How To Tip repair - best practices

[scdub]

Hi Folks,

Like many of you, I have encountered many broken knife tips and am even responsible for one or two. A little chip off the tip is a pretty easy repair (see below), but when a larger chunk is lost things get a bit more complicated.

I’m happy to be known as the weird knife guy, and as a result I often get rusty, dull or broken knives from friends and co-workers to work on. I just finished re-tipping a knife and thought it would make a good case study.

I did a forum search btw and found a variety of advice but nothing that consolidated all of the good advice together, and that’s what I’d like to do here.

The knife in question is a very nice Spyderco Southard which belongs to one of my partners. Awhile back he sent me this photo and asked if I could help:



I said for sure, and a few weeks later the knife showed up on my desk with a note. The owner wanted suggestions as to how to shape the tip, but said he was “anti-tanto”. I cut a smooth curve in a piece of paper, layed it over the knife, and sent this picture back to him.



He liked the looks so l got started.

The key point to know is that if you overheat the knife blade during the repair process, you can ruin the heat treatment of the knife permanently. Much of what I’m sharing below is about avoiding that scenario.

I’ve probably fixed a dozen or more tips by now and have learned some good lessons.

Shape: It’s almost always going to be MUCH easier to grind the spine down to the edge, rather than vice-versa. So in other words, if my buddy HAD wanted a Tanto point, I’d have talked him out of it. In the case of this knife, the three reasonable choices were: A) the drop point I suggested, B) a straight clip point, and C) a trailing point clip. Note that A and B are exponentially easier to create than C, simply due to the geometry of trailing points.

Tools: Again, if you can avoid power tools, you completely avoid the overheating issue, so if you can tackle the grinding with a stone (ideally diamonds as they cut fastest) or some other abrasive, do that. Be aware that most regular files won’t work well on the hardened steel of most knives.

While many different tools can work, (I’ve used a Dremel successfully but it’s much harder to get a smooth curve/surface), a belt sander or low-speed belt grinder might be the best tool to use with a large tip break. Please watch this very short video:

Note that I’m carefully lining up each stroke and making them as consistent as possible. This is key in achieving a smooth curve (or straight spine).

Also note that I use light pressure and dip the knife in water after every pass. Dipping is easy to do with a belt sander/grinder - and more difficult with other tools.
I recommend AGAINST a grinding wheel. They spin very fast and therefore can generate friction heat very quickly. Also the wheels can fracture (causing injury) if exposed to water, which makes dipping less convenient.

Another key point: STOP with any power tools BEFORE you grind all the way to the edge. The very tip of the knife will be instantly overheated by high speed abrasives, you won’t be able to dip fast enough to protect the heat treatment.

So, this is where I stopped before moving to a diamond plate:


I’m using an inexpensive (~$8) double-sided diamond plate here and getting closer. I’m using essentially the same tip-trailing motion, and constantly checking the scratch pattern between passes. Look close and go slow:





And done. Use magnification to confirm that you’re ACTUALLY at a point (sorry for the bad magnified pic):

I still need to sharpen it up (which will refine the tip slightly) and lube the pivot and then back it goes.

Really sweet knife…

If you have any helpful tips/critiques to add or would like to show off a tip repair please feel free!

 

[tinfoil hat timmy]

Nice write up. Thanks.

Useful Information here.

 

[karnaknives]

Great work.
I would have done it the same except I’ve only ever used diamonds and other abrasive stones.

 

[Officer's Match]

Really nice job, it looks great. Thanks for the, err, tips.

 

[Obsessed with Edges]

Nice work.

I've used the sander belts for this type of thing, but not the sander... I don't have one (yet, anyway).

I cut a 3" x 21" / 120-grit zirconia-alumina belt at the seam, laid it flat and glued it down to a board. Then just draw the blade spine along the length of the belt while gradually lifting the butt end of the knife until the spine at the very tip is flush. Then lift & repeat the passes. Even as used without power, I've been impressed at the speed of metal removal with these belts. They're very aggressive - much more so than any of the stones I've tried for the same task. Much of that speed is simply due to the extra abrasive surface length afforded for each pass. I've used the method for fixing both broken & severely bent tips, as well as simply changing the profile of the tip to suit my preferences, and re-pointed severely worn, rounded or blunted tips on very old or heavily-used knives.

I realize there's a big speed advantage with a powered grinder, especially for very large-scale tip damage as in your example. But for the smaller breaks and bends at the tip, I've been pretty happy with the method I've employed using inexpensive materials and with minimal worries about heat damage. A couple examples are below, of tip repair or regrind work I performed using this method.

BTW, In order to safely apply some fingertip pressure when grinding, I used a wine cork pressed onto the sharpened, upturned cutting edge of the blade, which worked well enough to keep my fingers out of harm's way, as well as preventing accidental blade closure with non-locking folders. Other items could be used for this as well, like a wooden block or anything similarly suitable.

Kershaw Leek broken tip in ZDP-189 (before & after repair - took about 45 minutes at a relaxed pace):

This used to be a spey-profile tip in a Buck 301 folder. From the factory, the tip's point actually rested above the liners when closed, which I didn't like at all. Reground it to remove the 'clipped' portion of the spey's tip and changed it to a spearpoint profile, with the tip nestled beneath the liners when closed (2nd & 3rd pics) to suit my preference.

 

[scdub]

I've used the method for fixing both broken & severely bent tips, as well as simply changing the profile of the tip to suit my preferences, and re-pointed severely worn, rounded or blunted tips on very old or heavily-used knives.

Oh I like the sound of that!

It’s always tricky for me to be precise when pointing/reprofiling a damaged/rounded tip, and the idea of long smooth drags is very appealing - I might actually get a nice long piece of marble bathroom backsplash to mount it on before I buy groceries later today…

 

[Obsessed with Edges]

Oh I like the sound of that!

It’s always tricky for me to be precise when pointing/reprofiling a damaged/rounded tip, and the idea of long smooth drags is very appealing - I might actually get a nice long piece of marble bathroom backsplash to mount it on before I buy groceries later today…

That's a good idea. I used to do some sandpaper sharpening of knives using SiC paper over a hard backing. When I was in that mode, I'd occasionally eyeballed some of those backsplash pieces of granite, marble or crushed glass or whatever, at Home Depot. I'd thought then about using them for the sandpaper. But I never got around to picking a piece of that up. I did eventually pick up an inexpensive 2" x 10" x 12" granite reference plate, which was perfectly sized for the sandpaper sheets. Might have to look at the longer backsplash pieces again, with the cut belts in mind.

 

[catspa]

Good work.

I recently did an Endura that the guy’s dad had given him before he died, and he was thrilled to have it back with a tip again, didn’t even notice it being 3/8” shorter.

A Tormek works well for retipping if you keep moving laterally so as not to wear a groove, but I’ve also used a 1x42 belt sander slowed down to about 1/4 the regular speed. Most times, retips are brought to me when I’m sharpening at a swap meet or other public venue, with the Tormek already set up so I just use that. I once did a FFG retip on a disc sander, worked okay after I wrecked a couple junk knives climbing the learning curve.

You’re right about dropping the spine being the easiest method. Raising the edge to meet the spine takes some serious blending to match the factory grind. I prefer to grind the profile first, then reset the bevels. It’s doable, like for a Buck 110 (on which a noseover looks really weird), but tricky. I made a special tool rest jig, ran my fine wheel on a foot switch, and had my GF misting water from a squirt bottle about once a second.

I’ve drip and mist cooled grinding wheels for years, never had any problems, maybe I’m just lucky. If they get wet and freeze though, whole different story.

Parker

 

[scdub]

Might have to look at the longer backsplash pieces again, with the cut belts in mind.

I’ve drip and mist cooled grinding wheels for years, never had any problems, maybe I’m just lucky. If they get wet and freeze though, whole different story.

I might be overly cautious about this - but since I’ve got the belt sander I can just use my grinder dry and not worry about it.

 

[catspa]

That style belt sander is useful for woodworking also, especially with a 90 degree fence. My Delta has an adjustable table on the disc as well.

1725 rpm bench grinders are not very common, most run at twice that speed. If you find a slow one, grab it.

Meanwhile, you can slow down a belt drive belt sander quite a bit with pulley and wheel swaps. The direct drive ones, not so much.

Parker

 

[Equipped4life]

scdub Well done!
Thanks for sharing your methodology!

Obsessed with Edges
Thanks for the great idea to use a cut open 3x21 belt!

 

[3fifty7]

Nicely done, I’ve reprofiled a couple of Spyderco tips too. One by choice and one by force, and CharlieMike did my Yojimbo 2 after my wife dropped it on a tile floor.

I don’t have my Spyderco Southard with me today but if I recall correctly the tip is pretty robust, especially for a hallow grind. I’ll have to take a closer look at it this evening.

 

[ecallahan]

This is helpful, thanks!