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Threading with out a shoulder
- Thread starter Cr23484
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- Apr 23, 2018
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Sure! You can turn the cutting tool upside down, run the lathe in reverse, and thread from Left to Right. This allows you to cut RH threads correctly without a shoulder, as in starting from the head down. If you search around, there are a lot of photos and descriptions for this process.
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If you mean to thread a rod as in the threaded section on a bolt, the answer is yes. It helps to have a groove at the end of the thread though. Threading involves multi[ple passes and it is difficult to stop cutting in exactly the same place in each pass. The issue is if ytou overshoot a previous pass, you will be making a deeper cut there is a possibility of breaking the threading tool or damaging the work. You could do so by making each successive pass shorter but this will result in an incomplete thread at the finish. With the groove at the end of the thread, you have a region where there will be no thread so the danger stated above won't exist. The groove depth can be to the root diaqmeter of the thread without compromising the strength.
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I would still start in a groove. The procedure typically involves setting the new cut depth before engaging the half nuts which will result in a groove anyway. The groove allows a little leeway om positioning the start of the cut. Additionally, if there is any backlash in the drive, that has to be removed before the thread starts.
Cutting threads from left to right also works well when you have a shoulder. One thing to be aware of if you have a threaded mount on your spindle is the possibility of unscrewing the chuck when operating the lathe in reverse.
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Easy, practice by puting a 3/4 rod in your lathe. measure an inch past the end and reduce the next inch to 5/8, a nice wide grove, leaving an inch at 3/4. Thread that inch , you'l have an inch to stop the lathe, back the tool out and rapid back to start.
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I think I understand where you're going with this, C.
The Emco Compact 5 does not have half nuts that disengage the leadscrew. You have to shut off the lathe as you approach the end of the thread and the lathe has to coast to a stop before running into the shoulder or crash, one of the two. You either have to have the timing of a God or be very lucky not to run into a shoulder OR you can rig a hand crank system. Sherline lathes use a hand driven crank to do this very thing because Sherline lathes don't have a half nut, either. Quite frankly, this is not a disadvantage because the Sherline lathe can cut class 3 threads all day long (the operator develops a very strong left arm, though).
If you want to turn threads on that lathe then my suggestion is to devise a way to drive the leadscrew by hand. You should still cut a thread relief (what the other guys are calling a groove) that is 0.003" - 0.005" deeper than the minimum diameter of the thread. This allows for a space to run the cutter into at the end of the thread and also allows for clean termination of the thread without adversely affecting the strength of the threaded section.
The Emco Compact 5 does not have half nuts that disengage the leadscrew. You have to shut off the lathe as you approach the end of the thread and the lathe has to coast to a stop before running into the shoulder or crash, one of the two. You either have to have the timing of a God or be very lucky not to run into a shoulder OR you can rig a hand crank system. Sherline lathes use a hand driven crank to do this very thing because Sherline lathes don't have a half nut, either. Quite frankly, this is not a disadvantage because the Sherline lathe can cut class 3 threads all day long (the operator develops a very strong left arm, though).
If you want to turn threads on that lathe then my suggestion is to devise a way to drive the leadscrew by hand. You should still cut a thread relief (what the other guys are calling a groove) that is 0.003" - 0.005" deeper than the minimum diameter of the thread. This allows for a space to run the cutter into at the end of the thread and also allows for clean termination of the thread without adversely affecting the strength of the threaded section.
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