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Threading......Again

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  • Paul Alciatore
    replied
    Dead sharp tool. At or just a mite below center. Good steel. Good cutting fluid or just plain motor oil would work. Start out with fairly light cuts, perhaps only 0.005" to 0.010" deep per pass. Start off as slow as the lathe will go - well, at least 25 or 50 RPM.

    You should make a nice chip. If not, something's wrong. After you can cut at this crawl, then go for slightly faster speeds and perhaps deeper cuts.

    Some steels (perhaps other metals also) will have a raised edge. After cutting the thread to the proper depth, a finishing cut may be needed on the OD to bring it to size. Don't try to cut deeper with the threading tool as this will make a very loose fit on the nut. You can do this manually with a broad faced tool to span several threads. I say manually because you should not disturbe the threading set-up until you have a proper fit on the nut as you may have to do a final pass or two with the threading tool after cleaning up the OD. A quick change tool holder that provides positive repositioning of the tools when swapped is a must here.

    Paul A.

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  • topct
    replied
    Our old friend Thrud knows about this I bet.

    ------------------
    Gene

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  • jimmstruk
    replied
    i had same problem. trouble was using cold rolled jim

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  • SGW
    replied
    Drill rod can be uncooperative, but the 6061 ought to thread reasonably well.

    The compound ought to be angled this way \ relative to the work, not / that way. I assume you have that correct, but if you don't it would likely cause all kinds of trouble.

    Do you get a chip coming off the tool?

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  • Al Messer
    replied
    What spindle speed are you using and are you using direct drive or back gear? I have found that small stuff like 1/4" dia. likes a fairly fast cut to cut clean and as has already been mentioned, use plenty of cutting oil. I like dark Sulphurized pipe threading oil myself. It may not be kosher, but I try to rough in the threads with the lathe tool and finish them off with a good quality die.

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  • Your Old Dog
    replied
    I had trouble on my SB9 because someone had the spare gear (48tooth stud gear) was interchanged with the screw gear. It's supposed to be stored there but if you switch them out left for right then all is messed up. It cuts threads but not any that will match the rest of the world !

    Discovered the problem while on the throne with a fresh copy of "How to run a lathe". It was a very productive morning!

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  • Guest's Avatar
    Guest replied
    hit it with a file is what I do, dont fear making the od a little small <.248- .246 is great. for 1/4" 20 tpi.

    is the tool sharp? touch it up with a hand held diamond hone and oil the part big time.

    we all make some rough threads at first, after you get the tool grinding down and get faster they start looking and working great.

    threading is one thing that makes for a good machinist, you want to get good at it.

    best of luck

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  • PaulG
    replied
    Thanks for the replies.

    I tried a 1/4 6061 rod and a 1/4 drill rod.

    I'll go back and check the center line of the tip but I had checked it before I started and it was dead on. I am using a new 60 pre-ground HHS bit.

    My goofus lathe of course has the compound marked with 0 as parallel to the bed so it would need to be turned 60 from that position. But of course it's only marked to 40 degrees. So I had to use a protractor set to 30 and measure that from perpendicular to the bed. I suppose it could be a little off.

    The diameter of the threads after advancing the compound .035 is about .285. Measuring a 1/4-20 bolt across the threads, it's just under (.246) 1/4. I guess it's not cutting much just displacing the metal.

    I'll try just cutting at 90 tomorrow and see if there is any difference.

    For some reason I thought this might be easier. I'll get it figured out.


    [This message has been edited by PaulG (edited 06-28-2005).]

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  • Carl
    replied
    The compound must be 30(or 29.5) degrees from perpendicular NOT parallel to the turning axis of the lathe. Some lathes, including mine, read 60 degrees when set properly.

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  • J Tiers
    replied
    What rkepler said,

    plus, if that is hardware store rod, it is generally made apparently of annealed silly putty, and will throw up a huge burr anyhow.

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  • rkepler
    replied
    Are you sure that the cutting edge is on or below center? What you're seeing can happen if the edge is above the center, it'll sort of mash things around forming something that looks a bit like a thread. It's also possible that you're using a left hand tool for aright hand thread, or the leading edge is simply gone. Check those things.

    You should be seeing swarf coming off the edge of the tool, the first few passes will look more like a wire, later passes will look more like a real chip is being formed.

    [This message has been edited by rkepler (edited 06-27-2005).]

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  • mochinist
    replied
    <font face="Verdana, Arial" size="2">Originally posted by PaulG:
    I know this topic has been repeated many times, but I am just getting around to figuring out how to thread on the lathe.

    I must be doing something wrong but I can't figure out what. When I cut threads the diameter gets mush larger and the thread form doesn't look symmetrical.

    Just tried to thread a 1/4-20 rod and after I am done the threads are .285. So of course it's too large for a nut to fit. Also the threads don't look right. Compound set at 30, the tool square with the work, feeding in with the compound. The pitch gauge matches the threads.

    My guess is that whatever I am doing wrong is causing both the threads to look asymmetrical and the diameter to get larger.

    Any ideas on what to try next?
    Maybe a tap! ;-0
    </font>
    I would offer to help you out, but your post confused me. I don't know how you ended up with a bigger diameter than what you started with. My suggestion is to get a detailed book on the subject or maybe take some pictures of what you are doing so we can better understand what you are doing wrong. Also try using the search button, I am sure this has been went over in detail by someone like forest in the past, and he seems to be a pretty good teacher and can explain how to do it better than I can.

    Leave a comment:


  • PaulG
    started a topic Threading......Again

    Threading......Again

    I know this topic has been repeated many times, but I am just getting around to figuring out how to thread on the lathe.

    I must be doing something wrong but I can't figure out what. When I cut threads the diameter gets mush larger and the thread form doesn't look symmetrical.

    Just tried to thread a 1/4-20 rod and after I am done the threads are .285. So of course it's too large for a nut to fit. Also the threads don't look right. Compound set at 30, the tool square with the work, feeding in with the compound. The pitch gauge matches the threads.

    My guess is that whatever I am doing wrong is causing both the threads to look asymmetrical and the diameter to get larger.

    Any ideas on what to try next?
    Maybe a tap! ;-0
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