Cutting Threads moving away from headstock , running lathe in reverse
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    Default Cutting Threads moving away from headstock , running lathe in reverse

    I am sure this issue has been discussed here, I can't find it. Looking to buy a 9" SB with threaded spindle nose.

    However, having learned the pleasure of running spindle in reverse and single point cutting threads with the carriage moving away from headstock,

    threading tool upside down, (which has potential of unscrewing chuck or Faceplate) I am wondering what results ppl here have had, with this procedure.

    I realize some may do this with a collet held center/faceplate arrangement. It seems to me if the typical screw-on chuck is put on fairly tight

    and esp if the tailstock back things up......it probably could proceed with little trouble?

    TIA for any replies or links to previous discussion of this procedure.

    David Lawrence

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    I don't know for sure. I have gotten away with with sketchy set-ups with no problem but, I try to not make a habit of it. My favorite way of cutting left hand threads is to run the spindle in reverse and the cutter upside down, so I have the toolpost on the right side and run the carriage towards the chuck. I have never done this on a threaded nose.

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    Well David, I suspect you could consider the imagined force of the cut as if you were trying to use that tool to tighten the chuck on. It is a scary endeavor, to have the option for all hell to break loose, but I would say as long as you are only shaving off 5 or 10 per pass, consider the force the tool is putting on the cut. Probably not more force than you used to put the chuck on, for sure. The tailstock with a live center would be decent "insurance", a dead center would add to the scary factor.

    I use this same mentality when doing lackluster work holding in milling setups as well. "Could a 1/4 inch mill move that part before snapping? probably not..."

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    I'd be a lot less worried about unscrewing the chuck than I would about having the cutting forces lift up on the carriage since there is no mechanism to keep the front of the carriage down on the ways. Cutting in the normal orientation, the cutting forces push the carriage down and keep it in contact with the bed.

    All of my lathes have threaded spindles and I have never had a chuck unscrew. But then, I've only been running South Bend lathes for 65 years or so.

    Clean threads and a nice positive "clunk" when the chuck bottoms out seems to keep things in order.

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    A simple approach - requiring extra work - just cut a LARGER and COARSER right hand thread (chuck running forward) prior - then you know the chuck is on there tighter than needed to "unscrew" doing LESS WORK to cut a SMALLER and LESS COARSE thread running in reverse (assuming no difficulties like running threading tool into a shoulder )

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    Quote Originally Posted by carlherrnstein View Post
    I don't know for sure. I have gotten away with with sketchy set-ups with no problem but, I try to not make a habit of it. My favorite way of cutting left hand threads is to run the spindle in reverse and the cutter upside down, so I have the toolpost on the right side and run the carriage towards the chuck. I have never done this on a threaded nose.
    With a screw on chuck, it's simply bad practice and unsafe. A big question is, can you even get your tool around to the back? Also, if you get your chuck on "tight enough" to do the threading, you might not ever get it off again. Sometimes threaded chucks have been on so tight as to have to be dismantled in-situ and the backplate turned off the spindle.

    Also, the setup you have described would cut a RIGHT-HAND thread, not a LEFT-HAND. For a LEFT-HAND thread, the spindle direction would be normal (FORWARD).

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    Quote Originally Posted by SLK001 View Post
    With a screw on chuck, it's simply bad practice and unsafe. A big question is, can you even get your tool around to the back? Also, if you get your chuck on "tight enough" to do the threading, you might not ever get it off again. Sometimes threaded chucks have been on so tight as to have to be dismantled in-situ and the backplate turned off the spindle.

    Also, the setup you have described would cut a RIGHT-HAND thread, not a LEFT-HAND. For a LEFT-HAND thread, the spindle direction would be normal (FORWARD).
    OP didn't say anything about the tool being in back, or cutting a LH thread...

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    I find threading outward easier on my nerves, for one thing. We occasional do milling using threaded faceplates. This was always my biggest concern, was having the milling force unscrew the fixture. I run a center bolt through the fixture and spindle to lock it down. This way it can't unscrew.

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    Would you mind expanding on your setup or posting a picture? Is the through bolt machine with 60 deg center to hold and drive the work piece?
    thanks

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    Quote Originally Posted by Charlesc View Post
    Would you mind expanding on your setup or posting a picture? Is the through bolt machine with 60 deg center to hold and drive the work piece?
    thanks
    without seeing your setup it's hard to say what would be practical, but anything to tie the chuck to the spindle. I have a thru hole in the faceplate and run a long piece of allthread through it and the spindle. Make a plug with a through hole on the back of the spindle, then just tighten it down with a nut on each end.

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    [QUOTE=lalatheman;3511136]
    ... pleasure of running spindle in reverse and single point cutting threads with the carriage moving away from headstock,
    threading tool upside down, (which has potential of unscrewing chuck or Faceplate) I am wondering what results ppl here have had, with this procedure.

    Stop for a moment. How much single point threading do you really do?

    1) dies
    2) parts held in collets
    3) it's not that tough to thread towards the headstock, I do it often.
    a) dial gage on the bed to tell me when to unlatch the halfnuts
    b) a groove for the threading tool to enter at the inboard side of the cut.
    4) yes I have done the operations you suggest above with a threaded spindle.
    a) the chuck has not unscrewed.
    b) on a small lathe like a 9" SB, you will be taking a tiny bit of a cut at all times.
    5) some have been known to put a setscrew or other locking device on a threaded chuck.
    a) I've never found that to be needed.

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    wasa gonna say.... if I was doing the job and the part could fit in a collet, then I would use a collet.

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    SB 13 inch. Standard dog plate and face plate. When they are threaded on they are about flush. A through rod would hold them on but not sure how the work place is held to the plate. Is the through bolt machined to a 60 deg point? It would have to be machined each time it was used unless I'm missing something here.

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    Many do back-side threading toward the tail. I don't do so because I think that tends to lift the saddle/carriage rather than push it down. Pull-out is likely the reason many like to thread toward the tail. I agree it could off-spin the chuck if the chuck was not tight but not very likely if the chuck is tight...big dangerous surprise with spinning off...
    I have never had any problem threading and consider it as easy as normal turning.
    My trick is to put a tab of tape on a chuck jaw and and nearing and passing my last thread (so one part turn away) I look up at the tape coming up to perhaps 12:00 and pull out..That allows pull-out right on the spot.
    Pull with the compound at 29-30* pulls the bit away from the chuck so that is another reason for 29-30*.

    Pull out with the cross is fine if not running into ma shoulder stop.

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    Quote Originally Posted by michiganbuck View Post
    My trick is to put a tab of tape on a chuck jaw and and nearing and passing my last thread (so one part turn away) I look up at the tape coming up to perhaps 12:00 and pull out..That allows pull-out right on the spot.
    Confession time: I really cheat when single pointing.

    1) I use the dial indicator on the bed, set to go just one revolution and hit zero when I want the thread to end.

    2) I don't pull the tool back when I hit the zero, I just unlatch the half nuts. This means the end of the thread is
    a groove around the part.

    3) after the part is just about done, I use a cut-off tool with the end ground to a radius, to make the V groove
    at the end of the thread, a nicely radiussed groove. Stress relief and all.

    Only real trick here is when the part is being threaded up to an inboard shoulder - the advancing compound will bring
    the threading tool *closer* to the shoulder as the threads come to size. This requires a bit of compensation in the
    planning.

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    Way to go jim A++

    Chet

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    You did not say what size thread you are cutting. Unless you are cutting a large dia. coarse thread with heavy curls coming from the tool, I would not be the least bit concerned. Also at low RPM's there is little to no problem with starting inertia wanting to break the chuck loose. My concern is more with engaging the half nut. Either you have a small undercut and start with the half nut already engaged, or a longer one to give you enough time to engage it while the spindle is already running.

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    The last trick I forgot to mention, is where possible, leave a sacrificial section outboard of the threaded area, turned
    down to the *minor* diameter of the thread form, or as near as you can guess it. This way you know when you are
    getting close for testing for fit-up. Once the part's done, that bit gets cut off.

    My biggest error is always making the major diameter too large, and forming sharp-V threads. That alone will
    keep the gage piece from threading on.

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    When I cut rifle barrel tenons and thread, I cut the major diameter at .995 x
    the nominal diameter. A 1.0625" is cut to 1.058" thus giving me the proper clearance and flat tops.

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    I think every lathe newbe or person having trouble turning threads should pick up a slug of mild steel ¾” x 4” or better and practice threading and measuring threads, cut a thread of the slug diameter and then the next size smaller. Practice to-an-under-cut/ to- a-shoulder /back-side to-the-tail / a-left -hand -thread / with an insert/ with a HSS bit and anything/everything one can think of.. Even make up a thread like a 5/8- 10 and figure out the specs for an odd thread. Having both ends such a practice slug would have a person at near master by the time that slug was down to 1/8 inch. Seems a lot of new guys try the new thing on a needed part they might fail on.
    Yes for $5 or so one should buy How to Run a Lathe,
    And this book would give some knowledge about cutting tools shapes and how thy work.
    SOUTH BEND How To Grind Lathe Tool Cutter Bits Manual: Misc.: Amazon.com: Books

    steel slug
    4140 Steel Round Bar Stock - 1-1/4" Diameter x 12" Length | eBay

    Might also put centers in the slug and practice turning a part between centers.
    Last edited by michiganbuck; 03-22-2020 at 11:18 AM.

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