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Thread: How to Knurl?

  1. #1
    Hanz's Avatar
    Hanz is offline Cast Iron
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    Haven't done much knurling on my lathe. I have an aluminum handle, 1 1/2" od, and I want to knurl a 2" length.

    Do I plunge in, and then feed sideways? All in one pass? I assume a very low back gear rpm, and what about feed rate?

    Thanks-Hanz

  2. #2
    JoelS is offline Cast Iron
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    Plunge in quickly, before the part has made a full revolution. Yes, do it in one pass whenever possible, especially with aluminum. Use low RPM, a fast feed (about .025 ipr) and lots of oil. If you donít have a pinch/scissors type knurler, do yourself and your lathe a favor and get one.

    Do a search, both here and at the HSM site. You should be able to find some good information which might be helpful. Knurling without double tracking can be a real pain sometimes.

  3. #3
    jim rozen is offline Diamond
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    Knurl at the slowest speed you lathe offers.

    Do not move the tool until the knurls track
    correctly.

    Use plenty of cutting oil and keep the chip
    brush *away* from the knurls!! You ain't
    lived till you've ruined a knurling job by
    passing an entire acid brush through the
    job!

    Knurling is the operation that puts the most
    stress on a lathe of all of them. Support
    the work as solidly as you can (center, four
    jaw chuck) and consider that it will try to
    shift sideways into the chuck if that is the
    direction you are feeding. If feeding to
    the right it will try to open up the center
    in the part.

    ONe trick I was taught was to shift the knurling
    tool *slightly* at an angle to get it to pick
    up tracking rapidly.

    No matter what, practice on a scrap piece first.

    Jim

  4. #4
    Doug is online now Diamond
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    Hmmmm.....both you guys say to use plenty of oil.

    The knurl making company I buy from say it makes no difference whether it's done dry or with oil. My experience agrees with that. The only useful function of the oil would be to lube the knurl axles.

    We do our production knurling at around 1000rpm on 1" diameter aluminum. These are done on a CNC lathe so we program a short burst of coolant onto the knurl before it hits the work for lubrication. Very fast feed, maybe .050ipr or faster. NEVER dwell a knurl tool on aluminum. And never run back over the knurled area if possible (with some end feed knurl heads you have to). Do the knurl in only one pass.

    Aluminum is one of the worst materials to get clean knurls in. The material flecks badly, this is why you don't want to dwell or run back over.

    One of our repeat jobs is a fairly coarse diamond knurl on 1" aluminum bar. The parts are control knobs that get black anodized. The flecking shows up after the anodizing where flecks break loose and leave white spots on the parts. Old time anodizers used to dip black parts in india ink to cover the white. I use a felt tip marker where needed.

    Before I got into the knob job I assumed diamond knurling on aluminum was no big deal. After experiencing the problems I started looking for consumer products with diamond knurled aluminum knobs. There aren't any to speak of. Instead of diamond knurl they use a straight knurl, but it's not really a knurl. They're made from extruded bar stock with the knurl pattern being created in the extrusion die.

  5. #5
    jim rozen is offline Diamond
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    I would point out for the sake of accuracy
    here that Doug may be doing his knurling
    jobs on a very large, rigid NC machine.
    Trying to plunge to depth on a smaller
    hobby lathe (and here I count my 10L in that
    catagory) does not work terribly well.

    Knurling is an extrusion process, the
    material is being extruded up into the spaces
    in the rollers. Extrusion processes are
    often carried out with some kind of lube.

    Jim

  6. #6
    jwaggs is offline Aluminum
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    Did I read somewhere that the diameter of the knurl wheel is important in relation to the item to be knurled? It would seem that for the knurl wheel to track it would have to have a diameter equal to the bar being knurled or the bar diameter would have to be an even multiple of the knurl wheel diameter.

  7. #7
    CCWKen is offline Senior Member
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    Yes Jwaggs, that's true but few go through the check to find the best pitch for the diameter. They simply run the knurl and can't figure out why they're getting lousy knurls and chips.

    According to my chart, a 21tpi (medium) or 14tpi (course) should give you a near perfect knurl on 1 1/2" stock.

  8. #8
    JST's Avatar
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    I know for a fact (experience and confirmation) that a straight knurl need the right size.

    I have been told that a diamond knurl does NOT need the "right" size. I must admit, I do not quite understand why. I also do not have a diamond knurl setup, so I have not tried anything about it.

    Anyone care to explain why that is wrong or right?

  9. #9
    gglines is offline Senior Member
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    J

    I have experimented with calculated diameters and knurling and found it makes absolutely NO difference with a diamond knurl. The knurling wheels on my Eagle Rock scissor-type knurler have lots of slop on their pins (by design I think). I've run these experiments on stainless, mild steels, and aluminum.

    The secret to a good knurl in my experience is. . . lots of knurl pressure. I have always knurled with a lot of cutting fluid too, but I'll try it dry and see if it makes a difference.

    Like Jim, I may have donated an acid brush or two to the cause [img]smile.gif[/img]

    George

  10. #10
    TheMetalDoctor is offline Titanium
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    When I knurl I always leave about 1/8 inch of extra stock to start the knurl on and after I have finished the knurl, face the extra material off and put on an appropriate chamfer. So, if the knurl starts wrong you have a chance to correct it before rolling over on the finished diameter.

    When I begin the knurl (using the scissor type knurling post) I first pick up the o.d. with the knurling wheels (on center) and screw the adjustment nut down until the wheels are touching on both sides. Then back off and move over to this extra material on the face,(knurling wheels engaged by about 1/16th on the horizontal) set the wheels into the part just a tad and turn the lathe spindle on and let it go a full turn, watching to make sure the knurl meshes properly . If I get proper mesh I back out the knurling tool and tighten the knurling adj. usually one flat on the hex adj. nut and not losing contact with the part with either wheel. Then, turn the lathe back on and plunge in to the same point again checking for proper mesh and if so begin to manually feed the carriage to the left until my knurl is done. I use copious amount of lube because the knurling tool will pull small flakes off the surface and you do not want those to stay on the part, but float away with the extra oil you are putting on. Not flushing these flakes away will cause them to adhere and give you plating headaches. I never try to finish the knurl in the first pass as you may "overknurl" and cause major flaking. This all requires some practice and BOTH HANDS. Practice, practice, practice, then go for the finished part.

    If I have multiple parts I will lock the knurls at a point that gives me an almost complete knurl and do successive parts in one pass.

    The knurling tool needs to be square with the part or you will leave a helical spiral on the surface. No problem if the knurl is narrower than your knurling wheels.

    Clear as mud, huh ?

    TMD

  11. #11
    CCWKen is offline Senior Member
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    I have been told that a diamond knurl does NOT need the "right" size.
    Yep, you're right--size doesn't matter but the TPI does. It WOULD be the same for straight knurls too. It's like matching gears.

    If the TPI doesn't fall close to a factor of the stock circumference, the knurl will start to over or under track. The teeth will start to slide into the previous track and cause chips. Makes for an ugly knurl too. Adding oil will just make it slide easier.

    Divide the circumference by the reciprical of the TPI (Pitch). This gives you the Pitch applied to the stock. If there's more than about .2 (off zero) in the decimal, you'll get a messy knurl. If the division results in no remainder (.0), you'll get a perfect match.

    Cir
    ------ = Stock Pitch
    Pitch


    Knurl---TPI----Pitch
    Fine----33----0.03030
    Medium--21----0.04762
    Course--14----0.07143

    USING 1 1/2" STOCK--

    Fine Example:
    1.5 x Pi
    -------- = 155.5 (Not a good match- ".5")
    0.03030

    Medium Example:
    1.5 x Pi
    -------- = 99.0 (Perfect match ".0")
    0.04762

    Course Example:
    1.5 x Pi
    -------- = 66.0 (Perfect match ".0")
    0.07143

    So for 1.5" stock, a Medium (21tpi) or Course (14tpi) knurl would give the best results. A Fine (33tpi) would cause the pitch to HALF-TRACK (.5) on the stock. (Really ugly knurl)

    The same applies to straight knurls.

    Forgot to add:
    If you want to use a specific TPI knurl (Fine, Medium, Course), then you need to adjust the diameter of your stock for the best fit. Therefor; to use a FINE TPI knurl on 1 1/2" stock, you'd have to turn the stock down to 1.496 or 1.494. This would give you a stock pitch of 155.1 and 154.9 respectively. This falls within the .2 off zero.

  12. #12
    jwaggs is offline Aluminum
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    CCW
    Good explanation. That is probably why I have had mixed results with knurling. Sometimes by accident the TPI matches the diameter and the knurl looks great [img]smile.gif[/img] . Other times it is off and the knurl goes from bad to worse .

  13. #13
    Michael Az is offline Senior Member
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    Some time back I started adjusting the diameter of the stock to match the knurls like Ken explains. So far all my knurls have come out good. Before it was hit or miss.
    Michael

  14. #14
    Arbo is offline Aluminum
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    OK, you have my attention. I have been doing some knurling, with mixed results. How do I figure the pitch of my knurls. I have a home-brew clamp type knurling tool and am using .750x.375x.250 bore knurls from Grizzly. The knurls have the diagonal lines that make the diamond pattern when used together in a clamp type tool. Thanks in advance.

  15. #15
    JST's Avatar
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    JST is offline Diamond
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    CCW, by "size" I did mean one that comes out to the right pitch....

    Straight knurls are obviously crummy gears. Easy to see the pitch issue.

    However, I was told by folks who ought to know that diamond knurls are different and don't have the same sensitivity to pitch.

    I didn't see then, and don't see now, why that should be the case.

    Maybe it's just more "slop" available in diamong knurls? I don't quite see that either..

  16. #16
    CCWKen is offline Senior Member
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    By size, I was thinking the diameter of the knurls and confusing myself, I guess.

    The Diameter of the knurl has nothing to do with a good knurl. It's the Pitch of the knurl that counts. The tooth pitch is what you are using. That's the distance from tooth to tooth. If that distance divides equally into the circumference of the work, YOU WILL GET A PERFECT KNURL.

    It's the same principle for ALL knurls JT. Diamond knurls are just two diagonal wheels. Each wheel will run in it's own track. If the circumference of the stock doesn't match close to the pitch of the wheels, you're going to get a bad knurl--Straight or Diamond.

    All these wheels do is displace metal--like a press. The chips come from the teeth of the knurl sliding into the previous track. (Hard on knurls too.) I'm just telling you guys what has been working for me. It will take the "Hit-n-Miss" out of knurling. Don't belive me--Give it a try.

    I set up an Excel Worksheet with diameters from .250 up to 1.374 (most of my work) and keep it in the shop. When I need to knurl, I look at the chart for the best knurl pitch. It has Fine, Medium and Course columns with the calulations already done. I try to hit ".9", ".0" or ".1" for the best knurl job. If you hit Zero, you should not get any chips and a perfect knurl--Straight or Diamond.

  17. #17
    CCWKen is offline Senior Member
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    Arbo said:
    How do I figure the pitch of my knurls. I have a home-brew clamp type knurling tool and am using .750x.375x.250 bore knurls from Grizzly.
    Arbo, that's pretty much a standard "size" knurl. I have three diamond sets and a straight that are all that "size". What matters is pitch. My three diamond sets are Fine(33tpi), Medium(21tpi) and Course(14tpi). I looked in the Grizzly catalog (and did an online search) but didn't find their knurls so I have no idea what you may have or what they offer.

    You may have to call Grizzly and ask them or Count the teeth. Sorry

  18. #18
    JST's Avatar
    JST
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    CCW: I see we agree.....

    I wonder what the other guys over on Chaski meant then........I surely understood them to make a distinction.

  19. #19
    Arbo is offline Aluminum
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    Ken, I did a bit of research last evening. I have three different sets of knurls with different pitch. I counted the teeth on the ones I have mounted now, and came up with 48 teeeth. According to my calcs, that gives me 20.371 TPI. That should give me a knurl pitch of .049088.

    SOOOOOO....Assuming a 1.5" work piece

    (1.5*3.14166=4.71249)/.049088=96.0008556.
    Perfect match? Am I understanding correctly?

    Thanks!

  20. #20
    tnmgcarbide's Avatar
    tnmgcarbide is offline Titanium
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    nobody's mentioned the knurls that cut instead
    of displace. they put very little pressure on
    the part, but i guess they're not technically
    knurling (an extrusion process) not as pretty as
    a regular knurl-job with the proper 'crowns' on
    the peaks. they just cut a diamond cross hatch
    instead.

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