Can somebody explain to me the basics of knurling? My machine shop teacher showed me how, but screwed it up and explained nothing as he did it. /: Also, the knurls I wound up with I kind of flattened. I found I had to drill the piece out a little more after I'd already knurled it. It hung on the drill and spun in the chuck. Oops. The chuck flattened all of the knurls nearly out of existence. Can I repair this by knurling again, or do I need to take a light cut (it's just a handle, so dimensions don't matter much) before knurling so I'm starting with a smooth surface? The piece is steel. I don't care about how it looks, I just don't want to damage the knurling tool.
It is simple enough -- the knurling rollers displace metal, pressing it down in one area to form the grooves, and allowing it to rise in between, to form the peaks.
You do need to make a fairly strong knurling pass, so the knurls will self center when they come around again -- otherwise you will wind up with double-pitch knurls or other problems.
You want to flow a lot of oil through the interface between the knurls and the workpiece, and to be running a very slow spindle speed.
The best standard knurling tools are the scissors style, which applies one knurling roller to the top of the workpiece and the other to the bottom, putting all of the force into the hinges on the scissors knurling tool, instead of requiring the cross-slide and the compound to provide all of the force. (But I'll bet that the school only has bump knurlers -- but that the machine is strong enough to handle it.)
Not necessary -- it will give a starting place for guiding the knurls to pick up their step.
Unless the steel is thoroughly hardened, you probably *can't* damage the tool, except by running it dry -- remember *lots* of oil, and slow speeds.
Next time you need to work on something already knurled, take some soft aluminum or copper stock (say 16 ga (0.625") or so and put it between each chuck jaw and the workpiece, giving you a better grip and avoiding damaging the knurled finish.
Good Luck, DoN.
* Notice that above I said "standard" knurling tool. There is another style which cuts the knurls, instead of deforming the workpiece. It results in crisper knurl finishes, but they are typically *very* expensive, and won't be found in a school shop. They can be identified by the fact that they present a sharp edge to the workpiece instead of the middle of the roller.
If you go back in the RCM archives on groups.google.com, you'll find any number of opinions on how to knurl. I've got a copy of a small book on the subject that I found in the library, basically it says your work circumference has to come out even with the diametrical pitch of the teeth on your knurl. Kind of like cutting a gear blank, if you don't have the right diameter on your workpiece, you'll end up with fractional teeth and it won't be right.
It's hard to damage a knurling tool unless you're trying to knurl hardened steel or something.
The best way I've found is to leave a band proud on the surface that's the correct diameter, then knurl that. If you look at a Starrett mike sleeve, you'll see what I mean. You can size the band so you get a good knurl the first time around. A scissors-style of knurling tool helps, too. You probably won't find one in a school shop, though. Enco used to have cheap import ones if you want to go on their website and see what one looks like. Might be a good school project to make one.
Others will say just to ram the tool in there with as much force as you can, sizing doesn't matter. If you've got sufficiently ductile material and a heavy enough cross-slide with enough lube, it'll probably deform the material enough to get acceptable results. You might also deform other areas that you may not want bent, too.
It's not that hard to calculate what your desired diameter would be on the workpiece surface once you know the diametrical pitch of the knurl. It's basic machine shop math.
"B.B." wrote in news: snipped-for-privacy@news-ia.supernews.net:
Here is a link to good knurling info:
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Over rolling, that is to say dwelling too long, blank size too big, or taking two passes, will cause the knurl to flake. I would turn the handle down if that's acceptable and start over. Other wise your knurl is likely to be full of needle sharp flakes. A trick I've used on engine lathes is to engage the knurl into the work with the spindle stopped, then start the spindle and knurl. If you are traversing to put a knurl on the work that is longer than your knurl is wide, remember to break the leading edge of the knurling tool with a 45 degree chamfer. The best thing to use, if they are available to you, is a convex knurl.
The method I was shown in high school machine shop, was to advance the toolpost-held style knurl gently to the workpiece (kinda like taking a scratch cut to check thread pitch). With the knurls in light contact with the workpiece, rotate the chuck by hand to see if the pattern is correct (nice shaped diamonds), and that the knurls contact the work flat/full width of the knurls.
When the knurls are set correctly for the nice diamond pattern around the diameter, the knurls can be advanced more tightly into the workpiece, and power applied.
Cutting oil required, and slow rotational speed, then knurls can be advanced more and hand or power fed along the workpiece.
It may say that, but it's *wrong*. Only when knurling a straight knurl would that be true. Diamond knurls compensate for less than perfect pitch by wandering side to side. You can achieve a perfect knurl on *any* diameter.
Smart people don't knurl finished parts for that reason. Knurling is one of the heaviest of operations we perform on lathes. It should be done before finish cuts are taken.
It's also a waste of time. It's much easier to learn to knurl properly, then the size won't matter. When you have enough experience, you can start a knurl 100% of the time without splitting, diameter be damned. Just make sure your knurling tool has a bit of side clearance on the rollers so they can hunt to maintain perfect alignment with the established knurl.
Exactly! I didn't bother mentioning diameter in my reply, because I have found it to not matter.
And even if you calculate the proper pitch for a diameter -- which diameter do you use? The first pass pitch diameter? The average? The one at maximum depth? If it matters, what is right for one will not be right for another.
I think that it might make a difference with a very shallow knurl pass, which is not what I ever use. With deep starts the knurls are self-correcting, as you suggest.
Ayup. Ive never calculated knurls/diameter etc. I didnt know you were "supposed to". My old homemade pinch knurler doesnt know that either.
Still makes nice knurls just the same.
Gunner
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