Need Help!- KNURLING

[KENWILD1]

HELP
TRYING TO KNURL ON A HAAS SL 10 WITH A DORIAN KNURLING TOOL 20 T.P.I.
THE WHEELS MEASURE 5/16 WIDE AND I HAVE TO HAVE A 3/8 WITH KNURL
THE PRINT CALLS OUT FOR A STRAIGHT KNURL MEDIUM DEPTH
THE PROBLEM IM HAVING IS THE TEETH WILL NOT MESH . IT SEEMS LIKE THEY ARE KNURLING ON TOP OF EACH OTHER. ALSO IM POKING IN THE DARK WITH SPEED AND FEED

IM AT 250 RPM'S
AND FEED OF .01 PER REV.

ANY HELP WOULD BE MUCH APPERICATED

KEN

[bl409]

Ken,
Are you trying to knurl 3/8 diameter? If so some times you need a different pitch knurl for different diameters. With some knurl pitches and some diameters they will not track correctly because when the part and knurl rotate they will end up on the same track on the part. Try a different pitch knurl maybe a 25 or 21 abd see if it gets better. Good Luck, BL

[justgary]

I just happened upon this thread, and I'm not a very experienced knurler, but the only times I can get knurls to work out without overprinting is to feed the knurler heavily into the work before you let the spindle rotate all the way around.

Stated another way, I rock the spindle back and forth by hand as I sink the knurls about as far as I want them, then start the spindle (my lathe will allow me to rotate it by hand). If you don't let them bite enough to capture the pattern before they come back around, they will overprint like you are seeing. If the pattern is deep enough when it comes around, the knurler will set into it instead of starting a new pattern. Once the pattern sets, a few rotations will make it all uniform.

I have not tried straight knurls, but it should work the same way. For CNC, I'd feed them all the way in before the spindle turns very far. If you can do it, you might even try the rock the spindle trick to set the knurls.

Knurling is a strange beast that makes no sense when you think about what should happen (overprinting due to an overlap). Lucky for us, it only works how you would expect if you baby it. It works properly if you force it.

Regards,

- Just Gary

[ckirchen]

Originally Posted by KENWILD1 HELP

...please stop yelling...

Successful knurling requires that the workpiece circumference is an even multiple of the circumferential distance between teeth on the knurling wheel.

For example, consider your Ø3/8" knurling wheel with 20 tpi. The wheel has a circumference of 1.1781" (.375*pi) and will make 23.5619 teeth per revolution (.375*pi*20). However, there is no such thing as .5619 of a tooth; so it's probably 24 teeth per revolution. Doing the math backwards, the actual OD of the knurling wheel is Ø.3820" (24/(20*pi)) and it's circumference is 1.2" (.3820*pi). This equates to one tooth every .05" of circumference (1.2"/24), aka the circumferential distance between teeth.

To apply that to your workpiece, you need to make sure that you have an even number of teeth wrapped around it; the workpiece circumference divided evenly by .05" will result in clean teeth (i.e. no fraction of a tooth). However, if you are at the wrong OD on your workpiece, even by a small amount, you will get a fraction of a tooth left over after one revolution of the workpiece, and the knurling wheel will not be aligned with the previous revolutions' worth of knurls. Then it will start cutting new knurls slightly offset from the previous ones. And it gets worse with every revolution the workpiece makes. This is the overcutting you're seeing.

So, let's say the print calls for a Ø.75" knurled surface. The circumference is 2.3562" (.75*pi), which does not divide evenly by .05"; it equals 47.1239 teeth (2.6562/.05). Round down to 47 teeth and work backwards; 47*.05/pi equals a workpiece OD of Ø.7480". You could just as easily round up to 48 teeth if you wanted to; I picked 47 teeth because 47.1239 is closer to 47.

Now, it gets a little more complicated than that because there are pitch diameters to consider, tolerances in the knurling wheel, and you can have different weights of knurls.

To make it easy, calculate what the theoretical OD of the workpiece should be (Ø.7480" in this example) and then add a small amount to it (say .005" or .010"). Test the knurl on the oversize OD, and if the knurl is not lining up, slowly advance the knurl (don't clog it). Once it lines up, note the position. Next, if the knurl is too deep, remove some stock off of the workpiece and advance the knurl again until the teeth line up. Once you're satisified with the result, record the position and the workpiece OD for future use. Then, during the run, use those two numbers and the parts should be consistent.

I already mentioned it briefly above; but it's worth mentioning again. Ensure that you don't clog the knurling wheels with the extra material on the workpiece. The finish quality suffers and so does the life of the knurling wheels.

Hope that helps,
Chris Kirchen

[Technical Ted]

LOL - I was just doing the math as Chris was posting. As he stated the teeth on the knurling wheel are spaced every .050. If you're feeding in just enough to put a mark on the .375 dia then you couldn't be off any more if you tried. (.374 x Pi = 1.175) Now if we round off to 1.150 & divide by Pi we get a diameter of .366. If you feed into that diameter before the part rotates a full turn you shouldn't have any problem. At .010 feed you'll be at that depth in 1/2 a revolution.

PS Once the grooves are formed you can go in deeper if needed. The teeth will fall into place.

[justgary]

Oh, great! Now you guys have taken all of the magic out of knurling. You two are probably just like all of those who keep telling me that the earth is round.

Seriously, thanks for explaining what to me was a big mystery. It makes sense that at some feed depth you'll hit an integer tooth count, but I had never taken the time to look at it long enough.

Now the "feed it deep, feed it early" method of starting knurls will be much more reliable for me, since (as you can imagine) even that didn't always produce the best of results. I think I'll break out the knurler and practice!

Regards,

- Just Gary

[Technical Ted]

Ken - Any luck?