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

@lewm 

I never thought of asking ChatGPT but since you mentioned it ...

 

I started with "what is the effective mass of a holbo tangential tone arm" and got the textbook answer for vertical effective mass.

Then I tried "what is the effective horizontal mass of a holbo tangential tone arm" and got a better answer, though a bit waffly:

Holbo tangential tonearm has a very high effective horizontal mass, which is characteristic of air-bearing linear trackers, as the entire moving carriage assembly contributes to the inertia in the horizontal plane. 

While the exact effective horizontal mass is not a single published specification number, it is generally considered to be: 

  • Significantly higher than its effective vertical mass of 7.5 g.
  • Closer to the total tonearm mass of 31.6 g (which is the mass of the moving part, including the arm wand, counterweight, and carriage).
  • In some similar air-bearing designs, the effective horizontal mass can range from 40 g to over 100 g or even more, as additional weights are sometimes added to achieve a specific low-frequency resonance point. 

Then I put my original question in again, and got a refinement as ChatGPT added the horizontal component.  It learns:

The effective vertical mass of the Holbo tangential tonearm is 7.5 grams. This places it in the low-mass category, generally suiting it for high-compliance cartridges. 

In tangential (linear tracking) tonearms, the effective mass is typically specified differently for the vertical and horizontal planes. 

  • Effective vertical mass: 7.5g
  • Total tonearm mass: 31.6g 

The effective horizontal mass of linear tracking arms is generally much higher because the entire arm assembly moves horizontally, which can be in the range of 40-100g for some models. However, the Holbo design has a very small effective mass for the sideways (horizontal) movement, which is cited as 31.6g before adding the cartridge and mounting hardware. 

For optimal performance, this low effective vertical mass is best paired with cartridges that have high compliance to achieve the ideal resonant frequency range of 8-12 Hz. However, the manufacturer claims it works well with a range of cartridges, including some lower-compliance moving coil options. 

 

 

 

 

 

My titanium bolts arrived eight days after I ordered them, and two months earlier than expected.  The slow boat from China must have been a hovercraft, at least. 

Because the pack did not include nuts, I have to wait for the next boat, bearing aluminium bolts and nuts, before I can try either.

Cut long bolts shorter

put a pair of nuts on first, use the top of one as a guide to cut the bolt

when you back off the 1st nut, force it using pliers, whatever, it will straighten the threads for you, 

file anything loose

now the threads are straight and the other nut is undamaged

@elliottbnewcombjr 

Good advice, but I needed to cut mine longer!

All my boats have now arrived from China.  One had aluminium bolts with washers and nuts, another titanium bolts and the last one titanium nuts.

For wood bodied carts such as ClearAudio, that have no mechanical receptor, plastic cartridge bolts may be considered.