Nova wheel cross contamination

[Neural]

Ok, I've heard people here and there swear that this can't happen, but it is quite obvious that it *is* happening.

I go from 600, to 1200, to 3000, then to 8000, 14000, 50000.

Somewhere between 3000 and 50000, my stones are picking up scratches that are in the 600 to 1200 range (easily visible to anyone here that has experience with cutting).

The only way I can think of to clean them would be to run a hard stone on them for a while.  I've got a piece of black jade that I can use to "dress" just about anything, but if anyone else has info they can pass on, would love to hear it.

[mirkaba]

Maybe you should rinse your stones between wheels.

[Mark]

Bob said it, rinse between wheels.  I have a bucket of water on the floor and i used to dunk the preform and shake it after each wheel.  Not sure if it helps that much, but i used to do it religiously.  In my case, I believe i leave a wheel too early when i see scratches.

Mark♦

[christopherl1234]

Jon,

Years ago I read a blog on the net where an American miner in Australia swore that his 14,000 wheel was actually putting scratches on his opal. So he would only take his opal to 1,200 and then go directly to polish. He later found that going to 3,000 worked better. I did a little experiment and carefully examined my opal after my 14,000 wheel and sure enough I would see scratches. I then stopped using my 14,000 wheel and the scratches no longer appeared and my polish was much better. You might try it out. If you do please tell me if it worked as well for you as it did me.

[hulagrub]

Jon, on your Genie, you could use a little plastic dish for each wheel, with fresh water for each mesh. But like Mark said, rinse your stone.

[Neural]

Skipping from 8000 to 50000 isn't *real* bad.  Will check that out.

While I appreciate all the info on washing the stone between wheels, doesn't it kind of defeat the purpose when the Genie pulls it's spritz water from the area that the cut material is washed into?

[hulagrub]

Use a little tub of water, for your spitter and dump it between wheels.

[Mark]

There was a time when i seemed to be plagued with scratches.  I thought that i could be cross contaminating my wheels and started dipping my cab after each wheel.  I determined for the most part, that my scratches were from not doming the cab well enough and leaving a tiny flat spot.  I started grinding long ways from top to base along with from bezel to top of the dome to be sure i didn't get flat spots.  That cured most of my problems.  I have noticed a few times, mostly with softer stones, that i sometimes get scratches from certain wheels.  This only happens with the soft stuff and i believe its because i have a couple of non Nova wheels that seem to be graded differently than the Novas.  As funds become available, I am ridding myself of the non Nova wheels and just going all DP Novas.  It seems to me that for the softer wheels, you should be consistent and stick with one brand so you have a smooth transition from one wheel to the next.  I have an 8000 off brand that seems like it should come before the 3000 Nova.  The 8000 seems much grittier than the 3000 Nova and sometimes scratches the cab when i go to it.  I have learned with softer stones to skip the 8000 and just go to the 14K Nova next.  So it seems there can be several factors with regards to scratches and you need to narrow down the exact cause and come up with a workaround.

Mark

[Freeform]

I agree 100% Mark. Cross contamination can happen. But not all so often when working the stones we love which are generally around 7mohs.    I have yet to talk with any cutter that hasn’t gone through this headache.   The way I solved when I noticed it happening to me years ago. Was to make sure I wipe and dry my stones in-between sanding and polishing stages. And simply look hard for all scratches. And then to remember to always cross cut each successive stage.

I can’t say with Nova wheels, never used them. But the best way to test whether or not you’re really taking the time to properly sand and pre-polish your stone. Cut a piece of Obsidian. Time yourself compared to cutting a piece of opal.  They generally should work about the same time in my book. (Unless you spend more time orientating the Fire in precious opal)

The black glass will show your straches ten fold over a white stone.  At least then you can get an idea of the time it really takes to sand all sratches out. Which will develope into faster and easier cutting technqiues.

[Mark]

Shain has a good point which has been mentioned around here on various threads, check your cab after each wheel.  If i find a bunch of scratches, i stay with the last wheel until it looks good enough to go to the next wheel.  If you find the scratches 2 or 3 wheels past where they happened, you will never get them out with the current wheel.  You have to go back to where they started.

Mark

[rickn]

If the scratches are right in the center of the cabs it may be that your shaping has left a small flat spot right on top. The hard grinding wheels are just a shade smaller than the soft wheels and what looks like a good shape may leave a small flat spot or dimple on the top that the soft wheels cant get to. Also it usally isnt easily seen till your two wheels past down the arbor. Its seems more prevailant on the larger cabs. You can use the twin floursent shop lights with a wet cab to see if this is your problem. Any distortion of the light at the center is a flat spot. This was the problem I was having and thought for sure it was cross contamination of my wheels.

RickN

[Michael S Hoover - Redrummd]

I use aluminum oxide dressing sticks to clean my NOVA wheels occasionally.  I do not need to clean them for cross contamination issues but due to build up of microscopic metal pieces that want to blacken the stone on lighter colored stone.  Each of my wheels has its own fresh water supply and cowl so it is about impossible to get any contamination but it will occur with the splash system if you do not change the water especially after a long session of sanding withthe 600 grit wheel in a three wheel tray....

I also use the dressing sticks to stop the hydroplaning that occusrs once they NOVA wheels wear slick as they get close to worn out.