DIY linear tonearm

Made the VEE's today. Used 14.9 high tensile m3 set screws First pic is a 3mm cobolt drill ground at 90deg with a 0.25 radius, no polishing on this. I used a bit of hookup wire as a guide.

Other 2 pics are the forge, guide and 3mm drill. Screw the set screw into the bottom of the round bit put it on the anvil insert the modified drill and whack away. The 16mm bar is only to hold it upright so I don't hit a finger. It worked really well.

I polished the VEE's starting with valve grinding paste going down to 1micron diamond paste. I did try to take a photo with the microscope but all I got was the reflection of the scope lights, so gave up.

Last pic is the tungsten ring installed on an aluminium rim. I made this fixture so I could screw the wheel on and machine the rim down to square it up after parting off.

For those with a lathe this is how I trued up the rings in the rims. You could do this on a drill press bringing the quill down on a bearing.

YouTube


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Last pic is the tungsten ring installed on an aluminium rim. I made this fixture so I could screw the wheel on and machine the rim down to square it up after parting off.

For those with a lathe this is how I trued up the rings in the rims. You could do this on a drill press bringing the quill down on a bearing.

YouTube


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Warrjon,

Really nice work! I'm attaching a picture with a red arrow (I hope). Is this the fixture you mentioned, or is it something that can be bought?

Hugh
 

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Hi hjam


that fixture is an ER32 collet block held in a 4 jaw chuck. Can be bought from eBay for about $40. The fixture I made is the bit of steel sticking out. It has an m3 bolt tapped into it that the wheel screws to, The wheel is tapped m3. If you blow the pic up you can see the bolt in the centre of the wheel. The wheel seats back against the steel which trues up the wheel for facing.



Niffy the rings are a 0.05mm interference fit. To get them on I used the saddle of the lathe to start them, then the de-wobble tool in the video to push it on and square it up.


Carlo the rings are 2mm size K polished carbide I bought from eBay. The only machining I did was to rim to hold the ring. I made the rims slightly thinner than the 2mm rings which actually mic'ed at 2.12mm and 2.11mm.
 
Vee's made from m3 14.9 high tensile cup point set screws. Cup point was all I could get and I did not machine the cup off, just punched the radius in the bottom. The cup is 120deg and I didn't bother polishing the 120deg part only the 90deg bottom and radius.


Polished to 1micron. The image in the radius is the reflection of the microscope. I think they came out ok.

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Vee's made from m3 14.9 high tensile cup point set screws. Cup point was all I could get and I did not machine the cup off, just punched the radius in the bottom. The cup is 120deg and I didn't bother polishing the 120deg part only the 90deg bottom and radius.


Polished to 1micron. The image in the radius is the reflection of the microscope. I think they came out ok.

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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 ?
 
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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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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..."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..
 
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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.
 
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