Tonearm Mounting Assumptions

wanders · Nov 20, 2014

I purchased a new (to me) Thorens TD-125 on which I plan to mount a Grace 940. There is an armboard in place that can serve as a model for fabricating new armboards. That board is drilled, but not for my tonearm. The Grace User Manual lists: effective length = 237mm, overhang = 15mm. There is no template.

Based on this information, can I make these assumptions? 1) The spindle-to-axis length is 222 mm; 2) If I scribe a line on a blank armboard at 222 mm from the spindle, I could center the mounting hole anywhere along the scribed line? The only limitation on the mounting spot would be to ensure the arm could move freely.

Son-of-Vere · Nov 20, 2014

wanders said:
I purchased a new (to me) Thorens TD-125 on which I plan to mount a Grace 940. There is an armboard in place that can serve as a model for fabricating new armboards. That board is drilled, but not for my tonearm. The Grace User Manual lists: effective length = 237mm, overhang = 15mm. There is no template.

Based on this information, can I make these assumptions? 1) The spindle-to-axis length is 222 mm; 2) If I scribe a line on a blank armboard at 222 mm from the spindle, I could center the mounting hole anywhere along the scribed line? The only limitation on the mounting spot would be to ensure the arm could move freely.

I'm in the same boat as I have a hole to drill in a ROK to get the slightly longer arm to fit. Your math works out the same as mine so that should work. You can put the hole anywhere you want as long as it's 222mm from the spindle center.

As a side query, do all TT measurements involving the spindle get measured from the center?

wanders · Nov 20, 2014

If you mean from the center (as opposed to the edge) of the spindle, I would certainly think so.

grottyash · Nov 20, 2014

Pivot to spindle distance is 222mm as you say - you can always check this over at vinyl engine. You are also correct in your second assumption.

sfrykh · Nov 20, 2014

222mm is the correct mounting distance for the G-940, that is where mine is mounted and sounds excellent. The manual is at VE. If you can't get it PM me and I'll email a copy to you. And yes any where along the arc will work for mounting.

Scott

wanders · Nov 21, 2014

sfrykh said:
222mm is the correct mounting distance for the G-940, that is where mine is mounted and sounds excellent. The manual is at VE. If you can't get it PM me and I'll email a copy to you. And yes any where along the arc will work for mounting.

Scott

Thanks, Scott.

I've got the user manual from VE. It's a little short on info, so I thought it best to check assumptions.

Warren

wanders · Dec 2, 2014

Close-Out

Finished rehabbing the deck and installing the Grace 940. I'm still learning the vagaries of this unipivot, oil damped arm. Lots of variables to deal with; but it's starting to sound very good. Thanks to Scott for his help on this arm.

Thought I'd include a photo of this poor man's beam compass. I read the idea originally on AK from a member who used paint stirrers. I thought it was a hell of a good idea an tried it out. After some experimentation, I thought this $3 metric yardstick worked a little bit better; but all credit to the OP for the idea.

sfrykh · Dec 2, 2014

Glad it worked out for you. Looks real good. I really like the Grace Unipivots they seem to work well with a wide range of cart compliance.

Scott

melofelo · Dec 2, 2014

great job:thmbsp: Looks superb:yes:

Son-of-Vere · Dec 2, 2014

Looks good, I like how the grain worked out on the armboard.
But gotta' ask, how did you square up the pencil? Anything other than 90 deg. and it's gonna' be way off. Paint stirrers would be too thin I'd think, that yardstick looks pretty hefty, so kudos on that.

wanders · Dec 2, 2014

Son-of-Vere said:
Looks good, I like how the grain worked out on the armboard.
But gotta' ask, how did you square up the pencil? Anything other than 90 deg. and it's gonna' be way off. Paint stirrers would be too thin I'd think, that yardstick looks pretty hefty, so kudos on that.

Two things on the 90 degree: I concentrated on making a perpendiculat drill hole - measure the hole edge on both sides from the end of the ruler. A drill press is best, but I have a hand drill jig that is pretty good. Second, for my table, you can remove both platters and get a flat surface then check the distance from the pencil mark to the center of the bearing hole. I recall that the OP glued two or three extra thickneses of stirrer on the pencil end to increase the thickness.

Son-of-Vere · Dec 2, 2014

Ah, got it. Measure twice.
I had the convenience of a perfect 1" center hole for the bearing mount and I had it stripped to the deck. I checked several times before I committed to the hole saw, it was kinda' nerve racking.

Tonearm Mounting Assumptions

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