In that version (I’ve revised it now as, at the time I hadn’t realised that the printer had drifted out of adjustment), the contact between the ball and the ‘cage’ was single point and very light (the cage can move freely and weighs 0.33g). With the new version there’s no contact at all between the ball and the cage (as it was supposed to be in the first place).
In both versions, there is one point of contact between the ball and the glass and one contact between the ball and the cup. The ball sits in a small polished spheroidal depression in the brass; the ball can roll sideways a little (by about +/- 1mm) if external force is applied, but the weight of the component and glass always results in a centring force.
3 sheets of a suitable type of glass - please let me know if you know a good type eg Pilkington 10mm hardened or Fraim type glass
3 balls made of ceramic you have identified (again any hints as to good suppliers would be appreciated)
3 small brass cups with height lower than the balls - perhaps I can make a dent in them myself and polish it myself, and find one of the things Yeti mentioned to stop it from moving around??
Should sound better than a random chromed ball bearing…
The glass: 10mm toughened. I’m not sure the supplier of the material makes as much difference as the quality control of how the toughening is carried out.
Silicon nitride balls were purchased from fleabay (grade 5).
Brass blanking plates (for stopping the ends of water pipes) were purchased from fleabay.
The black cage that prevents the ball from rolling too far is a 3d print I designed.
The small depression in the centre of the brass cup was made using a 5/8" grade 10 chrome steel ball bearing (i.e. through hardened bearing steel) positioned using a custom made jig (also 3d printed!). This ensures accurate centring, a good surface to the working area of the cup and also work hardens the area.
Thanks Xanthe.
That sounds fun and doable with my skill set, ie brute force and guesswork!
Perhaps I could just wrap a strip of gaffa tape around the ball to Restrict its movement within the cup?
Is your jig effectively allowing you to tighten a bolt down onto the top of a chromed hardened steel ball bearing that gradually presses it into the centre of the brass base to create an even dent?
Then polish gently with what grade of sandpaper? Or wire wool?? Using a polish like Brasso??
I’m not sure the gaffa tape idea is a flyer. For the ball used to make the dent it’s too imprecise and too soft. For the ceramic ball it will be in intimate contact (unlike the plastic cage) and add unwanted damping.
I used a much simpler method of making the depression… I dropped a 2kg steel weight on the ball from a consistent 400mm height - consistent energy = consistent dent!
(Even though the brass cup was placed on a strong, flat steel plate, I did have to slightly grind the bottom surface of the cup back to flat though.)
@Xanthe I have just been scrolling through this thread out of idle curiosity. I already own a Fraim and am not in the market for balls and cups. However I am blown away by your expertise and helpful and generous spirit. Also by your grace under “fire”. It makes the thread a pleasure to read.
I meant it only for the nitride balls long term, not for the impact zone of creating the dent.
But thinking about it it would also probably turn into a nasty gluey mess after a few years.
The manufacturing process sounds a bit more tricky than I thought.
How about drilling a hole in a circle of wood of suitable thickness and diameter to fit into the brass cup - then giving it a good whack with a hammer?
Would that tend to deform the flat base so as to render it wobbly/unstable?
That should work, but to ensure centring you need to make sure the hammer strikes completely perpendicular and with the face of the hammer parallel to the surface on which the brass rests.
Yes it will deform the base enough to make it rattle; but grinding it flat again is easy (320 or 600 grade wet or dry paper used wet, supported on a flat glass plate).
Easy, get a sheet of 'Wet or Dry" paper - i.e. a silicon carbide abrasive paper ( ‘grey sandpaper’ ) designed to be used either wet or dry. Cut a piece about 75mm wide by about 100mm length, wet it and hold it on top of the glass plate. Take the brass cup in the other hand and, pressing in the middle of the brass cup, using circular movements, rub its bottom on the wet or dry paper until it’s flat again. Rinse the abrasive paper in water and repeat for the next brass cup.
Make sure it’s its bottom you rub on the abrasive paper, not your own!
There’s a problem with those. The base thickness is just 1.15mm, that doesn’t allow much room for forming an indent on the bottom. The type of brass stop end for water fittings that I used are probably better.than core plugs as they are about 3mm thick at the base.
For a 14.3mm silicon nitride ball, I’d suggest using a 20mm to 25mm ball bearing (steel) to form the indent.
To decide where to position the 3 balls under each glass, did you hold the Naim box underneath and tilt it to test where the weight is distributed within it, then put the points in a configuration that is likley to stabilize that?
And perhaps look at a photo of what’s in the box too, to see where the heavy components are?
e.g. if a transformer is in one corner, put a ball close by or directly under it?
made of ceramic you have identified (again any hints as to good suppliers would be appreciated)
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