Threading table on my lathe is wrong or I'm an idiot.

Here is my chart. I have the levers in the positions that yielded 4.5 TPI.

20230430_173513.jpg

20230501_211403.jpg

Here's the stud gear, 48t:
20230501_210344.jpg
20230501_210347.jpg

At first I didn't notice the stud gear change and I did it with the 24t stud gear because 24t is all I have ever used (never cut a pitch this coarse before). That gave me 9 TPI. Then I swapped the 24t out for the 48t and given the 0.5 ratio between 24 and 48, totally expected to get 4.5TPI. But instead I got 4.0. Moving the lever to the position you see it in, gave 4.5 TPI.

To rule out slop or anything, I ran with a sharpie along 12" of round stock. Consistent 4.0TPI when it should be 4.5, and consistent 4.5TPI when it should be 5.0.
 
RJSakowski said:
More likely, the gear selector rail is off by one gear. Perhaps, a P.O. did some work on the gear box and reassembled it incorrectly.
Click to expand...

This is most likely I think because previous owner did rebuild it. But if it was correct with 24t stud gear then it should be correct with the 48t stud gear, right? The more I think about this the less sense it makes. I am questioning my own sanity now. I must have measured pitch wrong (many times consecutively) or something.
 
that chart makes no sense.
first the chart goes from 4, 4.5 to 6 then back to 5.5 then there is another 6 ... Something is really wrong there.
the 6 back to 5.5 is wrong, and so is going back to 6..
just enlarged it in an image editor... wrong.. its a 5
 
I just found this picture...

Screenshot_20230501-235150_Chrome.jpg

The placement of the gears on your lathe don't seem to match what is in the picture...

You may want to check and make sure all of the gears are installed in their correct locations...

Here is a picture of my Logan before it was disassembled...

20161129_103925.jpg

I'm missing one of the reversing gears in the picture...

The 36t gear is mounted on the stud and the 72t gear is 'in storage' on the sector. In your picture, it appears that you have a larger (maybe 54t) gear on the stud with your 48t gear on the sector. I don't know if that would make a difference, as it seems the overall gear ratio would remain the same.

Just a suggestion.

-Bear
 
Last edited:
682bear said:
I just found this picture...


The placement of the gears on your lathe don't seem to match what is in the picture...

You may want to check and make sure all of the gears are installed in their correct locations...

Here is a picture of my Logan before it was disassembled...

View attachment 446462

I'm missing one of the reversing gears in the picture...

The 36t gear is mounted on the stud and the 72t gear is 'in storage' on the sector. In your picture, it appears that you have a larger (maybe 54t) gear on the stud with your 48t gear on the sector. I don't know if that would make a difference, as it seems the overall gear ratio would remain the same.

Just a suggestion.

-Bear
Click to expand...
Right, it looked like the manual picture before I swapped to the 48t stud gear.

Before I swapped (as in the manual picture):
-24t in stud gear position
-48t in spacer position

After I swapped:
-48t in stud gear position
-24t in spacer position

There is one difference between my picture and the manual picture though; the manual shows an idler gear that is larger than the 48t gear. My idler gear is smaller than the 48t gear. That shouldn't have any effect, but it might be evidence of some prior foul play. If that larger gear isn't on the idler shaft, then where is it? And where did this smaller idler gear come from? I guess I need to open up the QCGB and take inventory of what's in there. Could be this lathe's guts sat in a coffee can under someone's bench for a while and maybe cross-pollinated with other lathe's guts.. .
 
I've done my best to count the teeth on the gears in your picture... the one on the stud looks to be a 54t? The 48t is in the position of the idler gear...

Screenshot_20230502-024955_Chrome.jpg

I think they should be swapped...

Am I correct about this? I'm not trying to be argumentative... just trying to clarify...

If you do determine that you need a different gear or gears, let me know... I may have what you need... assuming that your gears are a 16DP...

-Bear
 
Last edited:
The gear marked with the question mark in post #18 should be swapped with the one marked 48t. If it is a 54t gear, it would explain your results.

In its proper position, it only reverses direction and the number of teeth don't matter so when you used the the 24t gear with the 48t gear in place of the 54t gear, it would thread correctly according to the chart and all your thread settings in the gear box are right.
 
682bear said:
I've done my best to count the teeth on the gears in your picture... the one on the stud looks to be a 54t? The 48t is in the position of the idler gear...

View attachment 446463

I think they should be swapped...

Am I correct about this? I'm not trying to be argumentative... just trying to clarify...

If you do determine that you need a different gear or gears, let me know... I may have what you need... assuming that your gears are a 16DP...

-Bear
Click to expand...
Mystery solved! I am an idiot!

I cannot believe I missed that. I counted those teeth twice; once before I swapped them and again after I had the issue. Putting the idler in the stud gear position is an easy enough mistake to make, but counting the teeth of idler instead of counting the teeth of the stud after they're already in place? That's just bone headed.

Thank you for pointing this out to me. I might never have figured it out.
 
You must log in or register to reply here.
Back
Top