Enigman
starting to spend too much on rocks
Member since December 2013
Posts: 163
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Post by Enigman on Mar 21, 2014 12:48:41 GMT -5
Hi all, I am tumbling a variety of glass colors that started as 1 to 2 inch chunks, sized just like any other crystal stone. All the stages have gone well with very short run times to achieve the necessary grinding and smoothing. The stages all used ceramic media as filler. Stages 1 and 2 used large ceramic, and stages 3 and 4 used small ceramics. In all stages there was more glass than ceramic fill. I also inserted a stage 3-1/2 which had 1000 grit aluminum oxide. Everything up to stage 3.5 went as expected with consistent homogenous finishes and no visible impact damage except for a couple of edge spawls. In those cases I trimmed off the spawled area with a wet saw and moved the stone back to a previous stage. I have run five pounds of glass through many iterations of the early stages to process it all. Shown below is the first batch to go through stage 4 with aluminum oxide polish. The barrel was about 60% full with about a half cup of small ceramic fill. The run time was 72 hours. The good news is that the sides of the stones polished up to a high gloss. The bad news is that the edges show significant damage that I interpret as impact damage. All the stones exhibit some degree of damage and the level of damage seems to depend on the color of the glass, with aqua and clear glass showing the least and purple and cobalt showing the most. Also some of the polished sides have small spawls right in the middle of the face that did not exist after the 3.5 stage. This all points to impact damage. It is also possible that the ceramic media is too course for use in the polish stage with glass, even though the ceramic is well used and smoothed from prior tumbling, although if that was the case I would have expected scratches on the side faces and there aren't any. The side faces are glossy and pristine with the exception of the few spawls. This is the first time that any stages have shown any difference between edge and side finishes. The edges are now much rougher than they were after even as far back as stage 2. I can feel the rough texture easily. The stones with the least damage have only a sprinkling of tiny white dots on the edges. I suspect I am going to have to return these to the 120/220 stage with ceramic media or the 500 grit stage and rerun these with HDPE pellets for media and a higher media fill level to reduce impact. Then go forward again through 1000 grit and polish. Has anyone seen this happen before? Any suggestions on how to avoid the damage and get an overall consistent polish? Any help would be appreciated. Here is a typical sample:
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Post by 150FromFundy on Mar 21, 2014 15:24:37 GMT -5
That's how my first batches of Obsidian (black volcanic glass) turned out. Glass and obsidian are pretty soft and can be difficult to get a mirror shine on. Although, there are a few members on RTH that have mastered this.
You didn't say if you were using a rotary, or a vibe. Based on you using ceramic pellets, I going to assume a vibe.
It may be as simple as using more ceramic pellets in the polish stage. When I polish my cabs in a vibe, I fill the bowl almost to the maximum level with ceramic pellets, then a add the few pieces (20-30) that I am finishing. The idea here is that the cabs only contact polish and ceramic media and do not hammer upon one another.
Darryl.
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Enigman
starting to spend too much on rocks
Member since December 2013
Posts: 163
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Post by Enigman on Mar 21, 2014 16:11:21 GMT -5
Nope. I am using a rotary, a dual 3 pound barrel. That's why at about half full I am assuming that the pieces are falling down the slope too hard. There was no mud in the barrel, just a thin watery solution so there was nothing to stop the pieces from free falling down to the bottom as the barrel turned.
Yeah, I figure I am going to have to load up the barrel with media to at least 3/4 full. I'll try using more polish to promote mud, and plastic pellets since they are good for cushioning.
I'd love to hear from someone who has been successful with obsidian?
Thanks.
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Steve
has rocks in the head
Member since June 2005
Posts: 506
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Post by Steve on Mar 21, 2014 16:53:53 GMT -5
When trying to do glass in a rotary use lots and lots of plastic pellets - overfill to 7/8 volume. The frosting you're getting is as you've already surmised is impact damage.
For best results with glass and obsidian use a vibe.
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Enigman
starting to spend too much on rocks
Member since December 2013
Posts: 163
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Post by Enigman on Mar 21, 2014 18:40:29 GMT -5
When trying to do glass in a rotary use lots and lots of plastic pellets - overfill to 7/8 volume. The frosting you're getting is as you've already surmised is impact damage. Yeah, I just restarted the batch in stage 2 to get rid of the edge damage. Then I'll move it back up through stage 3. At stages 3.5 (1000 grit) and 4, I'll switch to plastic media really full. No can do. I live in an apartment. I can control the noise of a rotary and isolate it from the floor so it doesn't transfer next door, but a vibrating tumbler would be much harder to silence. The vibes would travel right through next door both down and sideways. Someday when I have a garage again that's possible. For now, I have to find the right trick for a rotary. Thanks.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,154
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Post by jamesp on Mar 21, 2014 20:22:20 GMT -5
Fill it 7/8 full as Steve mentioned has worked for me. Man made glass has another challenge. The baby blue one has much less frost. I have tumbled table top glass. I believe it is tempered to break into smaller pieces. It rounds very quickly. ie, it is soft. Other glass is much harder. When mixed, the hard glass will polish best, the soft glass the least. Better to tumble like glass. That damage looks like it may have happened in the early stages. Be sure to dry test samples and observe them dry after each step. Mixed types of glass are a challenge. Those look like they saw severe impacts. I would think you would have heard the rattling. I add sugar to thicken to a light syrup. That gives great shine for a rotary. Fill to 7/8 and listen-should be quieter and gentler.
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The Dad_Ohs
fully equipped rock polisher
Take me to your Labradorite!!
Member since September 2012
Posts: 1,860
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Post by The Dad_Ohs on Mar 21, 2014 23:26:01 GMT -5
I agree with Jamesp, especially about adding the sugar to form the slurry... at the later stages of tumbling the 1000 grit doesn't form a slurry as does the coarser grits earlier on do. the addition of sugar forms a syrup that will help cushion the material and allow the grit to move through at a more uniform rate, giving you the results you desire.
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Enigman
starting to spend too much on rocks
Member since December 2013
Posts: 163
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Post by Enigman on Mar 22, 2014 0:16:46 GMT -5
Nope. I dry inspected every stage looking for any variances and there was completely even finishing after every stage up until stage 4. In fact, a very close inspection of the damage indicates that the glass in stage 4 FIRST went to a high polish on the sides AND edges and then during continued tumbling it began knocking flakes of polished material OFF of the edges and corners. It looks exactly like when the clear coat on a car paint job goes bad and begins flaking off. You can see that if you look closely at my photo above, especially the two stones at the upper center and right.
WOW! That's a great idea. I never would have thought of that.
How much sugar would I use in a typical three pound barrel?
Yeah, I noticed that the slurry basically remains watery at 1000 and finer grit. As I mentioned I think that contributed to the stones falling with more impact. There's also a lot of surface foam when I open the barrel.
Love the sugar idea. I wonder if you could use bottled corn syrup in place of water, or use Sierra Mist or something with a medium viscosity. I guess it's six of one, half dozen of the other. Either you use pre-made syrup and thin it out, or use water and thicken with sugar. Same same.
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Steve
has rocks in the head
Member since June 2005
Posts: 506
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Post by Steve on Mar 22, 2014 1:16:31 GMT -5
Another option for thickening the slurry is fine saw dust.
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jamesp
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Member since October 2012
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Post by jamesp on Mar 22, 2014 4:34:42 GMT -5
Ok. Glad you do the dry test. Got to find out what stage the chipping occurs.
I have used syrup, Karo(sorghum)syrup to be exact. But it is expensive compared to good ole white sugar. Sugar has several advantages. It maintains it's thickness for weeks. And it reduces bubbles by reducing splashing. As Mario mentioned, the slurry is thin and offers little padding in 1000 grit(include 500 grit stage)stage.
and sugar greatly lubricates the batch. If you unload the contents of the tumbler into a bowl you can push the rocks around in the bowl and feel how lubricated they are. To the point they are like picking up a watermelon seed. Most abrasives perform best w/lubricant. I have never experimented w/sugar in coarse or 220 stage because of Mario's point.
Probably the most important of factor is the fact that it maintains it's thickness. All it takes is 12-24 hours without padding or thick slurry and your load can get frosted. That is the main reason I use sugar.
Times that I have polished past my patience zone of 7 days I have added more polish at 7 days and tumbled to 14 days. That created a very high polish. But still not as good as a lotto.
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jamesp
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Member since October 2012
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Post by jamesp on Mar 22, 2014 4:43:48 GMT -5
Oh, start w/a cup in a 3 pounder. Run it with the polish and check it an hour or so later. It should not ever be as thick as pancake syrup. Let's say mineral oil. And the liquid level in the tumbler should be say a 1/2 inch below the rock level.
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Enigman
starting to spend too much on rocks
Member since December 2013
Posts: 163
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Post by Enigman on Mar 22, 2014 10:17:35 GMT -5
Oh, start w/a cup in a 3 pounder. Run it with the polish and check it an hour or so later. It should not ever be as thick as pancake syrup. Let's say mineral oil. And the liquid level in the tumbler should be say a 1/2 inch below the rock level. Okay, I'll give that a shot. I have a stage 3 barrel completing on Monday so I'll try it in the 3.5 stage. I'll report back on what happens. Thanks.
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jamesp
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Member since October 2012
Posts: 36,154
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Post by jamesp on Mar 22, 2014 10:54:20 GMT -5
good luck Enigman. glass is a challenge so just warning you
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Post by phil on Mar 22, 2014 18:48:16 GMT -5
I read on another board that you have to slow down the tumble action (speed) for the final stages of glass.
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jamesp
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Member since October 2012
Posts: 36,154
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Post by jamesp on Mar 23, 2014 3:45:03 GMT -5
Looks like a lot of methods get er done.
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Enigman
starting to spend too much on rocks
Member since December 2013
Posts: 163
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Post by Enigman on Mar 23, 2014 10:48:11 GMT -5
I read on another board that you have to slow down the tumble action (speed) for the final stages of glass. Hmmmmmm. How would I do that safely on a changeable basis? My tumbler is the speed it is according to how it is made. (the pulley ratios) It's current barrel rotation speed is about 60 rpm. I thought about trying to slow it down with an inline rheostat, but when you use a rheostat (aka dimmer switch) on an induction motor, if I remember correctly, the amperage pulled goes UP as the rpm goes DOWN. That means more motor heat. That may not be safe over a long haul. On my tumbler the roller shafts are coated with a strip of clear vinyl tubing. If I strip that off that changes the diameter of the drive roller to be smaller and the rpm of the barrel goes down. Permanently. Plus being then only a metal roller, there would probably be slippage. Have you found a way to "temporarily" change speed that is safe? Thanks.
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Post by cpdad on Mar 23, 2014 13:22:21 GMT -5
install a dimmer switch....remove the cover off the motor...lots more air...let'em roll...kev.
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Post by phil on Mar 23, 2014 13:28:14 GMT -5
Dimmer switch like Kevin says probably easiest. Secondary set of rollers coming off the original set is more work, but then you'd have two sets of rollers, one for rough, one for final polish.
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mrbouldersmash
off to a rocking start
Member since March 2014
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Post by mrbouldersmash on Mar 27, 2014 21:06:19 GMT -5
i would use that as a pre polish (white levagated alumina) and nuts/nut shells. and as above cerium oxide to bring out the polish, together you can get dreat depth to your polish. best i can say for a rotary tumbler. tony
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