DIY 12" Tonearm: i need your advice! - diyAudio
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Old Today, 12:39 AM   #1
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Join Date: Feb 2015
Default DIY 12" Tonearm: i need your advice!

Hi all, greetings from Italy! First of all I apologize for my "not so fluid" written english but I will do my best to express my problems.
My grandfather is an excellent turner and i've decided to use his skills to build a 12" tonearm: I decided to make a Schick-alike 12" tonearm because I love his looking: simply atonishing!! but I have encountered some uncertainties while planning the tonearm geometry: i want a bended tonearm tube (like many 12" great tonearms) but i don't know the bending angle and the lenght of the two parts!
I am a newbie in DIY Hi-Fi, but studying some tonearms geometry I think that I have fonunded a solution and I need your confimation.
First of all I have to specify that in this project I am using Schick's dimensions wich are:
Mounting distance 304,75mm
Offset angle 17,11
Overhang 12,82mm
eff. Length 317,57mm

Let's have a look at this picture:
Click the image to open in full size.

The violet rectangle is the shell, the red Dot ("D" letter) is the diamond of the cartridge, the "P" is the pivot of the tonearm (so P-D is the effective lenght), and the angle "O" is the offset angle.

I would like to know if the two segment "P-A and "D-A" of the tube and the angle "A" must be of a predetermined dimension or I can simply decide them arbitrarily (as long as the Offset angle and the effective lenght are mantained).

I suppose that I can freely decide the two segments' lenght and the "Alpha" bending angle, creating a template with paper and pencil but I am wondering if my conclusions are correct: can you help me?
Thanks a lot!

p.s. actually I am also working on my garrard 301's new plinth with Atp 12 T tonearm!

Last edited by Zcattuz; Today at 12:52 AM.
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Old Today, 02:59 AM   #2
diyrayk is offline diyrayk  United States
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Quote:
Originally Posted by Zcattuz View Post

Let's have a look at this picture:
Click the image to open in full size.

The violet rectangle is the shell, the red Dot ("D" letter) is the diamond of the cartridge, the "P" is the pivot of the tonearm (so P-D is the effective lenght), and the angle "O" is the offset angle.

I would like to know if the two segment "P-A and "D-A" of the tube and the angle "A" must be of a predetermined dimension or I can simply decide them arbitrarily (as long as the Offset angle and the effective lenght are mantained).

I suppose that I can freely decide the two segments' lenght and the "Alpha" bending angle, creating a template with paper and pencil but I am wondering if my conclusions are correct: can you help me?
Thanks a lot!

p.s. actually I am also working on my garrard 301's new plinth with Atp 12 T tonearm!
Your analysis is correct. Overall length, overhang, and offset angle are what counts, and you are free to choose the combination of segment lengths DA, PA, and angle A that get you there.

I should say 'effective length', not 'overall'.
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Last edited by diyrayk; Today at 03:10 AM. Reason: brain burp
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Old Today, 07:14 AM   #3
Calvin is offline Calvin  Germany
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Location: close to Basel
Hi,

I'm also at the process of making my own 12" arm.
Just visit my website under Projects/Phono/TheKiller tonearm
Maybe You find one or the other idea useful too.
The Schick-Arm uses ball bearings similar to a Rega or a Linn arm.
Having both and tweaked both, my decision for the new arm was to not use ball bearings, but reuse the cardanic bearing of a Technics.
It seems to me that high precision alignment (and adjustment) of ball bearings is beyond most DIYers skills and tools.
The problem hereby is that two bearings share one axis and need to be perfectly aligned.
The cardanic bearings of the Technis are also ball bearings, but smaller in size and instead of an inner cage which fits to an axis, there's a adjustable Pin on which the balls rest. Each of the four bearings features its own pin, which allows easy and precise adjustment without specil tools.
Also the two vertical bearings come readily mounted and aligned in a aluminum axle.
Similarly the two horizontal bearings are mounted and aligned within the inner aluminum cardan ring.
The static friction value of these bearings seems generally lower than for the larger ball bearings.
Technis specced the standard steel ball bearings with 7mg and the Ruby ball bearings with 5mg.
Linn speccs their bearings at 20mg and up.
I also like that the Pivot centre of the cardan meets the geometric centre of the bearing.
With a ball-bearing bearing the horizontal part is way off of the Pivot centre.

I wonder if the Schick arm has no antiskating mechanism?
Maybe that works for certain pickups and arm geometries, but in general Antiskating has its merits.
My Shibata pimped Denon DL103, mounted in a Rega RB300 required considerably more AS than I initially thought (adjusted with useage of a special test trecord).
There are other parameters that You may want to be adjustable, like Azimuth, Overhang and VTA.
Optics do play a major role also, but don't decide on Your design only on that basis.

jauu
Calvin

Last edited by Calvin; Today at 07:21 AM.
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Old Today, 02:42 PM   #4
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Join Date: Feb 2015
Thanks for your replies, knowing that my Idea about the tonearm geometry is correct is very comforting!

@Calvin: I visited your website and I found it really interesting: congrats for your work!
I know that in HI-FI what matters are "ears" and not "eyes" but at the moment I am planning to build this 12" tonearm just for fun and not for a real necessity: I have a ATP 12T tonearm ready to be mounted on my garrard 301 In addition to that I am really confident on my grandfather's skills and instruments, he has a equipped workshop and lots of instruments to work metal. As soon as I will start the work i'll post some pics here to receive your feedback!
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