Knurling Question

[IrbaileyParticipant @irbailey]

I'm looking for some advice on knurling.

I've done plenty of normal knurling on steel, brass and aluminium, but this project is a little different.

I'm making a Fairbairn-Sykes style Commando Knife which requires knurling on a curved surface.

I made a test piece from aluminium and tried it by placing the knurling tool on the work, then removing it, moving along and repeating as required. Whilst it sort of worked, I wasn't happy with the result as it was a bit of a mess.

I've included a couple of pictures of the brass handle I wish to knurl. The two blue lines are the area I wish to knurl (the end line is where it will be parted off)

Any help/suggestions would be very much appreciated.

Many thanks,

Ian.

[IrbaileyParticipant @irbailey]

[Bo’sunParticipant @bosun58570]

Hi Ian,

You could try individual tangential knurls separated by a grooving/parting/vee tool.

Good luck.

[BizibilderParticipant @bizibilder]

You used to be able to buy a hand held knurling tool that you gripped like a pair of pliers. it had three knurling wheels . Not sure if they are still available.

this thread   HERE    has a picture about 8 or 9 posts down.  This one has a screw for closing the knurls but I've seen very similar ones where a good strong hand grip will work.  Obviously with the hand grip you can vary the distance between the knurls.  

Edited By Bizibilder on 19/03/2023 09:55:56

Edited By Bizibilder on 19/03/2023 09:57:34

[JohnFParticipant @johnf59703]

Well there are two problems, you need to follow the contour of the work and the knurls also need to be square on to the profile as well, [ assuming standard knurls]

Just an idea ! make a straight feed two wheel knurling tool that has the head articulated so it can follow the profile, thus the head and wheels swing left & right. As for the in feed to follow the contour then it's either by hand, eye & feel or make a profile follower similar to the ones where the taper turning attachment used.

Possibly an overkill for a one off ? Whether it will work I know not but my first thoughts – lets see what the team come up with

John

[IrbaileyParticipant @irbailey]

That would definitely make things easier.

The originals were knurled in one and after studying pictures, some of them do look as if they were done in sections, some better than others! This was the 1940's, so CNC wasn't involved. I'm guessing how well they came out depended on the lathe operator. I can see why they changed from knurling to grooves in the latter production and current handles, as it must have simplified production tremendously.

I wondered whether slowly moving the pressure on the work and edging it along with the carriage would work?

Ruining it after getting this far would be a bit depressing to say the least!

Ian.

[IrbaileyParticipant @irbailey]

Thanks for the advice. I was still replying to the first comment before I realised there were more!

This will most likely be a one off, maybe not, but certainly not something I'll be making batches of or repeating on a regular basis.

These are some original handles for an idea of what I'm trying to achieve. Obviously making the grooved version would be easier, but I do enjoy a challenge!

Edited By Irbailey on 19/03/2023 10:15:48

[HollowpointParticipant @hollowpoint]

You might be able to do it freehand with enough leverage, maybe try a thin knurl on the end of a very long handle in a similar way to how metal spinning is done.

[egaParticipant @ega]

FWIW, to my eye the grooved version looks better!

[John HaineParticipant @johnhaine32865]

This may not be too helpful but I would engrave them on the CNC with a rotary axis.

[Mick B1Participant @mickb1]

The 'proper' way might be to mount the knurling tool on a long-radius turning fixture or a copying attachment so as to follow the curve. In all probability you'd have to make the gadget plus a template, so you've got the decision to make as to whether the knurled finish is worth that, the grooves being so hugely easier and functionally similar.

Edited By Mick B1 on 19/03/2023 11:27:57

[BazParticipant @baz89810]

Looks to me as though the original knurls have been done in bands as they don’t match up exactly so just set tool square to work and stab it in, wind it out,move along setting square to work again and repeat process. For what it’s worth I far prefer the bottom, grooved version.

[noel shelleyParticipant @noelshelley55608]

Possibly done by pressing ? Noel

[IrbaileyParticipant @irbailey]

Thank you all for your suggestions. Much appreciated.

I'm still not sure which direction to go, but the groove/knurl combo is looking like a possible option.

Thanks for taking the time to reply. I'll post the results (good or bad!) once I've decided which direction to go in.

Cheers,

Ian.

[Clive FosterParticipant @clivefoster55965]

Thinking about my experience of using the hand held squeeze knurler device mentioned by Bizibilder it might be possible to keep sufficiently even pressure on the tool to create a good looking knurl by twisting the tool slightly so it runs from side to side. The technique works fine on a long(ish) parallel shaft.

Can't see any reason why it shouldn't follow moderate slopes and curves. Obviously if the slope is too steep or the curve too great it's going to dig in. Given an adequately shallow curve or slope it obvious issue is keeping the right level of pressure on the tool as it runs up and down the the cuve. I imagine it will take several strokes to form the knurl squeezing harder with successive runs. For ordinary small knurling you just squeeze until the knurl looks deep enough.

Here is a picture of the tool Bizibilder refers tor :-

Certainly hasn't been made for years and rare then. Found mine maybe 40 years ago in the "going to throw away" box at an experienced machine tool and tooling dealer who didn't realise what it was and how effective it could be. Having used one I knew better and gladly handed over an extra £1 for it on top of the price of the big Pollard drill I went to buy.

Minor correction to what Bizibilder said. The screw sets the squeeze depth not the clamping load. I'd think screw clamping could be dangerous if the tool gets away from you. Although the adjustments imply it can be set to handle work over 2 inches – 50 mm in diameter I find it starts getting cumbersome over an inch – 25 mm or so. But what it does do it does really well. Had to knurl some 6 mm pins to fill some no longer needed holes in a part being modified yesterday. Longest party of the job was finding some stock and mounting in the lathe. Squeeze and repeat 8 times gave me 8 pins 10 mm long ready to tap in.

Links to drawings and build instructions for that and couple of similar ones in the thread linked to by Bizibilder.

Clive

 

Edited By Clive Foster on 19/03/2023 15:52:05

[IrbaileyParticipant @irbailey]

That looks like a very useful tool.

Daft question, but I'm assuming it pulls itself along the work?

Even dafter question – does a normal tool post mounted two wheel knurl also pull itself along the work if the carriage is free?

I'm 100% 'self taught' on lathe work and I've always knurled by running the chuck on the lowest RPM and the same with the feed rate (it's a Myford ML7-R)

I ruined a lot of material before I was able to get a nice diamond pattern, but I'm now wondering if I've been doing it correctly and possibly making life hard for myself.

Ian.

[Clive FosterParticipant @clivefoster55965]

Irbailey

Need to lean it a touch and push slightly sideways to make it move along. It's a feel thing really. Given the right mix of squeeze force with a modest push and gentle lean it walks sideways very controllably.

If you hold it dead square when you squeeze it stays in place. Just the ticket for doing knurled head screws.

Toolpost mount types you feed side to side using saddle feed. On lighter machines its probably better not to try and make a full knurl in one go.

Clive

[IrbaileyParticipant @irbailey]

Thanks Clive.

That makes sense.

Using a tool post mounted knurling tool in the past I've made one pass with fairly light pressure, then added pressure and reversed the feed to go back over the work and so on until I'm happy with the depth and cut pattern.

To be honest, I'm still not 100% sure how to go about my handle, but I've learned a fair bit today and everyone's help has given me food for thought and some different ideas on how to approach it.

Thank you all for taking time to reply to my question, it's very much appreciated.

Ian.

[davebParticipant @daveb17630]

I bought one of these knives from Brick Lane street market in London about 60 years ago. Ex military tools and hardware was sold at most markets and many specialist shops in those days, seldom see the stuff now! The handle on mine was ribbed, I've seen many more over the years but never one with a knurled handle. Interesting thread, knurling is tricky enough on straight sections, I'm intrigued to see how it turns out.

Daveb

[IrbaileyParticipant @irbailey]

Posted by daveb on 19/03/2023 18:38:52:

I bought one of these knives from Brick Lane street market in London about 60 years ago. Ex military tools and hardware was sold at most markets and many specialist shops in those days, seldom see the stuff now! The handle on mine was ribbed, I've seen many more over the years but never one with a knurled handle. Interesting thread, knurling is tricky enough on straight sections, I'm intrigued to see how it turns out.

Daveb

There were three patterns. First and second were knurled, the third – which is still in production today – was ribbed. The first two patterns are fairly rare these days and usually a second pattern will fetch £600-£700 and a first pattern double that or more depending on condition.

I'm also intrigued to see how this turns out.

There's a high possibility of wasting some brass here…still, won't be the first time!

Ian.

[pgk pgkParticipant @pgkpgk17461]

Is the following a stupid idea?
I use a frame based knurl which is simple to set up and avoids pushing with the toolpost. Imagine such a system but with a longer length of threaded hole for the screws that adjust the knurl pressures and put a strong spring between those screws and the knurl heads. If that spring is long enough and of the right 'power' then the amount of deflection of the knurls to move over the curve of the workpiece wouldn't affect the knurl pressure change by much and give an even finish?

pgk

[Clive FosterParticipant @clivefoster55965]

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

[IgnatzParticipant @ignatz]

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.

[Clive FosterParticipant @clivefoster55965]

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

[mark costello 1Participant @markcostello1]

Where's Sir John when We need Him?

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