Pins for a knurling tool - how hard should they be?

I want to knock up a knurling tool along these lines:

I have wheels and am reluctant to cough up £18.60 for a tool which I could make from offcuts in an hour or so.

What I don't know is how hard the pins should be - I assume that they should be hardened to some extent, but obviously not to the point of brittleness.

My experience of hardening high carbon steel is limited to making cutting tools. Maybe here I should deliberately not heat for long enough to through-harden?

Any advice woud be welcome.

Robin.

You could use mild-steel and case-harden them.

Alternatively, use a hardening grade steel (silver steel) harden them but temper them to blue, soaking them at the tempering temperature for a few minutes.

I once used molten lead kept just on the point of crystallising, to temper a set of small leaf-springs. It's slightly above that temperature but the springs seem fine. Lightly alloying the lead with some tin-lead solder might reduce the temperature suitably.

In fact unless you are going to be using the tool day in, day out, I'm not sure you need harden the pins at all. I'd be inclined to use silver-steel for its inherent toughness and precision finish, but not hardened.

Ditto. If they wear, make some more and harden those.

What lathe do you have as a push knurling tool needs a heavy duty Spindle and chuck. I have a clamp type tool which is so much less hassle and gentler on bearing and chucks.

Made it from scratch and use hardened dowel pins to hold wheels. It will knurl about 3/16" to about 2" diamiter and I have 3 change sets of wheels from a push set I was given.

David

Blue is softer than straw? I would (if I could see the colours🙂 ) temper them as hard as possible, so to straw colour.

At the risk of annoying dc31k, or whoever it is that complains of not answering the precise question tabled, I would recommend making a scissor type of knurling tool, rather than a push type - so much easier on the machine (and workpiece, if of thin section).

I have a push type (if I could find it) that I would give away (less the knurls, of course) as I think they are cheap carp. The knurler came as part of a set of tool holders I bought, thinking a set was good value. I won’t make that mistake again.

+1 on the clamp style tools.

The push type are more trouble than they are worth, in my opinion, especially on smaller machines.

They also have the advantage of holding a set size if you are knurling multiple parts.

Jim

Normal procedure is to use standard hard, parallel, location dowel pins as axles for the knurls to run on. Cheap enough that its not worth rolling your own and exactly the right size for the knurls.

Boneham & Turner do appropriate sizes for around 10 p to 15 p each and are quite happy to send small quantities although most of what you pay will be for post and packing. I got 10 of two lengths in 7/32 diameter for about £ 10 to suit the wheels for my Marlco and P&W knurlers.

Wheels from Zoro seemed good value and work well. Didn't trust the uber cheap ones. Not sure what was on my Marlco when I got it but a fairly innocuous bit of steel ripped the teeth off one leaving it sort of D shape!

If you want 1/4" by 3/4" long pins I have a mega overstock and could easily send a few if you pay the postage.

Clive

Clive F is spot on, unless you really want to make your own?

Tony

Good tip about dowel pins.

I replaced my own hardened silver steel pins with modified scrap Clarkson end mills. I don't know how hard the shanks of these are but they are standing up well in my knurling tool. I lubricate them with moly grease.

At the risk of just repeating what others have already said, when I made my (clamp-type) knurling rig - to a Graham Meek design - I just used silver steel. I don't do knurling very often and consider the pins to be a consumable and as such, easily replaced if necessary. I had a look at your albums and your lathe, if it's the one shown, appears to be a slightly more substantial one than mine. If it were my lathe, I wouldn't be subjecting the spindle bearings to the forces required for a push-type knurl.

Just my view.

John

Agree with John that the pins should be considered consumables. Change when you change the wheel.

Surface finish appears to be important. There is a difference in how free running a new wheel is on a new pin when compared to an old one even though there is no easily visible difference in surface quality or wear.

If you plan to make your own push tool may I suggest that you follow the Pratt & Whiney design where the pivot is offset so one wheel is effectively underslung.

My experience is that this style is less likely to mis register producing double knurls. Subjectively it seems to need a bit less force than the common style of pivoting push knurling tool. But that may be due to the push tool in question being hobby bran whilst P&W were a high end maker of machines and tooling.

That said I still consider the "nutcracker" hand squeezed style excellent for casual use. Mostly because set up time is about 30 seconds!

Clive

Is it possible in practice to traverse the nutcracker by hand?

Or is it intended for knurling the same width as the knurls themselves?

Even with this limitation it seems a great idea.

I used HT bolts, 40 years ago and it still works fine. Noel.

.

That’s an interesting arrangement, Clive ... I’ve not seen it before.

MichaelG.

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Edit: __ the tool doesn’t appear to have been worthy of patent, but I did find this knurl-making machine whilst searching:

https://worldwide.espacenet.com/patent/search?q=pn%3DUS1287732A

Edited By Michael Gilligan on 18/04/2021 11:35:09

ega

Leaning a bit to one side will cause the nutcracker to traverse so you can make longer knurls.

A bit of a knack to it, especially if your knurls are sharp edged rather than having a slight bevel, as the edge can dig in a touch producing random lines. Most likely if you get a bit heavy handed. Takes several passes to get a full depth knurl.

Main disadvantage is that the depth setting is a bit iffy. I just do it by eye.

Obviously not for harder materials, light alloy and the ordinary range of steels are fine but anything a bit obdurate needs too much squeezing.

Drawings for one like mine were published in Model Engineer, 29 January 1999.

The American Magazine Popular Mechanics published a more man sized version in May 1965. Google books link to the article here :-

**LINK** ,

https://books.google.co.uk/books?id=buQDAAAAMBAJ&q=knurl#v=onepage&q=knurl&f=true . Have to work off the screen as it can't (I think) be printed. Link found by MichaelG in a previous thread.

Can be found on Archive.Org too so download is possible but very slow.

Clive

Edited By Clive Foster on 18/04/2021 11:44:50

If you have the wheels make a clamp type tool , much more predictable/ repeatable and definitely kinder to your machine

Clive Foster:

Many thanks for the comprehensive response.

Getting back to the OP question, I notice that the ME author, R V Howis Senior, tempered his Silver steel pins to blue.

Edited By ega on 18/04/2021 12:52:21

PS I couldn't immediately find the other article on archive.org but was able to "Snip" the google pages to jpg.

The PM device seems more suitable for making in the amateur workshop.

You don't need to harden the pins.

All journals benefit from having the cheap part softer, and they can even last longer as a result, so mild steel will be sufficient.

Its difficult to imagine an amateur wearing the bore of a knurling tool such that it does not work, so any accurate material will do for what you need.

Thanks for replies. I actually have a cheap clamp-type tool, which works OKish in brass, but I've never got the thing to produce clean knurls in steel. I think it's partly to do with the arms being too floppy and partly to do with the difficulty of twiddling the wheel fast enough to get a deep enough cut on the first rotation of the work to give registration on subsequent turns. Minimum speed on my lathe is 65rpm.

I'm looking at better designs for clamp tools, but the reason for my post was that I wanted to make a lash-up push knurler for a job in hand an wasn't sure how hard the pins needed to be. I'm confident that the the lathe bearings are up to it.

I ended up buying a 'single point' diamond wheel from Zoro and, as the consensus was that I didn't need to harden the pin, I lashed up an ugly tool with an untreated silver steel pin:

The good news is that the pin seems fine. Bad news is that I can't put enough force on using a QCTP - so I need to make something more in line with the cross slide screw. Or make a proper clamp tool. One lives and learns!

Robin.