Darkside lap starting to polish curved!

[Spaghetti888]

I'm wondering if anyone has had their darkside laps start to polish curved facets? Mine has started to do this with the last couple of stones.

I'm prepolishing with 3000 on a batt and get very sharp facets with that, then when i goto polish with my darkside,  i am getting funny curves along the edges of my facets.

I have also gone from 1200 to darkside with the same issue.

This is just a recent thing...any solutions?

[FlashGP]

Is your lap flat?

Do you sweep across the whole lap or just polish in one place on the lap?

One of my darkside laps is very flat and I don't have the problem you describe.

My other Darkside is new and not so flat.  I expect it would curve the facet if I kept the stone at tbe same Place on the lap.

Laps also cut faster on the outside.  If you don't sweep the stone, it can cut faster on the outside, changing the facet edge and  curving it,

[Shivan]

I have only used 60k diamond and oxides on my darkside lap, but have not had any problems with rounded facets as yet.

[Aussie Sapphire]

Darksides can be resurfaced if they have worn to a point where they are not performing as they should.


Something to keep in mind.


Cheers
Leah

[fossickeract]

  Spagettie888,
         Its not the lap! A kink or curved facet edge is something judges look for in competition stones and indicates that the facet has moved during polishing and that move has not been extended right across the facet.
           Often caused by a slight adjustment made with height or cheater or both to get the meet points perfect which is Ok but the adjustment then needs to be polished across the whole facet or a kink appears on the facet edge, and if done repeatedly the edge becomes curved.
             Ok if you haven't made such an adjustment then the facet has moved itself. The pressure of polishing may be pushing the dop ever so alightly into the quill, cotton bud and metho clean the jaws of the quill and ensure its tight on the dop. Another possible cause is flex in the dopping glue, two part Araldite is known to flex slightly. On one occasion I have been careless not using enough hardner resulting in the stone rotating slightly as the dopping epoxy being soft in the centre allowed the stone to rotate under pressure. These dopping issues only become apparent during polishing especially on the table. I hesitate to poke a bullants nest but
     “ Laps also cut faster on the outside.  If you don't sweep the stone, it can cut faster on the outside, changing the facet edge and  curving it,” First published by Vargas in 1969   retracted in later editions, but an unfortunate furphy often repeated. This is not possible, think about it if any part of the facet cut quicker it would cease to make contact with the lap and stop cutting. Sweeping across the whole lap is a recipe for scratches, gathering up excess polish and swarf but each to his own no offense intended.                                       Ted

[Spaghetti888]

Thank you everyone for the replies! All taken on board.

Ted, thanks for that information, I wasn't aware of all that...after reading that I'll have to be more mindful with the cheating!

 

[Orange Pirate]

Another possible cause is flex in the dopping glue, two part Araldite is known to flex slightly. On one occasion I have been careless not using enough hardner resulting in the stone rotating slightly as the dopping epoxy being soft in the centre allowed the stone to rotate under pressure.

I moved away from Aralite for that very reason. 'JB Weld' seems to be a 'firmer' epoxy cement with, in my opinion, a lot stronger bond. Not that, that is automatically a good thing and brings it's own issues.


Cheers
OP

[FlashGP]

Another possible cause is flex in the dopping glue, two part Araldite is known to flex slightly. On one occasion I have been careless not using enough hardner resulting in the stone rotating slightly as the dopping epoxy being soft in the centre allowed the stone to rotate under pressure.

I moved away from Aralite for that very reason. 'JB Weld' seems to be a 'firmer' epoxy cement with, in my opinion, a lot stronger bond. Not that, that is automatically a good thing and brings it's own issues.


Cheers
OP

I have found a little bluetac in the end of the cone dop so it covers the cutelet helps when heating the dop to remove the finished stone.

Ted, thanks for the info re Vargas.   I'll check my sources.  Am pretty sure I got the info from either Don Wilkinson when I first learned to facet (he died a few years ago), Jim Perkins' book that came with my faceting machine, or Broadfoot and Collins' "bible".

So far I have overcome the scratching issue by using facial wipes and Snake Oil to continuously clean the lap when using diamond and using a steady drip of water onto the rong where I apply the Batstick.  This washes enough dissolved polish across the lap to polish without allowing it to build up.

So far I haven't cut anything softer than Quartz so I don't know if the technique works for softer stones.

Regards
Gordon

[FlashGP]

Ted

I have a copper prepolish lap I have to sweep.  There are still remnants of machining marks on it and if I don't sweep it cuts grooves into the facet.

It is a lot better sonce I sanded it but it still needs sanding a bit more.

Regards
Gordon