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Post by Bluesky78987 on Sept 17, 2012 20:05:21 GMT -5
Here's a question for you techies, so I can try to figure out something that's been nagging me.
At approx what RPM does a Genie (or other cabbing machine other than flat laps) run?
Also, 8" wheel means 8" diameter, right?
Thanks.
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quartz
Cave Dweller
breakin' rocks in the hot sun
Member since February 2010
Posts: 3,341
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Post by quartz on Sept 17, 2012 21:59:40 GMT -5
Genie runs at 1725 R.P.M., as do any direct driven [no belts] cabbers. Some machines have a belt drive that allows a little on either side of motor speed by using a set of stepped pulleys, most of these motors run at 1725 too. Motor speed is shown on the tag attached to the motor housing. Yes, 8" means 8" diameter.
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Post by Bluesky78987 on Sept 17, 2012 22:00:31 GMT -5
Perfect answer, thanks! Now I can go do some math.
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Post by johnjsgems on Sept 17, 2012 22:00:56 GMT -5
1725 and yes.
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Post by Bluesky78987 on Sept 17, 2012 22:04:21 GMT -5
Even better, two people with the same answer! It's a miracle!
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Post by deb193redux on Sept 17, 2012 22:19:32 GMT -5
it is interesting to wonder what is the best speed. the 1725 ends up being related to 60hz and motor phases. presumably the makers of diamond wheels design the diamonds and bond to work best at 1725 RPM x diameter x pi - but even then they have to assume a material of a given hardness and also a particular flow of coolant. they also have to assume a particular pressure form the user. while a variable speed would address this, it would take a real instinct and lots of experience to pick the best speed for a given stone. I think great cabbers instinctively vary their pressure for each material to get a consistent feel.
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Post by johnjsgems on Sept 18, 2012 8:11:05 GMT -5
Most diamond wheels are rated for 1725. The expanding drums also. SC wheels generally much faster because most metal working bench grinders run 3450 rpm. Some polishing operations would be better at lower speeds. Pretty much all the very large (like 12") home made buffs run very slow. I think that is mostly because the closer you get to the outer surface the faster it turns and the more likely to launch your almost finished cab.
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Post by Bluesky78987 on Sept 18, 2012 10:49:36 GMT -5
Ok. So what I am trying to determine is why (it appears) that working on a wheel like a genie or cabmate or whatever, seems to be more aggressive and faster than working on a flat lap.
According to Quanah at Ameritool, the RPMs at the max setting on my 8" unit are 2800. Assume you're working at a point on the disc near the outer edge but not all the way there - say 3" from the spindle - 6" diameter for travel path. That means in one minute, a given speck of diamond touches your rock 16,800 (times pi) times. (RPM x Pi x Diameter of path).
For the Genie discussed above, it only goes at 1725 rpm. But your rock is always 4" from the spindle, or 8" diamter of travel path. So in one minute, a given speck of diamond touches your rock 13,800 (times pi) times.
So the Genie takes fewer "bites" at your rock per second. So why, oh why, is it so much faster at removing material? I'm assuming here that the wheel is a hard wheel, so we have apples to apples. Is it really faster? Seeing how many cabs some of y'all crank out, it HAS to be faster. Are the diamonds on the wheel set up to be more agressive or something?
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Post by deb193redux on Sept 18, 2012 11:16:31 GMT -5
I think you can't decide that on RPM alone. you would need to consider the size/shape industrial diamonds that were used and the bond type. Wheels may have sintered, nickel-plated, or epoxy type bonds. Plates are generally nickle plated. You would also need to consider the flow of water (cooling) and how each throws off the water (removal of cuttings). Also do people end up using different pressure against a wheel vs a plate. I like to get under a wheel and rotate the cab up against the downward motion of the wheel. The motion is in my fingers. With plates and vertical belt sanders, I find myself using less pressure and moving the stone in a circular pattern - the motion is more in my wrist.
I don't know enough about any engineering differences in the diamonds used to give a more direct answer to you question.
As for total output, I find it quicker to move across several wheels than to change belts on my expando drums, and I would assume to change plates on a flat lap. I plan to phase out my expando drums because they break my rhythm a bit.
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Post by johnjsgems on Sept 18, 2012 11:23:40 GMT -5
Technically the motor shaft is turning 1725 rpm. The outside of the wheel would turn faster (I think). The circumference would be pi X diameter or 18.85". Seems like if you are 6" out on the lap you would have same speed. Difference could be Diamond Pacific uses higher concentration of diamond than used on the laps. Myself, when I tried to cab on a lap, I had trouble with laps grinding too fast. I attributed it to learning on wheels and having a hard time gauging how much pressure to use. Maybe you push harder when using wheels than you do with the lap. I'm pretty sure everybody uses synthetic diamonds.
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Post by Bluesky78987 on Sept 18, 2012 12:15:54 GMT -5
It has to be something in the "Aggressiveness" of the way the diamonds are attached (have heard faint murmerings of this with respect to saw blades), as Dan alludes to, as well as how hard the user presses. I've never used a wheel, unfortunately, only a lap, so can't compare.
Somebody on here (Krystee?) switched from wheels to flat lap lately, wonder if they have a thought about how hard you press. On my flatlap, the hardest I press . . . let's see.
Imagine your rock is a marshmallow and you're pushing it against your table. The pressure I use on the flap lap, at the hardest I ever press, would be enough to maybe squish the marshmallow to half it's current size. Maybe a little harder than you would commonly use to (rough) file a big toenail. How hard do y'all press on your wheels?
Agreed that changing plates on the flat lap takes a little time.
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Post by deb193redux on Sept 18, 2012 12:18:33 GMT -5
John: the RPM is constant at the hub or out at the surface for any rigid object. What changes is the SFPM surface-feet per minute.
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Post by FrogAndBearCreations on Sept 18, 2012 14:35:32 GMT -5
I started on a flat lap and I do not press/push but keep a light even touch and let the diamond do its work when I start to get impatient its time for a break oh and to change between laps is a snap as all of mine are set up on their own masters and arbors so its just a matter of loosening a set screw, remove/replace, tighten set screw and away I go!
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Post by johnjsgems on Sept 18, 2012 18:37:35 GMT -5
You are right Daniel. Same rpm just a lot more surface rotating. But, with a flat lap or large flat buff it sure feels like it is flying near the outer edge.
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RocknCritter
spending too much on rocks
Member since November 2008
Posts: 489
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Post by RocknCritter on Sept 18, 2012 22:14:49 GMT -5
Here's a link that might help. www.tasonline.co.za/toolbox/pump/powtip.htmWhile this is for an impeller, the physics should be the same for any rotating object - right? Also, doesn't the Ameritool come stock with a 180 grit lap for the first step compared to the 80 grit on a Genie? If grinding on a flat lap seems slow, try faceting sometime. The machines might only spin at 100-200 rpm. As a side note, my darn nephew just decided on his post graduate studies. He's doing for a doctorate in quantum physics. So when questions like this come up, I think of him. He obviously got all the brains while I got all the rocks ;D
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Post by Bluesky78987 on Sept 19, 2012 15:46:42 GMT -5
Cool calculator! Could have saved me some math.
Anyway, yeah, the Ameritool comes with 180, but you can also get 100 and 80 (which help a lot). Wish there was a 50 too!
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RocknCritter
spending too much on rocks
Member since November 2008
Posts: 489
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Post by RocknCritter on Sept 19, 2012 21:27:16 GMT -5
Cool calculator! Could have saved me some math. Anyway, yeah, the Ameritool comes with 180, but you can also get 100 and 80 (which help a lot). Wish there was a 50 too! Check with John at JSGems. He should be able to get a 60 grit lap for you.
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Post by johnjsgems on Sept 20, 2012 7:52:51 GMT -5
Patience Grasshopper! 80 or 100 will work just fine.
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Post by FrogAndBearCreations on Sept 20, 2012 8:16:42 GMT -5
the rougher the grind/disc the more it will chip the harder stones
I have an 80 grit wheel and am sure glad I did not go any rougher as it causes chipping
the only way to control that I have found is to put a slight bevel on the back edges of the cabs
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RocknCritter
spending too much on rocks
Member since November 2008
Posts: 489
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Post by RocknCritter on Sept 20, 2012 21:46:47 GMT -5
Not only will a coarse grit lap chip harder stones, it will completely destroy softer materials in seconds. After using a 60 grit, it's a good idea to follow up with the usual sequence of 80 to 220 grit, etc. Think of laps like the 60 grit like using a cannon when a shotgun is more than adequate. If your not careful, you'll blow up something you didn't intend on.
Another option if flat laps are cutting a little slower is to stick with softer materials like angelite, seraphinite, cobaltite, turquoise, some opals and rhyolites and many more stones. These can be started on the 220 grit or even the 280 belt/soft wheels. The first two can even be worked and finished with wet/dry sandpaper. All of these will just be obliterated at the first contact with a coarse lap/wheel.
When it comes down to it, it's all a matter of adapting the tool to the task.
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