Cut knurling - a cut above the rest?

Most knurling tools in use in home workshops rely on forcing a hardened, knurled wheel into the workpiece as it rotates in the lathe. This causes the workpiece to deform plastically and equally it requires a hell of a lot of force. This process is called "form knurling":

There are "tangential" holders that hold 2 knurling wheels at opposite sides of the workpiece. This can help to reduce the load on the tool, the lathe and the workpiece but still requires a lot of force on the wheels and they still have to be either forced into the work or tightened into the workpiece.

The other type of knurling tool uses a sharp edged knurling wheel that is fed sideways along the workpiece from one end, cutting the grooves as it goes.

This is a single wheel version:

And they also come with two wheels:

One key difference between the single and dual wheel versions is that it is possible to cut cross hatched knurls in one pass. The single wheel tool would need to cut one set of grooves in one pass, then have its head angled so that a second set is cut at an angle to the first set.

Although Cutwel may not be regarded as a discount tool shop, you can see that even so, these wheels aren't giveaway cheap:

And usually you'd be wanting a toolholder to be using them with. But make sure you are sitting down before looking closely:

So you can see why you might not see so many of these in the average home workshop.

Anyway, I managed to win a similar tool through the homeworkshop.org site not so long ago. I haven't got round to trying it yet and TBH I don't make a lot of hand tools that would benefit from it - but that's not really the point. 

Here's what I've got. It's a German "Böni" brand.

They are still in business and these products are still shown on their website.

But it came with a user manual that has a wonderful smell of cutting oil. It would be rude not to refer to that.

How to use it:

And a parts list / section view:

One thing I noticed fairly early on is that the "arms" are fitted the wrong way round (see the first photos above). I suppose this allows the knurls to be used on smaller diameter workpieces than the specified 20-65mm. However, when fitted this way, the graduation marks for the adjusting screw aren't visible from above. No big deal but it had me puzzled when I was reading the instructions.

The wheels run in needle bearings, although there's no thrust washer as such. The wheel thrust is taken directly by the face of the needle race, which seemed strange. But the parts list confirms this is correct and indeed there's a note telling you that "only the engraved side of the needle bearings is hardened" so you must fit the bearing with the part number visible and against the knurl wheels. The bearings are INA (German!) HK1015.

The adjustment wheel has opposing left and right handed threads, so turning it brings the wheels together symmetrically about the workpiece. The thread has a pitch of 1mm, so each turn moves them 2mm closer.

In the mini tool set that comes with it, there's a quaint little plastic collar that fits on the hex key with graduations. So you can actually set the depth of cut with some accuracy if you are that kind of person.

The toolholder shank has been machined. They come in either 20mm or 25mm square. 

We can see that the end of the shank was originally faced off in a lathe during manufacture and thus we can be fairly certain that it was originally a 25mm shank.

And now it's 3/4" (19mm). No problem - in fact that's handy, as most of my Multifix toolholders (for the Bantam) are for 20mm tools and the toolholder turret on the Tree expects 3/4" tooling for it to be on centre, being of US origin.

There are a few wheels with it, including a pair on the tool itself. They are all "straight" ie the teeth are parallel to the lathe axis. The tooth pitch is 1.2mm or 1.6mm although others are available, down to 0.5mm. Most are fairly sharp and of course they are double sided. FWIW, it appears compatible replacements are available from Chinesium outlets.

The tool presents them to the work at a fixed angle - which is 30 degrees on this example which is fitted with the BG2065 "holder set". This means that the knurls from one wheel are at 30 degrees to the axis and 30 degrees the other way from the other wheel. The result is "diamond" knurling with the grooves at 60 degrees to each other. Other angles of 0 and 45 degrees are available apparently.

The angle referred to in the knurl descriptions seems to refer to the angle of the crest of the teeth - either 90 or 105 degrees here.

So, after some gloating and "researching", I may be forced to actually try the thing out. That will come next....