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back to TD150 Mk II index page

Here are some proposals for a subchassis replacement for the TD150 project.

 

1)

Above image #1: Just for reference.   The original equipment subchassis is fabricated out of 3 separate pieces of stamped sheet steel.  These are spot welded into a single rigid piece.  Well, maybe semi-rigid.  As seen in the deflection testing, this frame will flex under the weight of its own platter system.  The object of this exercise is to devise a frame of the same dimension that will not deflect from the weight of its assembled components while in operation.

First concept.

2)

Above image #2: a 3D solid showing the top aluminum plate, the phenolic supporting layer is epoxied underneath. 

2a)

Above image #2a shows bottom phenolic layer with its elaborate cut-out pattern.

 

2b)

Above image #2b: a screen dump from the CAD file showing a top view layout.  The red line from platter center to the armboard tonearm mount describes the pivot to spindle distance.  In this scheme there is a web of solid phenolic centered under this line to provide strength in this direction against any possible dynamic stress or strain along this axis as the weight of the tonearm rides the described point.

Weights:

For reference, the original subchassis frame with bearing installed weighs 1.8 lbs using a postal scale.

The calculated weight for this subchassis with bearing installed is estimated at: 1.8 lbs with the following component breakdown

5052 alloy .125 inch thick top plate has a volume of10.32 cu in.  Weight is 1 lb
LE phenolic, .250 inch thick support layer has a solid volume of 13.72 cu in.  Weight is .69 lb
steel bearing housing has a solid volume of .409 cu in.  Weight is .117 lb
brass bushings (2) solid volume combined is.074 cu in.  Weight is .023 lb

Both subchassis are weighed without the armboard or tonearm attached.  Total weights appear nearly identical in this comparison.  There will be no need for a spring upgrade to use this frame.

Method of calculation as follows:

The CAD program calculates the volume of any solid.  I used that figure.  Specific gravity of a material is to be found within reference books like Machinery's Handbook and at numerous locations found on the internet.  The specific gravity for Phenolic macerated fabric & cord is 1.36 - 1.43.  I took the average figure of 1.4

specific gravity of a material = G (in pounds)
specific gravity of water at 62 deg. F = .0361 (pounds per cubic inch)
material volume = Vol (in cubic inches)

Formula: G x .0361 x Vol = weight in lbs

example: Phenolic layer.  1.4 x .0361 x 13.72 = .6934

example: aluminum layer. 2.7 x .0361 x 10.32 = 1.006

 

Second Concept, actually it's Rev 3:

This frame will make a sandwich of PVC between upper and lower aluminum plates.  No cut-out patterns.  Just flat plates with a perimeter shape to match the first concept. Aluminum plates are 1/8 inch thick in 5052 H32 alloy.  The PVC is type 1 with 1/16th inch thickness

Also included in this design is a new bearing housing in Brass.  

 

3)

The design also features a vertical extension framework, in LE phenolic, centered about the platter bearing.  The Design intent of the extension is to lower the center of gravity, add mass and provide a fixture for holding counter weights.

3a)

 

The lower disc has an array of holes for mounting ballast weights.   Assembled weight, before adding ballast, is calculated at 3.07 lbs.  Standard frame with bearing weight is 1.8 lbs.  The greater weight of this design will reduce influence from the over hanging arm and armboard.  This, in itself, will improve stability of the sprung platform.  Additionally, ballast weights may be placed strategically to counter-balance the offset of the over-hanging tonearm and armboard, improving stability further.

3b)

 

Image 3b: a section view of the proposed bearing housing.