Single Point Threading Between Centers

[erikmannie]

Hopefully this will work because I am underway. I parted off some lengths of 1” steel hex, faced and center drilled both sides & chamfered one side.

My setup is a dead center in the spindle nose, faceplate, driving pin, dog on the hex bar (doesn’t seem to be a problem), and a live center.

I am turning this down to 20 mm OD, and we’ll see what happens with the single point threading and chamfering.

 

[erikmannie]

The bolt will be an M20-2.5. The major diameter is 20 mm.

I am turning at 620 RPM with .005”/rev feed. My passes are .889 mm with CF.

This is the sub optimum finish that I am getting.

 

[macardoso]

Out of curiosity, why the love for turning between centers?

I get when it is necessary (e.g., a shaft with existing centers and concentric features), but for a shop made bolt, why not rip it out in one operation with a 3 jaw chuck? Face, OD turn, thread, Part off partway, chamfer in situ, finish parting off.

 

[benmychree]

The finish really does not much matter since you are threading it and will very likely finish/deburr the tops of the threads with a file. Good finish is why I like to use TPG inserts, those molded inserts that you use are not very sharp at the cutting edge; good for roughing, especially with a interrupted cut, but not so nice for finish work.

 

[Lo-Fi]

Probably the cutting force making the dog/driver flex and vibrate. Agreed, I'd pop in the three jaw and support with the tailstock center.

 

[erikmannie]

Here is how it is going. The thread relief OD is 16.1 mm for a minor diameter of 16.933 mm.

 

[erikmannie]

Out of curiosity, why the love for turning between centers?

I get when it is necessary (e.g., a shaft with existing centers and concentric features), but for a shop made bolt, why not rip it out in one operation with a 3 jaw chuck? Face, OD turn, thread, Part off partway, chamfer in situ, finish parting off.

Well, it is not for practical reasons. I tend to not be very pragmatic. I like doing stuff the old ways: gas welding, stick welding, manual machining, and the like.

 

[erikmannie]

The finish really does not much matter since you are threading it and will very likely finish/deburr the tops of the threads with a file. Good finish is why I like to use TPG inserts, those molded inserts that you use are not very sharp at the cutting edge; good for roughing, especially with a interrupted cut, but not so nice for finish work.

I saw your inserts; they were flat and smooth. I wondered about those; are those for light cuts? I switch to HSS for light cuts.

 

[erikmannie]

Probably the cutting force making the dog/driver flex and vibrate. Agreed, I'd pop in the three jaw and support with the tailstock center.

I did some with the 3J (and 4J), with and without tail support. That worked very nicely indeed.

 

[benmychree]

I saw your inserts; they were flat and smooth. I wondered about those; are those for light cuts? I switch to HSS for light cuts.

I use the TPG inserts with double end Aloris holders and use them for nearly all the work I do, the holders have adjustable chip breakers and work well for both rough and finish work. I have them in both positive and negative rake (negative for interrupted cuts).