Axminster Diamond Stone - a few daft questions

[Glynne]

I've just bought a replacement stone from Axminster as they are currently on offer and the difference is amazing.
http://www.axminster.co.uk/axminste...-bench-stone?gclid=CJ7RkvT2pb0CFXMPtAodVysA6w
Before slinging the old away, I was just wondering as to whether I could put it to any use and not knowing anything about the construction of these thought I would ask.

As the stone wears out, is this down to diamond particles being removed from the stone or being worn down (but remaining on the stone)?
If it is the latter, then presumably you might be left with a stone with a finer grit albeit not very sharp for cutting - so perhaps you could use it for lapping?
Accepting that the diagonal lattice structure means the stone won't be completely flat, will it be flat enough for attaching a coarser grit paper for initial shaping / sharpening?
I probably sound like a real cheapskate as the new stone was <£12 but it would be good if I could find a use for the old one.
Thanks,

Glynne

 

[sdjp]

As the stone wears out, is this down to diamond particles being removed from the stone or being worn down (but remaining on the stone)?

Maybe!

It depends on the stone. Generally speaking, the cheaper stones lose grit over time, because the attachment between the diamond and the plate is the weak part.

Diamonds tend not to 'wear' like most materials - they are so hard that the rate of wear would be negligible. However, the grit particles can crack, and get smaller in that fashion (and then those fragments _can_ wear the other particles a little). This is a slow process, of course, but some diamond grit particles are more susceptible to fragmenting than others. (In some power grinding diamond stones for very hard materials, this friability is deliberate, to ensure that the cutting surface is aggressive).

The third way that a diamond stone can loose it's effectiveness is for the diamonds to sink into the metal support. (Consider - diamond is hard enough to cut into the metal, right?). In this case, you can often restore some cutting power by removing a little of the supporting metal - the normal technique is to use a loose abrasive grit that is hard enough to remove the metal, but not affect the diamond - which is a pretty wide range! Lapidary saws is one case where this is a regular process - typically an aluminium oxide grit block is used to 'sharpen' the saw. If this is the problem, then sanding the surface with some silicon carbide paper (maybe plus some loose grit) might restore cutting action. It also might wreck the stone (too much and the diamonds fall out), and would be easy to make the stone non-flat. Still, if you were about to bin a stone, it might restore enough to it for dirty, non critical jobs - provided you're happy to accept the risk of ruining it.

If this is the case, then it'll function as a finer grit - but because it's a little uncontrolled, you can get the odd bigger particle, and this can be at risk of leaving scratches.

If you have access to the imaging tools, you can generally get a good indication by looking at the diamond particles. The metal plates are conductive, you just stick it in your scanning electron microscope, cracked diamond particles stand out, as does a reduced diamond density (you'll probably also see empty sockets). Honestly, I've no idea if other magnification devices would be good enough - I've been throughly spoilt by access to big toys!

 

[Glynne]

Thank you for the comprehensive reply.
It has to be nearly 40 years since I went near an electron microscope and so I'm a bit long in the tooth to resurrect my physics career!
I've kept the old stone just in case a flash of genius hits me, but I'm not holding my breath.

 

[andys wood shed]

Just try cleaning it

 

[Glynne]

I tried that Andy and it is genuinely worn compared to the new one.
Just seems a shame to throw away a reasonably flat metal plate.

 

[tomf]

It's back up to £23 now, could have done with one.

 

[carlb40]

It's back up to £23 now, could have done with one.

Yeah it was a 1 week only offer.

 

[carlb40]

I tried that Andy and it is genuinely worn compared to the new one.
Just seems a shame to throw away a reasonably flat metal plate.

Maybe just continue to use it, but after the new one as it will be finer now compared to a new one.

 

[SteveF]

if it is flat still

u could apply diamond paste ?

Steve