Barrel threading - how?

[Usmc0844spare]

[fast54vw]

Just google cutting threads in a leave. Depending on what gear ratios the lathe has set up And the speed the lead screw is turning will make the cutter move exactly the same every time

[Usmc0844spare]

Just google cutting threads in a leave. Depending on what gear ratios the lathe has set up And the speed the lead screw is turning will make the cutter move exactly the same every time

[randomBytes]

Single point thread cutting is a very common operation on a lathe.
It's easy once you get the hang of it, but you always need to pay attention.
And yes, there is a drive shaft that drives the carriage at the correct speed
to cut a given pitch thread.

[ar15barrels]

Most lathes have 2 gearboxes.
The first gearbox sits between the motor and the spindle and determines the spindle rpm.
The 2nd gearbox is fed FROM the spindle and turns a leadscrew known as the feedscrew.
The gearbox sets the pitch relation between spindle and carriage.
The carriage is what carries the cutter across the part.

In use, you have a threading dial that has a series of numbers like 1-2-3-4-5-6-7-8.
You pick a number and stay with the number through all the cutter passes and the cutter will follow the same path.

So if I am cutting 1"x16 threads for a tikka, I cut a 1" diameter thread tennon and then cut 16 pitch threads on it.
The thread cutter is placed in position near the end of the tennon and then you watch the threading dial until your chosen number is approaching and then you engage the feedscrew as the dial comes to your chosen number.
When the feed screw is engaged, the carriage (and therefore the cutter) advances across the part being machined until the feedscrew is disengaged.
After disengaging the feedscrew, the cutter is re-positioned to the starting side and run through the same process until the threads are complete.

You definitely do NOT remove the part from the lathe setup in the middle of threading as it's more difficult to "catch" an existing thread and follow it.

[geedavell]

Most lathes have 2 gearboxes.

You definitely do NOT remove the part from the lathe setup in the middle of threading as it's more difficult to "catch" an existing thread and follow it.

And you never take your machine "out of gear" to spin the chuck by hand.
Ask me how i know!

[67Cuda]

In use, you have a threading dial that has a series of numbers like 1-2-3-4-5-6-7-8.

Lathes are different, mine is even threads on any line, odd threads on numbered only.

[Dgr1dman]

Lathes are different, mine is even threads on any line, odd threads on numbered only.

[ar15barrels]

Lathes are different, mine is even threads on any line, odd threads on numbered only.

Mine is like that too, but it's still a "best practice" to stick to the same start number vs using different numbers because using the same number guarantees you catch the same start on the leadscrew.
Also no need to confuse someone with minutiae that was asking the most basic question.

[ar15barrels]

Metric is a whole different game on standard lathes!

oh yeah baby.
Engage the nut once and never disengage until the threads are done!

[baih777]

Easiest.
Take your barrel to Randall to have it threaded.
And watch.

Setting the barrel up to the axis of the barrel bore . Is key to getting it straight.

[Usmc0844spare]

Thanks all... found a basic youtube vid on threading and it all makes a lot more sense now. In laymans terms, there is a physical link between the chuck and the carriage that basically enables the machine to mechanically do the same motions each time.

[kcstott]

I remember my trade school days and the lathe single point lecture and demo day. I just took what the instructors said as gospel as i didn't know enough to ask a question let alone argue.
follow the direction in the book, that's all we could do. 30 years later it's like looking back on when you learned to walk

[kendog4570]

All lathes will cut the thread pitch of the lead screw, and MULTIPLES of that pitch, when closing the half nuts any place on the screw.
Rule of thumb for closing half nuts:
Even No of threads/any line
Odd No of threads/any number
Multiples/any place


Not so sure about division numbers Example 8tpi lead screw/4tpi thread wont work on my lathe. Yours may be different.

8, 16, 32, 64,128, 256 works OK on mine. Haven't had the occasion to cut 128's or finer yet!

[kcstott]

All lathes will cut the thread pitch of the lead screw, and MULTIPLES of that pitch, when closing the half nuts any place on the screw.
Rule of thumb for closing half nuts:
Even No of threads/any line
Odd No of threads/any number
Multiples/any place


Not so sure about division numbers Example 8tpi lead screw/4tpi thread wont work on my lathe. Yours may be different.

8, 16, 32, 64,128, 256 works OK on mine. Haven't had the occasion to cut 128's or finer yet!

My machine will do from 8 to 56 with no gear changes. with gear swaps I can go to as little as 2, 2.25, 2.5, 2.75, 3, 3.5, 4, 4.5, 5. 5.5 tpi including the odd ball 19 tpi
I can also swap gears to do metric from .11 to 2.56 mm pitch.

6 TPI lead screw on my machine.