Knurling

[FulmenParticipant @fulmen]

Nah, this whole “pitch diameter” thing is a red herring. What you need to do is to plunge in radially with a minimum of engagement. Once you’re deep enough it will track properly, you can then feed axially.

[jaCK Hobson]

On jaCK Hobson Said:

You tube (and now, common sense) tells me knurling tools have a pitch and so work best on certain diameters. Small diameter changes might make a difference? I can’t knurl.

No doubt this will create a furore of comments, but here goes.

The “Mechanical and Metal Trades Handbook” by Europa Lehrmittel, list at the foot of page 92 a section on Knurl. Knurling is covered by DIN 82 (1973-01) and gives 5 different examples for which there are 3 different equations to find the correct diameter from which to start knurling to achieve the desired result. All formulae take into account the spacing of the Knurl

There are in this section 6 different standard DIN Knurl spacings. Clearly if the circumference of the work is not divisible by the spacing then there is going to be a miss-match.

Before anyone says this is a metal forming process I am aware of this. The problem is the stock size to start off with will become the pitch diameter of the Knurl. Thus it is this diameter that is needed to start with, not the crest diameter.

Once this point is mastered Knurling is no longer a nightmare, just another machining operation, (see above).

Regards

Gray,

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for the DIN reference, Gray, and for the lovely example.

MichaelG.

.

Edit: __ there’s a useful glimpse of the Oriental version of the standard, here:

https://www.globalfastener.com/standards/detail_20682.html

[Graham MeekParticipant @grahammeek88282]

Thanks Michael,

The link gives visually the 5 different examples mentioned in the handbook.

Regards

Gray,

[Michael GilliganParticipant @michaelgilligan61133]

Just found this very well-presented 10page document:

https://www.hommel-keller.de/wp-content/uploads/2019/09/Technical_information_zeus_knurling_technology.pdf

MichaelG.

[mark costello 1Participant @markcostello1]

I can remember in the past,Sir John Stevenson knurling a tapered piece of steel. Wonder if the article still exists..

[David George 1Participant @davidgeorge1]

The blacking om my knurling tool was done by heating and oil bath diping and repat till it was black. Recently I have had it chemical blackodised at a company in Long Eaton not far from me. With a few other parts

David

 

[Howard LewisParticipant @howardlewis46836]

Have to admit that it seemed logical for there to be a whole number ratio between the work diameter and the knurl wheel diameter.

However have found that  unlike gear wheels, it doesn’t seem to matter much.

I just set my scissor type knurling tool, for a diamond knurl, (or more rarely straight) and just bash away, setting as low longitudinal feed.

Is probably totally wrong, but it works for me! maybe with that sort of luck, I should start backing horses?

Howard

[FulmenParticipant @fulmen]

You’re absolutely right Howard. Once you get deep enough the wheels will track.

[Gary WoodingParticipant @garywooding25363]

I’m with Fulmen and Howard on this one – for form knurls at least (cut-knurling is different). If the initial pressure is sufficiently aggressive then the knurling wheels will slip into correct synchronisation after the first revolution of the workpiece. A convenient way of starting with a high pressure is to commence with the knurl wheel(s) halfway on the end of the workpiece and moving sideways when the pattern has been established. If you start to get it cross-knurled then simply increase the pressure.

I use my home-made and designed scissor knurl shown in the photo, together with a nice 3D-printed box for it that also holds some different wheels. All the knurling shown was done with the tool – in steel, brass, and aluminium.

[Michael GilliganParticipant @michaelgilligan61133]

I suppose it depends upon whether or not the finished diameter of the job is important.

MichaelG.

[HopperParticipant @hopper]

I have never had to change diameters to get a good diamond knurl. Just wind the wheels in until the pattern is right and then feed back and forth along the length, increasing depth of knurl at end of each second pass. Never seen anyone else in machine shops using a set diameter for knurling either. Maybe not best practice according to the German engineers at DIN but it works for me and many others IRL.

The knurling tool I made off internet plans that look closely identical to Gary Wooding’s design above works just fine without needing special diameter etc for diamond knurling. But not for straight. Maybe the DIN dimensions might help there? But IRL it is just as easy to use a single wheel plunged in.

[jaCK Hobson]

On jaCK Hobson Said:

You tube (and now, common sense) tells me knurling tools have a pitch and so work best on certain diameters. Small diameter changes might make a difference? I can’t knurl.

This is a myth.

The difference in circumference between the top and bottom of the knurl pattern is about THREE times as much as the depth.  People will say all sorts of things about calculating the correct circumference, but at what depth? Top of the knurl, bottom of the knurl or at what point in between?

The reality is that is you use a positive approach to establishing the knurl it will rapidly self-adjust to a regular pattern, a ‘bastard’ knurl is almost always the result of starting with too shallow a cut.

Neil

[Gary Wooding]

On Gary Wooding Said:

A convenient way of starting with a high pressure is to commence with the knurl wheel(s) halfway on the end of the workpiece and moving sideways when the pattern has been established. If you start to get it cross-knurled then simply increase the pressure.

This works for me.

Neil

 

 

 

[Neil WyattModerator @neilwyatt]

Just an observation… but if you use a scissor tool with straight knurls, the diameter has to be irrelevant as the two knurls align with each other without issues, regardless of their initial setting.

[FulmenParticipant @fulmen]

Just to be clear, I’m not saying the “pitch diameter” trick is wrong, just that it’s usually not necessary. If you want a shallow knurl or need to plunge in at full with in hard materials it might be required.

@Neil: It should be done at top diameter to allow the wheel to track properly from the start. As the cut progresses the rollers ability to self align will keep it from changing the pitch.

[Graham MeekParticipant @grahammeek88282]

I did think my comments would start the ball rolling.

The formulae in the DIN Spec, is as simple as it comes. The required diameter for STRAIGHT knurling = the finished diameter – 0.5 X t (the spacing of the Knurl). Thus once the product of 0.5 x t, is known, (and written down), it never needs to be done again, or until the Pitch of the knurls is changed (t ?).

Depending on the diamond pattern it is 0.67 x t or 0.33 x t.

You will notice at no time have I mentioned calculating the CIRCUMFRENCE, there is no need. I do remember an article in Model Engineer many, many years back which went into oodles of calculations to get the Correct Pre-Knurl diameter. This article did work using the circumference as it’s basic theory. To my mind it was this article that put people off even considering doing any form of calculation when it comes to knurling.

The Straight knurling tool on my Compact 5 is 1/2″ diameter by 3/16″ wide, and 80 T, (t= 0.498 mm). Turning a blank to 1/2″ diameter and proceeding to knurl produces a mis-matched knurl. Reducing the diameter by 0.010″ (0.249 mm), (the required amount), gives the correct form. Both examples start with a 0.010″cut, so why the discrepancy?

This reminds me of one of my colleagues in the Toolroom who used to call the Knurls the “Graunch-O-Matic” tool. This being long and merry before Wallace and Gromit’s antics.

Regards

Gray,

[Graham MeekParticipant @grahammeek88282]

One thing I forgot to mention.

I never ever start the Knurling operation with the Knurls on the work. They are always off to the righthand side and applied to the work by self-act longitudinal feed. The cut already having been applied. Be it via the cross-slide, (straight knurl) or on the scissors knurl for diamond knurl.

Regards

Gray,

[DellParticipant @dell]

I seem to have opened a hornet’s nest , sorry but it’s good to get differing opinions, my Hemingway knurling tool kit turned up today so I am going to get on with that but put the tool holder mounting on the opposite side so I can use the tool in the rear tool post, it will at the very least get me doing things on the mill that I don’t normally do so will be a good learning exercise.

Dell

[FulmenParticipant @fulmen]

No reason to apologize, I’m sure I’m not the only one that has learned something new here.

I have always had good luck with the brute force method, but I also see the reasoning behind the more subtle approach. I also think Gray is on to something important, I realize now that I have been a little inconsistent in how I start the knurl.

[Martin KyteParticipant @martinkyte99762]

Going back to the ‘plunge knurling’ on the Myford, my concern has always been for the cross slide lead screw nut. On a non powered cross slide the lead screw nut is not the most robust example of its kind.

This is one of those strange intuitive feelings  rather than any proper stress calculation so I could be wrong. I have always considered the bronze headstock bearing and the spindle at that point rather robust in comparison.

regards Martin

[Graham MeekParticipant @grahammeek88282]

Hi Dell,

No Hornets nest here.

I offer my advice freely, based on 40+ years in Engineering, mostly as a Toolmaker. I do not say my way is the text book way, but it has been proved to work, practically, and countless apprentices in my charge have benefitted from my help.

The advice is “offered” in the hope that I can make some engineering tasks easier, and remove the mystique. Also by giving the advice I can save the readers time, by shortening the learning curve, and giving them consistent results at the first attempt.

Sadly like all advice it can just as easily be ignored.

Regards

Gray,

 

[Howard LewisParticipant @howardlewis46836]

I can only echo Graham’s comments  (Started in engineering in 1958 and retired in 2003, although not toolmaking, so both singing off similar hymn sheets),  to say that correct or not, and probably in my case, crude, it works for me.

I also set the knurls and then feed them along the work, rather than using an in feed.

I used to worry about the “correct diameter” to have right ratio to mesh the knurl with the work, but found that it did not seem to matter.

The way in which I use knurls is to form / distort the metal rather than to cut it deliberately.

Afterr knurling, I then chamfer the ends, to remove the metal that has been distorted above the shoulder.

Knurling is presumably used in this way, to “correct” a job that is undersize, and improve the fit in a bore.

Howard

[VicParticipant @vic]

[Howard Lewis]

On Howard Lewis Said:

 

Knurling is presumably used in this way, to “correct” a job that is undersize, and improve the fit in a bore.

Howard

I have seen old purpose-built commercial piston knurling machines in the USA that were once common in “gas station” mechanics shops back when such things existed. Basically a simple crude  lathe arrangement with knurling tools used to increase the diameter of worn piston skirts. All a lot of fun until the tops of the knurls wear down. But I don’t think they would be brining the knurls to a point, rather leaving them half done etc just to take up a few thou of wear.

[Author]

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