I’ve got about a dozen Völkel threading dies, mostly bought new. I’ve never had a problem with any of them – until now.

I’m attempting to make some knurled thumb-screws in 12-28 UNF using a recently acquired new Völkel 20mm round solid die.

No matter how gradual and long a chamfer/taper I placed on the end of the turned-down-to 5.48mm silver steel rod (not in its heat-treated state, obviously) I couldn’t get the die to start even with a spring tap follower held in the tailstock pressing on the back of the die stock (I’d have to show you to explain how I do this). All I ended up with was a piece of rod with a dog point on the end, even after attempting to thread under power.

For a sanity check, I tried the die on an existing steel 12-28 thumb screw made commercially many years ago; I couldn’t get the die to start on that either.

For a further sanity check, I tried threading a piece of 5mm brass rod with the die. Even though 5mm is nearly 0.5mm below the major diameter of 12 UNF and the rod was given a long taper at the tip, the die was difficult to start. I cut the thread successfully but cutting felt noticeably more difficult than cutting, say, an M6 thread with the appropriate M6 die.

The only way I managed to cut any kind of thread on the silver steel was by making the solid die into a split die using a diamond cutting wheel and opening up the die as far as possible in the die stock. It cut the thread but it was hard going, and I was disturbed to see how chipped and torn the threads were, especially from about 15mm in (see image).

I know this is silver steel, which is pretty tough even in its off-the-peg state, but the die teeth clearance just did not seem to be wide enough to cut a standard 12 UNF thread. When I shrank the die down again by loosening off the screw in the split I simply couldn’t turn the die on the existing threads in order to “cut to final size”; threading with the split fully opened had already cut the thread to final size effectively, as confirmed by its easy fit into the female thread the commercial thumb screw mentioned above belonged in. Another disturbing detail was that my now threaded silver steel had a major diameter of 5.35mm whereas before threading it had been 5.48mm.

Is this just an out of spec example from Völkel , or is there something I’ve overlooked?

P.S. In the picture, the tapered/chamfered end of the rod has now been sawn off.