What is the best way to grind glass, somewhat smooth?

Now before you rush to write down an answer let me tell you the details!

The chunk of glass is 28 inches wide by 28 inches long and 2.5 inches tall. Composed of 160 painstakingly cut strips of glass that have been glued together into a jumbo block. Now try as I might, when laminating things together of ever so slightly different size together you are going to get high and low spots - And yes, this would have been soooo much easier a job if I had smoothed out the rough edges before laminating - Pesky hind-sight. Unfortunately my planer doesn't seem to work so well on glass, who knew :) Anyway, I will post some pictures to give you an idea of what it is, that has to be ground down.
First off
• It does not have to be perfectly smooth
• A mottled surface would actually be appreciated
• It is not going to be a lens of any kind, all though light will be transmitted through it.
I have the following tools, but first - No I am not taking it 1700km to have it kilned. No, the local glass shop seems to have less tools then I do, at least in this scale.
• Angle grinders
• belt sanders
• orbital sanders - but really?
On the back side I used the angle grinder, with a metal grinding bit. Not to bad really all though the edges were taking a pounding. This was prior to applying resin and woven cloth, to give the glass a bit of tooth and reduce the high edges.

This is for an instructable I am working on.

Picture of What is the best way to grind glass, somewhat smooth?
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Prfesser6 years ago
You'll have to decide if a ground surface is ok, or is a polished surface desired.  For a polished surface you'll probably need to go down to about 600 grit, then use cloth and some sort of polishing compound (rouge, tripoli, etc.)  A ground surface can end anywhere after 200 grit, depending on the coarseness that is ok.

Doing by hand with abrasive paper, even wet/dry paper, will take a loooong time and a lot of paper.  Telescope makers (I've done this multiple times) use powdered silicon carbide abrasive and water, with another piece of glass as the grinding surface or "tool".  That will take a long time too. :-(  We usually start with 80 or 60 grit; for a big (>10" dia) piece of glass we begin with 40 grit abrasive.

As has been said earlier, a diamond wheel is likely to be the fastest method.  If you can wet-grind it will probably go a bit faster and smoother. Several grits of diamond wheel will probably be necessary.

Good luck!
iminthebathroom (author)  Prfesser6 years ago
There is a lot of stock to remove, I've started with 60 grit and will move up incrementally. I do not believe I will ever get to a polished surface due to the nature of the lamination's. I have searched and trolled the internet and have yet to find a treatment where people have done something like this, aside from at art glass shops where they will wire glass together and then fuse the layers in a kiln. Nothing quite like this however. What may happen is that I will make it as smooth as possible, then gel coat the top in epoxy or polyester resin. Crazing of the glass disappears beneath a cot of resin and restores the translucency I was looking for.
gluplug4 years ago
For reference, or alternate ways of working, here is setup for individual pieces. Small aquarium type pump provides top-fed water to keep wheel wet. Wheel is 8 inches in diameter, with a 4 inch wide foam-backed strip of 400 grit wet/dry sandpaper. See http://www.ogilumen.com/ogilab/hopper1.php#051513
alkaff5 years ago
use fine sander 300/400grit and on corner use flat metal for scrabing edges.
static6 years ago
I forgot to mention that a portable belt sander might be easier to use than the rotatory tools. Depends what you own, and what it cost rent what you don't
static6 years ago
While not going to level the high spots an acetylene torch may help bring smother surface. Not sure if the adhesive you use would take the heat, but you mention (no) kiln, and that would be hotter I think. Amateur astronomers still grind their own mirrors, the techniques they use are similar to what other suggested here. An automotive machine shop might have a cylinder head resurfacer that could do the job, but they probably wold charge more than what it would be worth to you.
iminthebathroom (author) 6 years ago
Thanks everyone, over the next week I will try a variety of your answers, post the results and select a best answer at the end!
seandogue6 years ago
Emery cloth is what I've used in the past. As was noted by danandlisa7, 120 or higher girt is appropriate.

Although....Rimar2000 has the easiest method. I just suggested the emery cloth because I've used it and it worked pretty well, and you may not own an angle grinder (i don't )
iceng6 years ago
Yes...  Some hardware stores sell "Wet Sandpaper" a very rugged
backing type of sandpaper does not tear up when wet.
I put it into an orbital sander, water my target regularly and orbit.

terribug6 years ago
If you don't mind a somewhat frosted finish, you can take it to the local autoship and have it sandblasted. Don't know what it will doto your seams, but it will dull the edges for you.
Beltsander 120 grit to start keep it moving so that it doesn't get hot
rimar20006 years ago
I've seen glaziers working hard on glass with hand grinder, using sanding disks like those of the accompanying figures.
iminthebathroom (author)  rimar20006 years ago
First thing I grabbed, flap disks are my grinding disc of choice. Didn't work so well on the glass though. Next up, I forgot I had some grinding disks specifically for grinding aluminum. After that fails I may have some turbo disks sent up, for polishing concrete or granite. These are more of a cutting disk, but I have been told they can be used on the side. Reduced life span though, but they are 14$ rather then 100$ If they work well, then I will spring for the big $ one.
Come to Argentina to buy them, here they are very cheaper. Surely are lower quality too, but they work.

Look this link to flapper discs. You must divide the price into 4.10.
orksecurity6 years ago
... and when you get past the finest grinding disks for rough shaping, you may need to proceed to increasingly fine polishes, depending on just how clean an edge you want.

Thought: Planer might not work, but a sander might, if you can get the right sandpaper.

Another thought: Glass dust can be Bad Stuff. Use appropriate dust control, dust mask, eye protection...
iminthebathroom (author)  orksecurity6 years ago
its slow going what I ever I use, and I wear a full respirator they use at work for asbestos removal.
Work wet
Diamond impregnated grinding disks - 3M make them, not cheap, but VERY rapid removal rates, usually used in an angle grinder. Nothing else is going to last.
PS. Use WET so make sure your tools are either airpowered or fully protected.
onrust6 years ago
I've had good luck scoring glass and grinding the edges SLOWLY with a cut off wheel on a 4" grinder. It will still give you white edges but it will be smother than a metal grinding bit. Can you make a small one to practice on?
iminthebathroom (author)  onrust6 years ago
That is what I acutally did in the pictures above. Tried a variety of abrasive discs from flat sanding pads, grinding discs and these odd flex type one they have at work. May try a flap disc but I don't think that will help. Perhaps I need to look up what rotary tools they use on granite, perhaps I need a diamond disc
iceng6 years ago
Use wet sandpaper a good smooth glass is accomplished with
600 grit wet sandpaper.
So you want to start with about 300 grit or less.
I have seen your work, you don't need more details.
It's slow work.

iminthebathroom (author)  iceng6 years ago
Slow for sure... Was almost going for a river smoothed look, undulations and the like.
frollard iceng6 years ago
+1. Angle grinder to get the BIG stuff off, 300 grit on a WET angle grinder, then work your way up.

(@ author, great project!)