On another thread no pun intended someone asked about the threading capability of the new south bend 8 x 18 lathe the following is based on my answer with a few more details added in.
One serious consideration when purchasing a lathe is threading capability. How does the lathe create the proper ratio between the lead screw and head stock.
Why does the #1001 SB need quick-change gears if it says that it can thread ?
I have never threaded and do not know anything about the QC gears.
Can someone enlighten us ?
Yes it will indeed thread!
In early days of of the screw threading lathe the only way to change the pitch of a screw being threaded is open the head stock cover, if it had one.( sometimes they were exposed) and change out the gears to set the ratio of gearing between the head stock spindle and the lead screw. these gears are furnished as a set with the lathe, Hence the term change gears and change gear set.
a set will allow for all common threads to be made either imperial , metric or both.depending on the lathe.
Modern production lathes have a gear box with a series of levers or knobs that allow to change the ratio of gearing in the head stock quickly .
this gearing also sets feed rate for automatic feeds.
Modern hobby lathes may be a hybrid you can quickly change thread pitches with levers or knobs but within limits like imperial threads or feed rates or metric threads . if you need to change MODE open the box and switch change gears.
the old way saves money on production cost but takes time to change out gears.
A full featured QC gear box is an expensive option. but in a job shop where things change fast an furious it save production time and setup cost.
the hybrid is a compromise it makes threading setup easier and faster and keeps costs reasonable.
Some of the small hobby lathes like taig and sherline have no head stock gearing at all . this is an added option.
Single point threading was one of the basic skills learned on the lathe in tech school for me. As a hobbyist one needs to decide how important the skill is and how important the threading capability of his or her lathe is. Added info:
Metric vs imperial most lathes I have seen are either designed to measure and function and are built either to be a metric machine or a imperial machine. the difference is the lead and feed screws are made to either metric or imperial standards. so if one has an imperial standard machine and wants to thread you need a transposition gear of 127 teeth or in the case of the 7 x mini lathes a 21 tooth gear. and this gives a close approximation.
So the lesson here if wanting to do serious threading get a lathe built for what you work with or are comfortable with. some machines are built metric and only aproximate us decimal inches. The newer imports have corrected this and use inch based screws.
CNC can be a horse of a different color. Look ma no gears. If the head-stock of a cnc lathe has a spindle sensor the computer can set the ratio of the spindle speed to the lead/feed screw electronically so you program in the numbers and the computer does the threading. just swith working units to metric or inches and the computer does the math
I/we still recommend learning to thread with a manual machine.
These are some things to keep in mind when selecting a lathe . Threading capability is one consideration. and selecting a hobby lathe can be tough. I learned to machine on a real lathe a modern south bend and a standard modern. full featured lathes with all the capabilities thereof.
My first home lathe a grizzly 7x10 champagne tastes on a ginger ale budget to say the least. The one advantage I had was a target of what a real lathe will do.I had to get what I could afford and not give away all capabilities . If I bought a taig (one of my first considerations) it would not thread at all.
One must still consider things like budget accessories size of work to be done old iron vs import, swing and center to center size available workshop space shipping weight shop location (Garage basement attic) and a few other things. I hope this helps the new folk.