A New Suspension System for Vintage Lathes

Following up on the progress of the restoration work on a vintage Presto disk recording lathe and the Agnew Analog Reference Instruments Type 6021 Toolpost with integrated oil dashpot, as described in our previous episode, we are now presenting the complete suspension assembly.

The main part is, of course, the Type 6021, a machined aluminum block containing the cutter head mount and an oil dashpot cylinder, along with a spring for adjusting the depth of cut.

After a long day in the shop, turning a plain rod with a spring retaining groove and a mounting hole did not seem exactly appealing, so it was decided to make the task more exciting by machining steps and hiding the mounting screw in a countersunk hole.

The Presto cutter head was mounted on a Type 1414 head mount adapter, which can also be used to mount similar monophonic cutter heads on a Neumann system.

Likewise, Neumann SX74, SX68, SX45, E559, M552H, Vinylium SC99, FloKaSon Caruso and various other cutter heads can be mounted on the Type 6021 directly.

The assembly includes a depth adjustment system and adjustable vertical stabilization by means of an adjustable oil flow regulator, acting as the plunger (or piston) of the oil dashpot.

One of the most frustrating issues of some vintage lathes is that the entire threaded rod holding the spring for the depth of cut adjustment, rotates several degrees with the knob, making depth adjustment very unpredictable, as it twists the spring and then slowly rotates back during the cut!
An elegant solution is the Type 6023 Depth Adjuster:

This is a small shaft with a flat machined on one side, acting as a bearing surface for the knurled knob. The threaded rod goes through the shaft.

A flat is machined along the length of the threaded rod and a screw at the end of the shaft engages the flat, thereby preventing the threaded rod from rotating when the knob is adjusted, but having just the right amount of clearance to allow unimpeded vertical motion.

The other end of the shaft is threaded for mounting.

A hole at the end of the threaded rod allows the mounting of the spring and the knob raises or lowers the threaded rod, adjusting the depth of cut. The Type 6023 is a simple 5-piece assembly which can be adapted for use with many different types of lathe.

The Type 6022 Dashpot Plunger is another elegant addition to the disk recording lathe tweaker’s arsenal, allowing fine adjustment of the amount of damping provided by the dashpot for the vertical stabilization of the suspension system.

It is essentially an oil flow regulator valve, designed as a plunger, with the flat piston end submerged in the oil within the dashpot.

The damping is adjusted by means of the knurled brass knob and locked with the brass locknut on top to ensure the setting does not drift.

The brass parts were originally designed for a smaller version of this dashpot, for use on a different lathe. The same parts were used for this bigger version, just needed to machine some more.

The longer rod was threaded and turned to provide all the features needed for operation and mounting.

The mount is a small bearing, allowing the rod to move back and forth, following the motion of the dashpot cylinder during large suspension excursions.

The Type 6022 plunger assembly can also be used with a variety of different dashpots for different lathes. Different versions can be made, with different piston diameters, rod lengths and mounting arrangements. To enhance the versatility of our products, we offer the cylinder and plunger assemblies of our dashpot units separately, while also offering to customize each as required to fit your particular lathe.

We also offer several simpler, bare-basics options at entry-level prices, as well as supplying professional disk mastering facilities the world over with exquisitely refined solutions for exceptional performance.

Whether you are just starting out or already a veteran, seeking a competitive edge to help you stand out, Agnew Analog Reference Instruments can supply the parts you need for your lathe.

Stay tuned for further progress on the Presto MRC-16 project and other lathe tweaks!

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