A Turntable of my Own, Part 2

A Turntable of my Own, Part 2

Written by Ken Fritz

Copper #90---Ed.>

Here we see the finished laminated fiberglass plinth sitting atop the 1 ½” thick machined aluminum sub-plate. You will notice the ¾” thick grey MDF pieces sitting between the main plinth and the tone arms. They are mockups of parts that will be machined from aluminum. You will notice Dinavector, Triplainer, and Kuzma Air Line tonearms in the picture. Since that time, I have chosen to use a pair of Kumza Air Lines and a Kuzma Four Point tonearm instead.

Here we see machined aluminum pieces that will be fastened to the main plinth. You will note mounting holes machined for specific arms to be used on this table.

This is an underside view of the 1 ½” thick aluminum pieces that will serve as a support for the 3 VPI double motor – flywheel drive units. The cored-out part viewed will later be filled with a matrix of epoxy resin and #9 lead shot. This will be used to increase the mass of the aluminum part.

Since the fiberglass shell for the main plinth will be filled with the same epoxy/lead matrix to increase the mass that will be necessary to make provisions for adjustment tools and signal cables from the tonearms to pass through the plinth. There will be 280 pounds of epoxy/lead matrix filling this plinth.

Here we see the main plinth and the 3 sub-bases for the VPI motors. Beneath that you will see the top large 1” thick aluminum plate that will be used as a support for all of the upper parts of the turntable. The bottom plate will become the top of the stand, yet to be constructed for the entire turntable. In between the two will be a Minus K vibration isolation device.

This is a closeup view of the machined aluminum plate to which the arms will be mounted. You will notice a bubble level which, in reality, is only there to cover an adjustment hole used to properly level the entire turntable. I am using a highly accurate German bubble level for looks only…..it adds a nice visual touch.

Here we see the platter with a 12” Starret machinist level atop. On the right side, you will notice a T-handle allen wrench going through the plinth down to the brass adjustment point that is used to level the table. The Starret machinist level has graduations equal to 1/1000th of an inch per foot. Pictured are the aluminum pieces I designed to hold the inverted bearing for the Sota vacuum platter I will be using. Here we see the anodized bearing cup supports installed on the fiberglass plinth. A steel mold was fabricated for casting the 1” thick lead disc that will be bonded to the top of a standard Sota vacuum platter. This steel mold was sent to a supplier in Ohio that casts lead parts for the medical industry. Two of these platters were poured, rather than just one, in case I thought some day I might make a second turntable. Yeah right.

Here we have a good friend of mine, an expert machinist, finishing out the lead discs. A closeup view of the machining operation. After the two lead discs are machined, they were sent to Sota Industries so that they could bond this plate to the top of the Sota sub-platter. After that process was completed, the acrylic/rubber vacuum disc was then bonded to the top of the lead disc.

Depicted here is one of the two completed platters that came back from Sota. They bonded and finished the edges of the platter in the same manner they finished their standard Sota platters. This lead disc added approximately 85 pounds to the weight of the existing Sota vacuum platter. Before I decided to implement an extra lead disc, I conferred with Kirk and Donna at Sota regarding the weight capacity of the ball in their inverted bearing system. They told me that David Fletcher, who was instrumental in the design and weight capacity of their inverted bearing system, designed it for a weight capacity of 150 pounds. After the platter was installed, a dial indicator was used to measure the runout of the lead platter. It was immeasurable, as was the runout on the Sota platter to which it was bonded.

[We will continue with Part 3 in the next issue—Ed.]

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