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Mounting hole-to-stylus variation / tolerance

Hi all,
I know this particular point has been touched on, raised, in some of the threads dealing with tone-arm-alignment in particular.
I truly think it deservers a dedicated thread since it has a more or less profound influence on various arm designs and their alignment.
It also has a profound influence in how accurate and beneficial any after market alignment tool will work for you!

We have had this far, feed back from Jonathan Carr, i.e. the variations and tolerances with regard to his product (Lyra).
We also had some rather powerful insights by Frank ..., who designs and makes arms i.e. the variations of various products he took note of.

Jonathan quoted, that his current products have a +/- 0.3mm tolerance from the 'standard' IEC...? of 3/8" or 9.52mm.

The findings of some contributors are different, possibly due to simple variations much greater than 0.3mm (Lyra's tolerance) or possibly due to subsequent movement of the 'motor' relative to the body, caused by rough handling, re-tipping, etc.

It is of most importance to get more feedback on this, due to the dependence of a close match to 9.52mm, on arms such as ALL of SME, to name but one. These rely on this to be fairly accurately aligned. If not, some pretty unacceptable misalignment follows as a result, if the stock alignment method is used.

Lastly, HOW can a 'normal' end-user measure this distance with some degree of accuracy?
I have no problem using a vernier (calliper) and measure a +/- 0.05mm variation.
I can not see that this tool will be of use in this case. Optical measurement (like tool-shops use) will be best I should think --- but who, I ask, has this at hand?

Greetings,
Axel
axelwahl
axelwahl OP
788 posts
 
Hi Dan_ed,

thank you for your thoughtful input.
Though, the key word here might just be --- IF --- or?
:-)
Axel
PS: IF that distance is way out, as some carts seem to be, the stock adjusting templates e.g. SME can become pretty useless. You suggest to buy a new custom template for each new cart ---- IF that distance we talk about is truly KNOWN! A lot of IFS...
dan_ed
2,451 posts
 
The only reason I say "if" is to keep my post in general terms.

I do have a means to infinitely adjust p2s and I do have protractor that was custom made to the effective length of my tonearm. I can change to any cartridge I want and be assured of the correct alignment. The distance from stylus to center of cartridge mounting holes is a "don't care".

But there is a correlation with what you are posting to this thread about. That is the correct effective length of any particular tonearm. I surprised to find out that sometimes there are differences of a few mm in the published specs for some tonearms. So, check your numbers before ordering a custom protractor. :-)
axelwahl OP
788 posts
 
Hi Dan_ed
I'm not all the way with this adjustable p2s (pivot-to-stylus) protractor.
It obviously is not the 'fixed type' that you warn about below.

>>> So, check your numbers before ordering a custom protractor. <<<

The issue with mh2s is that it is part of p2s, and in any fixed mh head-shell arm of some pretty high importance to know, i.e. certainly no mute point --- lest your overhang AND zenith are out = more distortion.

So, your warring is BETTER well headed!
In the meantime I will stick to my stock alignment, since I DO NOT KNOW as yet what my PW's mh2s actually is.

"IF" my p2s comes to 233.15mm (please note the .15! part of it) I should be in the pound-seat.
No need to mention the arm, since that spec is too well known by now, or? :-)

Axel
dan_ed
2,451 posts
 
The distance from the center of the tonearm pivot, to the [bold]stylus tip[/bold] is the effective length of the tonearm. This is the critical distance and does include the dimensions you are concerned with only because the overhang is parallel to this measurement. If you change the cartridge, all you need to is move the cart in the mounting holes until the stylus hits the arc again. That's it. Effective length is maintained and the mounting holes end up where ever they are.

In my previous post I probably should have left P2S out because this, along with overhang, were created to compensate for table/arm setups where the pivot point cannot be improved upon. I.E., P2S distance is fixed but to get the correct overall effective length the proper overhang would then need to be set. In such a setup the only adjustment of effective length is with overhang. The user has no other choice.

I never said that the protractor used had adjustable P2S. On the contrary, the arc on this style of protractor is fixed at the effective length of the tonearm it is being made for. If the maker of the 'table in question got effective length (and thus p2s) spot on there is no adjustment to the pivot point needed. However, if the pivot point is off by 1/2 mm that is enough to throw off the geometry. Although it will still reproduce music reasonably well, reducing this error will make an audible improvement.
axelwahl OP
788 posts
 
Hi Dan_ed
you say:
>>> If you change the cartridge, all you need to is move the cart in the mounting holes until the stylus hits the arc again <<<

You obviously didn't take note of, that we are talking about a SME V in my specific case, and the case I've been talking about i.e. ... "IF" my p2s comes to 233.15mm! plus +++ No need to mention the arm, since that spec is too well known by now, or? :-)+++

Seems there was a need to mention it after all.

In the case of 'fixed' arms there is no: "move the cart in the mounting holes" therefore one HAS TO RELY ON some reasonable proximity to 9.52mm s2mh...

You are OF COURSE right, that for arms other than that, it could be considered a mute point ---- until your mounting holes run out of adjusting space i.e. with some arms using an e.g. a Dynavector 17D3 Karat Cartridge.

Greetings,
Axel
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