Several years ago a Rubometric Die Head was purchased for a really good price at the popular online auction site. At that time an article was posted here about how it works, but I never showed the entire procedure for using the tool to make parts. Since an assortment of threaded studs for the lathe's T-Slot cross slide was needed, now was the perfect time to break-out the die head and document how I use it.

The die head shown in this article is a Rubometric 3/4" D. These particular die heads are German clones of the popular Geometric die heads that were originally made in the USA and the terms Rubometric and Geometric will be used interchangeably. In the states, the Geometric D die heads are much better represented in the used market versus other styles and plenty of used and new chasers for this style are still available for purchase.

The older article from when the die head was purchased is available here.

The link below is listings of the original Geometric Die Head manuals which have very useful tips on using these tools:

http://vintagemachinery.org/mfgindex/detail.aspx?id=3911&tab=3

Here's a link to the Rubometric Die Head product page:

https://test.akon-werkzeuge.de/en/products/die-heads/self-opening-die-heads.html

I'm not going to go over the basic minutia of operating the die head so please refer back to the manuals for additional information.

Before a threading job is started, the first thing that is usually done is to install the chasers and setup the die head for the proper thread clearance. With the die head closed and the coarse/finishing lever set to the finishing, you can adjust the tightness of the produced thread with the two cap screws at the base. A scale is provided on the die head to aid in this adjustment and it doesn't take much movement to make a big change in the feel of the thread engagement. Usually a few trial runs from the uncut raw stock are threaded to test the feel of the threads with a standard, which in this shop is usually just a regular nut.

With the die head setup and ready to use, the blanks are now made which in this case are 12L14 5/16" rod cut to the needed lengths with generous tapers on each end.

Each blank is held in the lathe at a set distance so the threads will be the same length.

Now you need to hold the die head to perform the work. With a general purpose lathe such as this, you can use either the tailstock or the tool post.

Tailstock Method

This die head has a 3/4" shank. This shank is held by a ER32-MT2 collet adapter which is then inserted into the tailstock. After the lathe is activated the die head is pushed onto the work via the tail stock to begin cutting the threads which will also pull the tailstock along the lathe bed. The length of the thread is set by using the locked carriage as a stop against the tailstock. When the tailstock stops moving after hitting the carriage, the die head will open and release the work. The selector lever is then moved from the coarse to the finishing position and the process is repeated. In this case the blank is then flipped around in the collet to cut the threads on the other side.

PROS/CONS of the tailstock method of holding the die head:

PROS

• The tailstock automatically aligns the die head with the spindle of the lathe. This is a big timesaver, assuming the tailstock itself is aligned correctly.

• The tailstock floating on a well oiled lathe bed allows the die head to find the nature center of the turning work and avoid binding.

CONS

• On a relatively small lathe such as this, the length of the ER32 adapter added to the weight of the die head causes the tailstock to tilt forward which requires the operator to support the die head to engage the work. This can be somewhat awkward and it's doubly awkward if the camera is in the way of the operator.

• The die head releases very positively and I've had the adapter loosen-up from the taper in the tailstock quill and require resetting. It hasn't spoiled work but it can be annoying.

• You should remove the tool post for better access to the die head.

Tool Post Method

Since this lathe is equipped with an Aloris-type QCTP, you can hold the 3/4" shank of the die head with a #250-104 boring bar holder. You will need to align the die head with the centerline of the lathe spindle.

Here I'm using a simple tool held in the tailstock to align the boring bar holder with the spindle.

The tool was made from a worn-out taper shank drill bit. The cylindrical segment at the end is a close fit inside the boring bar holder.

With the cross slide centered, sometimes I lock it from moving. Probably not necessary if you are careful around the cross slide crank.

It's also a good idea to double-check with a dial indicator that the tool post is aligned with the lathe spindle.

Usage is basically the same as when the die head was held with the tailstock, except the die head is advanced with the carriage hand wheel onto the work and a carriage stop is used to set the thread length. After starting, I usually help the carriage travel with a few fingers on the wheel until the die head fully engages. The die head will then pull the carriage along while cutting the threads. The lathe's lead screw is not activated as the power feeds are not used for this operation at all.

PROS/CONS of the toolholder method of holding the die head:

PROS

• The die head is easily advanced onto the work by turning the carriage hand wheel.

• Much less stickout from the boring bar holder compared to the tail stock. No need to support the die head while engaging the work.

• The die head is held very firmly in the boring bar holder and there is no chance it will work itself loose.

CONS

• More setup time to position the die head onto the spindle centerline.

Despite the extra setup, holding the die head with the tool holder is the way I almost always choose if I can cut all the needed threads at one time. It's just less awkward and a more pleasant way to perform the task. If you need to switch back and forth between general lathe operations and die head threading, however, the tailstock method can be more appealing.

If you only need to cut a few threads and don't feel like single-point threading, it's much easier to just use a traditional round die with holder to perform the work. If you have a decent amount of threading operations to perform these die heads will do it faster. If you have an old turret lathe with a lever operated collet closer and flood coolant (preferably dark oil) you can thread work with a die head much faster.

These Geometric die heads cost around $2000 new, so finding a deeply discounted used specimen is the only rational reason a home shop user will ever have one.