View Full Version : Knurling
08-28-2001, 07:28 PM
I haven't used a knurling tool for some years. Just bought one of those rotating-head, three-position tools.
First try on a piece of aluminum stock gave me the fine and medium runs coming out just fine. the coarse one shows one of the wheels in good contact with the stock, but the other wheel 'skidding'
Seems that unless the stock is some whole-number multiple of the knurl wheel diameter, it will give uneven results?
08-28-2001, 08:39 PM
No jokes about old-fart vision; I can still read Machinery's Handbook...
I used a hand lens to check the other knurls. All three have one wheel predominant.
I don't think it will cause this problem, but how do you get the wheels square to the work? They have 'clearance' with respect to the tool frame.
08-28-2001, 09:02 PM
If you have a wheel skidding I'd think your tool may have a problem. Does the wheel spin ok by hand? Can you see any run-out if it does spin? Since the tool is new maybe it has a burr or something. I rarely have tracking problems unless its a straight knurl. Then your od needs to be a mutiple of 1/64 or 1/32------Thats what my handbook says-----Straight knurls can be a pain because of tracking. Your tool is probably a diamond pattern though--- What works for me is -Run speed slow. Put the tool on center. Use plenty of oil. I really crowd the tool at the start manually to get the knurl started(tracking). Many people kick the tool at an angle so that the edge of the wheels can bite and start tracking. Once its tracking good then I start auto feed. If I even need feed. This is where I use my on judgment---I usually run feed .008 at slowest to .016 at fastest (per rev.) For me the best trick for good knurls is to keep those little chips blown out of the knurling wheels. If you dont have air to blow then use a stiff brush. If you cant get that wheel to turn freely then Id try finding out why. Maybe you got a bad tool. Are the wheels permenately mounted? Can you take it apart and inspect the bearing pin? Maybe the sides are too tight on the wheel. That wheel has got to turn for it to work right.
08-28-2001, 09:16 PM
Are you sure you got the tool on center. If being square to the work is a question then use a square or some kind of 90 degree gage to set your tool. Use an indicator on the side of the tool-----crank the cross-slide back and forth to check. I always put the ole eyeball on it and that is good enough. If I understand you correctly about having a predominant wheel on the other two then it sounds like your tool is not on center.
08-29-2001, 06:21 AM
Knurls have a given pitch, is in per inch.
In order to knurl a nice looking knurl the diameter of the stock has to be a multiple of the pitch, on the circumference.
I had neve had any problems with a knurl tool till I used an Aloris, the coarse knurls are a 16, the old Armstrong tools use a 14.
Doing the math the 14 pitch knurls will work with fractional sizes of stock close enough so that if you dial it in deep at first it will come around and match. Not so with a 16 pitch Knurl.
Pain, for instance, if you wanted to knurl a 1.5 diameter shaft with a 16 pitch cutter, you need to reduce it to 1.492 dia.
I know a real pain, but if you want a good looking knurl, this is what you have to do.
I can't add much: be sure the knurling head is on the centerline, and if it doesn't come out even, reduce the diameter a little and try it again, as Halfnut explains.
Even with everything set up properly, it's sometimes still hard to get the knurls to track right. I sometimes find that if I start just at the edge of the work, with about half the width of the knurls in contact, it will start a little better because you can get more pressure on the amount of surface area in contact. Once it's tracking properly, you can move the knurls across the work (slowly, of course) and they'll keep going correctly.
A LOT of cutting oil helps, too, to keep the chips washed out.
08-29-2001, 10:03 PM
Not an answer to the specific question, but on the topic of knurling:
I used to have a lot of trouble getting a double impression off one of the knurling rolls. (I have a shop-made straddle-type tool.) I tried turning the stock circumference to a multiple of the pitch, sometimes it would help, usually not. (I'd never worried about it with other knuling tools.) After struggling for months I gave up and decided to order a new set of rolls. I looked in the MSC catalog, and at the front of the knurl section there was a paragraph of hints on knurling problems. For double impressions they suggested stoning a couple thou off one of the rolls. Eureka! I measured my rolls and, sure enough, one was 2 or 3 thou bigger than the other! I set up my tool post grinder and ground the larger one down to match, and now I get perfect knurling, and rarely have to worry about stock diameter.
Regardless of the type of holder you have you must start with a lot of pressure so that you get a deep impression immediately. That way, when the tool starts its second lap around the workpiece it can readily drop into the established pattern.
08-30-2001, 06:14 AM
I like it, I have struggled long and hard making pretty knurls with an Aloris tool.
I set tool low, get top wheel in the groove so to speak, then reset and get the bottom one into edge of first and knurl to some depth, then I reset to center, making sure that both are in and finish.
Troublesome, but I like my knurls to look good. Other guys in shop wonder how I get it done, have explained but I still see some **** looking knurling.
08-30-2001, 07:03 PM
Now I don't feel so dumb for asking. I can see it's not a walk in the park, and I didn't even know it was a cutting operation; I thought it was forming.
And I can see that (like a lot of the tuff in the hobby) some plain old practice and fiddling will help.
08-31-2001, 05:04 AM
There are two types of knurls: deforming and cutting.
Deforming knurls are most common and work well for most applications. Lubrication is useful because of the extreme pressure metal to metal contact involved. This produces a smoother surface texture on the knurl faces.
The cutting types have the wheels at a 45* angle to the work and at right angles to each other and produce less stress on the spindle bearings and nicer knurls. Dorian's is about $700 and each cutter is $50 - but the only way to knurl tough stuff.