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Thread: Threading in reverse?

  1. #1
    Join Date
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    Post Threading in reverse?

    In james a Harvey's book machine shop trade secrets page 182 fig 8-6 he speaks of using a single pointed threading cutter inverted so that it is upside down and runs the lathe in reverse and cuts from the headstock toward the tailstock can anyone enlighten me on the procedure and it's benefits I understand one is removing the problem of stopping the machine accurately before you reach the undercut or non threaded portion at normally the end of a cut are there any other benefits?and is this normal practice seems like a good idea if it works Alistair
    Please excuse my typing as I have a form of parkinsons disease

  2. #2
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    A couple of advantadges I can think of. One, the chips will fall off the tool easier. Its nice to have gravity on your side. Two, the stress on the machine is similiar to using an upside down cutoff tool mounted on the back side of cross slide. Three, as you mentioned the ability to keep from crashing onto a rear shoulder. But where this really shines is on internal threading where you cut on the back side of the bore from the inside out
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  3. #3
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    Alistar;

    I've never tried the procedure but I have heard of it numerous times so, it must work.

    I would think the same rules would apply i.e. Use a threading gauge to set the tool bit parrell, the top, now bottom of the tool bit, must be on center and the compound would need to be set at the proper number of degrees pointing from left to right so the compound feed would be into the cut.

    Heck just try it on a sample part. You'll soon find out if it works.

    Good luck!

  4. #4
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    Of course, one must be careful not to unscrew the chuck on some lathes, like mine.
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  5. #5
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    If anyone will post the description, I'd be interested. I understand the basics, but would like to know how it works with regard to threading to a shoulder, i.e. how do you position the tool at the start of the cut for both internal and external threading? Do you cut a runoff groove the depth of the thread, and then move the tool back into this groove and dial to depth before starting the next cut? Also, which edge of the tool should do the cut -- leading or trailing?
    Lynn S.

  6. #6
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    <font face="Verdana, Arial" size="2">Originally posted by Evan:
    Of course, one must be careful not to unscrew the chuck on some lathes, like mine.</font>
    Yup. That was one of my "Learning Experiences".

    Has anyone devised an easy way to "lock" something (like a 4-jaw or a 5C collet chuck) to the spindle of an SB9 to prevent this? (other than over-tightening the chuck?)

    I've threaded to a shoulder by running the tool upside-down and the lathe in reverse, and it works great otherwise. Oh, well the very first threads I cut were inadvertently left-hand thread, but that's another story.

    Science. If you don't understand it, don't talk to me about how it's going to end the world.

  7. #7
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    Reverse threading?

    I could understand if you are cutting up to a shoulder. But starting from a relief cut seems pointless. I can stop whitout any problems.

    Please explain to me how you are going to engage the tool bit and the halfnut in a spinning piece of stock and start at the same thread begining?

    Maybe I am just a little slow.
    Rustystud

  8. #8
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    Reverse threading? That's not how I understood it. I have an SB9. Threading up to a shoulder is a little scary for me, since I don't want the thread cutting tool to crash into the shoulder.

    Well, if you can turn the tool upside down and run the lathe in reverse, you thread away from the shoulder and still get right hand threads. Get it? Or am I missing something here?

    So I'll run the machine forward, with the feed engaged and the tool backed out of the cut, until I reach the start of the thread (and before I crash the shoulder). Stop the machine, engage the cutter into the thread. Run the lathe in reverse until the other end of the thread is reached. Stop the machine and back the cutter away from the cut again. Without a threading dial, don't disengage the halfnuts, just run the machine forward and stop before you reach the shoulder again. By hand, turn the lathe until the cutter is at the thread's start. Crank the cutter to the cut and repeat.

    Apologies if I'm misunderstanding the question or telling you what you already know.

    Edit: fix stupid spelling errors


    [This message has been edited by Wirecutter (edited 02-23-2006).]
    Science. If you don't understand it, don't talk to me about how it's going to end the world.

  9. #9
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    Well, sometime back, I started doing all my internal threading in blind holes by this method. I have never tried it for external threading against a shoulder but see no reason why it won't work well. The "tailstock" side of the tool does the cutting and is "backed" into the cut at the start of each cut. I set the tool by "ear"--run it into the hole by hand until it barely touches the bottom of the blind hole, run the Crossfeed back to "Zero", back the compound screw into the cut and engage the half nuts when the right marks match on the threading dial.

  10. #10
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    Alister
    Maby this will help.
    http://img.photobucket.com/albums/v6...ion-thdg-1.jpg

    Ivy McNeil
    I haven\'t failed I just found 10,000 ways that wont work

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