Angling for 90° - tangential pivot tonearms

Thanks super10018.
This is how I made it. The iron part was made of about 25 layers of thin tin can iron sheet secured with two component resin adhesive. This way I could give it exactly the shape I carved in the aluminum plate, as resulted from my Excel file.
 

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Hi Consty,

The rendering looks very good, but to me seems that the vertical dimension it is a bit big and could generate a negative momentum. However, considering the limited space you have in the bottom of the TT, good idea to expand the TA in the upper line.

Hope ur bearing arrive regularly soonest. I may use bearing that I have in the garage while waiting my new ones that I keep just in case.
However I am not a fast guy in doing things.

Rgds

Adelmo
Hi Consty,

Did you finally use the ceramic bearings? If yes what were the dimension if possible to know.

Tks n rgds

Adelmo
 
Hi Consty, I took a look at that bearing type on line and they seem to be skateboard type. I would like to consider using something similar on the turn-away of my RTA, and although i have a magnet return stop need something practically zero play, so your first hand experience would be very useful, would you describe them that way please?
M
By the way i currently use a tapered nut in a tapered seat with a rubber spring for pressure to ensure good contact/coupling.
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Hi Mike56,

I'm not sure I understand how do you intend to use the ceramic bearings but the ones I bought on Ebay were the cheapest I could find. So they had a little bit of play. Obviously any bearing will have more or less play, otherwise it would stiffen. But overall they run smooth.
 

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Consty,

That's an excellent accomplishment - both functional and attractive. I think the inverted arm/bearing carrier and the top mounted magnetic attractor are very good ideas and shouldn't give you any trouble. Congratulations and enjoy your new PTA.

Did you pre-load the bearings? That can make a difference in how well they turn and how quietly.

Adelmo,

I hope the last 20% heals quickly.

DD,

If you're out there, you should be proud of what your nearly-2500-post thread has brought to life over the years. Contrast Consty's with the photo of mine in post 2461.

Doug
 
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Consty, i know i am on the wrong specific thread, but the RTA i play around with is, without doubt, correctly oriented to the groove at all times, i.e. 90 degrees whatever the situation or position on the record, warp etc, it's just not Pivoted, however i find your and others work intriguing as well.
Linears and Radials need an arrangement to move the arm away for record loading and more critically back in position both level and radial repeatedly easily and accurately, whilst remaining well coupled through the base to the plinth. my current arrangement turns away OK, but is a bit stiff because of the bearing type. Consequently i might try bearings like yours and pre loaded like Doug suggests should remove play ensure repeatability and coupling with ease of movement. The pic in 2486 shows the arm turned away and you can pick out the post bolt the bearings mount on. As always if i can borrow some experience from others it helps a lot! i am not yet sure exactly how to pre load.........
M
 
Hi dtut and Mike56,

No, I haven't preloaded the ceramic bearings. This would have increased friction too much. But I used M8 wave washers for securing the two 608 bearings on each pivoting M8 screw.
Mike56, indeed, in your case you can use preloading to achieve both stiffness and ease of movement. Your design looks very familiar to me since I played with a similar design type some time ago. The three white ceramic balls provide the rolling base for the TA, isn't it? :) The difference between your design and mine is that you make the linear TA base pivot while changing the record, something that allows for a short TA which is very good. I made it fixed in a position similar to the one in your picture and this forced me to use a long TA which was not very good.
 
I do wish to find a better turn away bearing Consty so that's an interesting way to consider, thanks.
Yes, the three ceramic balls are the rollers for the carriage, so it is a non recirculating ball bearing carriage, which should operate with constant contact and no play.
I like the three as it provides for more predictable contact pressures in the transition whereas 4 requires more perfect alignments.
However, when pivoted in, these rails place the stylus on the radial line with the rails directly over it, there is no arm length at all, which is most unusual, so the vertical motion needed to accommodate warp is taken by a paralelogram motion, and the cartridge does not change orientation in warp movement (as a pivoted one does, both short or long) at all whilst remaining tangential to the groove throughout the transition and without skating. There are other compromises of course, but it is sound in these respects.
A pic of the arm in position to play and a video of the separated paralelogram carriage are attached for your interest (or otherwise!) and to add to the explanation.
M
 

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It looks great, congratulations!
How do you adjust VTF? I think you should have a weight somewhere on the oblique aluminum rod extending from the parallelogram.
And another challenge for this design is to make sure that at all times the center of gravity of the carriage stays inside the triangle described by the three ceramic balls
 
Absolutely correct on both counts Consty, here in the pic you can see the CW, also how light it needs to be, just 5gms plus the small lift arm, also at different times i use a front weight to ensure the CG stays comfortably in the triangle, in this pic out towards the camera, like many things, once understood, all that's the easy bit, before understood a challenge! Current version doesn't have the front CW. so, it has an ideal geometry in my opinion, measures well, and sounds good to me...........
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