Knurling

[Ian S CParticipant @iansc]

Another use of staight knurls is on the shaft of an electric motor were the laminations are pressed on, this to prevent the armature rotating, almost like very fine splines. My only knurling tool is a straight one,home made to a similar pattern to one in Stan Brays’ book Introducing The Lathe. It took about 20 min to make (Bic lighters work well). Ian S C

[John Wood1Participant @johnwood1]

I have a ‘Myford’ type scissor knurling tool which works fine but the tension knob is a rather small, knurled hand-turn affair, and I find it very difficult to get enough pressure to make a deep enough knurl. I have resorted to turning it with a pair of pliers, just to gain pressure, but this seems wrong somehow so, can anyone tell me what I am doing wrong? If not I will replace the tension nut with a hex one and get the spanners out!

 

thanks,   John

[Ramon WilsonParticipant @ramonwilson3]

Hi John,
I’m sure you will find that this is a much easier operation if you set the knurls to the diameter to be knurled by using the hand nut to bring the knurls into contact with the workpiece, retract the tool off the diameter and then apply the (depth of ) ‘cut’ by turning the nut – small amount found in the first instance by trial – then starting the lathe and feeding the knurling tool gently but firmly back onto diameter. This puts the cut on gradually and you will feel it as it goes ‘over center’  bring it back slightly and then apply sideways feed if required. If the pattern isn’t deep enough, retract, apply another small amount and feed on gently again – the knurls will  pick up again providing the speed is kept low.

 

Originally I did as you describe – cramming the knurls takes quite some pressure – but once shown this way have never had a problem – much easier on machine and operator!

 

Hope this helps – Ramon

[mgjParticipant @mgj]

May also be worth looking at the knurls.

 

The ones I use came from Hemingway as part of a kit. They are obviously razor sharp and very neatly cut. I’ve seen others that were equally obviously not of such good quality. So perhaps if the knurl looks a bit on the “blunt” side, therein may lie an answer.

 

A suggestion, because I don’t know.

 

I can vouch for the Hemingway kit – it was actually published in ME back in the 80s I would think. Sorry don’t have a reference. anyway, if anyone is thinking of doing a bit of tool making, that whole kit is very good. (Usual disclaimer)

 

The tension nut is about 1″ od, with a small 1.5″ ish built in tommy bar. Firm finger pressure is all it ever needs. Also never knurled under power feed – always by hand. No claim that one is better – just an observation.

Edited By meyrick griffith-jones on 04/02/2010 18:05:04

Edited By meyrick griffith-jones on 04/02/2010 18:07:52

[Steve GarnettParticipant @stevegarnett62550]

Posted by meyrick griffith-jones on 04/02/2010 18:02:39:

The ones I use came from Hemingway as part of a kit. They are obviously razor sharp and very neatly cut. I’ve seen others that were equally obviously not of such good quality. So perhaps if the knurl looks a bit on the “blunt” side, therein may lie an answer.

 

Interesting to note what it says at the end of page one of the document I posted a link to on page one of this thread – it suggests that having flats on the surface may help with tracking problems.

 

I should hasten to add that I have never tried flattening the surface of knurls, so I have no idea at all as to whether this is true or not. It seems reasonable to assume that if you have really sharp teeth, it will make the initial deformation process somewhat easier, and probably require less force for the same result, but I can’t really see the tracking improvement claim for blunt ones myself – that seems a bit far-fetched, at least at first glance. 

 

Incidentally, the one thing I always do before using the knurl tool is to clean out the wheels carefully, especially at the bottom of the teeth. This seems to make quite a difference to the surface result you can get – for fairly obvious reasons. The last thing you want is slivers of metal down there, because that that really can screw up the surface finish.

 

 

Edited By Steve Garnett on 04/02/2010 22:37:12

[John Wood1Participant @johnwood1]

Thanks for the tips guys. My tool came from the Myford stand at last years Midland exhibition and the wheels certainly look sharp and clear cut. I think Ramon’s technique sounds right and I will try that out tonight. I suppose it’s obvious now I am told, why isn’t it obvious when I have a problem and try to bend my mind to it? I know I’m no expert but ‘er indoors reckons its more to do with my age! Nice.

 

All the best,  John

[mgjParticipant @mgj]

Yes- i use a version of the technique given by Ramon, in that I use the overcentre bit to position the knurls/cross-slide, and then start the machine and add pressure until I’m happy with the cut. Then I start moving sideways. Also I’ve never, for good or ill, applied a lead in angle. Don’t know why I chose to do that, but it works for me.

 

Its beginning to sound that it doesn’t matter too much what you do, as long as knurls are sharp, speed is slow and lots of coolant?

[Chris TriceParticipant @christrice43267]

Posted by John Stevenson on 02/02/2010 09:42:21:

I have proven that diameter isn’t a factor.

I took a bar of steel and machined it into equal steps at random diameters, each diameter a few thou less than the previous one and ran a knurl along the whole length.

 

The whole length came out perfect regardless of diameter.

 

I do a lot of knurling that has to be accurate as regards no twist and even.

 

 

 

This is a 30mm steel bar knurled in one pass at 500 rpm and flood coolant.

 

John S.

 This is not a contradiction so much as a posed question but if you had a longer bar and continued to have the diameter reduced, at one point, surely, the number of grooves cut by the knurling wheels have to jump to a lower number because there wouldn’t be enough circumference to fit all the grooves of the larger diameter in? If they were short lengths of bar rather than one long one, all turned with very slightly ever decreasing diameters and each started individually, you would surely get to a point where suddenly you were getting a smaller number of grooves? I emphasise I’ve not done a lot of knurling but the one occasion I did, it was needed on an aluminium bar and that was diameter critical, possibly because the metal was so soft by comparison to steel. I can see angled (diamond) knurls slipping to fit the grooves as they’re formed but straight cut ones I’d have thought would have no inclination to slip into anything if they fall between the initial grooves on the second rotation. Any thoughts anyone?

[Ian S CParticipant @iansc]

The only knurl I have is one suggested byL.H.Sparey, the wheel is the flint wheel from a disposable lighter, took about 20min to make, its got a bronze bush in the wheel running on a needle roller from a roller bearing. I’v collected about a dozen spare wheels because I thought they may not last long, but the original is still OK after 20 years, its been used on some fairly hard steels. Staight knurl pattern. Ian S C

[John OlsenParticipant @johnolsen79199]

Well, I have one job I knurled with a pair of diagonal wheels to get a diamond knurt, and one of the wheels did a beautiful job, while the other did a shallower knurl at half the spacing. This is in a scissors type tool, so figure that one out. I have seen comments in print about if you are not happy, take a light skim and try again, so I think this sort of thing is not too uncommon. But I wasn’t planning to send that project to an exhibition.

 

One thing I find a bit problematic is feeding the knurl sideways on a longer job. I plan a modification to the holder to overcome this, because the leverage is just too much and tries to move the  tool rather than traversing nicely. But few of the jobs I do would need more than the width of the wheels anyway.

 

regards

John

[Ian S CParticipant @iansc]

I see I’v written twice about my cigy lighter wheel tool, the previous time I mentioned Stan Brays’ Introducing the Lathe. Back down the thread Chris Stephens suggested knurling was more like spinning metal, but I would say the nearest other process would be rolled threads on bolts, in fact bike spokes are threaded in a machine with three little rollers that pinch on the end of the spoke and rotate around the fixed spoke wire forming a thread.

If you want to make the lighter wheel knurler, try and find  a wheel with straight grooves, my one is a degree or so of straight so that for long knurls it forms a slight spiral, about 1/4″ in 6″. Ian S C

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

The (workpiece) metal under the knurling wheel is in a condition of plastic flow – that is well beyond the yield point . Under these conditions the flow of metal is fully three dimensional – exactly like squashing a piece of plasticene . If the knurling has not gone wrong at the earliest instant of contact then the work compensates for the pitch mismatch by moving the embryo knurl tooth around the circumference of the work . This effect is very small (1 thou or less typically) but the cumulative effect over many knurl teeth is  large .

 

After the knurl has engaged some way way the knurl and work run together just like gears but the common point of the two pitch circles can be anywhere – top of tooth bottom of tooth or somewhere between but unless you are very unlucky the common point of the two pitch circles will be in the middle third of the tooth height and the process will stay stable .

 

There is nothing to prevent anyone wanting sparkling clean knurls from from doing the job a bit scientifically and gearing the knurl to the work and /or the other knurling wheel and doing the whole process under controlled conditions – knurling is after all only a degenerate form of multistart screw cutting .

 

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Just to be clear- the plastic flow /tooth migration action described above does not go on for ever – it occurs only during the ‘bedding down’ period and is useful in making the knurling process a bit more error tolerant than simple geometry would suggest .

 

Many engineering components are now made by ‘rolling’ processes – things like splined shafts , gears and external screw threads are the most common .

 

I have made knurled components in the past by an indexing and slotting process – very much like engraving an index dial but using cutting tool at first one steep angle and then at the inverse steep angle  – thus generating a diamond pattern . Pedantically there is an error doing it this way in that you are cutting a straight line rather than a helix but on short sections of work you just can’t tell the difference . Takes a bit longer than roll knurling but all under control and finish can be superb . Could do deeper knurling this way with a powered engraving cutter .

[WALLACEParticipant @wallace]

Been thinking about this – imagine the first turn of the workpiece – the knurl is pretty much going to deform it – and when it comes around again, if the peaks and valleys don’t quite line up with the knurling tool, then it will cut it away until it does . .  (maybe ‘shave’ is a better term) – not so much on the peak of of the knurl, but certainly down the sides.

 

So the action is cutting (as can be seen by the swarf which usually comes off) and forming – but the cutting action will only contiune until the workpice is the ‘right’ size.

  

I’ve only ever used a clamp tools and never have any problems at all on EN8, stainless etc.

 

w.

   

Edited By WALLACE on 15/11/2010 20:33:14

[chris stephensParticipant @chrisstephens63393]

Hi Wallace,

Don’t forget that a lot of metals work harden when they are deformed, which could have a pronounced effect on the job. Best to do it quickly, with a scissor type knurling kit to get better pressure, than faff around doing it a bit at a time and risk the dreaded hardening.

chriStephens 

[Clive FosterParticipant @clivefoster55965]

My two most reliable knurling tools seem to be rather rare types.

 

One is a hand squeezed three wheel one rather like a front pivot nutcracker in concept.  Two wheels in the bottom handle one in the top aligned so the work piece will be trapped between them.  Handles are folded sheet steel, decently thick, and there is a post with several holes in it at the front so the handle spacing can be adjusted to accommodate different material sizes yet still permit squeezing with normal size hands.  Goes up to approaching 3″ diameter and is very effective.  Theoretically a stop screw lets you set knurl depth but in practice its not effectively engineered.  Anyway its a very hard squeeze to knurl over depth unless the material is really soft.  Fine on alloy, brass, common steels etc. but I’ve never been brave enough to try stainless or potentially obdurate steels.

 

Seem to remember drawings for one just like mine appearing in ME mid 80’s or thereabouts although mine was thrown in for free with a lathe bought from a dealer when I picked it off the floor “obviously no good”.  But we had one at work so I knew better.

 

The other is a Pratt & Whitney two wheel pivoting type, bought mostly ‘cos I have a P&W lathe and no-one else bid on E-Bay so it came cheap.  Its arranged so that the in use the pivot point is rather below centre height so the lower knurl is pulled up into the work.  Conventional pivot head two wheel knurls are designed so the pivot is on centre height so the knurls contact the “work sort of together more or less”.  The P&W variant seems not to suffer double knurling troubles.

 

Clive 

[Sub MandrelParticipant @submandrel]

Someone did a 2-part article on calculating the exact diameter for knurling. I have a home-made scissor knurl and never worry about diameter. I eventually ended up using zigfire’s approach by trial and error and now reckon I have  a 9/10 success rate and the fails are always due to too little pressure.

 

Neil

[WALLACEParticipant @wallace]

Agree with all above to have quite a bit of pressure on  especially  at  the start to force the tool into any inpartially formed valleys and not jump out and make new ones ! The commercial one I have even has an eccentric on one of the arms to put a bit more force on.

 

That and gallons of suds.

 

I usually run with thwe power feed set as fine as it will go – works for me but must admit I’ve never tried it differently !

 

 

w.

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