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DIY linear tonearm
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Old 25th February 2020, 09:54 PM   #3491
warrjon is offline warrjon  Australia
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Quote:
Originally Posted by dahlberg View Post
When you say "polished to one micron", does that mean that you went from ???? down to 1micron diamond lapping paste ? And how did you manage this ?
I started with fine valve lapping paste, used to lap engine valves. I then polished with 5 micron down to 1 micron diamond paste. I spent a lot of time with the 5um to get the scoring out from the valve paste. To polish I used toothpicks with the point slightly sanded and used them in a cordless drill.
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Last edited by warrjon; 25th February 2020 at 10:11 PM.
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Old 25th February 2020, 10:10 PM   #3492
warrjon is offline warrjon  Australia
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I hate doing jobs twice. I drilled the holes for the wheels too low making the cartridge mounting surface 3mm too high. So I need to make another carriage. Oh well.......
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File Type: jpg P_20200226_095715.jpg (600.5 KB, 195 views)
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SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P
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Old 26th February 2020, 12:09 AM   #3493
hjam is offline hjam  Canada
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Originally Posted by warrjon View Post
Hi hjam


that fixture is an ER32 collet block held in a 4 jaw chuck. Can be bought from eBay for about $40.
.
Thanks warrjon!
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Old 26th February 2020, 05:47 AM   #3494
dahlberg is offline dahlberg  Sweden
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Originally Posted by warrjon View Post
I hate doing jobs twice. I drilled the holes for the wheels too low making the cartridge mounting surface 3mm too high. So I need to make another carriage. Oh well.......
Looks like a carbon fiber/styrofoam sandwich, right ?
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Old 26th February 2020, 05:59 AM   #3495
warrjon is offline warrjon  Australia
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0.5mm carbon fibre with 3mm balsa core. It's pretty rigid as it is so when I get the under tray added it should hold up the house.

Look on the bright side - this time i will get everything more symmetrical. I made the frog (as my wife calls it) and machined it rectangular and the reference point this time will be the polycarbonate.
.
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SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P
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Old 26th February 2020, 06:22 AM   #3496
nocdplz is offline nocdplz
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..."polished to one micron"...
then Mr Micron really exist: even alone, even for diy machinists: I thought they traveled only in good company, calling them affectionately cents and so on - I will have to resign myself to that sparkling evidence :-)

Rings. ah, perfect for a wedding with their wheels. I wondered how that section could be turned and parted (in tungsten carbide!) - a very special, custom shaped tool? diamond grinding on a special support after parting? what a dumb, to buy them is much simpler.
Beyond jokes, great job Warren; but why to redo that nice, lightweight carriage? can't understand: i like frogs, even those crushed by a truck

carlo
for a word of comfort, always ask your wife..

Last edited by nocdplz; 26th February 2020 at 06:26 AM.
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Old 26th February 2020, 06:38 AM   #3497
warrjon is offline warrjon  Australia
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Originally Posted by nocdplz View Post
Beyond jokes, great job Warren; but why to redo that nice, lightweight carriage? can't understand: i like frogs, even those crushed by a truck

carlo
for a word of comfort, always ask your wife..

Because the holes holding the wheels were too low and I would have needed a 3mm spacer between the cartridge and carriage or the stylus would not have touched the record. My rings are larger diameter than Niffy's. I neglected this when I drilled the holes for the VEE's. I could take it apart and fix it but quicker to make a new one.


Our cat loves frogs........... as long as it's not on the turntable.
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SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P
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Old 26th February 2020, 07:51 AM   #3498
dahlberg is offline dahlberg  Sweden
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Just for prof of concept showing a "whacker" and a reference pivot, radius 0,221 / 0,107mm. That's probably a bit small but...

Click the image to open in full size.

http://www.dahlbergaudiodesign.se/im....221_0.108.png
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Old 26th February 2020, 04:32 PM   #3499
dahlberg is offline dahlberg  Sweden
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The tungsten 1mm drill shafts are 3,1mm.
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Old 26th February 2020, 06:51 PM   #3500
niffy is offline niffy  Europe
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Hi Warrjon,

Your carriage looks kind of familiar.
The shape of the top piece of my carriage is just a part of the overall structure. One of the major aspects of my design is that the carriage passes both above and below the rail. This massively increases rigidity, the overall structure being over 20mm thick rather than 4-5mm. Think of a monocoque chassis of an automobile. Generally the rigidity of a structure is proportional to the third power of its thickness. A 20mm section will be in the region of 64-125 times as rigid as a 4-5mm section. Of course this is a generalisation and is dependent on how the material is distributed and the shape of the carriage.
My carriage has buttresses that sit either side of the cartridge linking the top an bottom plates together. This eliminates what would normally be considered the headshell, the cartridge sitting in a recess within the front of the carriage surrounded on 4 sides. The recess is only a fraction of a millimeter wider than my cartridge and only just extends past the pins at the rear, I had to seriously modify the cardas tags to get them to fit. The headshell of most arms is just a flappy paddle and not at all rigid. The rear of the arm is similarly buttressed with the counterweight being a 3mm steel plate that sits in a recess at the rear of the arm and rides just above the record. When the counterweight is locked in place it adds to the rigidity of the rear of the arm. The whole carriage has only a 2.5mm clearance above the record and the stylus only lifts 2mm out of the groove for queuing. Small compromises for better sound quality.
Having the carriage passing below the rail will also help to keep the centre of mass low. Ideally you want the centre of mass to be level with the vertical pivot point/axis. Having the carriage passing below the rail will also act to prevent the carriage from being accidentally derailed.

The shape of the carriage was developed over many iterations, fine tuned to give the highest possible resonant frequency and best mass distribution.
Here's a couple of diagrams and photos.

Bearings 5.PNG

Bearings 6.PNG

IMAG0459.jpg

IMAG0462.jpg

IMAG0421.jpg

Niffy
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