".

Anyway, if you wanted to grind from the spine towards the cutting edge, would you do it holding the knife perpendicular 90 degrees to the wheel, or parallel with the wheel, or just mess around with it and see what works?

If doing it from the spine, I would hold the knife parallel to the stone (edge facing the operator), with the wheel turning away from the operator.

Here's the thing about a chef's knife and the curve of the blade. A chef's knife in general is used with some point in contact with a cutting board at all times. The knife is rocked on its arc into the material. That said, I have one very good quality chef's knife from Europe that has a rounded nose that very slowly rolls away from sharpened to the spine. The theory is that it is safer, since it doesn't have a point. The reality is, while it chops very well, I hardly ever use it without having to have another knife out at the same time. Sometimes you just have to use that tip to sneak into something. That's why I would make the new curve working from the edge side. It isn't going to take much blending to put a new point on that blade. I've done it to a couple hundred pocket knives at shows where guys have handed me knives with broken tips. You have to be more careful doing it from the edge on a folding knife, because the tip can end up outside the case, and that's bad. There, you have to do at least some of the work from the spine.

All in all, the knife pictured is not far away from being perfectly usable and it won't take much in the way of artistry to make it look like it has never had an accident, either way you go about it. If you work it from the spine, you're going to end up with something that looks like a drop point pocketknife blade, unless you do a lot of blending well back into the spine. Working from the edge, you just have to blend the curve into a slightly tighter final radius. I know I could have done it in the time it took me to write this.

This is the one operation where I use the SG-250 at 220 grit on knives. If you open the surface up with the coarse side of the grader, it will remove knife quality steel at a surprisingly fast pace.

[grepper]

Thank you Jeff!  Should be a fun project.

Mark

[Elden]

I understand the reason for using the wet wheel approach. To me, there comes a time when the dry grinder or belt sander comes into play. Mark's knife in my opinion, for whatever it is worth, is not to that point yet. A knife was given to me to work over that had an unknown (to me) amount broken off. What was apparent was that the broken off line (approximately perpendicular to the spine) was close to an inch long. By using a dry grinder carefully, the tip was restored in good time and in great condition i.e. temper unaffected. The Tormek was then used to shape the edge and for sharpening.

Dry grinding works great if the temperature of the blade is carefully monitored. Unless a person does not have temperature sensitivity in their fingers, it is easy to tell when steel becomes too hot to hold (at the portion being ground, not the convenient holding spot). Dip it in water, as Rhino said, at that time. The steel is well below the temperature of the temper being affected at that time.

I think, as seen above, there are differing opinions on which edge (or maybe both) to grind. That should be determined by the user as to what use they have in mind for it. I like a knife to have a pretty good point on it (like a boning knife), but the user may not. I don't care for drop point knives, however, the user may prefer a drop point.

[grepper]

Jeff,

It worked!  Following your instructions, starting @ 220 grit and moving the knife just as though I was sharpening, in very little time the break just went away and it formed a new tip!

The cool thing about it was that it happened rather automagically.  It was like..., well...,  Zen. I just sort of wiggled my hands and arms around, and watched the Tormek and the knife give birth to a new tip.  I even like the shape better than the javelin that it was before!  Not a drop point, but not a spear either. Just a nice, even curve.

Obviously if I had been particular about the tip shape I would have had to do it differently, but I'm extremely pleased, especially for the first attempt.

The knife still needs some work as the center area of the edge is not flat, but that should not be too difficult to fix.

http://www.screencast.com/t/xO5ncMNLs

Thanks for the assistance!

Mark

Happily, life is a grind!

[Mike Fairleigh]

Impressive!