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Straight line knurling?

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  • J Tiers
    replied
    Originally posted by Baz View Post
    ......
    I'm not sure why people are talking about 'screw machine operators' and special knurls. What's in your workshop - a cake mixer?
    Simply because those folks doing that want the knurl to work first time, every time, just by running the knurl over the part. No "finesse", no "wait until you get this condition", no nonsense.

    So, it shows that far from being totally uncritical, there is a way to pretty well guarantee perfect knurls, and every other way needs some "finesse".

    Does not mean it won't work, just means there is some compromise. That might be either diddling with it a bit, or accepting a knurl that has distorted teeth from the wheel not quite fitting the pitch, etc.

    It works one way perfectly every time, and a lot of "fractionally assed" ways.... some half assed, some 15/16 assed, some 31/32 assed.

    Knurling is another one of those things that the "home shop experts", like to show their superiority with, quite brutally frankly speaking..... Always a good subject for a fight.

    "I have no idea why people are talking about a cake mixer, what's in your workshop - mixing bowls?"

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  • Baz
    replied
    If you think of it as two gears being brought together you know form your own experience that they will mesh (although not optimally) at a range of depths not just pcds aligned so the exact diameters are not critical and that the final outer diameter of the job (which may change due to extrusion outwards in the process) will tend to match to the inner diameter or bottom of the knurl teeth (allowing for the swarf pounded into them) so the knurl tooth outer pitch isn't the measurement that matters.
    I'm not sure why people are talking about 'screw machine operators' and special knurls. What's in your workshop - a cake mixer?

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  • J Tiers
    replied
    Originally posted by Paul Alciatore View Post
    For a straight, Vee knurl, once it settles down to a single pattern (not double the rate on the tool) you can keep going deeper until you get sharp tops on the knurled pattern and it will not skip to another pattern. There is a bit of slip as each tooth of the knurl is formed and the 1X pattern is the one that dominates.

    Just go in hard and then continue to full depth. It works.
    You will still have issues starting it , but, as I said, the wheels will "slip" to conform after the pattern is established. Works even better with an angled knurl. Getting it started is the place that issues appear.
    .

    Screw machine folks can't *ick around like that, they have to do it right the first hit, so they pay attention to diameter and pitch. Their knurls even come in DP sizes to fir common stock diameters.

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  • Paul Alciatore
    replied
    For a straight, Vee knurl, once it settles down to a single pattern (not double the rate on the tool) you can keep going deeper until you get sharp tops on the knurled pattern and it will not skip to another pattern. There is a bit of slip as each tooth of the knurl is formed and the 1X pattern is the one that dominates.

    Just go in hard and then continue to full depth. It works.



    Originally posted by J Tiers View Post
    Cramming works because there is usually a depth that actually works out, and knurling is not too dependent on the exact depth, although the pattern definition can vary. The folks who say they just cram it in are actually stopping when they find the right setting, they may just not realize it.

    That said, you are in fact correct, and knurls for screw machine work were sold according to (IIRC) diametric pitch or a similar measurement. There were methods to set up perfect knurling using them and the turned diameter. Screw machine folks want it to "just work" and work every time with no adjustment, just one setting and go.

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  • pinstripe
    replied
    Originally posted by Yondering View Post
    None of the experienced machinists who taught me recommended doing it like that; they all said to take a deep bite all at once
    I spoke with someone from Accu Trak when I was buying my knurling tool, and he said the most common problems they see can be solved by getting the tool in faster. This is from their web site

    Since proper tracking is usually established after only one complete revolution of the part, the secret to sucess is to RAM THE DIE INTO THE BLANK!! By forming a deeper, wider impression on the first revolution, the die teeth are more likely to step back into the initial grooves the second time around. Many tracking problems we solve are merely a matter of increasing the feed rate. For bump knurling from the cross-slide, the feed rate should be be fast enough so that the part is completed in 5-20 revolutions. Other solutions to tracking problems include: altering the blank diameter slightly, stoning or grinding the die O.D. approximately .002 smaller, honing the bores .002/.003 over nominal size.

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  • old mart
    replied
    I have done various diameters with straight knurls without problems, possibly just luck. Maybe the knurl, which is normally advanced slowly into the surface of the work just finds itself lining up each revolution.
    Only a test piece of the same diameter would prove whether you can achieve a straight knurl that long.
    Attached Files
    Last edited by old mart; 01-23-2020, 05:06 PM.

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  • BCRider
    replied
    Yondering, I might well be doing what JTiers described after reading his post again. I also don't think I wrote my last post very well either.

    I do drive it in fairly well right away. It's not a light "just striking" first go. But I found that if I REALLY drove it in that I'd push in more than just enough needed to get nicely folded in and swaged tight crests. And then the knurl's appearance suffers again due to the excessive pressure and no where for the metal to move to.

    So I tend to be just a touch light. A good bold pattern but a first go that might need just a few more thou to get clean folded in and swaged neatly crests instead of the slightly open not fully formed crests.

    But the odd time it's not enough and I get a doubled pattern regardless Or a doubled pattern on one wheel of the scissors diamond tool that I also use. And when that happens at that depth on the first dive in often it doesn't fix itself and there's nothing for it but to cut that portion down and try again.

    Bob, I've also gotten that kink you describe on longer straight knurling and even now and then on diamond knurling when I used the bump tool. It SEEMED like it was related to using too much pressure. As in more than needed to just close up and form clean crests. But I don't do many long straight knurls/coining runs generally. Mostly I do the coining on short smaller size press on knobs for cap head screws to make locking screws for things. But a couple of times when I needed multiples I did so straight coining runs of a couple of inches long and that is where the straight runs often show a bit of a kink in the pattern at one point. But it didn't matter since I was going to cut most of it away in the process of making short rimmed capped knobs. But on a part intended for a nice clean longer run it would not look nice at all.

    I've also noticed that my diamond knurling jobs seem to have a slight spiralling to the pattern. Is that what you describing?

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  • Bob La Londe
    replied
    I have done linear knurling with a bump knurl with good results, but sometimes on LONG pieces it gets a slight visible twist to it. Also depends I think on the weight and rigidity of your lathe. One trick to improve that is to make a fixed tool post to replace the compound for hard turning. On short pieces like knobs and handles, I've not noticed any visible twist affect. For my own tools I generally don't care. If it gives a good friction grip for the hand I could care less what it looks like.

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  • Yondering
    replied
    Originally posted by BCRider View Post
    I don't think we actually stop feeding in at the right point. At least I don't. I feed in until I get a complete shape with nicely defined top edge that is fully swaged closed.

    Mind you more than once I've gotten a double start and upon feeding in a bit more it switched to a single. But often times the forms look "blurred" for those cases. Like the knurls are not quite matching the patter but are being smeared or pulled to fit. And then the knurling does not come out all that well. So now I tend to start the feed, stop an check with a light "registering only" pattern. If I'm getting a double strike I'll push in slightly more and check again. If it doesn't switch by the time I'm in around .01 or so I stop and machine off the pattern and shave the stock down with a .003 to .004 cut and try again. That usually does the trick. But a few times the results have been a little rough when the knurl and part pitches didn't quite jive but were sort of "close enough".
    OK, you just described what J Tiers said. IMO that's a poor way to do it though, and maybe an artifact of trying to use a bump knurling tool. None of the experienced machinists who taught me recommended doing it like that; they all said to take a deep bite all at once.

    Using a proper scissor tool or even a bump tool on a very robust lathe, if you feed/clamp enough before turning the lathe on there's no need for a light trial spin or anything like that once you get a feel for how far the knurls need to bite. Taking a heavy bite all at once (not doing what Tiers said) gives a better knurl start to finish with no doubling or blurring of the pattern at the start.

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  • J Tiers
    replied
    "Joe Pie" on knurling.....

    https://www.youtube.com/watch?v=9Zwi0ZAUCUc
    Last edited by J Tiers; 01-23-2020, 05:30 PM.

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  • J Tiers
    replied
    You basically described the process of "stopping when it's right".....

    But, there are just two choices...

    1) The knurl works out perfectly around the FINAL average diameter.

    2) The knurl does not, but the wheel slides a bit on each "tooth" so it ends up being "basically the same result" as being even around the average FINAL diameter.

    If it did not END UP being even like "1", or "2", there would be half "teeth".

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  • BCRider
    replied
    I don't think we actually stop feeding in at the right point. At least I don't. I feed in until I get a complete shape with nicely defined top edge that is fully swaged closed.

    Mind you more than once I've gotten a double start and upon feeding in a bit more it switched to a single. But often times the forms look "blurred" for those cases. Like the knurls are not quite matching the patter but are being smeared or pulled to fit. And then the knurling does not come out all that well. So now I tend to start the feed, stop an check with a light "registering only" pattern. If I'm getting a double strike I'll push in slightly more and check again. If it doesn't switch by the time I'm in around .01 or so I stop and machine off the pattern and shave the stock down with a .003 to .004 cut and try again. That usually does the trick. But a few times the results have been a little rough when the knurl and part pitches didn't quite jive but were sort of "close enough".

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  • Speaker77
    replied
    Originally posted by Ian B View Post
    John Stevenson once posted a photo of a tapered workpiece that he'd successfully knurled; I thought this was pretty good proof that the diameter doesn't need to be calculated when knurling. I tend to use machine oil on the work & rollers, and like others say, mash the knurls into the work.

    Ian
    This isn't the tapered workpiece example, but another thread that John started on straight knurling

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  • Yondering
    replied
    Originally posted by J Tiers View Post
    The folks who say they just cram it in are actually stopping when they find the right setting, they may just not realize it.
    That is not an accurate statement.

    You're implying that to use this method, we keep pushing the knurl in until it tracks right; that is not what happens.

    When I do this, and I think most others too, I tighten my scissor knurling tool on the edge of the knurl area to what I think the work and tooling can handle prior to any revolutions of the part. Once it's tight, then I turn on the lathe and the knurl just tracks right. There is no "stopping when I find the right setting".

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  • Black Forest
    replied
    This afternoon I made a holder for one of the straight knurl wheels. I mounted the 35mm stock in the chuck and had at it. I crammed the wheel into the work at 200 rpm and gave it a .97 mm per rev feed. The knurl turned out perfect for the 25mm that I tested it. This roller will be for a bottom roller for my leather splitter that I will motorize.

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