Angling for 90° - tangential pivot tonearms

Nice design dampdau.
You can reduce the bearing friction by using unipivot. Something like attached picture.
Regards
 

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Hello Hiten, thank you for your nice painting an your design suggestion.
but look at my last post, the arm is balanced to 1.5 grams and the friction comes from rubbing over the paper. In the vidio i wanted to show that the arm follows the geomety on the drawing even under that conditions, moreover the magnetic system leads the stylus back on track. I checked the arm under balance, and youre rigth Hiten, there is a problem of friction in the horizontal wand bearing. maybe the washers are rubbing at the frame.


But a more severe point is I don't have a good idea for making a tonearmlift, does anyone have a sugestion?
A traditional lift is difficult to integrate. My tendency in the moment is to dip the backend of the arm because the way for lifting it would be shorter then at the frontside.


Uwe, awaiting your ideas
 
Really a clever realization, Uwe.
Are you using a Birch-Thales geometry, or a "non-Birch", Schroeder- like?
On guiding, my experiments drove me exactly to the same your conclusions: it must be precise, but not rigid.
On the arm lift, the problem is that it has to follow the arc described by the 2nd pivot, and this is not simple (Hiten, as you think, a lift in that position can be really dangerous) You may find something at #1704 #1719, design not used because it gave more complications than advantages.
After the compliments, doubts: the counterweight for the crank is interesting, but the difference between hor. and vert. mass does not bother you? of course it is always less than in a linear, but it is one of the problems of these arms, and not the last.
You talk about a variable anti-skating: another interesting thing, but how did you calculate the skating?

ciao - carlo
 
nocdplz- thank you for input,
I woudn't calculate, i would try to experiment running the arm on a glass platter, my stylus is in the moment a cheap conical. I plan to etstablish the scating-weight between the curved metal lead and the ambase, so it will at the first positions be more a anti-scating and will change by movement inside the platter to a force that holds the needle back, against the dragging force that wants to pull the stylus foreward.
Hilten, thanks to the Idea, but my fingers are not so tiny and I would prefer to fasten the Lift at the tonearmbase, if I imagine a additional scating mechanism it may end in the way where your suggestion would be connected, or near by.

I Think I will construct the Lift from bare metal and build it completely by myself, The Idea from nocdplz sounds interesting. In fact I have still the groundplate of the lift in my lathe, but didn't manage to get completely through the metal. Yesterday it was sunday and you couldn't make too mutch noise because of neighbors. It's germany i'm living at!

Cheers Uwe
 
That kind of lift should be much easier to be made on your arm, since your base does not turn - it's just a z-shaped (or u) lever connected to the crank - pushed (or pulled) by the lifter at the base.
Skating - I was asking because the question on these arms is really complex: I tried an analysis (# 1733) without getting useful results. and no one posted any clarification. As for the method of the blank disc, many doubts that it is really probative (as you know, there have been tons of discussions about)
carlo
lathing: not better near Florence
 
Hello again,
my last change was to implement double bearings, now the arm is much more precise. This was possible because I builded the arm from 4 mm profiles and my bearings are only 3 mm thick - an overhang of 2mm each side is the result. Also I was able to avoid all the small washers for adjusting the right distances between the parts. I now only have to push the bearings out of the fixation in the right direction.


so long, Uwe
 
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summer summary (sequel 1)

I saw that the size of the mp4 is quite small, far better than gifs and far easier to do - so I've converted the original AVI videos coming from Linkage simulations #1881. For all who don't use that program
Added the Miib geometry, the first to use pulleys.

carlo
many geometries, few tonearms...
 

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  • 1 BAERWALD&CO.mp4
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I couldn' d held my fingers still, so I adjusted the leading bow in another way. Now the arm moves from the inner position to the outer end by itself. Perhaps I don't have to implement antiscating!

Nice work, way too much counterforce but that is adjustable.
Just to give a breakdown of what I've found about the forces involved with this type of geometry, and if there is any fault in my reasoning, please advise so I can scrap it.
For the normal pivoting offset arm the components for skate force are geometry(offset angle), coefficient of friction(μ), VTF(g), groove modulation, angular velocity & cartridge suspension. (As well as gravity, the delta in modulation from 1st to the last groove, overhang etc etc)

The coefficient of friction(μ) x VTF(g) gives the drag force and drag force with magnitude of the offset angle gives the skating error. This is simplified and ignores the other factors because you either have no control over them or they contribute tiny effects on the final result.
This gives a generally lopsided smile profile to the skate force if graphed.

BUT with Doug's, Carlo's, the LT, your and my geometry, another complexity is added and that is the dynamic geometry as the angle between the main pivot, stylus, and arm wand (analogous to the offset angle of a normal tonearm) decreases during inward travel.
This changes the skate force profile when graphed, it gets less moving inwards, a fairly linear delta in the skate-force. (And might be the reason Frank's LT sounds so good, I'm thinking he has built in this anti-drag in his guide arm geometry, bloody genius if he did)

The compromises of normal anti-skate mechanisms will not work on our types of arms because they target a mean error.

Anti-skate on our arms need a variable force solution, a hell of a lot harder to accomplish, but by the same virtue if you get it right it will be way more accurate than a compromised anti-skate mechanism.

The way I'm approaching this problem is by countering the drag force with a variable magnetic counter torque mechanism at the horizontal pivot.

You could do the same but by changing the profile ever so slightly of your guide bar (As I think Frank might have done).

Nice work, good luck.

@Carlo

Thank you for the visualizations, looks very cool.
 
Well, I'm almost there with what is basically a straight up Schroder LT clone. Like many here I have limited tools so am attempting to build it with hand tools and a drill press, lol. NOT for the feint of heart. Some of the parts I've had to make several times to get right, first attempts were more 'picasso' than 'divincci'. I still need to check that my geometry is correct with the current base and rail, I may need to rebuild the base if it is off, also the guide bar that holds the magnet may need to be rebuilt. I agree with the above comments that it is important to get the 'gap' correct. And of course the variation of the gap along its travel. I use dental instrument abec 7 bearings for the lateral plane, for the horizontal bearings I used racing bicycle and fishing reel. The racing bearing are hybrid ceramic with treated racers, they hold the weight and are sealed, lubed and not free spinning, the other bearings do spin and spin. None of the bearings have any play. I think if I check the geometry and it is good I will finish the arm and begin testing. Currently the mechanism seems to work and wants to snap back into place, along its rail, with a very small nudge. I imagine getting this level and with proper geometry will be cool. I will post some pics at that point.