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Back to TD150 Mk II index page

This page will document subchassis rigidity of the TD150 by measuring deflection near the bearing when its own platters are fitted.  Then the same test will be given to a TD160 subchassis for comparison.

 

The three mounting points are located to support the subchassis next to the mounting points. The dial indicator is located next to the platter bearing and will read the amount of deflection to the nearest .0005 inches.

Pepsi cans are full. Wood squares are 1/2 inch birch ply.  Acorn nuts serve as the contact points.  Copper washers were used as shims under two of the acorn nuts to level the subchassis frame..

 

 

The test begins with the TD150 subchassis

150begin.jpg (48437 bytes) closeup view of the indicator reading under zero loading

150load_0.jpg (90451 bytes)

The TD150 subchassis frame set up on the 3 points.  Indicator is zeroed.  Waiting for the inner platter.

150innerplat.jpg (87341 bytes)

Loaded with inner platter.  Reading is .0025 inches

150innerplat_C.jpg (48511 bytes) close up of indicator reading load off inner platter

150outerplat.jpg (80457 bytes)

Loaded with both inner and outer platters (7 lbs).  Reading is nearly .007 inches.

150outerplat_C.jpg (44857 bytes) closeup of indicator reading load off both platters

150end.jpg (46682 bytes) Indicator read after both platters are removed.  Needle repeats back to zero.  Included to verify the process.

TD160 Subchassis

160load_0.jpg (84654 bytes) The TD160 subchassis is set ready for loading.  The indicator is set to zero and positioned near the bearing.

160begin.jpg (44596 bytes) Close up of the read.

160innerplat.jpg (86549 bytes)

With the inner platter installed.  Indicator reads .0035 inches.

160innerplat_C.jpg (45778 bytes) Close up of the read.

160outerplat.jpg (82385 bytes)

Both platter installed.  Indicator reads .0135 inches.

160outerplat_C.jpg (44729 bytes) Close up of the read.

160end.jpg (74603 bytes)

End of test.  Both platters carefully removed and indicator needle returns to zero.  A successful test.

What about the setup...?  Is it valid...?

It would be useful to test the "full" Pepsi cans and plywood squares for compression before getting too excited about the indicator readings taken above.  What follows is an effort to measure how much compression/deformation the cans and blocks take on under the loads of the above test.

The two finger indicators measure deflection under the wood blocks and

 

....and on top of the wood blocks.  Readings are taken with platters installed and before installation.

Largest indicator reading was from the top of the wood block.  Just slightly less than .0005 inches.....max.

 

 The Pepsi cans (full) and plywood squares do compress somewhat under the loads in this test.  This amount of compression is less than 4/10 of one per-cent of the chassis frame deflection reading.  I'll just include this as error, allowing myself a 10% error margin under the best of circumstances.

 

 

What's the point....?

The goals are to achieve 1) precise tonearm alignment and 2)  the most constant platter speed.

Tonearm alignment:  If, when under load, the subchassis can flex a small amount then the parallel relationship between the tonearm mounting and the platter will be in motion.  A loss in the precision of your tonearm alignment.

Constant platter speed.  If the subchassis can flex dynamically while the platter is in motion, the distance between platter and motor pulley can also be in motion.  Consider also the flexible belt which will stretch and contract as the distance between platter and pulley changes. The AC synchronous motor will maintain a constant speed but the belt length will get longer and shorter.  Platter speed accelerates and decelerates (minutely).  Platter speed becomes less constant.

My goal is to find a way to have absolute rigidity of the subchassis frame under load.  Similar to a non suspended table with a massive base. Zero movement of the base.  Yet I want to have the benefit of isolation provided by the spring suspension of this table.  In time it will be seen how close I can get to that goal.