How does knurling work ?

Posted By Al
August 2002

I think I understand the process, but it doesn't seem like it should work.

From what I understand, you put the knurling tool on the work piece and move the lathe saddle along the length that you want knurled.

My question is how do you get an even number of knurls around the circumference of the work piece?
Do you have to calculate the diameter or can any diameter be knurled?

Also, when you start moving the knurling tool up and down the length of the work piece do the knurls automatically line up, or is there a trick to it?


response to Al by Jim Glass

Getting a knurl to track correctly is often a challenge. I have tried reducing the work piece diameter a tad to keep the knurl in sequence with the previously made impressions. Never seems to work.

Technique varies from one machinist to the next. I'll try to explain mine. Start out with knurl square to the bed or spindle and on center. Position the knurl away from the workpiece then dial straight in so "only" the first 1/16" to 1/8"
recieves the knurl. Check to see both knurl wheels make contact. Run the lathe at about 100 RPM. I continue to dial in untill a diamond shape pattern is observed. Once the diamond pattern is visible the power feed is engaged at a slow rate. .003-.005/revolution. If a deeper impression is desired back the tool away and return to the workpiece end and repeat. Don't try to get the full impression on the first pass unless it is the fine knurl. Use plenty of cutting oil.

In addition, I recomend the sissor type knurling tool. Most of the knurling preasure is on the tool itself. Conventional knurls put enormous preasures on the spindle bearings and crosslide screw and nut.


Response to Al by Jerry(3)


First time I needed to knurl, I couldn't get the knurl to track, so I looked at the thing and (as I had previously read and forgotten) I saw a gear. Aha....this has a "pitch"!

So I looked at the knurler, and measured it, then set the work diameter so there were a theoretically even number of knurls around it (no partials).

Worked fine, like the book said. I figured the pitch diameter to be the turned surface, as it displaces material and averages more like the surface.

Probably close is OK. A small diametral error is 3 x on the circumference, so a 20 thou knurl tooth is a 7 thou diameter change. You can get closer than that, and a couple thou is likely OK.

So yes, you can easily knurl a small range all around each of a series of diameters for a given knurler. Others will NOT work worth a hoot.

response to Jerry(3) by Forrest Addy

Knurls are goofy looking gears. Turn the diameter to be knurled as Jerry (3) suggests - to an even multiple of the knurl pitch. A tad one way or another makes no difference in the function of the knurling job so long as the knurls track.

I start a knurl by giving the tool a good initial mash to ensure the knurls have something positive to track on. Most materials work harden to some degree and time spent carefully schlepping the tool back and forth is a good way to roll a nice even knurling job into crumbled metal. It's best to apply as much force as the machine and part can stand, complete the knurl expiditiously and move on to the next operation.

Practice knurling before you try it on the production part.


respone to Jerry(3) by Harold Vordos

"So yes, you can easily knurl a small range all around each of a series of diameters for a given knurler. Others will NOT work worth a hoot. "

NONSENSE! I've never found a diameter I couldn't knurl, first time, no effort at all. Have you ever watched a knurling tool track? Have you ever wondered why knurling tools are not built very tight? Do you see the side motion? Need I say more?

Regardless of diameter, you can get a perfect knurl. You just have to know how to start the knurl. I have never used any type of tool aside from the old conventional two roller model that presses against the part, not pinches the part. The scissor type tool may or may not yield the same results.

If you want to start a good knurl, you must NOT be timid about starting your knurl. If you allow the knurling tool to dictate, promise, you will have lots of trouble.

A great deal of frustration on my part from fighting knurls that had to be held to specific finished diameters led me to the procedures below. I do not mention lubricating the knurling tool. We all know that lubrication is important in knurling. I use sulfur based cutting oil for steel and stainless, which yields excellent results.

For those of you that think making your machine actually do something is hurting it, you are likely to dismiss this method, but if you're tired of fighting knurls, even more tired of having to machine to some theoretical diameter, and don't mind asking your machine to perform its duties as it is built to do, then try this:

For starting a knurl from the edge of a part: Make sure you have a little material you can face off your part when you use this method. It tends to mush over the edge of the part.

Start your machine at a reasonable speed. Knurling should not be performed real fast, but it should not be dead slow, either. I always prefer a reasonable feed rate. If you can feed at .010"/.015 ", do so. Your part should have already been face, although slightly too long. That allows the rolls to attain a uniform depth because of equal pressure. Pick up the surface of the part to be knurled so you know where it is relative to your dial. Try to NOT imprint any of the knurl on the piece, but if you do go too far and it does make some marks, try to keep them as shallow as possible. Once you know where your tool will pick up, move the carriage so the knurling tool will pick up only about 1/16" of end of the part to be knurled. With the lathe running, quickly plunge the knurling tool to what you think is about proper depth. It doesn't matter if it is not. If the knurl is going to track properly, you'll know it immediately. If it does, back out slightly and run your knurl to the length you wish, then reverse the machine, or the feed, and track back, feeding the tool to proper depth to achieve a sharp V knurl. Anything less than that is hardly worthy of being called a knurl. If, by chance, the tool splits, turn the top roll by hand to some random location and try the process again, having cut away the existing knurl to avoid the old one guiding the new one. I've never had this method fail, though you might have to try a couple times to get there. When I knurl to the end, after I face to clean up the end I generally chamfer to slightly larger than the depth of the knurl. If finishes up the knurl nicely, and generally removes the area where you started the knurl, which tends to be slightly undersized from the abrupt beginning.

To knurl not starting from an edge:

Mark the area to be knurled. Same feeds, speeds as above. Pick up the diameter, same as above. Start your lathe, rapidly sink the knurling tool in to the part, all the while moving your carriage to one side or the other. Be certain to load the knurl, don't allow it to just lightly make contact. Your knurl will generally start without splitting. If it does split, move the top roll, repeat, but move to an area that has not already been knurled. Once you have the knurling tool tracking properly, go to depth and run end to end under power feed until you have a sharp knurl. I've found that you can go over the split knurl and remove it nicely once you have the tool tracking properly and at a reasonable depth so it is not influenced by the split knurl. I've NEVER failed to get a good knurl using this method.

If you find your knurls growing "hair", the best method to clean them up is to sand blast. That tends to remove the hair, not just flatten it. Keep in mind that a nice bead blast of a knurl, particularly one in stainless, really looks good when the rest of the part is highly polished. When I built tools that was one of the things I used to do to make my work stand out. Very effective.

Good luck with your knurls.

I have been plying around with "fancy" kurls for years and sometimes they work and sometimes they don't. What I mean by fancy are those that are other than stright lines, I have patterns such as stars, Greek key, flowers, leaves, intertwining rings etc. these are also sometimes refered to as milling wheels, they were popular in the 1870's & 80's and most were made in France, Most of the big machine shop supply houses used to sell them. Does anyone out there use these? and whats the trick? also I have a number of patterns that I have both the male and female knurl, also have some patterns in different diameters with more repeates of the design on the larger ones. Thanks

I have been taught to have my Rpm's as slow as they'll go 86 rpm and my feed as fast as they'll go and everything turned out all right most of the time, well some times anyway I notice your feed rates are slower will this make a big difference?

I've had about the same experience as Harold with knurling. Never saw a diameter I couldn't knurl with a two wheel toolpost mounted diamond knurler. I have no experience with scissors type knurling tools, but most of 'em look like flimsily built things, which is maybe why people have trouble knurling with them. I get a real kick out of folks telling me I'm abusing my lathe in some way knurling like this. Obviously they've never worked as a machinist where time is money, and you take the biggest possible hogging cuts until close to finished size. Compared to that, knurling is a pretty delicate operation, and even in a commercial environment, crossfeed screws, nuts, headstock bearings, and ways last for many years if kept properly cleaned and lubricated.

how I knurl
tool post dead straight
knurling tool (scissor) on center
I always knurl from chuck out
200rpm
biggest feed I have
spindle on & engage feed before contacting work-piece
spindle stopped and in neutral I get on work with good drag on piece
spin in neutral to see if tracking
if so....engage feed and turn spindle on
usually tracks
once again I could show you easier than tell you
by the way
my first time in forum

Rivett.I have quite a few of the decorative knurls you refer to.I also have some knurls that are "mother
Rivett,I have a number of knurls of the decorative type you refer to.Some of mine are the reverse of what they should be,i.e. convex rather than concave.These are "mother" knurls.I take my mother knurls and make regular knurls with them.I think some of these decorative knurls were only meant to be used on soft metals like gold,silver,or brass,because their designs are very deeply embossed.I make knurls by making a design on a flat strip of tool steel.I made a straight shank knurl holder that can be held in the vertical mill.Then,the knurl blank can be rolled back and forth down against the flat plate until the knurl is embossed.Getting the knurl to exactly the right diameter to take the design,say a repeating curled up ocean wave,is the tricky part.I wish I could find original info. on how the old timers used to do it.SMALL differences in the design on the flat master plate will be "evened out" by rolling the knurl back and forth against it.Sometimes I originate a design by making a punch of ,say,the wave,and stamp it along a row on the master plate.The punch can also be made so that the punch can be held in the milling machine spindle,and pushed against the master plate with enough force so you can go back over the row of impressions and hammer them deeper.The milling machine can thus be used to space the stamp marks evenly,and in an exact straigth line.


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P.S.,needless to say,the master plate must be hardened before using it to impress the knurl.I recommend,if it is O1,hardening it and drawing it to a medium straw color.The knurl can be hardened in the same way.Brownell's PBC non scaling compound can be used to keep the surfaces perfectly clean and scale free while hardening.I use transmission fluid as a quench for O1.The PBC will have to be removed by boiling the part in water after hardening.It flys off if a water quench is used for W1,but I use O1 for knurl making due to the danger of cracking the knurl,or the master plate.I use W1 to harden the end of stamps,but not the whole stamp,as it will split when quenched if you heat the whole stamp.Brownell's Gunsmithing Supply is in Montezuma,Iowa.

Reading the early post, I don't follow the recommendation for the use of lubricant.
Knurling is after all a process of upsetting the workpiece surface, it is not a cutting or machining process.
The knurls displace the material that the knurl wheel/s impinge against.
Therefore there are considerable forces involved.

I hate knurling! However, when I have to, I prefer the caliper knurls. What I do is have the wheels 2-3rds engaged with job; adust caliper until full form achieved (winding cross slide back& forth), then engage feed and plenty of coolant (sorry Damien!)