Knifemakers, Machinists: Help Me Jimp

[Bolster]

If you are a knifemaker or machinist, I could use some advice on how to shallow-jimp the spine area of my beloved Caly Jr. I want to jimp the area in the oval below, fairly shallow, just enough to get some thumb grip. I'm pondering three options: (1) I could vice the knife horizontally, in my mill, and run this small bit crosswise, across both the FRN and the metal catch ("metal catch," what is the correct word for that?). I've no idea if the bit could make it through the metal catch; don't know how hard the catch is. (2) Same approach as above with a countersink. (3) I could vice the knife vertically and use a cutoff wheel to make shallow jimping cuts. I'm fairly certain the metal catch would not be a problem with this method, since it's grinding not cutting, but I'd be getting square(ish) rather than V-shaped jimps.

Alternately, I could do any of the above ONLY in the FRN portion to either side of the catch, and leave the metal catch alone. Should still give the thumb some purchase.

So...how would you skin this cat?

(PS: Since I know you'll want to know: the lanyard hole is filled with glow powder in epoxy. An experiment from long ago; still works.)

[JRinFL]

Not a machinist or gunsmith, but have you considered using a metal checkering file?

[gdwtvb]

The correct term for the 'catch' is lockbar. I would advise you against your proposed modification. I'm not sure if or to what extent the lockbar is hardened, but modification of the locking mechanism on a knife is asking for trouble...as is using any powered equipment to modify plastic. I think anything that would cut into the lockbar would melt and most likely ruin the scales. If the scales can be removed, option 3 might be acceptable, but I would make sure to only modify them farther forward to avoid weakening the scales near where the pivot pin is located. (The pin just above the lock disengagement notch.) I would suggest a slower and more controllable approach, a round hand file at a well lit workbench with the scales suitably clamped in a vise.

I know that people do perform decorative filework on lockbars with no perceived damage to knives, so my hesitation may be unwarranted. Take my advice for what it cost you.

Grizz

[Evil D]

What you want is called a "checkering file".

[Pokey]

Not a machinist or gunsmith, but have you considered using a metal checkering file?

What you want is called a "checkering file".

That's the first thing that I thought of. Get a piece of flat aluminum, lay out lines and practice until you get the hang of it, then show us how it turned out. I've thought of doing this on a thumb ramp or two.

[Bolster]

Hm, OK, thanks. I've done diamond checkering on wood, but don't have a checkering file for metal. If it's a similar process, the issue is getting the lines started. I'll look into it. Hadn't considered doing the job by hand, but if it works, great! Thanks for the lead.

According to Brownells, a checkering file is really only for laying out lines; the actual creating of "peaks" is done with a triangle file. I would imagine a mill could also lay out lines, being that it's accurate to .001.

I had not considered jimping on the thumb ramp of the blade's spine (much as I would like it) because I assumed the blade would be way too hard for any file. It is after all ZDP189. Has anyone successfully filed jimping onto a post-production, hardened blade spine? Brownells says: "Use of these files ...on hardened surfaces will ruin the teeth - dulling them almost immediately."

Is the lockbar hardened?

[JRinFL]

I had not considered the hardening aspect. I would guess the lock bar is hardened, but not to same level as the blade steel.

[Pokey]

Hm, OK, thanks. I've done diamond checkering on wood, but don't have a checkering file for metal. If it's a similar process, the issue is getting the lines started. I'll look into it. Hadn't considered doing the job by hand, but if it works, great! Thanks for the lead.

According to Brownells, a checkering file is really only for laying out lines; the actual creating of "peaks" is done with a triangle file. I would imagine a mill could also lay out lines, being that it's accurate to .001.

I had not considered jimping on the thumb ramp of the blade's spine (much as I would like it) because I assumed the blade would be way too hard for any file. It is after all ZDP189. Has anyone successfully filed jimping onto a post-production, hardened blade spine? Brownells says: "Use of these files ...on hardened surfaces will ruin the teeth - dulling them almost immediately."

Is the lockbar hardened?

Here’s a checkering job that was done some time in the past 52 years; it’s probably not as crisp looking now. The friend that did it laid out the lines on a piece of pipe and practiced on the pipe to get warmed up. He used a checkering file and a triangular file. You really want serrations, not checkering, so there wouldn’t be as many steps. Really, serrations are only uni-directional checkering, right? Why couldn’t one do checkering on the lock bar/back of the handle?

Laying out the lines with a mill would make them super accurate.

Oops! I didn’t realize your blade was ZDP-189, you’re right, it’s probably harder than the tools. The blades I have are much softer than ZDP-189.

Between the hardness of the blade and that of the lock bar, I would imagine the lock bar is the softer, “sacrificial” part with regards to wearing.

You could buy a byrd knife, or a Value Folder as a guinea pig and try it out.

If you do it, show us how it turns out.

[Bolster]

That's some beautiful checkering. I like how the gunsmith kept the peaks sharp right up to where they stop; think about how difficult that would be, to file deeply enough without going "over" in the slightest. That's challenging in wood checkering too, but the stakes are higher in metal! Thanks for the inspiration.

Yes, you're quite right, I'm looking to do serrations not checkering.

BTW, I know that for wood checkering there are all kinds of nifty attachments for your Foredom flex shaft that allow you to do faster, more accurate checkering. I would imagine there is some powered device for metal serrations/checkering as well? Dunno.

[Bloke]

For what it’s worth, I’m a Tool Maker by trade ...

If I was to jimp the lock bar and FRN, as suggested, I’d most likely use a checkering file also. Set up with a guide to keep it square and straight.

The only way I can think to jimp the spine and keep it pretty looking, would be to set up on a tool and cutter grinder. It would be a fair slow process as you can’t take more than about a 0.001” cut per pass and you’d need to dress the wheel as you went.

Personally not something I’d undertake even if I owned or had excess to a tool and cutter grinder.

Either ways, just my $0.02c worth. :)

[Xplorer]

To do the jimping by hand, measure and pre-mark the cuts. With the knife in a vise (jaws lined with leather or rubber) set up guide rails to keep the mark you're working on positioned perfectly and choose the correct shaped diamond file to achieve the jimping size you and shape you want. It's slow and tedious but you can get there with patience. I would not suggest going very deep into a lock bar.
I couldn't find a pic of me hand-filing jimping but as you can see here, you can make whatever shape you want with diamond files if you're careful and patient.


By far the easiest way to do it is to lock up the knife in a mill vise and choose the carbide end mill that matches your width and shape requirements. But, I'm guessing if you had a mill in the garage you might not have asked..so diamond files are an inexpensive way to get the job done.
Here's the result of a ball-end mill cutting jimping through G10 and a hardened blade.



I suggest these potential methods because I too like to do things myself, but I should add that I don't actually suggest trying this for the first time on a finished knife unless you're willing to risk ruining it. Practicing on scrap metal until you're confident you know what's going to happen would be my best suggestion.

[Bolster]

By far the easiest way to do it is to lock up the knife in a mill vise and choose the carbide end mill that matches your width and shape requirements. But, I'm guessing if you had a mill in the garage you might not have asked..so diamond files are an inexpensive way to get the job done. Here's the result of a ball-end mill cutting jimping through G10 and a hardened blade.

Big, big thank you, Xplorer. Yes, I have a small mill (400 lbs), but work mainly with aluminum and soft steels and have no experience machining hard steels. The V-shaped cutter (#1 in my photograph) is carbide. I'm surprised and pleased to see that carbide can make a shallow cut through a hardened blade--although I recognize there's a big difference between your Bridgeport (?) and my Grizzly. I had assumed grinding might be the only possibility for a lockbar. Your work looks top-notch to me; congrats on the beautiful results. Thanks for sharing pix.

Recommendation to practice before cutting on a nice knife: Received loud and clear!! I'm in no rush to mess up a knife that has served me well for a decade.

[Xplorer]

In that case it's going to be easier for you than I expected. I still suggest trial run(s) on scrap metal. Unlike aluminum, you have to take shallow cuts in hardened steel but the carbide (sharp carbide) will cut through it no problem. I would suggest taking no more than 0.010" per pass and finish the last pass by cutting only 0.002" at higher speed. Refer to speed/feed chart to get your spindle speed correct for the size and number of flutes on your bit.

Also, remember that if you cut this while the knife is assembled, I would expect the lock bar to vibrate within the knife handle because it's got just enough side to side play to move freely within the handle. The results will not be good if vibration is allowed. I would only do this if I'm able to clamp the parts securely. That will likely require disassembly and possibly pinning the parts, but I'd have to look further into it to know how I'd do that.

Best regards

[Bolster]

My first attempt at jimping. Thanks to the advice in this thread. Practicing on one of my hacking knives. An odd knife because the wood scales are proud of the spine, so most the jimping is in the wood. But a bit into the spine as well.

[ZrowsN1s]

My first attempt at jimping. Thanks to the advice in this thread. Practicing on one of my hacking knives. An odd knife because the wood scales are proud of the spine, so most the jimping is in the wood. But a bit into the spine as well.

Looks clean. Good spacing

[Bolster]

Slowly working up to jimping a Spyderco...at this point I'm a jimpin' fool...JIMP EVERYTHING!





I like the feel of the results of the 45 degree bit, as seen below on the aluminum mini hack saw. Those furrows are cut 20 to the inch. The .050 metal cutting disc jimping on the utility knife is nice, too, those are 10 to the inch and considerably more aggressive.

[JRinFL]

Some people just want to see the world burn jimped. :D

[Xplorer]

Looking fantastic! :)

I find that the angle of the cut, width of the cut, depth of cut (relative to the width), as well as the width of the spacing between cuts all make a difference in the way it feels and how much it grips. Then, if you bevel or round the spine you get more looks and different feels. There's lots of possibilities you can play with.. :D ..until you run out of stuff to "jimp". :)

[Bolster]

Looking fantastic! :) I find that the angle of the cut, width of the cut, depth of cut (relative to the width), as well as the width of the spacing between cuts all make a difference in the way it feels and how much it grips.

What are your favorites, Xplorer? Angle, width, depth, spacing? Which grinding or cutting bits do you prefer? Do tell.

[Xplorer]

...What are your favorites, Xplorer? Angle, width, depth, spacing? Which grinding or cutting bits do you prefer? Do tell.

Jimping is something that I only want on certain knives and not at all on others. Honestly, if I had to pick a favorite it would have to be no-jimping. I'll say up front, I'm not a fan of fine (tiny) jimping. But, the size and the shape of the jimping are decisions I make based on a bunch of aspects within each individual knife and the intended application, often the user is a big factor as well. Most of the time it's only an indexing point that helps you know where your thumb is on the spine without looking, in which case all of the decisions about variations are cosmetic and subjective IMO. Other times it's actually important for adding grip (like knives intended for use in water or while wet) an then I go for larger gaps, and deeper cuts. If fish guts are likely going to be involved I go even wider and deeper so they're easy to flush out.
I use carbide end mills mostly. Some are micro carbides in 1/16" and 1/32". Most are square-end but i also use some ball-end mills for rounded troughs.

Here's a 1/16" (.0625") square end mill, cut at 90 degrees, .050" deep with approx. .060" spacing. The troughs in the cuts were polished and then the spine was rounded. The rounded feel on this size and spacing is one I will admit I like. :) It's a good combination of grippy/not too finger abusive/good looking IMHO :p .