Trying to make sense of the threading charts

5/16-18 V M8-1.25 is a good example of where confusion can occur. I suggest that you use a glass (magnifier) for examining Imperial or Metric threads. Mx-1.25 from 25.4 V 20 from 25 is so close that a slight light leak on the guage is the only givaway.
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Those numbers sure are super close, Bill - I'm learning some painful lessons here but with the help here I think I'm starting to dig myself out (at least I keep telling myself that).
 
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Success - I took a 1/2 rod, drilled and tapped an M8 1.25 thread to match the shaft's crooked threaded end. I threaded on the rod and mounted the shaft in the lathe. Used a dial indicator to find the high spot and used the rod as a lever to gently bend it down until it was close to 0. Checked it all around - it's good now. Made quick work of it. Whew.

So now I feel like I've climbed out of the 9th circle of Hell up to at least lever 6... we're goin' up. I can now assemble the gears and start cutting test patterns again, start matching them with the thread gauge, etc.
 
"And remembering 50 years back on a ship in the South Pacific that was a thousand miles from spare parts."

From another post, it is the whole point to any craft that is hobby status. The day I don't learn something is the day I will dig a hole in the back yard and crawl in. That is what seperates us from monkeys, for lack of a better term. Making do with what we have. . . And just think, once you have threading down, making a couple of spares for when it happen next time.
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I put the machine's gears back together, with the proper configuration for the Imperial thread cutting, according to the chart:
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I inserted a think plastic label about the thickness of a dollar bill in between the gears to give them some slack. I put the belt back on the lowest speed and carefully turned the machine back on after that. I noticed that the clutch gets activated and starts clicking.

When I start the machine with the belt tension removed and slowly engage the belt, there is no clicking initially, but if I should apply a bit of load on the spinning chuck, then the clutch will start clicking. Not sure if that's normal or if it indicates that something is a bit too tight now.
 
There is an overload clutch on the drive side between the motor and the spindle. Mine got loose, I think the spring went soft but so long ago that I don't remember. That is where the 'clicking' is coming from. It may be something too tight or may be the spring too soft. This is where your judgement comes into play. Rotate the spindle by hand and 'feel' for a tight spot.

There is an interlock between the power feed and threading feed.(half nuts) That's not a distinct likelyhood, just a possibility. On a new (to you) machine, the 'feel' of the spindle and gearing will be 'iffy'. Being able to bring the gear train in or out by sections will be an assist here.

Trying things first with the gear train out will point to the area where the tight spot is. Then uncouple the quick change box by letting the selector hang loose. Take things in sequence to get a feel for the machine.

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I played with the gears some more trying to isolate the tightness. I disconnected the 127 tooth gear from the stud gear and the problem still remains, so it's nothing to do with the threading parts. Maybe that spring is soft - I don't know, but I'm suspecting it now. That whole power pulley is wobbly... there is a lot of play on that shaft me thinks.

I'll have to look at the diagram to see what all is in there and how to get to the spring. Gonna tread lightly - don't wanna create any more problems than I already have.

The work around is to start the machine with the belt disengaged and then engage it slowly - works every time.
 
Started making my first cuts in mild steel (12L14 cold): 18tpi, speed 130 - the machine runs ok - have to take small cuts: .005 to .003 - just taking my time and trying to get the hand coordination figured out. I keep the half nuts locked all the time, and run the machine FWD and REV each time. Starting to get a hang of it, though I still make mistakes frequently.

I get quite a bit of chatter, though even at the lowest speed - maybe because I'm feeding straight in, not at an angle. Maybe that's the next adjustment I can make to see if it helps reduce the chatter.
 

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While not an absolute necessity, many people feed the cutter straight in, most use a 30 (+/-) degree feed to keep the working face of the cutter working on one side. There are several considerations for threading, not the least being to never stop rotation with the cutter engaged. Usually a groove cut at the nominal depth of the threads as a place to allow the spindle to "run down" after the pass. This is particularly important if you use carbide tooling, the tip breaks easily.

Keep in mind, for my purposes, the depth of cut is 0.002-0.005 thou. More might be appropriate for larger threads, I cut small screws. 1/4-20 to me is large. I do cut larger threads, but it's rare. Much of my work is in the range of 2-56. A final finish pass to clean things up when you have the proper size. A good learning tool is to cut to a nut or a die to get a feel for the last couple of passes.

There are many people more appropriate than me to answer questions on threading. It is a subject as complex as the lathe itself. One thing I have found, again my personal perspective, is that 130 RPM is the high end of speed for threading. That's why I built a 3:1 reduction gear long years ago. Larger machines have a system of back gears to this end, the smaller machines have other methods for keeping speeds down. A very common version from years back was to use the hand rotation. The ultimate to me was a small steering wheel bolted to the spindle pulley. That allowed threading even medium hard steel at a controlled pace. My recommendation for hand rotation was for more than plastics. I became part of that discussion around the time I built the reduction gear so I never pursued the idea.

Once you have the machine working to (more or less) your satisfaction, it would probably generate more responses by starting another thread asking for input on threading. There are many different subjects about a lathe, literally the "queen of the shop". A good starting point for the novice is at
. Quinn has many videos on the various shop subjects. She starts here, with links to further expand your knowledge. I follow (loosly) her web site still. There are many details where I feel a need for other approaches than my own.

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Bi11Hudson said:
One thing I have found, again my personal perspective, is that 130 RPM is the high end of speed for threading. That's why I built a 3:1 reduction gear long years ago.
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Bill - sounds like a nice solution for our lathes - can you share design drawing or at least a photo of what one looks like?
 
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