Internal & External Threading on mini lathe

[redvan22]

When I did mine, I threaded from the backside of the bore outwards. I used a left hand threading bar for this and reversed the spindle. You can also use a right hand threading tool flipped upside down, with the cutting edge at the workpiece center (and the rest of the tool above the center).

Search for Joe Pie reverse threading. Then the carriage moves toward the tail stock. (Much lower pucker factor for a beginner, than doing a normal inner thread blindly.) I made a start groove inside the part and then threaded outwards. I'd do the inner threads first, then match the cap to the inner threads.

If you want to thread with a normal right hand tool, conventionally, then I suggest mounting a dial indicator to tell you when to stop! Nothing like crashing your lathe - even a mini-lathe. I have, it isn't good. And yeah, go as slow as you can go and not stall...

Yes, I've seen Joe Pie's video about reverse threading. Really want to try that.

 

[WobblyHand]

Yes, I've seen Joe Pie's video about reverse threading. Really want to try that.

Make inside threading almost care free.

 

[markba633csi]

You may have difficulty parting off stainless, depending on how much torque and rigidity your lathe has. It may stall the machine, overheat the motor
or even break the parting tool.
Just pointing out what to expect. Parting off steel on small machines is often difficult generally speaking. It's perfectly acceptable to just cut off the stock with a hacksaw and then face the end to clean it up. If the material begins to work-harden this may be the only way to go.
All the best anyhow
-Mark
ps wear face protection just in case

 

[RJSakowski]

Hi,
I want to make a capped tube with a screw in cap out of 303 stainless. I'm not sure about the diameter at this point because I'm unsure about the threading aspect and that may change the diameter, unless I can cut any thread at any diameter (please forgive the lack of proper terminology). I'm thinking of a total length of 1 1/4" and a diameter around 1/2 - 9/16". The cap will have a turned down section at the end so I can drill a hole for a key ring. I'm hoping for a fine thread so I can get several turns of the cap to ensure a tight fit. I want the cap to have external threads so it screws into the tube leaving a seamless joint maintaining the tube diameter when finished.

Zero experience using the gears and cutting threads but I need to know how to do this for an upcoming project. I've cut threads on a lathe before in shop but then used a tap to make the matching threads in a hole. Never made both on a lathe.

I'm thinking about making the cap first, 1/4" in length, plus threads. Parting it off and then making the tube.

I figure if I make the cap first leaving enough to turn down the end for the key ring, then make the tube, I can assemble both pieces, turn down the end, and take a finishing cut across the entire length then part it off.

I know I'll have to change the gears for all the operations but that's not a big deal. (Lathe I used in shop simply had levers to set gear ratios, not a mini lathe. Need to actually change gear configurations just in case anyone reading didn't know this.)

What I need to know is this:
- Can I cut threads of any desired diameter, both internal and external or do I need to adhere to standard sizes?
- It seems to me that cutting 28 threads per inch on 1/2" diameter stock could also be cut on a 1" diameter stock so starting diameter doesn't matter, does it?
- Anything I need to know about cutting internal threads? I want to use a fine thread so I can get enough turns of the cap to ensure a tight secure fit. I realize I will need to make an internal threading tool. Buying one doesn't seem practical right now since this project is so small.

I know I'm overlooking some things but that's why I'm here.
Anyone see something(s) I'm missing and of course, answers to my questions will be much appreciated.

Michael

You will want to cut the external thread first so you can use it as a gage when you cut the internal thread. This is particularly true if you are making a non-standard thread.

 

[redvan22]

You may have difficulty parting off stainless, depending on how much torque and rigidity your lathe has. It may stall the machine, overheat the motor
or even break the parting tool.
Just pointing out what to expect. Parting off steel on small machines is often difficult generally speaking. It's perfectly acceptable to just cut off the stock with a hacksaw and then face the end to clean it up. If the material begins to work-harden this may be the only way to go.
All the best anyhow
-Mark
ps wear face protection just in case

I only use 303 stainless to avoid the work hardening. I'm a hobbyist, no aerospace stuff going on here.