Tonearm mounting distance.... advice please

[take5]

Im looking for a bit of advice please, regarding tonearm mounting distance.

Ive just bought a lovely plinth for my Garrard 401, and I want to mount my Fidelity Research 64fx arm on it. The plinth comes with a blank wooden arm board, ready to be cut.

Geoff/Oldius is kindly going to help me with the mounting distance, using his Feickert contraption.

The distance I want is 231.5, Spindle to Pivot, and Im sure Geoff can do that. (with me supervising, of course :) )

Now, this is the bit that confuses me.
That arm will then be fixed there. It cant be moved.
Fine, if I have a cartridge and headshell which allows some leeway in positioning the cartridge. I can adjust it to get the correct angles etc. For example, I have an IO in a Fidelity Research headshell. I have some leeway in the headshell as to where the IO sits.

But, I also have a Fidelity Research cartridge which is different. The cartridge is integral to the headshell. There is no further adjusting possible.
Im hoping/assuming that since the cartridge and arm are both Fidelity Research, then this will just fall into place once I get the hole cut in the correct place.

But say the cartridge doesn’t then “line up” with a protractor? What can I do?

Or, say in the future I wanted to use a different integral/one piece cartridge/headshell, and it was a slightly different length to the FR version. How do I adjust for this?

Any help would be much appreciated.

[struth]

you cant really.overhang gets adjusted from headshell side. if the cart cannot be moved in the shell then your stuck I think. unless the tube can be adjusted

[walpurgis]

Would it not be possible to make or have made a sliding base to the arm mount? Something like the Acos Lustre arm uses. I've done so in the past. If it's made of well chosen material and sensibly designed, it should not impact on the sound quality.

[hifi_dave]

Mount the cartridge on the arm and measure the distance from stylus to pivot. That 'should' be the recommended length.

The FR fixes with a large nut and washer underneath, so you could make a slight elongated slot, like SME, which will give you a bit of leeway.

[tiguan]

Could you share photo of plinth and armboard.

[awkwardbydesign]

For my Oracle Delphi I made mounting plates like this. The board is drilled off-centre, so it can be rotated and the distance to the TT spindle will vary. You can make similar circular arm boards from the same material as your plinth, and change or rotate them for adjustment. If you have a router you simply make a circular opening one ply deep and set the arm board in level. Or not, if you want to change the height.
http://i1134.photobucket.com/albums/m604/awkwardbydesign/Oracle%20Delphi%20Mk1/oracleparts010.jpg (http://s1134.photobucket.com/user/awkwardbydesign/media/Oracle%20Delphi%20Mk1/oracleparts010.jpg.html)

[Barry]

I would imagine Fidelity Research designed their FR-702 cartridge with the SME/EIA mounting stub to fit the FR 64 arm, so the correct geometry ought to be obtained if a spindle-to-pivot distance of 231.5mm is used.

It ought to be pointed out that many Japanese arm manufacturers do not necessarily follow any of the three recognised arm geometries (Baerwald, Loefgren or Stevenson) and tend to "do their own thing" (which is often closer to Stevenson's geometry than to that of the other two). So the combination of the FR cartridge with FR arm, may not allow you to use a conventional alignment protractor (which usually has alignment markings for Baerwald's geometry, with the null-points at 66.0mm and 121.0mm).

If the arm comes with an alignment protractor use that, otherwise don't worry as there is no provision to adjust overhang - you will have to assume that FR 'got it right'.