DIY linear tonearm

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#501
No no... I am talking about the arm itself, not the borosilicate tube that the bearings roll across.

For the arm (what the cartridge is directly attached to) I am concerned about resonance, etc.... I already have 10mm borosilicate tubing, so that part isn't the issue.
 
#502
From the looks of the Cantus and measuring from a photo, I think it is 16mm guessing by the size of the bearing. 2 mm thick.

Lexx21, for the support arm weight is not an issue, in fact fill it with sand to dampen resonances. For the tone arm and counterweight tube, lightweight is an issue. I used CF tubing from a kite shop. FunWithWind dot com SkyShark Carbon P90 tubing. It is super light and stiff.
 

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#503
For those interested in dimensions, the one I can give is the center of tube to cart mounting bolts is 2 3/8", hope this will help. Ideally this should be adjustable, I originally built the fixed carriage without adjustments, then came to realize that adjustments were indispensable for setting tube length and azimuth. Polycarbonate might be heavier, but not as rigid for a given size compared to carbon fiber.






Colin
 
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#504
Sorry 'bout that Lexx. Did you see Veteran HIFI- Simply Black, Their's looks to be alum. or quite possibly titanium. Also their shaft length is definitely shorter than OC3.
@v.a- is yoours 2-3/8, adjustable or OP3. I know you previously said yours to be between 2 and 2.5".
 
#505
Mine is 2 3/8", it's a compromise, between too short which gives more sensitivity to VAT on slight warps and almost insensitive to warps. Much has to do with the slung height, that's why I tell anyone who wants to build it to go no bigger than 10 mm for tube width.


Colin
 
#506
I found all the parts I needed but the 10 mm glass tubing, so I ordered it on line. I have more than I need so if anyone needs some, I should have three extra tubes (they are 12" long). I' have extra 5/8" CF arrow shaft for the arm tube if anyone needs that (easy to find at a sporting goods shop). Used if for a uni-pivot design and works great with a little foam stuffed in the end for resonance. Shouldn't need foam with a short 2 or 3" arm tube.
 
#511
That's the sort of thing that I am looking for. Height of the tube would impact the VTA, so that has to be correct. I suppose that you can adjust the length of the arm so that it is center line with the spindle of the turntable.

I had thought about using a micrometer to adjust the vta, but that would just allow for fine adjustments.
 
#512
Ralf,

I would have given the height of the glass tube over the lp but this would need to be adjusted for Vta of cartridge and would vary from build to build and carriage design. This setting shouldn't be fixed but should be variable to raise/lower and levelling for the glass tube.



Colin
 
#513
Some comparisons of materials

Borosilicate Glass
Density (g/cm3).............................. 2.23
Poisson's Ratio................................ 0.2
Young's Modulus (GPa).................... 64
Mohs............................................. 5.7
Tensile Strength MPa....................... 282
Bending Strength MPa..................... 69
Speed of Sound m/s......................... 5640

Polymethylmethacrylate
Density (g/cm3).............................. 1.18
Poisson's ratio................................. 0.35~0.4
Young's Modulus (GPa).................... 3.2
Mohs.............................................. 3.0
Tensile Strength (MPa).................... 70
Flexural Modulus (GPa)................... 2.9
Speed of Sound (m/s)..................... 1840

POLYCARBONATE
Density (g/cm3).............................. 1.2
Poisson's ratio................................. 0.37
Young's Modulus (GPa).................... 2.0–2.4
Mohs.............................................. 3.0
Tensile Strength (MPa)..................... 55–75
Flexural Modulus (GPa).................... 2.3
Speed of Sound (m/s)..................... 2270
 
#515
tvi,
what you didn't include was the materials' damping factors.

glass 0.033
acrylic 0.07
polycarbonate 0.033

if the tubes pick up any vibrations, none are going to get rid of it very quickly, the acrylic being the best of the three mentioned.

I'm using carbon fibre (non-twill) tubes for my design, which have a damping factor of 0.061 before modification, they are slid over 3mm steel threaded rods.
 
#516
Or, we dont rely on the tubes themselves to provide damping factor but a system itself, around the tubes to prevent and transfer vibration away from the tubes. Hence in this application the base should be the biggest mass,. A series of vibration control tuned to.cover the spectrum seems to be the ticket here.



Colin
 
#519
vynuhl.addict said:
Or, we don't rely on the tubes themselves to provide damping factor but the system itself, around the tubes to prevent and transfer vibration away from the tubes. Hence in this application the base should be the biggest mass. A series of vibration control tuned to.cover the spectrum seems to be the ticket here.
Colin
Click to expand...

Hi Colin,
seems to be a bit of misconception here.
If vibrations were to be 'led away' from the tubes, that means they would still vibrate.
Mass on its own does not damp.
'Tuning' resonances just swaps one set of frequencies for another, superimposed on the same general background of vibrations.

And don't forget, these 'pathways' along which you want to send vibrations are two way. A lot can be understood by remembering the old Newton's cradle toy.

Vibrations are best dealt with at source. This is not possible with energy from the stylus/cantilever, but damping can (and should) be added to all the undamped parts of the arm, and its support (along with the turntable and record itself).
 
#520
With the o rings over the threaded rod and a pressure fit for the glass tube with and o ring inside at each end I've had no further need for damping. We must also take into consideration that in general no damping in itself will cover all of the sonic spectrum. Carbon fiber seems to be pretty flat across the board, since the arm here is so short there is no real need.to.damp the carriage, atleast in my case where the cart mount is 10mm polycarb, and the same with the t piece that holds wand and bearings. There is a set of holes drilled in a + configuration that provides some decoupling between the wand and bearings while maintaining rigidity. If you tap the glass.Tube it's a dull thud, you will never eliminate any of this no matter what you fill it with, you can only.control it of course. Ideally it should not have any significant length.of decay to a tap, as this will cause feedback, all in all pretty simple and can be done by ear.



Colin
 
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