threading info

Hi all.
Not sure if this is the correct place for this thread but here go s.
Has anyone got a lathe with a 4TPI lead screw , as i have just got hold of one and need some info on screw cutting on it.??
Thanks in addvance.
Chubbs

chubbus said:

Hi all.
Not sure if this is the correct place for this thread but here go s.
Has anyone got a lathe with a 4TPI lead screw , as i have just got hold of one and need some info on screw cutting on it.??
Thanks in addvance.
Chubbs

Click to expand...

Not trying to be sarcastic but you're being more than a little vague. Yes, I have a lathe with a 4TPI lead screw, but I don't think that's really the question you need answered????

Derek Smalls said:

Not trying to be sarcastic but you're being more than a little vague. Yes, I have a lathe with a 4TPI lead screw, but I don't think that's really the question you need answered????

Click to expand...

What i am after derek is a Indicator table to suit this lathe so i know were to drop in for repeat cuts.There are 6 positions marked on the dial plus the half ones , the gear on the dial indicator has 24 teeth.I am used to a lathe with an 8TPI lead screw but it has a 4 position plus half ones , i do have a indicator chart for this lathe but i dont think it will be the same would it?????? appreciate any help.
Chubbs

Screw Thread Cutting | Smithy - Detroit Machine Tools

About 2/3 of the way down fig 3-83. It will be very similar to what you are used to.

4 TPI on the screw, so every 4 teeth of the gear corresponds to one inch of relative movement between the carriage and the screw. 24 teeth on the gear means 6" of movement per rev of the dial, hence the six divisions you see on it. Each large division is one inch of travel, each small division is 1/2" of travel.

So, it works out that you can pick up:

ANY WHOLE number thread on any Large division(1" mark).

ANY EVEN number thread on any small or large division(1/2" mark)

4 or any multiple of 4TPI threads, ANYWHERE, on any large division, small division, or half way between small divisions.

Hi.
Thanks for all the info lads , i think i now have all the info i need to attack some threading Great site this .
By 4 now Chubbs.

Derek Smalls --

My compliments on your clear and concise explanation.

John

I will add to Derek's list:


Any Multiple of 4 TPI you can close at ANY point

Any Even number thread on any line

Any Odd number thread on any numbered line (1-6)

Any thread with a 1/2 fraction on any even numbered line (2, 4, 6) (See Note below)

Any thread with a 1/3 or 2/3 fraction on lines numbered 1 or 4 (See Note below)

Any thread with a 1/4 or 3/4 fraction on the same line where you started (Carriage should be positioned to the start position for the first cut, +/- 2".)

Note: For the half and third fractions the important point is the spacing of the lines. For the half fraction you can start on any line that is a multiple of 2 from your starting point so 1, 3, 5 will work as well as 2, 4, 6. You could even use 1.5, 3.5, 5.5 as that group also has a spacing of 2. Likewise for the thirds; you can use 1, 4 OR 2, 5 OR 3, 6. Again you can add halves to any of those numbers. Just keep to the same set of numbers for any individual thread being cut.

The six inch synchronizing distance was obviously intended to allow easier cutting of threads with the third fractions. On a more normal, 4" thread dial the only way to do third fractions if to use the same line for each cut. But there is a compromise involved because it takes longer to come back to the original line if you are doing a thread with fourth fractions or to a suitable line for half or third fractions.

Derek Smalls said:

4 TPI on the screw, so every 4 teeth of the gear corresponds to one inch of relative movement between the carriage and the screw. 24 teeth on the gear means 6" of movement per rev of the dial, hence the six divisions you see on it. Each large division is one inch of travel, each small division is 1/2" of travel.

So, it works out that you can pick up:

ANY WHOLE number thread on any Large division(1" mark).

ANY EVEN number thread on any small division(1/2" mark)

4 or any multiple of 4TPI threads, ANYWHERE, on any large division, small division, or half way between small divisions.

Click to expand...