DIY Schroeder Tonearm???

[Paul Ebert]

Since Jarno 'resurrected' this thread, I'll ask a few questions:

Does anyone know of a good way to make a smooth, crimp free bend in a small diameter (say, 1/4" OD) tube? The tube would probably be titanium. I need a way to make the horizontal offset angle bend (of the headshell with respect to the tube). A 1/4" tube bending tool would be great, but I have no idea where to find such a thing. Any ideas?

Does anyone know if there is a 'standard' number of degrees for this angle? If so, might you know what it is?

I'm back to considering building one of these since my efforts at reducing the horizontal effective mass of my air bearing tangential tonearm haven't been satisfactory. How to work the headshell and this angle are the most significant challenges in my mind at this point (which probably means I'm missing something or delusional or both... ).

Thanks.

Paul Ebert

[berlinta]

Hi Paul,
Your best bet would be to fill the tube with fine grain sand, heat it up to at least 250°C and use a wooden pole/rod of not too small diameter to bend/wrap it "around". If you are to use such a wand for one of my arm-designs be warned that you will need an additional counterweight, offset to maintain lateral balance. This will compromise the simplicity of the design unless you settle for a single, low slung counterweight that will have to be severely offset(giving the whole thing a somewhat "kaputt" look :-)
Oh, btw, why Titanium? Remember, this design doesn't depend upon fast energy transfer to dissipate parasitic resonances in the armboard...
There are several exel sheets that offer Baerwald and/or Loefgren arm geometry figures(offset angle is one of them) on the net(search the vinyl asylum archives..)
Good luck,

Frank Schröder

[krishu]

Hi Jarno,

you do not need to drill the magnets when drilling the steel discs behind them to carry the string.

Apart from this, it is hard to drill the magnets. It is very likely to destroy them by doing so...

Cheers
Christian.

[Jarno]

Hello Christian,

I haven't looked into the actual construction of the tone-arm, I just came across the question of drilling hard material. Being an mechanical engineer I know you can make holes in all sorts of metals using EDM or spark-erosion (and some other rather high tech processes), this technique doesn't exert pressure on the metal you want to "drill" therefore, when making a hole using EDM you don't run the risk of cracking the material.

I think this thread is rather interesting, maybe I will try to make an arm using this method. Oh well, have to finish my Laadegaard first.

Regards,

Jarno

[Paul Ebert]

Originally posted by berlinta
If you are to use such a wand for one of my arm-designs be warned that you will need an additional counterweight, offset to maintain lateral balance. This will compromise the simplicity of the design unless you settle for a single, low slung counterweight that will have to be severely offset(giving the whole thing a somewhat "kaputt" look :-)
Oh, btw, why Titanium? Remember, this design doesn't depend upon fast energy transfer to dissipate parasitic resonances in the armboard...
There are several exel sheets that offer Baerwald and/or Loefgren arm geometry figures(offset angle is one of them) on the net(search the vinyl asylum archives..)
Good luck,

Frank Schröder

Thank you for the response, Frank. OK, I'll skip the bend, perhaps doing as you did with the Model 1. I'll look for the Baerwald spreadsheet (I vaguely recall that the Baerwald geometry is more common - is that correct?).

Why titanium? Well, I could have my friend with a lathe make a tube for me out of some gorgeous wood, now that you mention it! I was able to purchase titanium tubes with a very nice finish for my tangential arm (I am not good at finishing metal), so I figured I'd use that again without giving it much thought. So, what criteria should I use for tube selection? Besides wood, I could probably use carbon fiber (from a kite frame piece) or ceramic (McMaster-Carr sells high alumina ceramic tubes quite inexpensively).

Thanks again,

Paul

[berlinta]

Hello Paul,
Yup, as far as the stiffness to mass ratio is concerned titanium, certain ceramic composites and even carbon fiber are excellent choices. But, looking at a typical length, outer and inner diameter for a tonearm wand, they all have a fundamental resonance(and multiples of that) quite far up(3-7kHz typically). The reasoning that the high frequency content of most records is low(therefore it is supposed to be a good thing to push the fundamental structural resonance as high up as possible) doesn't apply here since the equalization of the signal encoded in the groove leads to an overproportionally high amount of high frequency "mechanical energy" aka vibrations being fed into the arm(wand). The best armwand is one with as low a susceptability to being excited across the audio band as possible. Any pronounced spike(s) will give your reproduction an artificial quality, (tiny) broadband deviations are easier to live with.
If you use titanium make shure you dampen the armtube sufficiently, - lots of room for experiments!

Cheers,

Frank

[WolfgangB]

Hi everybody,

Could somebody give me the measurements of following parts of the Schoeder Type 2 tone arem (see piocture):

1. Diameter of tonearm tube
2. Diameter and height of counter weight
3. Diameter and height of tonearm base (aluminium)

Thanks in advance.

Kind regards,

Wolfgang

[Claus]

Hi

Another metode to bend a tube, would be fill the tube with water and freze it down, then bend the tube while the water is frosen.

Claus

[AuroraB]

((---or fill it with with fine sieved sand.......))

Sorry, wasn't reading back......
but heating it in addition will help in the bending process.
Alu get's markedly softer above 150 deg C.

[Magura]

All you guys that have made a tonearm, why is it you dont make drawings of them to compare and help others to start from where you are and develop things further, rather than starting from scratch???

If you made just reasonable back of a napkin drawings, you would be able to help the project to develop, instead of just imagining what eachother makes.

I have been following this thread for a while. I would like to make a complete turntable sometime this summer...if all else equal...but the approach you guys are taking dosnt make it easier. I am a toolmaker in diecasting...have all the reight machinery for such a project. If i sterted from the point you are at now...i am quite sure i could bring a lot to this project, instead of having the same trouble you had years ago.

Many well made project you guys have got here. A much higher quality of work than you see in the other sections of the forum.

Magura