DIY Tonearm Build

[YaBoiMrNick]

Hello fellow DIY'ers. Im building a tonearm (as well as a DIY Record Player) but I wanted a second opinion on my tonearm design. Here is a drawing of my design. I focused the drawing on the pivot assembly, not the entire tonearm.


The tonearm (made of Carbon Fiber) sits on a Triangular shaped piece of Carbon fiber tube, and the tube has a small magnetic ball placed at the top apex of the triangle, that attracts another magnetic ball placed inside the tonearm tube. The design allows it to rotate around the top triangle point, and the magnets keep the tonearm from moving forward or back. The goal is to eliminate any bearings and have a very low friction design. It is also worth mentioning that the magnets won't bee that powerful, as i want the tonearm to move up and down with as little resistance as possible. There will also be a counter weight on the end of the tonearm. Any thoughts on the design will be appreciated [ATTACH=CONFIG]n1311862[/ATTACH]

[mattsk8]

VPI does something similar on their Scout turntable, except I don't think they use magnets (I could be wrong?), I'm pretty sure it just rests on that "needle" it pivots on. FWIW, it's a great concept, and I hope to see you make it!!

[deschu]

You might want to consider how the tonearm is constrained, as it appears that the arm is not constrained in position in the horizontal plane, nor does it appear to be constrained against roll.

For example, just listing out how the mechanism works in terms of X, Y, Z position and roll, pitch, yaw orientation (6 basic kinematic degrees of freedom). I would think that a traditional tonearm pivot, for example, needs to be free in pitch and yaw, but otherwise constrained.

For contact surfaces, ball bearings can be great, you may also want to consider small synthetic sapphire ball and flat components.

It's in the verge of being off-topic, but I've always carried a fantasy of using AirPot's extremely low friction dashpots in a turntable application. Their graphite piston-on-glass tube design and manufacturing tolerances are just incredible for the price when you want something smooth.

[YaBoiMrNick]

You might want to consider how the tonearm is constrained, as it appears that the arm is not constrained in position in the horizontal plane, nor does it appear to be constrained against roll.

For example, just listing out how the mechanism works in terms of X, Y, Z position and roll, pitch, yaw orientation (6 basic kinematic degrees of freedom). I would think that a traditional tonearm pivot, for example, needs to be free in pitch and yaw, but otherwise constrained.

For contact surfaces, ball bearings can be great, you may also want to consider small synthetic sapphire ball and flat components.

It's in the verge of being off-topic, but I've always carried a fantasy of using AirPot's extremely low friction dashpots in a turntable application. Their graphite piston-on-glass tube design and manufacturing tolerances are just incredible for the price when you want something smooth.

The mechanism i showed is only for the Up and down movement, I was gonna design one for the horizontal movement, later. I was thinking of having the tonearm on a magnetic ball, allowing it to stay attached, but move freely as it needs to, all while constricting the roll movement

[deschu]

I'm sorry, I don't quite follow you.

Also, magnets are very tricky to finish to a precision surface and are not particularly hard. While a nickel plating can be hard and lapped to a nice finish, that's far more work than putting magnets near other materials that carry the peak stresses.

I haven't thought about the details, but your low level signals from the cartridge could be impacted if they are run near a strong magnet---you may want to check for this and any related winding/twist/shielding/etc. with a few basic scrap parts before getting too invested in a magnetic design. I'd love to see it work though!

[mattsk8]

If I'm understanding deschu correctly I completely agree. In your original design, you wouldn't be able to make adjustments for azimuth, VTA, cartridge alignment (usually done at the head of your tonearm), tonearm length, etc, with the design you're proposing. If you look at the "lateral counter weight" on the VPI I posted the pic of, you see how the tonearm slides through the lateral counter weight (which is the part that rests on the needle)... you make most of those adjustments there- you can both spin the tonearm in that counter weight (for adjusting azimuth), and you can move the arm forward and backward horizontally in that counterweight. You would also need to make a way to adjust the vertical tracking angle (VTA) of the tonearm, which would more than likely be something you would add to the base, where the tonearm is mounted to your turntable's plinth.

[Whitneyville1]

It's really hard to design and build better arms than are currently available. Many have nearly a half-Century of development in them now, and I'm not sure if you build better for anywhere near the price of a tonearm "off the shelf".