Cutting a clean shoulder

[smfr]

I've had to make a lot of small spindles with threaded ends for a Stuart Beam linkage, and I have a question about the best way to make a nice clean shoulder.

Let's say you have some 3/16" drill rod, and need to turn down the end for threading. It seems that however I do that, I end up raising a lip on the unturned section, so that it becomes a few thou too large; big enough to prevent a close-fitting collar from moving over it. Is this inevitable? Do folks generally use a file or emery paper to knock down that lip? Or is there a trick to cutting the shoulder that doesn't raise the edge of the shoulder?

 

[Jasonb]

A sharp tool will throw up almost no burr but its always best to ease any external corners with a light touch of a fine file, At the same time just round the end of the threaded portion. On larger items I'll use a tool with the edge set a 45deg to the lateh axis to put a tiny chamfer on the edge.

Also on small stuff like this I tend to use HSS not indexable tools.

 

[Florian]

Or is there a trick to cutting the shoulder that doesn't raise the edge of the shoulder?

Well, I usually do it this way:

First you turn it down to almost the diameter you need and almost the length you need.
Then you face-turn the shoulder with a very sharp tool bit which only cuts on the edge.
Finally you turn it down to the required diameter with the same tool bit.

What I want to say with "only cuts on the edge" is, that the tool bit is either gound or adjusted that way, there is a relief angle on the front and on the side.

Cheers Florian

 

[portlandron]

Second the use of High Speed Steel cutter it can be sharpened to a very fine edge that you can not get on carbide.
I also use a fine file to just touch the edge at a angle to remove any burr and remove the sharp edge which can damage a polished bushing when you do assemble.

 

[Coilmotorworks]

Piano wire is very tough to cut to start with let alone thread. High speed steel will not hold a fine edge used on piano wire. Turning small diameter piano wire with carbide is also quite a challenge as any deflection in the part will crack the carbide as the part rides up over the cutting edge or develops chatter. A good file works to remove most edges while the part is still in the lathe.

 

[Swede]

Ditto. I screwed a wooden tray to my lathe at the tailstock end. In the tray, I have a beater micrometer and calipers, some center drills and the like, and a few files, and I am constantly reaching for a file (usually a small one) to knock the burr down. With practice, you'll feel for it and remove only burr and not stock.

I also have a few small steel flats that I use as backing for silicon carbide paper.

 

[my65pan]

Well, I usually do it this way:

First you turn it down to almost the diameter you need and almost the length you need.
Then you face-turn the shoulder with a very sharp tool bit which only cuts on the edge.
Finally you turn it down to the required diameter with the same tool bit.

What I want to say with "only cuts on the edge" is, that the tool bit is either gound or adjusted that way, there is a relief angle on the front and on the side.

Cheers Florian

I do it a similar way except once I have it roughed I finish the diameter first and then come back and feed down the face of the shoulder. A set of jewelers files and various stones are handy to have also.

 

[Florian]

The reason I first finish the face is that I can use the bedstop to cut exactly to the same depth when finishing the small diameter.

Jeweler files are not bad but I prepare the files with a monodirectional cut (no cross-cut like most of the files have).

Cheers Florian