Lathe Threading Set Up

[ddickey]

I want to learn how to thread so I thought I'd head out to the garage and practice. I have metric and imperial gears for my lathe. The imperial are installed. I thought it was as easy as matching the pitch to the numbers on my lathe. I.E. 26TPI you set to 1 & II on the gear knobs. I noticed all these other letter and number combos that I do not understand. I'm continuing to search but in the meantime thought I'd post here. My assumption is that they are gear positions and teeth numbers. My motor also has a two position drive pulley. Here are the pics. Thanks for any help.

 

[T Bredehoft]

We can take the two pulleys on the motor out of contention, all gearing is after that, so regardless of the pulley the belt is on, the gearing will be the same, just faster or slower.
The first picture above, related to feeds in thousandths, not threads. Ignore that when thinking about threads.
with the motor off, put the gears in 1 and II, engage the lead screw, put an indicator on the tailstock (not on the ways) and read the movement of the saddle when you turn the chuck one revolution. this will give you the distance the saddle (threading tool) moves in one revolution. Divide 1 by that number ant it will give you the pitch. 26 pitch should give you .038 1/2 thousandths movement.

 

[ddickey]

Thanks,
There are letters and numbers. My assumption is that the letters are the position on the gear and the numbers are the teeth. Is this correct? If so how do I figure out the placement of the gears? I suppose I could do the test you describe and based on the distance I could figure out what gear is where.

 

[jocat54]

From what I can see on the diagrams to cut 26tpi you would use a 36 tooth gear in position c--28 tooth in position d--45 tooth in position e and your knobs (levers) in 2 and 1. Not sure there is enough info in the pictures to tell for sure but that is what I see so far.

 

[mikey]

Thanks,
There are letters and numbers. My assumption is that the letters are the position on the gear and the numbers are the teeth. Is this correct? If so how do I figure out the placement of the gears? I suppose I could do the test you describe and based on the distance I could figure out what gear is where.

Do you have the manual? That would give you more info.

You have a quick change gear box. The knob that selects gears 1-3 are inside the gearbox of the headstock and are never changed. They interact (via the output shaft from the headstock gearbox) with the gears in the change gear train and modify their output. Different pitches are possible depending on which gears are installed. Note that the #1 headstock gear has the most teeth so it cuts finer threads and the #3 gear is the coarsest and cuts coarser threads. The pitches double when going from #3 to #1: 18 X 2 = 36, 36 X 2 = 72; this applies to every column.

The letters correspond to the gears you have installed. Presumably, the stock gearing has a 28T gear in the A position, a 29 tooth gear in the B position and so on. Depending on which gears are installed, you can cut different pitches. The required gear for, say 26 tpi, would be A36, B26, D28, E45 and you would use headstock gear #2. With your leadscrew, it should cut 26 tpi.

Most/every quick change gearbox will primarily use a compound gear train as opposed to a simple train, which makes gear calculations a little more complicated but it's understandable. I suggest you read Martin Cleeve's book, Screwcutting in the Lathe; it will clarify a lot for you. Your manual should fill in the rest of the blanks.

 

[ddickey]

Thanks guys for the reply's. I think I have it figured out now. I did the test Tom suggested and determined I cut a 28 pitch. I now I knew what numbers the gears were and figured out where they were placed. I've included a pic of my change gears.
From what I can tell The large gear on the bottom is E and is coupled with C which is hidden.
The next gear up is D and is coupled with the B gear. Gear A is driven by B. The gear next to A must not be changed which would make sense as the small gear above has no adjustments. Does this sound correct?
No manual Mike. Thanks for the explanation though.

 

[mikey]

Thanks guys for the reply's. I think I have it figured out now. I did the test Tom suggested and determined I cut a 28 pitch. I now I knew what numbers the gears were and figured out where they were placed. I've included a pic of my change gears.
From what I can tell The large gear on the bottom is E and is coupled with C which is hidden.
The next gear up is D and is coupled with the B gear. Gear A is driven by B. The gear next to A must not be changed which would make sense as the small gear above has no adjustments. Does this sound correct?
No manual Mike. Thanks for the explanation though.

Hmmm, no pic?

To confirm a gear selection, slap a fine-point Sharpie in a tool holder and run it on the work piece to confirm the gear selection. Use a thread gauge to measure the pitch. This is better than making a test cut.

 

[ddickey]

Oh sorry.

 

[ddickey]

To confirm a gear selection, slap a fine-point Sharpie in a tool holder and run it on the work piece to confirm the gear selection. Use a thread gauge to measure the pitch. This is better than making a test cut.

Great idea.

 

[rlgustin]

Does your lathe have an English leadscrew? I am assuming it does, in that case when cutting metric threads do not disengage the half-nut doing so will change start point of thread. To cut metric threads just back tool out at end of thread using the cross slide and reverse lathe. It takes some practice.

Sent from my LG-D850 using Tapatalk