Threading dial missing timing mark

[zippyslug31]

I have a PM-1130v (probably not strictly relevant) and have been reading up on single point threading. In various videos on the subject, and in PM's manual (see red circle in image), they all show the threading dial with a reference mark to know when the hell to engage the half nut.

My lathe doesn't have any such markings on the housing of the dial. I've always assumed it was a manufacturing defect and it seems easy enough to add a pointer, but is there anything special I need to know first?

My plan is manually turn the chuck to orient the "1" on the dial into the 6 o'clock position and engage the half nut... wherever the nut actually engages should tell me where I need to place my timing mark. Is my thinking correct?

Again, I've never done any SPTing so I'm working in reverse to understand what I need to do with the lathe.

TIA

 

[Ulma Doctor]

The pointer position is not critical, it works the same wherever it is clocked

 

[zippyslug31]

The pointer position is not critical, it works the same wherever it is clocked

Not critical even if I was cutting threads for an odd TPI? So your saying it's only relative to itself and if I hit the mark, wherever it's physically located, is all good?
I had wondered this; good to know that I really can't screw it up if I end up placing the mark "off" by a little bit from bottom/top/wherever.
I'll probably just make an arrow out of colored tape to start with in case I need to move it later for whatever reason.

 

[Ulma Doctor]

Not critical even if I was cutting threads for an odd TPI? So your saying it's only relative to itself and if I hit the mark, wherever it's physically located, is all good?
I had wondered this; good to know that I really can't screw it up if I end up placing the mark "off" by a little bit from bottom/top/wherever.
I'll probably just make an arrow out of colored tape to start with in case I need to move it later for whatever reason.

Yes sir!
Even, odd, multi start threads, it makes no difference.
As long as the same spot is chosen, you’ll be fine.

Metric threads have no correlation to an imperial leadscrew, so the only way i’m aware to cut metric threads is to leave the half nuts engaged during the entire process, using the lathes’ motor to reverse direction at the end of each cut.

 

[Technical Ted]

Everything Ulma Doctor has said is spot on. If you want to "shift" (slightly change the the location of where the line is when the half nuts are closed) you can either a) add a spacer of the desired thickness between the apron and the threading dial to shift in one direction or b) remove a slight amount off between one of the two surfaces to shift the line in the opposite direction. Moving the dial closer or farther away from the apron will shift the rotation of the lines so you can get them to line up at the desired spot.

Or, if your marking plate is not keyed, you can loosen up the dial plate and simply rotate it to the desired location when the half nuts are engaged. Either way, make sure you hold a little pressure on the apron to remove any backlash.

Ted

 

[LVLAaron]

You should be able to take it apart and get it aligned. I took mine apart (1440) to get some chips out of it and found you need to manually adjust the line location like Ted said. 5 minute project once you take it off.

 

[RJSakowski]

The timing mark isn't critical in location but sort of. The the mark should align with one of the marks on the dial when the half nuts are engaged. If the mark isn't properly aligned, you can engage the half nuts a half tooth before or after the proper location and during the process of threading, you can hit the wrong point resulting in improperly cut threads. My Grizzly G0602 has

On some lathes, my Craftsman 6x18 being one, the thread dial is fixed relative to the thread dial gear. On others, the dial is adjustable. In the former case, engage the half nuts at a suitable spot and scribe a mark directly opposite one of the marks on the dial. In the second case, scribe a suitable mark at any location and rotate the thread dial to align.

 

[zippyslug31]

Just in case anyone in the future ever has this same issue, I'll add a quick comment on how I addressed the missing timing mark - it's not quite as easy as I was thinking by slamming some arbitrary mark on the body of the dial. I had a hunch there may be a little more to it than what I initially was thinking. This will probably be incredibly obvious to more experienced operators.

Specifically, it's helpful to align said mark with a line (probably best to stick with "1") wherever the half nuts fully engage smoothly. Since I'm new to all of this I learned that the half nut tends to find 'home' when you engage it at a specific spot, i.e. where the half nuts mesh into the lead screw. If you simply throw an arbitrary mark on the body of the dial, then your mark might not align with a line on the dial's face which makes using the dial a PITA. I did this at first and found that I had to remember to time my engagement just before my line came up, which was pretty annoying.

I tried moving the dial face (by loosening the Philips screw seen in the image in my first post) and this helped some. After some messing around with the dial face and some repositioning of my pointer, I finally found a nice location where all the lines allowed smooth engagement when they were either at (or were very close to), my timing mark. Should be noted that the dial faces on these import lathes are not perfectly symmetrical so some experimentation will be needed to find where the best location is for the various markings, YMMV.

After I found a good consistent spot, I made sure I had the dial face snugged up well and inscribed a permanent mark on the dial's body. Now my half nuts engage smoothly when the lines hit the mark.