Nail nick grinding

R

Randy3000

Joined
Jun 3, 2017
Messages
811
I have tried all manner of ways to grind nail nicks. Careful filing, dremels and cut off wheels, hot stamping, i even welded a contraption together to use my handheld drill and one of those grinding wheels for drills. I have never been satisfied.

i did the math, and for a nick D" deep, L" long, and a grinding wheel with radius R", we have the equation R=0.5D+0.125L^2/D. using D=0.04 (about half way through the blade) then 0.5D is really small so we can just say R=3.125L^2 as a useful approximation. So for reasonable values of the length of the nick, we need a wheel with a radius about 1"-3" depending on the blade style and how big of a nick we need. Finding grinding wheels that are thin and already have an angle on them so you dont spend an entire year of your life dressing an angle on a stone, especially on the smaller radius size, pretty much limits you to a few drill bit grinding stones and they are hard to find locally.

Then my angle grinder burned up. I salvaged the power cord and the arbor out of it and tried to clean as much of the winding up as i could for my scrap bin. That arbor set in a box for a month. Then i realized cut off wheels have a radius in the 1"-3" i need. I always have plenty of almost worn out cut off wheels around 1"-1.5" radius laying around my cheap self cant throw away. They are also 1/16" thick which is about perfect.

So i chucked the arbor in my drill press, dressed a cut off wheel on an angle, clamped a blade on a piece of angle iron, and cut the best nick to date.

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I should of bought an arbor a long time ago, they are cheap $2, i just hadnt thought about it or seen anyone do it. I have seen people use surface grinders, mills, and other fancy equipment i dont have, but no good cheap easy methods.
 
As far as the pin hole, i use a 118 degree 1/2" shank bit on a really level table. As far as flat tangs, i am at the mercy of the kiln gods and the hungover guy at the steel factory.
 
FWIW I use a 7" stone on a surface grinder, of a specific type that hold sharp angles well. I've often seen people recommending much smaller wheels, but personally I like a very sharp, well defined nail nick, with a nice swoop similar to the old punch cut nicks, but corner definition is the most crucial factor to me. Most nail nicks are way too rounded one the ends, and inside.

I settled on 20 degrees as the optimal angle.
 
Well, a 7" wheel has 3.5" radius, and so the nick is a bit over 1" in length. I dont think that part is extreme at all for large blades. Now the 20 degree angle is pretty extreme. Just curious, is that 20 degrees make the nick real wide or real skinny? 20 degrees from vertical or horizontal?
 
20 deg from horizontal, which is how angle and radius dressers for surface grinders index (off the magnetic chuck). Bear in mind this is ground to a sharp angle, so essentially the top of the nail nick plunges 90 degrees into the steel, this allows you to get a nick firm purchase with a nail. You don't want to be cutting a concave radius into the steel, but sharp 90 to whatever angle you prefer.


I just had to rebuild my computer so I don't have my photos, but I'll try to find you an example of my nail nicks, I spent quite a lot of time and money finding a stone that would hold a sharp edge, let alone keep me from having to redress every time I cut one. This size stone and angle allows me to get a very sharp, well defined nick that's got a wide "swoop" with a straight top and sharp corners, on very thin blades, my small slipjoint patterns usually start at 0.100 but aggressively distal tapered to practically zero at the tip. This was the sweet spot for the appearance I wanted, with plenty of depth for a very positive pull, but also scales very well into my larger patterns.


Length is determined by depth of cut obviously. If the nick is sharp enough, you don't have to cut as deep to get a comfortable purchase. I constantly get complimented on them by makers and customers alike, and asked how I achieve the results I get.
 
The users ability to open the knife is absolitely critical. If they cant get it open, they wont use it. If it slips off and breaks nails, they wont use it as often as they would like to. I have a knife that i made that i want to love so much but i hate the damn nail nick on it, and i never carry it, and it was positioned poorly and i cant really redo it without something real drastic appearance wise. It kills me, i did everything good but that nick and it makes it nearly unusable.
 
Here's a photo I had on my phone so you can see what I'm talking about. If you've ever handled a good quality antique slipjoint that the nail nick just grabs your fingernail and feels like it could cut it, you'll understand what's nice about a very sharply cut one, which requires stable work holding, and a very sharp edge. Traditionally these were always cut with a nail nick "punch" or "chisel". Which is literally a round edge hard steel chisel with a curved face, that has to be very sharp with the right geometry to cut cold or hot steel.

This of course is the absolute best technique, but requires the ability to make the chisel, experimenting with the geometry, and a feel for exactly how hard to hit it, or some kind of press rig that will let you accurately cut the depth. You can't buy one of these off the shelf anywhere, which is why they've become nearly extinct.


nick.jpg
 
For reference, the above blade is only about 2.5" long from the choil notch to tip, so, not a big blade.
 
Off topic but...
That’s a beautiful blade, what’s the pattern called?
 
Randy3000 said:
The users ability to open the knife is absolitely critical. If they cant get it open, they wont use it. If it slips off and breaks nails, they wont use it as often as they would like to. I have a knife that i made that i want to love so much but i hate the damn nail nick on it, and i never carry it, and it was positioned poorly and i cant really redo it without something real drastic appearance wise. It kills me, i did everything good but that nick and it makes it nearly unusable.
Click to expand...


Honestly, this area is one that *many* good slipjoint makers have neglected in my opinion, and what holds a LOT of knives back from being "great", instead being simply "good", and I can't help but have my eye immediately drawn to a messy nail nick.

Many makers and customers find them acceptible however, we each have our fixations, but IMO, this is an area that every "top" slipjoint maker has had to figure out how to get right.

I'm of the opinion that there are only 3 ways to get this "right", at least, that I've seen so far, I'm sure there are some other ways people have figured it out, but thus far its:

1) Cut with a fly-cutter ground to the right geometry (this necessitates it being done before HT though)
2) Cut with a properly ground stone either on a surface grinder, or a custom fixture. (can be done post HT and after grinding, which I favor, because I like to get really aggressive tapers, and it allows me to adjust blade profile somewhat to make everything perfect in the end, to my eye)
3) Cut with a nail nick punch/chisel. Has to be done pre-HT often, but offers the most flexibility for style, and the most elegant and defined cut, but much trickier.
 
I agree, that blade is spectacular! My blades are much narrower but i think that width of nick looks great on your example.
 
Dunno, that blade is only 18/32 tall. Photo I think makes it look a lot bigger than it is.
 
Also, that nick is bigger than I usually cut them on that size blade, cutting just a few thou less deep makes it look narrower, and slimmer. However, I wanted a deeper wider cut based on the overall design of that knife, and that's a more traditional look. I'm mostly influenced by the golden era Sheffield slipjoint makers, as opposed to the American style, so I like a nice swoopy nick.

The big advantage of the way I do them though, is that I can easily adjust each one, to each blade, until it just "looks right" to my eye.

That's something you can't really do with any other method that I'm aware of. The way you're doing it currently allows you some latitude to do that, but I'm sure you've realized, that you have to have a firm grip and be very careful, because any chatter or vibration will really make it look sloppy.


Another advantage is, I can use a 1-2-3 block against the stone, with the magnet turned off, to exactly square my nick up on a blade with a straight clip like that one, or a machinist square, lined up with the center of the spindle adapter, to locate it in X, based on some mark (although you have to compensate for the fact that it'll cut more on the thicker side a bit if you've got an aggressively tapered blade).




Anyway, I know you don't have a surface grinder yet, but if you could acquire one, and learn to use it, you'd be amazed at all the great things you can do with slipjoints and one. I actually have a kind of clapped out small one I use, just for cutting nail nicks. Think I paid $400 for. It's not accurate enough for general use in by my standards (I get a bit of a sub-standard finish), but it's more than adequate for nail nicks or cutting/fixing choils, or other similar work.
 
I used a 45 degree angle and went about 0.040" deep, but i could go to (theoretically) a 33 degree angle and get 0.040" deep and use the full 1/16" thickness of the cut off wheel. Or i could back off on the depth and use smaller angle if i had a larger wheel. They make cut off wheels pretty big. I could even go to a stone since it is a 5/8" or 7/8" arbor, should be easy to fit. I cant take a very good pic and get it online for some reason, it looks lower resolution online than on my phone, maybe imgur is compressing the jpeg. But the cut out is clean and no chatter issues i can see. It feels 98% solid while i am cutting.

I will get a surface grinder at some point, i have room for one. I recently built my heat treat oven and felt that was something desperately needed, but i got to save for awhile and then i can begin thinking about a surface grinder.
 
Randy3000 said:
I used a 45 degree angle and went about 0.040" deep, but i could go to (theoretically) a 33 degree angle and get 0.040" deep and use the full 1/16" thickness of the cut off wheel. Or i could back off on the depth and use smaller angle if i had a larger wheel. They make cut off wheels pretty big. I could even go to a stone since it is a 5/8" or 7/8" arbor, should be easy to fit. I cant take a very good pic and get it online for some reason, it looks lower resolution online than on my phone, maybe imgur is compressing the jpeg. But the cut out is clean and no chatter issues i can see. It feels 98% solid while i am cutting.

I will get a surface grinder at some point, i have room for one. I recently built my heat treat oven and felt that was something desperately needed, but i got to save for awhile and then i can begin thinking about a surface grinder.
Click to expand...

So, the guy that got me started making slipjoints, uses a setup he rigged, that utilizes a grinder spindle (like a tool post grinder, or similar), that he made a rigid mount for, on a big L bracket, that's bolted to the bench, the spindle is horizontal to the bench, and he made a hinged plate below it that he clamps the blade to, and just "picks up" into the stone he has mounted on the arbor. It actually gives good results as long as he dresses it regularly.

You can find spindles, like big die grinders on ebay, that are used to make various cnc routers, and mills, etc. on ebay, usually for decent prices, or you could rig a die grinder or similar to do the same, or build a similar jig for you drill press. The trick with getting good results with any of these methods, is rigidity. You need something you can clamp the blade to in a way it's not going to move, and actuate in a linear motion without any wobble.

If you talk to an industrial abrasives distributor, I'm sure they can find you a good, larger stone. In fact, they may be able to find you a hard stone that's already angled, and mounted to a shaft. Something for a large die or cone-wheel grinder. Hand tools usually have stones already mounted on spindles for convenience, and to avoid lots of balance or run-out issues.


For what it's worth, because of having that sharp 90 degree top of the nail nick cut, I can go significantly less deep if I want to and get a good nick. The problem when I first tried figuring this out, with a smaller 45 degree angled stone, was that you had to cut it very deep to get the proportions right. I actually can have a 0.020" deep cut on a smaller thin blade and it looks right, and feels great, with the size and angle I'm using now, although the above nail nick was probably 0.030 deep.

With the whole nick being somewhat radius shaped, you dont have an acute ledge to grab with the nail, and it has to be deeper.
 
That makes sense about the geometry of the nick. About the setup your mentor had, that sounds similar to what i tried to do with a handheld drill. The problem was the hinged piece under the grinding wheel that i lifted into the wheel, that hing had some play in it. I tried a few hinges and couldnt get a solid one. Also, my drill had some wobble to it. I may rig up a sturdier base for my drill press setup i have going and see if it feels more solid. I have a transformer i pulled out of a microwave and it has these half inch heavy plates around it, i will cut one off and weld a piece of angle iron to that and see what that does.
 
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javand said:
Honestly, this area is one that *many* good slipjoint makers have neglected in my opinion, and what holds a LOT of knives back from being "great", instead being simply "good", and I can't help but have my eye immediately drawn to a messy nail nick.

Many makers and customers find them acceptible however, we each have our fixations, but IMO, this is an area that every "top" slipjoint maker has had to figure out how to get right.

I'm of the opinion that there are only 3 ways to get this "right", at least, that I've seen so far, I'm sure there are some other ways people have figured it out, but thus far its:

1) Cut with a fly-cutter ground to the right geometry (this necessitates it being done before HT though)
2) Cut with a properly ground stone either on a surface grinder, or a custom fixture. (can be done post HT and after grinding, which I favor, because I like to get really aggressive tapers, and it allows me to adjust blade profile somewhat to make everything perfect in the end, to my eye)
3) Cut with a nail nick punch/chisel. Has to be done pre-HT often, but offers the most flexibility for style, and the most elegant and defined cut, but much trickier.
Click to expand...

I finally got set up for #1 above and am pretty pleased with my test cut. http://www.pictame.com/media/1717881578371519290_1724930730
I would ideally like to be able to do it after heat treat for the same reasons Javand listed...dialing everything in just right, but will probably live with the fly cutter for now.
 
tmerkl said:
I finally got set up for #1 above and am pretty pleased with my test cut. http://www.pictame.com/media/1717881578371519290_1724930730
I would ideally like to be able to do it after heat treat for the same reasons Javand listed...dialing everything in just right, but will probably live with the fly cutter for now.
Click to expand...

Looks good to me Tim, but you'll have to cut deeper probably if you put much taper in the blade, for a nick that far back it's not as big a deal, but it gets tricky if you like them up front. Course, most slipjoint makers don't put much distal taper, so it isn't a prob. It's a bit of an affectation of mine however, I like to see an aggressively tapered blade, and it really shows how well you've got your blade centered vs one that's only tapered near the tip.


I like being able to put my nick right where it "looks right" to me, after I've adjusted everything, and I'll admit, I've become a bit reliant on that. I'm wanting to move to method #3 more often, because I'm most interested in the old sheffield style work, and it just gives you so much latitude for appearance and shape of the nick (like curved nail nicks and match strikers, etc), but I'm having to really put some thought into things ahead of HT, that I used to not have to bother with.

Grinding the nick gives a LOT of latitude to change blade geometry, that you simply don't have if you've got things cut in before hand.

Obviously in a perfect world though, we master as many possible techniques as we can, so that we can tailor our approach for each piece. I think this is something many of us have forgotten, that the old makers would laugh at us for. Many simply figure out one way to do something, and then repeat until death. I want as many tools in my box personally as I can have though. My goal is to be able to make, anything I can possibly imagine, in a suitable manner, without compromising to accommodate a lack of versatility. Got a long way to go still though. ;)
 
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