Single Point Threading 101

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: Harold_V, websterz, GlennW

Poloris
Posts: 5
Joined: Fri Jul 09, 2021 8:17 am

Re: Single Point Threading 101

Post by Poloris » Wed Jul 21, 2021 9:48 am

The method I use is to use a boring bar on the rear and run the lathe in reverse.
There are some limitations as you can only cut threads in the same thread type as your lead screw.
Threading at 400rpm it gives great results.
I have made a "crash preventer" a wooden bench hook that sits under the control lever and prevents me engaging the lathe in forward rotation whilst threading.
This is the Youtube video that I learnt the method from.
Cheers Mark

https://www.youtube.com/watch?v=rjl8yDK1lH4&t=48s

Russ Hanscom
Posts: 1857
Joined: Wed Mar 15, 2006 11:10 pm
Location: Farmington, NM

Re: Single Point Threading 101

Post by Russ Hanscom » Wed Jul 21, 2021 12:13 pm

Please explain the limitation.

I have cut threads using a boring bar and running reverse, without regard to thread type, almost always standard V, or pitch. No problems that I was aware of.

Poloris
Posts: 5
Joined: Fri Jul 09, 2021 8:17 am

Re: Single Point Threading 101

Post by Poloris » Wed Jul 21, 2021 5:11 pm

The limitation is not being able to dis-engage the half nuts then re-engage them with accuracy to cut metric threads.
If you know a method to do this I would like to know it too.
Mark

User avatar
liveaboard
Posts: 1517
Joined: Sun Dec 08, 2013 1:40 pm
Location: southern Portugal
Contact:

Re: Single Point Threading 101

Post by liveaboard » Thu Jul 22, 2021 4:04 am

A thread making tip for this thread...
For a beginner, powerful lighting and a strong magnifying glass is extremely helpful.
Whatever error you're making is usually difficult to see with the naked eye; but when you see the work under magnification then you can figure it out easily.
Worked for me.

Russ Hanscom
Posts: 1857
Joined: Wed Mar 15, 2006 11:10 pm
Location: Farmington, NM

Re: Single Point Threading 101

Post by Russ Hanscom » Thu Jul 22, 2021 8:26 am

Yes, If you are cutting metric threads with an inch lead screw or cutting inch threads with a metric lead screw, there is a difficulty in locating the correct place to reengage. I have read of a procedure for determining the correct point, but do not remember it. I was cutting inch with inch.

User avatar
liveaboard
Posts: 1517
Joined: Sun Dec 08, 2013 1:40 pm
Location: southern Portugal
Contact:

Re: Single Point Threading 101

Post by liveaboard » Thu Jul 22, 2021 1:55 pm

I just reverse the lathe motor; it takes just seconds to rewind.
For long threads, I give a twist on the VFD and run it faster.

I don't have a threading dial, never used one.

User avatar
GlennW
Posts: 6988
Joined: Sun Apr 15, 2007 9:23 am
Location: Florida

Re: Single Point Threading 101

Post by GlennW » Thu Jul 22, 2021 2:56 pm

Russ Hanscom wrote:
Thu Jul 22, 2021 8:26 am
Yes, If you are cutting metric threads with an inch lead screw or cutting inch threads with a metric lead screw, there is a difficulty in locating the correct place to reengage. I have read of a procedure for determining the correct point, but do not remember it. I was cutting inch with inch.

Can't quite remember the details either, but I had to cut metric threads to a shoulder on my inch leadscrew lathe.

Three phase machine, so I remember retracting the tool and disengaging the leadscrew in the normal manner for threading to a shoulder and then having to swat the motor switch off immediately which engaged the spindle brake. At that point, as long as the leadscrew didn't make a complete revolution I re-engaged the leadscrew at some un-remembered point and reversed the lathe back to the starting point.

Only did it once a few years ago, but maybe it will come back to me exactly how I did it.

I want to say that I used the threading dial and only engaged in one particular spot to keep everything in time. In other words. The thread dial was engaged on "1". I made a pass and retracted the tool, disengaged the leadscrew, and slapped the motor switch off. Then as long as the leadscrew didn't turn a full revolution, I wiggled the carriage to re-engage at the "1" again and then reversed the lathe spindle to traverse back for the next pass and did it all over again...
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

shootnride
Posts: 283
Joined: Tue Jun 05, 2012 12:31 am
Location: Sacramento, Ca.

Re: Single Point Threading 101

Post by shootnride » Fri Jul 23, 2021 7:42 am

Tom Lipton has a pretty good video on metric threading with an inch lead screw.

https://youtu.be/HXt4TWa382Q

Ted
Some people raise the IQ of the room when they enter.........others when they leave.

Post Reply