methods of single point threading ?

B

Bob Kelly III

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A friend of mine mentioned something and a light bulb went off in the back of my head.....
could I........ try normal single point threading except keep the half nut locked onto the feed rod.....
stop the lathe, flip the forward reverse lever and back out the cutting tool turn the lathe on and back up the cutter, turn the lathe off, flip the forward reverse lever again and set the cutter properly then turn the lathe back on.....
My friend said that doesn't work for him as it looses Sync ...... Personally I don't see how it can, as both idler gears are the same,.... but when moving that lever they don't always mesh up good... and that might be why.....
has anyone ever tried that method ? does it work ? or avoid it with prejustice !
.....
I think reversing the motor sounds alot more Sure ...... still need that 3 pole switch though !
.....
later !
Bob......
 
That's the way I cut metric threads on my lathe. It works,but for standard threading its easier to use the threading dial to engage the half nuts at the proper time. No threading dial your stuck leaving the half nuts engaged and reversing the lathe.
 
COOL...another possibility then !!!!!
by the way I found the fishtail gauge with 60 deg V on it for something like $1.79 on banggood.com under tools/lathe tools.
thanks for the responce guys !
Bob.
 
I've split a thread once in my machining "career" by doing just that. Once the feed reverse lever is engaged, it sync's the spindle with the quick change gear box. If you disengage the feed reverse lever, you potentially lose the sync if the spindle is turned relative to the quadrant gears. I recall rotating the spindle for some reason by hand after disengaging the feed reverse lever, which if not returned to the exact position, guarantees a split thread. If nothing moves, you'll be OK, but . . .

I routinely engage the feed reverse lever and half-nuts and leave the half-nuts engaged. Stop the lathe when it's close to the end of the thread, jog or hand turn the chuck to the end of the thread, back out the cross slide and reverse the lathe back to the starting point. I find this to be quicker than disengaging the half-nut, returning to the starting point and then wait for the thread dial number to come around again after restarting the lathe. If I disengage the half-nuts, I typically crank the carriage back past the start point and keep going until the thread dial number come up again, engage the half-nuts, advance the cross slide and compound for the next cut, then start the lathe for the next pass.

Bruce
 
Hey Bob,

As stated above that is done everyday.

However, just remember that you already posted in another thread that
i) you have a screw-on chuck, and
ii) that it comes free easily....

Those two things could mean that your chuck tries to run across the floor if/when you reverse the lathe!

Be careful out there!

-brino
 
Threading with leaving the half nuts engaged works fine, but you still have to move the tool out of the cut after each pass, because otherwise it can dull the tool from going in reverse over the work, and it can also jam the tool and break something, because there is backlash in the gearing and lead screw and half nuts, so the tool will be pulling on one side of the thread when reversing. Back the tool out for each pass, just like you would when using the half nuts.
 
Bob Kelly III said:
A friend of mine mentioned something and a light bulb went off in the back of my head.....
could I........ try normal single point threading except keep the half nut locked onto the feed rod.....
stop the lathe, flip the forward reverse lever and back out the cutting tool turn the lathe on and back up the cutter, turn the lathe off, flip the forward reverse lever again and set the cutter properly then turn the lathe back on.....
My friend said that doesn't work for him as it looses Sync ...... Personally I don't see how it can, as both idler gears are the same,.... but when moving that lever they don't always mesh up good... and that might be why.....
has anyone ever tried that method ? does it work ? or avoid it with prejustice !
.....
I think reversing the motor sounds alot more Sure ...... still need that 3 pole switch though !
.....
later !
Bob......
Click to expand...
Do not flip the forward/reverse lever. You will lose sync. To reverse the carriage it has to be done by reversing the spindle. In your case, it would be winding back by hand since you don't have forward/reverse on your motor.
 
Humm quite a divided pack of answers here ....most for but some against !
it must depend on the lathe....
I guess there is no harm in trying ...I'll give it a shot and see what happens just for the learning experience !
i'll use some PVC nice and soft ! LOL I will let ya know what happens.
....
.....thank you very much for the responses !
Bob.....
 
Bob Kelly III said:
A friend of mine mentioned something and a light bulb went off in the back of my head.....
could I........ try normal single point threading except keep the half nut locked onto the feed rod.....
stop the lathe, flip the forward reverse lever and back out the cutting tool turn the lathe on and back up the cutter, turn the lathe off, flip the forward reverse lever again and set the cutter properly then turn the lathe back on.....
My friend said that doesn't work for him as it looses Sync ...... Personally I don't see how it can, as both idler gears are the same,.... but when moving that lever they don't always mesh up good... and that might be why.....
has anyone ever tried that method ? does it work ? or avoid it with prejustice !
.....
I think reversing the motor sounds alot more Sure ...... still need that 3 pole switch though !
.....
later !
Bob......
Click to expand...
with a flip up toolbar you can thread close to the shoulder also: https://www.model-engineer.co.uk/forums/postings.asp?th=52176&p=2.
 
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