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17th September 2014, 07:30 PM #1
Hercus 260 Metric - Help with Single Point Threading
Guys,
Need some help!
I went to cut an M12 thread today - first time... But despite having a rough idea of what I was supposed to be doing the pitch just didn't seem right and Im not sure it was picking up the thread in the right place on subsequent cuts every time...
Textbook of turning says that the thread chase indicator should be set on the smallest sprocket and chase a 1.75mm pitch on number 5's.
Gearbox is set to 5B (1.75mm pitch as per the plate on the gearbox), but what is confusing me is that the same plate also says that the stud gear should be 45. The picture identifying the stud gear in the textbook of turning is the little gear that is on the tumbler gears but this doesn't come off. I have a 45 tooth gear that is currently acting as a space on the end of the gearbox shaft, its a 50 tooth thats being driven by the 80 tooth idler gear.
Should the 50 be replaced by the 45 (i.e. make the 50 the spacer and drive the 45 with the 80 tooth idler?).
Any pointers?
Thx
J
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17th September 2014, 08:47 PM #2Senior Member
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threading
From what you have written, you have the thread chaser set on the wrong gear. It should be on the bottom or largest gear. The stud gear should be 45 and the 18 that would normally be there goes as a spacer on the outside of the screw gear.
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19th September 2014, 09:32 PM #3
Mal,
Thanks I'll change over the thread chaser.
Thanks for the gears picture on the other thread:
260ATM_STANDARD_GEARS-500x500.jpg
This confirms my suspicion that the 45 and 18 gears are the wrong way round on my lathe.
The stud gear didn't want to fall off the keyway when I un-did the nut (unlike the 45 and 60 on the end of the gearbox shaft) - I presume I can persuade it with a gentle pry-bar / screwdriver behind the stud gear? Or, is it held in place by more than just the nut on the end of the shaft?
Thx
J
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19th September 2014, 11:48 PM #4Senior Member
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stud gear
Hi Jon,
The stud gear should come off fairly easily, although it may bind on the key if the fit is particularly tight, the nut is the only thing holding it on. The only gear that is pressed on is the transfer gear (which just transfer a 1:1 ratio of the headstock speed to the stud gear), behind it on the same shaft, which is never removed. Be careful not to damage the teeth of the stud gear, small marks in the gears make a hell of a noise at speed.
If your machine has a reversing motor, the thread chaser is not really required, just leave the half nuts engaged through the entire threading sequence and reverse the motor after stopping and withdrawing the threading tool, reverse back past your starting point, far enough to remove any backlash, reset your new tool depth and put the motor into forward again. It doesn't really matter which of the two methods you use both will do the job, in fact try both it's good practice.
Turning your first perfect thread is very satisfying but now I personally do most of my threads with coventry die heads on a stripped down 260dgm, permanently set up with a bed mounted 6 station turret, which is very quick for the production runs I need to do, it would drive me crazy to have to single point everything. It helps if you have lots of toys to play with.
happy threading
Mal
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