Knurling Question

pgk

Interesting idea but I suspect the spring may need to be impractically strong.

Handwaving estimate of my squeeze force on the nutcrackers feels like something approaching half maximum and effective leverage ratio, taken from the single knurl pivot pin to the middle of my hand, around 5 to 1. According to Google health male grip force is a bit over 70 lb - 32 kg. So something approaching 150 lb - 70 kg of squeeze to make a nice knurl in steel doesn't seem unreasonable. In practice you'd be doing several lighter passes rather than one full knurl one so less force ought to work. But you need a decent squeeze to make anything happen at all so I'd be surprised if you could get away anything less than around 100 lb - 45 kg force on steel or brass. Maybe a softish alloy would be OK with less.

The corner dig-in on steeper curves issue still looks intractable.

Clive

Just my two-cents woth on thiz. But it seems to me that even if one had the benefit of some sort of 'follower cam' to move the cross slide in and out to match the curve of the knife handle (using a push style knurler) one would still obtain a rather 'iffy' knurl as the constant change in handle diameter would have the knurl pattern (regarding number of even points around the circumference of the handle) changing over the length of the handle, varying from even numbers of points through to bands where one would have 'extra bits' and back into areas of even numbers of points. I imagine a visual going in- and out of phase sort of thing. Same sort of chowdering as that series of banded knurls on the example knife handles.. but more smoothly obtained.

Ignatz

Thats an excellent point that probably can't be settled until someone tries it successfully.

My view is that so long as the actual knurl points appear to be the same size the changes in the number of points in each circle as the circumference of the handle varies will be seen as natural.

On a parallel workpiece you see straight lines along the job where knurl points at the same angular circumferential position align. Think of a stack of same size gears with the teeth lined up. This, probably, enhances the perception of straightness so long as the knurling depth is identical and the points the same size.

On a gently curved surface, like that handle, the corresponding lines will be curved as the knurl point row alignment diverges or converges to accommodate extra points per rev where the dimeter increases and loose excess points where it decreases.The depth of knurl and absolute size of the points will change slightly during this process to make space for extra points or remove excess ones. In practice for any reasonable combination of knurl size and workpiece diameter this difference in depth and therefore point size is very small.

Providing the knurl points are not perceptibly different in size these curves will enhance the perception of handle shape and look "right". Using patterns to alter the perceived shape of objects is an old established decorative technique. For both aesthetic enhancement and obfuscation.

I suspect that if the knurl point sizes become visibly different on a row to row basis the change will stick out like a sore thumb and, as you suggest, its going to look horrible.

Totally impractical of course but I do wonder if manipulation of knurl depth could be used to increase the permitted rate of curvature before it all goes to pot. There is an extensive literature on what happens to patterns when the curvature of the underlying surface changes. Some heavily mathematical concerning manifolds and some eyewateringly visual concerning decorative effects. Neither of which should be indulged in by any normal person, especially not on a dreary Monday morning, as being likely to be seriously injurious to personal health, wellbeing and sanity.

Brains leaking out of your ears or eyes popping out of your head!

Your choice.

I'll go with neither.

Clive

Edited By Clive Foster on 20/03/2023 09:54:14

Where's Sir John when We need Him?

Well...after a lot of reading and thinking, I decided it was time to have a go. I've got plenty more brass in stock.

I basically ran the chuck as slow as possible, and moved the knurling tool along by hand whilst trying to keep an even pressure on it by constantly adjusting the tool post.

Not an easy task.

Anyway, here's the end result. It's not great, in fact it's far from great, but it is at least nice and 'grippy' in the hand.

I think I'll keep it until my Birchwood Casey brass black turns up, and see how it looks once it's blackened. If I'm not happy, I'll probably take it off and make a ribbed version, or perhaps try separate knurls interrupted by grooves. Until I get everything loctited up and peen the tang thread, I can experiment a bit, which is all part of the fun.

Funnily enough, I did toy with the spring idea, my thoughts being making some sort of spring loaded tool holder with an old airgun spring.

Certainly an interesting project. Thanks again for sharing your thoughts.

Cheers,

Ian.

Ian, since the knurling on the originals is fairly uneven anyway, it looks perfectly OK to me. Nice job! Do you black the blades too?

Daveb

Cheers.

Not sure about the blade yet. I think I'll blacken the handle and guard first and see what it looks like.

The original first pattern knives were polished, as William E Fairbairn believed that a shiny blade gave a man a psychological advantage over an opponent. The later patterns were blackened.

To be fair, the most action this knife will see once it's done will be sitting in my desk drawer and possibly opening the odd envelope!

I have toyed with the idea of blackening it and giving it an 'antiqued' look.

Like many of my projects, it's very much a bit of a 'make it up as you go' kind of affair!

Ian.