Another new guy with threading issues, SB 9B - Page 2
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  1. #21
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    Quote Originally Posted by iwananew10K View Post
    His gearing is right for a 9" model B and as Ted noted anywhere the halfnuts close should be fine as its 8tpi.

    A good pic will clear things up I bet.
    and the thread seems to be changing after first pass.

  2. #22
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    Agree with all above that you can’t miss if the thread is a multiple of the lead screw…

    If for some reason you think the gearing is screwed just trace a shallow cut 6”+ on a piece of stock & pop a scale down, the line should track the 8ths perfectly.

    Good luck,
    Matt

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    Quote Originally Posted by Matt_Maguire View Post
    Agree with all above that you can’t miss if the thread is a multiple of the lead screw…

    If for some reason you think the gearing is screwed just trace a shallow cut 6”+ on a piece of stock & pop a scale down, the line should track the 8ths perfectly.

    Good luck,
    Matt
    Because 8 tpi will make perfect 1/8" apart lines on the part, then make 6 passes and see if it stays the same..then cut the thread and see if it changes... buy why does it change...

  4. #24
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    If the tool follows the thread perfectly on successive passes when the half nut is NOT being disengaged, then I can see the problem being ONLY one of two things.
    Either, there is a problem with the half nut engagement and they are not engaging on the lead screw the same each time, OR, the gearing is set wrong and the machine is not truly cutting 8tpi, but rather something very close to it.
    I can not imagine anything else being the cause of the problem in this case, unless I'm misunderstanding something.

    OP, you said this machine was a basket case, so perhaps you have some sort of non standard gearing????
    How many teeth on the spindle versus how many on the gear behind the stud gear? They should be the same, so the spindle rotates 1:1 with the stud gear. Stud gear and screw gear must be the same, with only an idler between them. If this is correct, then the problem must be in the half nut assembly.

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    What if your feed dials for cross or compound do not repeat the same when moved, something slips on the way to the lead screw..the half nut or the thread dial moves or does not engage the same every time, the spindle has end play, the part moves in the chuck, the tool bit moves a little left or right...
    if the thread does not track the same something is moving..
    Even with the wrong gear or the wrong thread it should not change IMHO.
    I could see a clutch slipping causing a feed problem but threading when you are supposed to be locked in solid to the feed/lead screw.

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    Quote Originally Posted by michiganbuck View Post
    What if your feed dials for cross or compound do not repeat the same when moved, something slips on the way to the lead screw..the half nut or the thread dial moves or does not engage the same every time, the spindle has end play, the part moves in the chuck, the tool bit moves a little left or right...
    if the thread does not track the same something is moving..
    Even with the wrong gear or the wrong thread it should not change IMHO.
    I could see a clutch slipping causing a feed problem but threading when you are supposed to be locked in solid to the feed/lead screw.
    Yeah, I agree, any of those issues could cause the problem, BUT, wouldn't any of those issues still exhibit themselves in the same way even if the half nut was left engaged and the spindle reversed?
    The OP states the his problem is ONLY happening when he releases and reengages the half nut.

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    Quote Originally Posted by Derek Smalls View Post
    Yeah, I agree, any of those issues could cause the problem, BUT, wouldn't any of those issues still exhibit themselves in the same way even if the half nut was left engaged and the spindle reversed?
    The OP states the his problem is ONLY happening when he releases and reengages the half nut.
    Agree if only then that is an area of most attention..for sure..

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    Thanks again guys. Hopefully I can get a few hours in the next couple of days to check the half nuts.

    Dave

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    Forget the half nuts, your problem is the gearing.

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    The 9" spindle is 24T and the inner reverser gear is also 24T so if he has 32T stud and leadsrew gears he has the 1:1 ratio for 8tpi.

    Unless there is a compounded idler in between,the gearing should be fine.

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    Quote Originally Posted by iwananew10K View Post
    Unless there is a compounded idler in between,the gearing should be fine.
    Exactly, but he won't tell us what he has for gearing between the two 32 tooth gears.

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    Quote Originally Posted by Ken-Bergen View Post
    Exactly, but he won't tell us what he has for gearing between the two 32 tooth gears.
    doesn't matter what it is.

    another possibility is the tool isn't held tight enough in the tool holder, but someone probably already mentioned that.

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    I would have hoped, after all these replies, that we could have been treated to some pics or a video from the OP

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    Nope, we just have to keep guessing.

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    Quote Originally Posted by iwananew10K View Post
    The 9" spindle is 24T and the inner reverser gear is also 24T so if he has 32T stud and leadsrew gears he has the 1:1 ratio for 8tpi.

    Unless there is a compounded idler in between,the gearing should be fine.
    Right, I certainly know that's what is "supposed" to be there, and is on every other 9 that I know of, but being that the OP says he built this lathe from a box of parts he bought, I'm thinking it should be confirmed. Although, I'm with you in that I can't imagine the machine going together any other way and working at all. Also, he hasn't mentioned if there IS any compound gearing between or not!

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    Here find the Army manual on the 9" if that might help..seem the Op said the thread path was changing..what might cause that.. again if that is the problem.. seems with eventhe wrong thread or gear the thread path should not change..

    http://www.wswells.com/data/9_workshop/CL670Z_army.pdf

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    Quote Originally Posted by michiganbuck View Post
    Here find the Army manual on the 9" if that might help..seem the Op said the thread path was changing..what might cause that.. again if that is the problem.. seems with eventhe wrong thread or gear the thread path should not change..

    http://www.wswells.com/data/9_workshop/CL670Z_army.pdf
    Right, thread path won't change, no matter what pitch you are ACTUALLY cutting IF you keep the half nut engaged and reverse spindle to return to beginning of thread. BUT, if you are cutting some odd ball pitch, let's say for instance instead of 8tpi, the machine is actually geared to cut 8-1/5 tpi, then, as soon as you release the half nut to return the tool to the beginning of the thread for the next pass, you will have a problem. When you re-engage the half nut, where you should for 8tpi(which is anywhere because the leadscrew is also 8tpi), the tool will NOT track right.
    In order to get it to get it to track right, you would need to figure out what position on the thread dial you can pick up the thread you are ACTUALLY cutting. If it's a real oddball thread, there may be only one spot in several rotations of the thread dial/spindle that you can pick it up correctly. Think metric threading! If you are cutting some crazy fractional thread, it is essentially the same thing.

    What a lot of people seem to be missing here is that the OP says that if he does not release the half nut at the end of the pass, but rather reverses the spindle, the thread tracks fine on the following passes. The problem ONLY happens when he releases the half nut and tries to pick up the thread on the next pass.
    That limits the cause of the problem greatly!

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    oh ..now I think I see what you are suggesting..dropping the half nut on a line, certain lines, would be hard to choose with not knowing the thread....what if dropping on exactly the same line.. should that make the thread path stay on track..but make the 8.5 TPI (wrong thread?)or what ever thread.

    8.5tpi would be .117/.118 and 8 tpi .125..perhaps the op could measure that..agree only .007 differance. but over a full inch would be easy to see. count 8 threads and measure there, 8tpi would measure one full inch and a 8.5tpi measure about .944 across 8 threads,
    Agree a thread pitch gauge good to have.

    Perhaps drop only on the same line ..then (next part) drop on 1 & 3.line if it proves to be a half thread.

  21. #39
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    Quote Originally Posted by michiganbuck View Post
    oh ..now I think I see what you are suggesting..dropping the half nut on a line, certain lines,would be hard to choose with an 8.5 thread....what if dropping on exactly the same line.. should that make the thread path stay on track..but make the 8.5 TPI (wrong thread?
    In the case of 8.5tpi, you would need to use every other numbered line, this is 2" of travel of the lead screw. For instance, you could use lines 1&3, or 2&4. But in this case, since we don't yet know what the machine is geared to cut, it's impossible to say. Same line won't necessarily work, may need multiple rotations of the thread dial to sync up, all depends on what the actual pitch is.


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