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Author Topic: Not sanding at higher grits  (Read 839 times)

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veesix

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Not sanding at higher grits
« on: September 21, 2017, 01:17:03 PM »

Hi, I recently got a setup using a 6" bench grinder and flat lap discs (attached using the existing grinding wheels as backers). I have an irrigation mist that sprays water onto the disc. I noticed that when I try to sand a flat piece at the higher 1200 & 3000 grits, there's no "pull" and it doesn't seem to sand. It's like there's surface tension preventing the piece from actually touching the disc. I can feel it if I take that same piece and put it on its side or if I'm working on a rounded top. I even tried to reduce the mist and turn off the water entirely but I get the same floating effect. The only other thing I can think of is that the grinder speed is too fast. It's a variable speed grinder and I have it down to the lowest setting at 2000 rpm. Would that be the cause? I've included links to the products below. Thanks!

Here's a link to the grinder.
https://www.amazon.com/Delta-23-196-6-Inch-Variable-Grinder/dp/B00HRM509A/ref=sr_1_1?ie=UTF8&qid=1506024795&sr=8-1&keywords=delta+bench+grinder+23-196

Here's a link to one of the higher grit discs I purchased. I'm very happy with the performance of their lower grit discs.
https://www.amazon.com/gp/product/B0711XNYJR/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

Here's a link to the mister.
https://www.amazon.com/gp/product/B0040QY2NQ/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
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Phishisgroovin

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Re: Not sanding at higher grits
« Reply #1 on: September 21, 2017, 01:28:54 PM »

I will let the professionals handle this one, but I myself think you have to lower your speed of the disk, water gets in between the stone and the disk at higher speed.

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irockhound

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Re: Not sanding at higher grits
« Reply #2 on: September 21, 2017, 01:34:37 PM »

You may need to say what grits you used prior to going to the 1200 and 3k.  Flats are much harder to remove scratches etc due to the larger surface area, if you add into that possibly skipping a critical step like the 600 grit it will spell disaster.  Post what you did leading up to the 1200.  Also the 2k is very fast and it probably is hydroplaning on the layer of water.
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veesix

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Re: Not sanding at higher grits
« Reply #3 on: September 21, 2017, 01:37:08 PM »

You may need to say what grits you used prior to going to the 1200 and 3k.  Flats are much harder to remove scratches etc due to the larger surface area, if you add into that possibly skipping a critical step like the 600 grit it will spell disaster.  Post what you did leading up to the 1200.  Also the 2k is very fast and it probably is hydroplaning on the layer of water.
I used 80, 180, 320. I skipped 600 because I didn't get that disc yet.
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irockhound

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Re: Not sanding at higher grits
« Reply #4 on: September 21, 2017, 01:39:38 PM »

That would kill it right there.  No way or at least not in human years (I just mean a long time) will 1200 grit remove 320 scratches especially given the issue with with it being a flat and the speed.  Get the 600 and things will be much better.

You can also buy a speed reducer from places like amazon or harbor freight.  Then you can lower the minimum speed below 2k.
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veesix

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Re: Not sanding at higher grits
« Reply #5 on: September 21, 2017, 01:51:01 PM »

Ok thanks, that sounds hopeful. I'll go through the process again once I get the 600 grit.
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Slabbercabber

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Re: Not sanding at higher grits
« Reply #6 on: September 21, 2017, 02:06:04 PM »

Your speed is still too high but that is nothing compared to the danger you have introduced.  Bench grinding wheels are meant to have pressure on the perifery only.  The binder is literally glass.  When one of these comes apart the velocity is similar to bullets from a gun.  I suggest you replace the wheel with one made of plywood.
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veesix

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Re: Not sanding at higher grits
« Reply #7 on: September 21, 2017, 03:06:21 PM »

Your speed is still too high but that is nothing compared to the danger you have introduced.  Bench grinding wheels are meant to have pressure on the perifery only.  The binder is literally glass.  When one of these comes apart the velocity is similar to bullets from a gun.  I suggest you replace the wheel with one made of plywood.
Ok, thanks for the info.
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Barclay

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Re: Not sanding at higher grits
« Reply #8 on: September 21, 2017, 05:16:15 PM »

i agree with Slabbercabber, you have created a VERY dangerous machine for the following reasons.

1) I don't see that the grinder is set up for water.  That likely means that the electrical is not protected from water.  Water + electricity is bad.

2) The grinding wheels are not designed to be used with water.  One of the limitations of the old silicon carbide type wheels (and these) is that they have to be spun completely dry otherwise one part of the wheel with water is heavier than the rest of the wheel.  The heavy part of the wheel comes apart explosively.  I saw a video yesterday of a guy who died when a wheel exploded into his chest.  To use the diamond flat disks it looks like you have to take off the wheel guards which increases your risk.  When the equipment manufacturer puts a safety device on the equipment it is a good bet it is needed.

3) Using this grinding machine without water cooling (as designed) will cause your rock to heat up a lot.  You cannot dunk the rock in water enough to keep it cool, plus we are back to getting the wheels wet again.  If you are lucky the rock will just keep falling off of your stick.  If you are a little unlucky it will crack or break up.  If you are very unlucky it will shoot pieces of the rock back at you.

This equipment was not designed for rocks and cannot be made safe to grind rocks.  Ameritool makes a very good simple swap top grinder at around $450.  I have one and love it.  Stay away from Inland Lapidary as their machines are junk (had one of those also).
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veesix

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Re: Not sanding at higher grits
« Reply #9 on: September 21, 2017, 08:17:46 PM »

Thanks Barclay, I appreciate the warning. I accept the risk involved and I've tried to minimize the electrical issues by sealing with silicone. I'll look into Ameritool.
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Slabbercabber

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Re: Not sanding at higher grits
« Reply #10 on: September 22, 2017, 04:51:14 AM »

You are using a GFCI.  Right?
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veesix

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Re: Not sanding at higher grits
« Reply #11 on: September 22, 2017, 08:54:57 AM »

You are using a GFCI.  Right?
That's right, it's connected.
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