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What considerations apply to material selection for cartridge mounting bolts?

I have found myself needing some longer bolts to relocate a Shure V15 Type 3 cartridge to a Holbo air-bearing system.

The Holbo tone-arm is a tangential tracker with a rigid rectangular 'launch pad' for the cartridge.  The pad is 3-mm thick which is much more than the fixed SME head-shell my dad bolted the Shure to some 45 years ago.  If it was supplied with longer bolts, they disappeared decades ago!

I will most likely have a similar issue with my Audio Technica VM540ML cartridge which is probably a better fit for the Holbo.  It was supplied with a head-shell 4-mm thick, but the bolts slots are recessed by over 2-mm.

A quick internet search turned up bolts made of stainless steel, titanium, aluminium, brass, plastic and nylon.  Some brass bolts are gold-plated (for corrosion resistance presumably).  As a one-time metallurgist, I know that stainless steels can be non-magnetic, or magnetic.

Plastic and nylon are lightweight insulators and immune to electro-magnetic effects like induced eddy currents.

The lower the material density, the lower effective mass of the cartridge.  Here brass is clearly the worst, being denser than steel and weaker than the other metals.

I presume that the main engineering requirement is to firmly couple the cartridge to the tone-arm but I have no idea how firmly.

The Funk Firm has an opposite view with its Houdini coupler which in effect splits the bolts in half, with an elastic suspension between the cartridge body and the tone-arm.  It seems to allow the cartridge body to swing easily to the left or right side.  Does anybody here use these?

richardbrand
faustuss's avatar
faustuss
800 posts
 

@richardbrand 

"Seems like we are both on the East Coast.

Just half a world apart ..."

Are you in Flaaahrida?

richardbrand's avatar
richardbrand OP
1,364 posts
 

Nah Ostraaaaihliah - down undah

lewm
14,655 posts
 

Are you familiar with "Supercar Blondie"?  She is a youtuber with many millions of subscribers, for reasons i don't understand though I don't dislike her.  In any case, she has THE strongest Aussie accent I ever heard.  Maybe she is from an area of your country with which I am not otherwise familiar, accounting for the distinctive intensity of her accent.

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richardbrand OP
1,364 posts
 

@lewm 

31.6 g plus weight of cartridge etc, would be the horizontal mass (maybe not "effective mass"; I don't know how to calculate that in the horizontal plane)

Because the arm pivots vertically, the effective vertical mass is what an actual mass would have be to present the same rotational inertia at the stylus.  It is much less than the real mass because most of the real mass is close to the pivot point. 

Rotational inertia = mass x distance from pivot.  Calculate this for each bit and add the results.

In the horizontal plane, there is no pivot.  The whole thing glides sideways, so the effective mass and the real mass are the same.  You just add the masses of all the bits together. 

Not sure if Holbo adds the mass of the balance weight when quoting the total tone arm mass, but they should.

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richardbrand OP
1,364 posts
 

@lewm 

"Supercar Blondie"

I had never heard (of) her but she sounds normal to me!

Maybe a bit posh - the way an Oz accent changes when its near money.  One really annoying habit common to younger Oz women is that they raise pitch at the end of a sentence and immediately launch into the next one.

I had been thinking of linking cars I have ridden in to my Garrard and Holbo turntables.

I think the Garrard equates to a pre-war blown Bentley two seater sports car - gnarly powerful motor, heavy chassis, clunky controls, surprisingly smooth ride.

The Holbo is like a Citroen DS (goddess) - sleek, button controls, rises when switched on, one of the best rides ever

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