On the popular online auction site, a Rubometric D 3/4" die head was listed for sale with a poorly-worded title. Since these die heads usually sell new in the four figure range, I didn't think my bid at the low initial starting price would be the highest for very long. At the end of the auction, however, I was surprised to find that I had won the die head (and more) for less than the price of a new set of chasers.
A Rubometric die head is a clone of the popular Geometric die head and uses the same thread cutting dies, called chasers. These die heads are usually used with a turret lathe to quickly cut threads in a production environment.
Here you can see the die head as I received it already installed in a ER32 collet block for easy holding in the workbench vise. You can see the die head has some surface rust from poor storage which perhaps influenced it's low final auction price.
At the front side of the head more rust is visible, but none of it is very bad and the die head still operates correctly.
After a bit of work with the Scotchbrite pads and some WD-40, the die head really cleaned-up nicely. Since these die heads are usually used in a production environment, used heads often display symptoms of a lot of use. I don't think this head was used much at all, however, as there is very little wear or scoring and the action of the head is still crisp and tight.
The worst of the rust just left some cosmetic staining.
These geometric die heads are available in several different sizes: 5/16", 9/16", 3/4", 1" and 1 1/4" from smallest to largest. Each die head size takes different threading chasers, so chasers for a 3/4" head won't fit the smaller 5/16" size. A 3/4" die head is really too big for my small lathe but it's still possible to do some thread cutting using the smaller sized chasers.
In this same auction lot I also received a nice selection of chasers! Four individual chasers make a set, with each one individually numbered (1-4) for a specific slot in the die head. Each set of chasers will cut one specific size and pitch of thread and the chasers are also available with different face angles for varying types of materials.
The way these die heads work is that you push them onto spinning bar stock to start the threading process. When the die head reaches a certain point, it will trip open disengaging from the freshly cut threads so you can pull the die head back without reversing the lathe.
This video shows the process of cutting threads, specifically 1/2"-13. The die head is held with a freely moving tail stock and the saddle was locked in place to provide the trip point. The tail stock is pulled forward via the cutting action of the die head and when this movement is stopped by the saddle the head trips open. This die head has a coarse/finish setting, so after the first pass the head is reset and the lever moved to the finish setting for the final pass.
Am I going to get much use out of this Rubometric die head in my hobby shop? Probably not, but that could be said of much of the tooling you acquire over the years for use in a hobby shop. It was a good deal and it just might come in handy some day.