Did you have tailstock support?

pgk

Are the knurls bevelled edge or plain ?

Helps if they are bevelled when when asked to travel sideways.

Emgee

For longer knurl lengths, I normally start at the chuck end and finish at the tailstock end. I normally use coolant to wash away any micro bits of what ever. At the start I wind back and forth for about a roller width to see that I am happy with the depth or definition of the knurl then cut down the length. I normally run quite a bit faster than you did, around the 200 rpm range on steel that diameter. Sometimes the knurl does not quite work out due to the pitch of the form not matching the diameter. A bit like gears. If the diameter is too big the top of the teeth become very pointy. If the diameter is too small the top is very wide. I normally just hand feed the carriage when knurling.

Ian, I also don't bother to calculate pitch but it was an observation of what can happen if going too deep.

When I have to do long knurls I get the knurls to get the correct pattern (timed together) which is not necessarily full depth and then traverse the length of the knurl then repeat a bit deeper till full pattern is achieved and use plenty of coolant to wash away debris. Having said that it’s not the easiest of jobs. Out of interest I have the lathe spinning at around 350 to 500 rpm depending on dia.

FWIW, I almost always use power feed, when knurling, but at the minimum feed rate so that the tool does not have to work too hard, and the knurl already formed can support over the maximum length of the wheel; just a few thou compared to the width of the wheel width.

What is being formed is approximately a spur gear so the tendency for the wheel to swivel from the forming / cutting forces has to be resisted by the knurl just formed . So for a 1/4" wide wheel, the feed per rev needs to be as small a proportion of that as possible. Possibly 0.004" / rev, with a low rotation speed.

If the clamp type tool is sloppy, that may contribute to the problem in that one wheel is not following the same path as the other (It should, since effectively two gears are being forced into close mesh.

Depth should only be sufficient to form a full height knurl. If in any doubt, take more than one "cut" so that the later cuts produce the full depth.

Howard

The swarf produced when attempting a long straight knurl is mostly due to the knurl teeth not being an involute or, for that matter, any other recognised efficient gear tooth pattern.

Besides deformation of the workpiece displacing material to form the 'umps and 'ollows of the knurl the actual shape of the spaces will be scraped to give enough space for free rotation of the knurl. As the knurl depth changes so does the shape. Hence the formation of swarf as the knurl deepens.

With the normal cross pattern the effect is masked because one normally never feeds the knurls to full depth so there is a bit of clearance in the equivalent of a gullet between the knurl teeth that the pyramids making up the knurl can deform into. The general insensitivity of knurls of reasonable pitch on work of mutually reasonable diameter is due to the material being shifted up or down during the process so that the final "pitch diameter" permits an integer number of knurls around a diameter at half knurl height.

But there must still be a little space in the knurl gullet above the peak. Force the knurl deep enough to more than eliminate that clearance and plenty of thin, needle like, swarf results.

Clive

That’s certainly part of my logic, Jason

But I also suspect [‘though cannot prove] that the knurls themselves become self-aligning when they are producing the helix .. Straight knurls however do not receive the same stabilising influence.

i.e. the helix is a ‘natural’ form to be produced by any tool traversing in the Z axis of a rotating workpiece, and the straight line is a very special case.

Successful straight knurling over a length greater than the width of the knurls probably has similar probability of success to that of balancing a pencil on its point.

I would posit that the pattern in Robin’s first picture is effectively a sawtooth effect caused by bursts of instability.

MichaelG.

If you are using a Clamp type knurling tool, and one wheel is cutting deeper than the other, it would seem that one of the carriers for the wheels is not pivoting easily on the holder. The purpose of the pivots is for the knurling wheels to centralise themselves about the work.

A clamp type holder should be positioned so that the line between the centres of the wheels is on the centreline of the work., and the cutting / forming pressure applied by bringing the wheels into contact with the work.

In the case where a single,"push" type knurl is being used, excessive pressure should be avoided wherever possible. a ) because it will cause slender work to flex, and

b ) because of the extra load imposed on the Headstock bearings.

If more than one pass is needed to give a full depth knurl, the wheels should engage with the earlier pass, in the manner of two gears going into mesh.. Only about 0.010" "interference" is usually needed. to produce a satisfactory knurl. Probably because some of the material is forced outwards by the process.

For this reason,knurling is often used to recover a slightly loose fit of of a shaft into a housing.

Despite concerns over needing an exact ratio between the diameters of the wheel(s ) and of the work, it does not yet seem to have caused me a problem.

Howard

Hi, I explained my findings of scissor type knurling tools with sideways slop in this Knurling Tool and this photo shows some of the pit falls with them.

You can see on the left of the pattern where the top knurl has been skewed to the left and the bottom one to the right and this is just a static knurling.

Regards Nick.

One of these could make some interesting knurls.

Knurling machine ?