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Old 10-25-2021, 09:38 PM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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Grinding

Ive been grinding a home cast concrete kitchen countertop, and I notice that using a ociliatiating grinder with 220 carborundum powder with water produces a rougher surface than 240 grit sandpaper- like a lot. Does that mean its better to use a 240 diamondpad on a flatmill? Ive always liked carborundum on a cast iron wheel. When grinding glass that is

Last edited by Michael Ahlefeldt-Laurvig; 10-25-2021 at 09:42 PM. Reason: Added last
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Old 10-26-2021, 08:14 AM
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All grit is not equal. When I buy it, I specify "Graded", otherwise you tend to get a mix. 60--90 is probably the most common mix. When I buy fine stuff, I specify optically graded 27.5 micron.

Sandpaper is not something I've ever considered as particularly engineered. It could also be the case that the countertop itself is contributing material.
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Old 10-26-2021, 10:24 AM
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Going off of what Pete said, my guess is that it has to do with whatever mesh the aggregate is in the concrete. If there's sand/silica particles that are larger than 220 they're going to abrade the surface as they get knocked loose.
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Old 10-26-2021, 09:04 PM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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I think my sand is fairly high quality consistent grit size. Gregs thoughts seem plausible though. So Ill modify the question as to glass,- does a high quality 220 diamond pad give the same surface as loose grit carborundum on an iron flat mill? There being no loose aggregates as such in glass.
I say high quality, because I have Chinese diamond pads and they get more useless the finer grit you go. The only one I find useful is a 80 grit for aggressive removal of material, its sort of like dragging the glass piece on asphalt from your car. When new you have to go over it with a cold chisel to remove the worst clumps of electroplated diamonds. Im talking electroplatedpads. Ive used HIS brown pads without problems, what are they? 400?

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Old 10-27-2021, 09:50 AM
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Diamond pads in my experience give a great surface with one long deep scratch, every time. Edge preparation of the piece you are making is critical as is good annealing, otherwise, edges crumble. It's why I use the dynafile.

I think the funniest thing on God's website is holding the piece on the road while driving.
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Old 10-27-2021, 03:19 PM
Rosanna Gusler Rosanna Gusler is offline
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ha! snort. god's . .....
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Old 10-28-2021, 06:45 PM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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Ive ordered 80 and 120 and 240 grit diamond pads for my slow rpm water feed Flex angle grinder, so Ill se if there is a difference to carborundum- Ill report back…
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Old 10-28-2021, 07:00 PM
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My recollection tells me diamonds want high water feed and high RPM. Is that my imagination?
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Old 10-29-2021, 06:48 AM
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Quote:
Originally Posted by Pete VanderLaan View Post
My recollection tells me diamonds want high water feed and high RPM. Is that my imagination?
That is my understanding as well.

Diamonds as a whole are problematic on multiple fronts. As a gemstone their importance is largely due to how they've been traditionally marketed to western cultures. In my own experience/practice with making jewelry I have never been interested in pursuing them in my work. Not that that really means much as I am still not experienced enough to have worked with faceted gems (haven't learned how to make a prong setting yet).

My take on their usage for making tools to cut hard substances is that it is easy to sell people on their importance. Cheap, electroplated blades will get the job done, but wear out at a high rate ensuring repeat sales. I've noted a current glut locally of cheapo Hazard Frought tile saws on the second hand market. I assume contractors are buying them for $75-$100, doing a tile job, and then reselling them for $25-$50. I've seen them at the Goodwill for $25. With all of the supply chain problems in general my guess is we will see prices go up along with everything else.

I think I've said it here before that they are overrated as both a gemstone, and as a tool.

Sorry for the long, tangential rant.
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Old 10-29-2021, 09:03 AM
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Inadequate water feed wears them out the fastest. What you grind makes a difference. I still vastly prefer silicon carbide but the tooling is now mixed. 60 Grit rough out diamond I got through David Patchen, then 120 silicon carbide grit feed, the 27.5 aluminum oxide drip fed. Then Pumice 0/3/4 . then panda Brand ( accept no substitutes!!) Cerium. A good baseball game on a TV while working insures a good surface.

Diamonds provide a mediocre to OK surface quickly for the visually impaired. That's my take. ...But grit is messy, no denying it.
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Old 10-29-2021, 11:51 AM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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In Swedish we have one word for just right. As for most things you do you know when you're there. Its not the more the merrier with speed and water, its the right combination. A 12000 rpm angle grinder will ruin a diamond tool in seconds
Ill have to digest Gregs thoughts a bit
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Old 10-29-2021, 01:21 PM
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Most of the grit tools I use run at about 300 Surface feet per minute, Water fed diamonds run as high as 700 but they can tough to control. Quantity of water? I can't say, more than I like though. I just know when it feels just right. even my hand held water fed diamond tools run at about 700SFM. 12000 RPM is way above my pay grade to comment on.
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Old 10-29-2021, 02:19 PM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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Yes thats sort of what I said. On a large flat mill the liniar foot speed must vary greatly between perimeter and center, thus “ the sweet spot” somewhere in between
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Old 10-29-2021, 02:43 PM
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It's where variable speed motors are sweet but sadly really expensive.
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