Cosmo:
Some 45 + years ago, I was also a mechanical engineering student as you are now. I had the benefit of a wonderful education in the practical side of mechanical engineering at Brooklyn Technical High School, graduating from there in 1968 and going on to study engineering at what was then called Polytechnic Institute of Brooklyn. Through my high school years and college years, I worked in machine shops, and became a journeyman machinist. I learned my trade from oldtimers and in old-time machine shops. To find a young engineering student such as yourself who wants to learn and do the practical side of mechanical engineering is special. Most young engineering students today seem to play with computer modelling or computer simulation and do not go near anything like machine tools or workshops. I am sure all of us on this 'board will try to help you all we can. You came to the right place to ask for help, and as an oldtime engineer and machinist, I find one of my greatest satisfactions is helping young engineering students and young engineers starting their careers along their journeys.
On the matter of internal threading: I am an old US dinosaur, so I think in inches rather than millimeters, however, I can convert mm dimensions and thread pitches pretty quickly in my head. 12 mm x 1,0 mm is roughly 1/2" diameter x 25 threads to the inch. This is a fairly fine thread and a fairly small diameter to use to start learning about internal threading. Here are some thoughts:
1. Learn to grind high speed steel toolbit blanks. These are inexpensive, and you can grind and re-use and re-grind them many times. You can also grind a cutting toolbit at either end of a high speed steel blank. You get two tools for the price of one blank. You can grind the lathe cutting toolbits from the high speed steel toolbits on a bench-grinder or even a bench-top belt sander.
Carbide tools are great, but they are relatively expensive and if you chip or break a carbide tool, you have to have a diamond wheel to regrind them. High Speed Steel toolbits are more forgiving, and you can grind them to any shape or type of cutting tool you need for a particular job.
2. If you want to learn about threading, you will need to get the following tools:
-a "center gauge" to enable you to properly position (we call it "setting up") the toolbit in your lathe relative to the centerline of the
spindle and work.
-a screw pitch gauge. This has multiple gauges and you use it to check that your trial cut of a thread in the lathe is the right pitch,
and you use it to check thread form as you cut the threads. You also use it to check the pitch of other threaded parts to determine
what pitch thread they are.
-a small pocket sized oilstone for stoning the cutting edges of your toolbits. An "India Medium Hard" pocket stone about 25 mm wide x
12 mm thick x 75 mm long is all you need. Using the oilstone to hone the cutting edges of a freshly ground lathe toolbit (only on high
speed steel tools, NOT carbide), you improve surface finish. You can also stone small radius' on the nose of the tool or refine the
final dimensions on special tools (like for cutting grooves of a specific width for "O" rings, etc).
3. My own advice to you is to get some scrap steel, perhaps 25 mm in diameter or a little bigger. Practice turning this steel to a specific
diameter and check yourself with a micrometer. Get some nuts of common threads, and these are your "gauges". Practice turning the scrap
steel to the correct diameter for a given thread size, then practice cutting OUTSIDE threads. When you learn to cut outside threads and
are comfortable with doing it- the working of the half nut lever and the cross feed crank has to become smooth and natural to you- then
you start thinking about cutting internal threads.
4. For internal threading on something like the 12 x 1,0 nuts, I'd suggest you get some high speed steel toolbit blanks and grind a small
internal threading tool from one of them. I grind small boring bars and internal threading tools from the high speed steel blanks and
these do a fine job of boring and threading in smaller diameters/fine pitches.
By grinding a boring bar and also grinding an internal threading tool from the high speed steel blanks, you will save a LOT of money, and
you will learn a great deal. I use 3/8" x 3/8" M-2 grade high speed steel toolbit blanks for the majority of work, same thing I've used
for over 50 years. On a common 6 inch bench grinder, you can grind the tools you need to bore and internal thread the 12 x 1,0 threads.
Again, you will need a center gauge to check the form of the threading tool you grind, as well as to do the setup of the tool in your
lathe.
A favorite saying of mine is "one step at a time", and this is how it is when you learn machine work. With a geared head lathe such as you
have, there is very little room for error. It is easy to have a crash (running the carriage or topslide into the chuck under power feed or when threading). Learn the machine, and get to where working the various controls is like playing a musical instrument or anything else you do automatically without having to look for keys or similar. Master grinding the toolbits, then master turning outer diameters to exact measurements, then master boring internal diameters... then try outside threading and when you get reasonably good at it, then you advance to internal threading. One step at a time. You are learning in your own shop without benefit of a mentor or oldtimer to look over your shoulder and work with you to teach you. A geared head lathe is not your friend, and if you make a mistake, it will not hesitate to snap off a toolbit or crash the topslide into the chuck jaws and start destroying other parts. Worse yet is if you get caught by the work or the moving parts. The lathe will pull you in and sever injury can result. In the least case, always wear safety glasses anytime you enter your shop. Your eyes are the most valuable sense and to injure them or worse is all too easy to do. I've been to the emergency rooms of hospitals a number of times over the years to get welding slag and fine chips taken out of my eyes. Never handle the chips (turnings) from your lathe bare-handed. Wear work gloves or use pliers or some other tools to handle the chips. The cuttings or chips from a lathe can cut into your hands or fingers like a sharp razor and cut right to the bone and cut tendons in a heartbeat. Never get the idea of handling the chips barehanded, let alone when the lathe is running and the chips are curling off of it. I did that a few years back, machining a small job out of O-1 (drill rod) in one of my lathes. Without thinking, I lifted the small spiral chip off the carriage wing as it spiraled off the work. Just that quick, I had a deep cut. It was as clean as a razor or surgeon's scalpel and deep. I got a pressure dressing on it, shut down the lathe and asked my wife to take me to the local hospital emergency room. It took 4 sutures to close that wound. I had been doing machine work a LONG time, but just got careless or did not think for that one moment. Remember to think and look things over before you start your lathe. Make sure the job is properly setup in the chuck, or between centers, or on a faceplate. A good habit is to bring the carriage and topslide over as close to the chuck and work as it will be when the job is turning in the lathe. Put the gearshift levers on the headstock in between gears so you can turn the headstock spindle by hand. We call this "pulling over" the spindle. By pulling over the spindle by hand, if there is an interference where the work or chuck jaws are going to hit the tool, topslide or other parts of the lathe, you will find it out and not have damage occur. You can then change your setup or adjust your toolbit position to eliminate the chance of a crash (when the work or toolbit or some other parts of the lathe are run into the work or chuck under power and damage results).
I'd suggest you get a basic book on lathe work, even if it is not specifically for your Madras lathe. SOuth Bend Lathe, in the USA, had published a basic book called "How to Run a Lathe". Copies can be found on ebay. This is a basic little book, and while it is written with South Bend lathes in mind, there is a great deal of common information you will find quite useful.
Best of Luck-
Joe Michaels
