jamesp
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Post by jamesp on Mar 22, 2018 6:33:19 GMT -5
I bought a load of bulk SiC. I sifted it into 100. 60, 40, 20, 10 and 4 because I have screens for those sizes. So some is super coarse. Observation is this. Regardless of grit size - 60 or 40 or 20 or 10 or 4, the scratches and pits are no deeper regardless of the coarseness in the rotary. ****This was verified by tumbling all rocks and glass coming out of the rotary shaped using 60-40-20-10-4 would get a decent 2nd step polish in the same amount of time in the vibe.**** Conclusion The grinding force in the rotary is limited and can not force the sharp abrasives deep into the surface of the rocks or glass. Same abrasives mounted on a wheel where pressure can be increased is a different animal. A 30 grit wheel will put very deep scratches with hand pressure applied on your rock but a 100 grit wheel will be limited to the depth of the scratch. It is all about the grinding force and a rotary tumbler exerts only a small grinding force. And a constant grinding force. However a larger diameter rotary barrel can exert higher grinding forces. And increasing the speed will increase the grinding force by higher impingement(dynamic) forces. I have a problem with shaping soft glass too fast. My weapon is to use 6 and 8 inch barrels. 30 and 60 RPM speeds. For the given grinding situation. 6 inch barrel at 30 RPM for slow grind, 8 inch barrel at 60 RPM for fast grind. But the grit be it 60-40-20 makes little difference in grinding speed. And the glass does not break down these SiC 60-40-20 particles very fast at all so they are reused. Captured at clean outs. And to help circulate and mix heavy 20 grit the 60 RPM with at least 80% barrel fill helps significantly. 20 grit is darn heavy. 20 grit is not used at 30 RPM due to poor mixing unless heavy clay slurry is used. Amazing the difference in 4 - 6 - 8 inch barrels and speeds 30 - 60 on grinding rates. Also amazing is how a super delicate long piece of thin glass can survive breaking at higher 80 to 85% barrel fills. My observation for the day
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Post by gmitch067 on Mar 22, 2018 9:03:24 GMT -5
Thank you for this insight jamesp+++ I guess that using 45/70-grit SiC in my 3A rotary is overkill, and I can return to 80 or 60/90-grit and get the same grind. Glenn
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jamesp
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Post by jamesp on Mar 22, 2018 9:43:18 GMT -5
Thank you for this insight jamesp+++ I guess that using 45/70-grit SiC in my 3A rotary is overkill, and I can return to 80 or 60/90-grit and get the same grind. Glenn Probably so. The 46 should last longer though.
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ohthatspretty
starting to shine!
Member since March 2018
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Post by ohthatspretty on Mar 22, 2018 10:41:00 GMT -5
Really that makes me wonder if a somewhat less coarse grit would do a faster job of first stage tumbling as there are more cutting edges hitting the stones at one time.
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jamesp
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Post by jamesp on Mar 23, 2018 5:05:39 GMT -5
Really that makes me wonder if a somewhat less coarse grit would do a faster job of first stage tumbling as there are more cutting edges hitting the stones at one time. Bet you are correct. However..... In a rotary with well balanced mix of rocks rotating at a good clip 60 grit stays 60 grit for less than a day. More like 12 hours in mine. So if you start with 30 for example, you may get 12 hours @ 30, 12 hours @40, 12 hours @ 50, 12 hours @ 60 ........... That is why starting with 60/90 is a joke in a 6+ inch barrel rolling at a good clip with a good mix of rocks and a correct barrel fill and the correct amount of water/slurry. 60/90 is probably fine for a small 4 inch barrel. I don't know the dynamics of small barrels like that, other than people say 30 and 46 grit does not circulate well in them. I am a very curious person. I did a clean out 18 hours after adding SiC 30 and captured the particles very carefully. Look at the virgin SiC 30 and SiC 30 after 18 hours in optimum rotary conditions with fine clay slurry additive:
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jamesp
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Post by jamesp on Mar 23, 2018 5:09:32 GMT -5
Or look at SiC30 after 18 hours as collected. This bottle was set on the vibe to vibrationally separate the layers of particle size. I had 80% recovery of original weight.: Don't be blind, know what your abrasives are doing
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jamesp
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Post by jamesp on Mar 23, 2018 5:34:16 GMT -5
I tumble glass. I will throw you a strange one. Glass shapes very fast, so you can know how fast it is shaping. It does not take 8 weeks like hard agates. It usually takes me less than a week in coarse for my particular glass product. Glass wears fast, the faster it wears the more gas you generate. Experimenting with 6 and 8 inch barrels at this time. Actually 6.75" and 9" HDPE barrels. I am getting double the grind time in a 6.75 inch barrel at 83 RPM as 9 inch at 63 RPM using 80 to 85 percent barrel fill. I also get about double the gas build up in the 6.75 inch barrels as opposed to the 9 inch barrels. Reinforcing increased wear rate. The tumbler shafts are at the same speed, the smaller diameter simply rolls faster, so the 63 and 83 RPM. So why does the 6.75 inch barrel out grind the 9 inch barrel. No answers for that one other than the shear speed. Work = Force X Speed ? I believe that is correct basically. Apparently rotational speed trumps in grinding rate. I don't know why and don't really give a rat's ass. I have been running 6.75 inch PVC pipe and 6.75 inch HDPE for a million years. And always felt they out performed the 9 inch barrels on the same shaft speed. *****Never run tumbles at 83 RPM in a 6 to 9 inch barrel with out filling barrel to 80-85% due to risk of bruising your tumbles. Be very accurate in your filling of the barrel and maintaining that 80+% fill(rocks do get smaller as grind makes them smaller). You can add slivers of delicate glass in the load to test for potential bruising. My glass tester of choice is glass microscope slides. They are tender and subject to breaking. Or obsidian needles off Ebay
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tkvancil
fully equipped rock polisher
Member since September 2011
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Post by tkvancil on Mar 23, 2018 9:50:40 GMT -5
Barrel speed is a big factor in grit usage. I began using 30 grit some time ago thanks to some of your posts jamesp . I use only Lortone 12# barrels these days, on two different tumblers. One set up rotates at about 30 rpm and the other at about 55 rpm. In the 55rpm set up 30 grit is basically used up in 3 days. No thickener/slurry additive in use. I start the batch on Sunday and open the barrel on Wednesday and top off volume to avoid impact damage. Usually have to add about 1/2 pound or so of rough. I let the barrel roll for the rest of the week after that as I believe there is a benefit to the finish rolling in the finer broken down grit. The 30 rpm set up is not as efficient. Upon opening after 3 days coarse particles can still be seen, probably in the 46/70 range. At the end of a week there were sometimes still coarse particles remaining from a fresh charge. To get the 30 to break down completely in 7 days at 30 rpm I use 25% 80 grit, 75% 30 from a fresh charge. Doing a clean out I leave about 1/2 cup slurry in the barrel. I think these methods help to lift the relatively heavy particles. Boiling it down to comparative observations for my set up ... 55rpm does the same amount of work in 3 days with no thickeners as 30 rpm does in 7 days with thickeners. I base this on volume loss and grit usage which by eye are roughly the same in the stated time periods.
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jamesp
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Post by jamesp on Mar 25, 2018 6:35:26 GMT -5
Barrel speed is a big factor in grit usage. I began using 30 grit some time ago thanks to some of your posts jamesp . I use only Lortone 12# barrels these days, on two different tumblers. One set up rotates at about 30 rpm and the other at about 55 rpm. In the 55rpm set up 30 grit is basically used up in 3 days. No thickener/slurry additive in use. I start the batch on Sunday and open the barrel on Wednesday and top off volume to avoid impact damage. Usually have to add about 1/2 pound or so of rough. I let the barrel roll for the rest of the week after that as I believe there is a benefit to the finish rolling in the finer broken down grit. The 30 rpm set up is not as efficient. Upon opening after 3 days coarse particles can still be seen, probably in the 46/70 range. At the end of a week there were sometimes still coarse particles remaining from a fresh charge. To get the 30 to break down completely in 7 days at 30 rpm I use 25% 80 grit, 75% 30 from a fresh charge. Doing a clean out I leave about 1/2 cup slurry in the barrel. I think these methods help to lift the relatively heavy particles. Boiling it down to comparative observations for my set up ... 55rpm does the same amount of work in 3 days with no thickeners as 30 rpm does in 7 days with thickeners. I base this on volume loss and grit usage which by eye are roughly the same in the stated time periods. Your findings parallel mine to a tee. Pretty sure rotational speed is #1 impact on grinding speed Ken. No doubt about it with 6 and 8 inch barrels. 63 RPM for 8 inch barrel and 83 RPM for 6 inch barrel - both have the same surface speed but the higher tumbling action at 83 RPM in the 6 inch barrel is out grinding the 8 at 63 RPM. The rocks touching the barrel are hardly grinding as they are attached to the surface of the barrel for the most part. It is the rocks in the center and top center that are grinding against each other the most. "The roll zone". Speed the roll zone and you will speed the grind best. The other consideration is the weight bearing down on the roll zone. Don't be surprised if the roll zone has more grinding force at 80 and 85% barrel fill verses 70% barrel fill due to the added weight. No doubt creeping past 80 to 85% fill the movement in the roll zone gets stifled and grind rate slows tremendously. Good to hear since you have apple and apple Lortone #12's, one at 30 and one at 55. I have 35 and 83 RPM for 6.75 inch pipe barrels. The 35 for 220, the 83 for coarse grind. 83 RPM seems way fast but at 80-85% barrel fill I tumble very delicate glass with ZERO breakage. At 70% fill and 83 RPM I would destroy my glass in hours in the 6.75 inch barrels. I consider such high speeds precarious and risky due to accurately filling the barrel to 80/85 when rolling glass, agates much safer. I am phasing out the 8 inch barrels and sticking with the 6.75 inch barrels. Less violent and faster grinds at high RPM.
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Wooferhound
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Lortone QT66 and 3A
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Post by Wooferhound on Mar 25, 2018 20:02:26 GMT -5
Good to hear since you have apple and apple Lortone #12's, one at 30 and one at 55. Uhmmm . . . Apple what ?!
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kskid
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Post by kskid on Mar 25, 2018 23:08:37 GMT -5
Bet you are correct. However..... In a rotary with well balanced mix of rocks rotating at a good clip 60 grit stays 60 grit for less than a day. More like 12 hours in mine. So if you start with 30 for example, you may get 12 hours @ 30, 12 hours @40, 12 hours @ 50, 12 hours @ 60 ........... Read more: forum.rocktumblinghobby.com/thread/82571/coarse-grit-observation#ixzz5Ap8qgm00X2 I use 36 & 8 oz. water w/o additives in a QT6 for rough out, but I leave it running for 2 weeks between cleanouts. It just fits my schedule better that way. Also agree with fill being critical. Too much leaves unused grit/too little leaves beat up rocks. Thanks for sharing the data - interesting stuff!
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