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micro pits and fractures caused by high speed?

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Author Topic: micro pits and fractures caused by high speed?  (Read 777 times)
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« on: December 13, 2015, 01:32:34 pm »

Hi All

I will try to make a long story short. Can high speed like a genie cause micro pits and fractures? Last year I bought a used genie with the thought it would speed up the time it takes me to make a cab. I repurposed the right side wheels wet 400 800 and 1200 grit diamond. Then I go to my flat lap for final sanding and polishing.

BUT I have problems seeing micro pits and fractures that I have never when I just used my flat lap. The stones take a good polish and no cerum oxide gets trapped in them but I can see it

In my frustration I replaced my 600 1000 and 2000 thousand sic on my flat lap and
 still ended up in frustration

Still no good omg omg

I found a 20 mu diamond 6 in disk that would fit on my flat lap then it was game on yes

so any input as to what is going on would be cool but for now I am going to look for a speed control for the genie

Bless
Shawn
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Debbie K
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« Reply #1 on: December 13, 2015, 02:03:59 pm »

I've heard of some folks having trouble like this when their arbors are not true. I don't know if that could be the case; you may check it by holding up something to it on a steady rest and seeing if it hits then misses.

I've had something like this happen when I roughed out with a 60 grit diamond wheel on quartz like stones. The microfractures weren't apparent until the final grits. I had to use the finer 200 grit hard diamond wheel to rough out and the problem seemed to go away. And I also found that some stones don't seem to like the diamond belts on my Expando drum, either. I've had to use silicon carbide belts on some stones.

I'm sure that others have had the same problem and will share what went wrong and why. I don't make that many cabs, so I'm sure that others will have better advice.

Debbie K
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« Reply #2 on: December 13, 2015, 02:24:26 pm »

Cooling may be a problem too. Is your Genie spraying enough water on your wheels ? Excess heat buildup will cause pitting & fractures in some stones. Try a lighter touch & more water when grinding and see if it helps.
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« Reply #3 on: December 13, 2015, 07:47:48 pm »

jakesrocks has it right more than likely.  Many stones are very sensitive to "blowouts" caused by water vapor expansion in the stone.  This is caused by too much pressure or moving the stone contact patch too slowly. 

I teach very fast movement in this pattern ////\\\\\//////\\\\\\\  Basically a very fast 90 degree movement pattern.  Then you flip the piece 180 degrees and do the same pattern again.

With the correct pressure and movement I have gotten to the point I practically dry polish Jade and a host of other stones on NOVA wheels.  Often a dip into a container of water and a wet bandaid on my finger is the source of water I use on a NOVA wheel.  You need to develop a "feel' for the drag.
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« Reply #4 on: December 14, 2015, 06:55:56 am »

   Are your wheels brand new?  New diamond wheels need to be broken in as they are very rough. Take a really good piece of jasper or agate and just cut like crazy for awhile. You will feel the difference in your hand as the diamonds smooth out. I usually use both misters under the wheel I am using to make sure there is enough water on it.
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« Reply #5 on: December 14, 2015, 10:01:08 am »

Hi All
Thanks for the input. I think 55fossil is correct. The wheels are not new but they have been recoated. I will try to break them in and see how that works. I will let you all know.

Again thanks for all the input.

Bless
Shawn
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« Reply #6 on: December 14, 2015, 04:35:17 pm »

Hi All

55 I think you were correct dancer5

When I got home from work I ran a slab of agate that had a straight edge on all 3 wheels that I recoated and then tries a cab that was on the waiting list with for same problems on all 3 wheels and did a quick buff and I saw no new microes  and a lot of improvement yippie

I got a late start today so I will give my final thought later. Have to do the family thing now.

Bless
Shawn
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« Reply #7 on: December 15, 2015, 07:27:32 am »

I had a similar experience with Rutilated Quartz last spring. I was using a 6 inch Crystalite RingLeader . Running 100 and 220 3M diamond belts the surface of the cabs were coming out with a frosted look from thousands of micro fractures on the surface. Shaft speed is a very positive 1725 RPM. Went to the 8" machine with a shaft speed around 1250 and had no problems with either Diamond or Silicon Carbide Belts. All of the belts are well broken in. Occurrences like this are not very common.
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« Reply #8 on: January 19, 2016, 01:23:58 pm »

hi All

Here is an update. Dressing the wheels helped a lot but did not get the stone where I want it to be. This is the stone I want to enter it in the kCC this month but I need input. A lot of my problems is because of all the transitions in the stone. So do I quit where I am at or does someone have a tip to move this stone to the next level? Pic's are after 14000 grit. help

Thanks for your replies in advance.

Bless
Shawn


* SAM_0440.JPG (274.05 KB, 1024x768 - viewed 15 times.)

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« Reply #9 on: January 19, 2016, 07:43:35 pm »

Something I started to do religiously with my genie this summer to cool the stone as well as avoid micro scratches was to make sure to change the water whenever going up to the next grit. With each water change, I also put a little dawn dishsoap as well as jet blue dishwasher agent. Helps to keep the stone slick and the wheels get a washing each time, ridding them of old muck. Don't ever seem to get fracturing or pitting anymore plus the shine has really increased
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« Reply #10 on: January 19, 2016, 11:26:11 pm »

I put a bit of borax powder in my saw so I figured it would do something in my cab machine. It seems to help. The water does feel slicker.
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« Reply #11 on: January 20, 2016, 07:07:32 pm »

Some folks that I know who own Genies have gotten rid of the pump/mister and gone with a drip systems to avoid the problem of cross-contamination from the recycled water.

Debbie K
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« Reply #12 on: January 21, 2016, 07:53:15 am »

Every problem I have had with the end product has been cured by going back to 600 grit with lots of clean water and borax.  I also add sodium nitrite to prevent rust.  Rust flakes can do damage to the surface.  I've also used potassium nitrate for the same purpose.
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« Reply #13 on: January 23, 2016, 08:36:37 am »

   I hate to say this, but I cheat. I use my mini sonic vibratory with 600 grit after the 180 wheel. I run about 20 cabs in with previously polished small stones. 2 spoons of 600 grit for 3 days is usually enough. Then I go back to my Genie and finish them by hand. There should be no scratches, just a nice buff finish that glows when the cabs are wet.
    Warning: Mixing hard agates with some jaspers leads to disaster. Try and use agate with agate, even the polished stone you use to fill up the barrel. Crystal pockets and vugs can catch grit that comes out in the last stage and leave scratches.
    I do not use a tumbler of any type to finish stones. I love working them in my hands and watching them turn into pieces of art (hopefully). But rather than dry sand on a worn belt to get tough scratches I prefer the tumbler to do the final grinding.
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« Reply #14 on: January 25, 2016, 03:07:50 pm »

Hi All

Thanks for all the input. This material is Charoite so I know that there is problems cutting it. I cut 2 of the all purple/white with minimal problems. This is my first try at a cab that has all of the different material that is in the rough. I spent a lot of time testing this weekend so I will list my results

1) cleaned Genie tray.lines and spitters. Stuck spitters in a small jar and ran.changed water and ran again.
2) Resanded stone on my nova wheel that I resurfaces with 400 grit no problems.Sanded with 800 grit recoated wheel no problems.
3) I went to 1200 on the expand big problems. Dressed belt and cleaned genie again and repeated step 2 Bad again
4 Repeated step 2 and tried 3000 grit on the expand Bad again
5) did step 2 again and switched to flap. At 1200 grit bad again.
6) Did step 2 again and tried to polish now I am done with this for not OK so my thoughts after all of is .

1) Charoite is really hard to cut.
2) Is it a grit related problem or is it a vibration problem dunno

My guess is it vibration problem.

Thoughts please
Bless
Shawn
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