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Author Topic: Edge Grinding, advice please.  (Read 4906 times)
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jim adams
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« on: August 31, 2014, 09:56:30 AM »

Hi everyone,

Please apologize for me gatecrashing this site but I think my question is very relevant to this forum.

I am currently producing pressed bowls using a dense self compacting concrete. The finished bowl comes straight out of the mold with a glossy almost glass like finish. The issue that I have is how to finish the top edge the only part of the piece that is not in contact with the mold. The bowls are roughly 18" in diameter with a 1/8" thick edge, the rim is pretty level straight from the mold but it still needs to be ground down evenly by a couple of millimeters and polished, the question is how?

All advice greatly appreciated

Jim

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Pauline
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happy happy happy


« Reply #1 on: August 31, 2014, 10:14:12 AM »

if it were glass you would probably be using some type of diamond grinding bit with water, either flat lap grinding wheel, or smaller scale on a dremel or stained glass type one such as this   http://www.ebay.co.uk/itm/glass-grinder-/181507706557?pt=UK_Crafts_Glass_Art_Supplies_CV&hash=item2a42b3cebd
no idea about concrete
good luck
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Moira HFG
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Ever the optimist


« Reply #2 on: August 31, 2014, 04:30:33 PM »

Yes, I think any of them would do the trick.

If you want them dead flat, a lap grinder would be best, but they're not cheap.
If you only have a few to do, you could use silicon carbide grit and water on a sheet of glass, working down the grades.
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jim adams
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« Reply #3 on: September 01, 2014, 01:38:00 PM »

Many thanks for your suggestions.

Just had a look at the lap grinder and I think it may do the trick, my bowls are quite large any recommendations on disc size?



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Moira HFG
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Ever the optimist


« Reply #4 on: September 01, 2014, 06:32:01 PM »

Well...the important thing is that you can fit the bowl you're working on inside any recess on the machine. Unless you are content to make it a bevel rather than a flat grind.

Or you could build your own!
https://www.youtube.com/watch?v=uF27Q4rdSUU

Or use a glass linisher maybe? Then the bowl can overlap the edge of the belt. (How deep are your pockets?)

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jim adams
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« Reply #5 on: September 02, 2014, 12:41:05 PM »

The large grinders are expensive so I may have a go at modifying a cheap secondhand potters wheel. I could fix a diamond disc to the wheel by tapping the center of the head and then use a bolt and washer to clamp the disc in place.
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Moira HFG
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Ever the optimist


« Reply #6 on: September 02, 2014, 02:42:33 PM »

That's a good idea.
It wouldn't be hard to rig up a gravity water drip over it - or you'd probably get away with splashing water onto the disc periodically.

Do post pics when you've made it!
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Glyn Burton
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WWW
« Reply #7 on: September 02, 2014, 04:33:56 PM »

There is a company in Paris called minereaux et machines (try googling) they sell a shimpo potters wheel as a flat lap. They will sell you just the diamond disks which are magnetic and the steel disk to stick on the wheel head. The guy speaks reasonable english and is very helpful. Have you thought of using a hand grinder/polisher? i use a Makita which is 110volt and connects to a water supply. The polishing pads hold on with velcro and go from a 60 grit to 3200 I use it on cast glass pieces and it works very well.
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Pat from Canvey
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Keep on blowing


« Reply #8 on: September 03, 2014, 12:16:13 PM »

If you Google the site, look at the top left where there is a union jack to allow you to translate the site. There is also a facility for you to download the pdf catalogue in English.
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