Knurling question

Hello experts,

Could someone take the time to explain how a knurling tool works? I am referring to the type which straddle the work and whereby you turn a hand wheel to force the two knurling wheels into the work. I think they are called "clamp type"?

My question is this: how can a knurling tool knurl different diameter materials? What happens after the knurling wheels has completed a complete circumference and it's ready to start its second turn and the lines don't match up?

A silly question from a beginner, so go easy on me please guys,

Mark

Edited By Mark Gould 1 on 22/05/2017 10:16:01

Think here an extreme. Say you only had five indents on a full turn of your item. It would make a different set of indents the next time around if the 'wrong'diameter, but there are incremental diameters where the knurl would superimpose 5, 6, 7, 8, etc knurls per turn. So ideally the diameters need to match the knurling wheel in use. Often knurling a little deeper will make the small amount of difference imperceptible.

Try it and see.

The technique is to clamp the knurls whilst it's running to reduce the starting load forces, then run the knurls forward and slowly run them back up the diameter and you should get a lovely looking knurl.

Michael W

Edited By Michael-w on 22/05/2017 10:56:27

It does happen that the pattern does not perfectly fit your chosen diameter but a slight skim wil get thing working properly.

Mike

The knurling tool does not cut the knurl, but makes the impression by forming and if you get it running right it forms the knurl regardless of size, sometimes if I start too light a double pattern seems to appear.

Ian S C

The pressure of the knurls extrudes material up from the original plain diameter. The material has to come from somewhere so the knurling wheel points sink below the original plain surface. Effectively the knurl pattern comes into balance with some above and some below the original surface. The process inherently has some leeway as to exactly what diameter the balance occurs at so the starting diameter doesn't have to be exact. In practice its rare to take a knurl right to sharp points so errors can be hidden in slightly sharper or slightly blunter points.

In practice for medium knurls on typical sizes of material, say half to one inch diameter, one more or one less knurl point translates to around 10 to 20 thou variation in stock diameter so extrusion variation can take up most errors. As its a symmetrical process which can go either up or down the actual range will be ±5 to ±10. If the workpiece is small or the knurl coarse you may get thin slivers of metal cut off the sides of the knurl points when the error is a bit excessive.

I rarely worry about stock diameter unless below 0.375". Just have at it until things look right works fine.

Clive.

Thanks everybody and especially Clive, that's the answer I was looking for. I was seeing the knurler as a gear which had to mesh with any number of other gears, regardless of size/amount of teeth etc. I am starting to understand why there is a certain leeway.

Thanks again,

Mark

if the depth of knurl is approximately the same as the width of the pattern, then between the top and bottom of the knurl pattern there are typically three integer numbers of knurls that could be made around the work for any given diameter.

Now knurls are not kept in fixed engagement with the work like gear cutters, and the simple truth (as Clive has explained) is that they will self-adjust by slipping into whatever number of knurls is a close match to the setting of the diameter.

It is possible to get a double pattern if you use VERY light pressure so only the tips of the knurls engage the work, but if you always start with a good engagement and plenty of pressure you should never have a problem with a 'bastard knurl'.

Neil

Thanks Neil!

One of the most hand knurling tools I have for small parts uses the flint wheel from a Bic disposable lighter, the idea came from one of Stan Bray's books. You can make this i an hour or so, cost zero.  Ian S C

Edited By Ian S C on 23/05/2017 12:28:27

I had no idea those flint wheels were that hard. Might give it a try, thanks Ian.