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Author Topic: Clamping round rocks  (Read 8572 times)

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nwbeachrocker

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Clamping round rocks
« on: January 02, 2017, 08:21:53 PM »

I am new to using a slab saw and have some very round nodules of agate I am looking to slab on my ls12.  Does anyone have any tricks to holding a round rock, that will allow more slabs to be cut from it before losing the ability to hold it?  I read somewhere about using plaster paris molds, but wasn't sure if this was a common or effective practice or not.
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jerrysg

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Re: Clamping round rocks
« Reply #1 on: January 02, 2017, 09:50:01 PM »

You didn't say how big the rock is but I would clamp it enough to make one cut. Then glue (epoxy, silicone or super glue) the cut surface to a piece of wood, corian or other uniform material.  Then clamp the wood etc. into the saw vise and cut away.

That first cut you make could be anywhere but I would make it close to the edge to just get a flat to glue.

I started with wood. Used a 2" x 3" and cut pieces about 4" long with a chop saw.  I don't have a lot of wood lying around and the disadvantage of wood is that it can only be used once.  It won't glue after its been in an oil saw.  I have now changed over to granite starting with 4"x4"x1" tiles that I purchased at a tile clearance outlet.  Glued 2 together with JB Weld and then cut them in half to get 2"x2"x4" to glue to the rocks. If I have smaller rocks I use either a 1"x1"x4" or 1"x2"x4" cut from a single tile.  The saw just cuts the granite off the rock at the last slab and the granite is reusable immediately with just a wipe with acetone or 91% isopropyl alcohol.

As far as the glue, I started with the silicone caulk/glue. It works if you get it thin enough but if it's too thick you can get some movement between the block and the rock which is never good in a rock saw.  I have never used epoxy but know lots of people who have. Again a hard epoxy like JB Weld is best.  I have now gone to super glue because it is fast and I can glue the block to the rock and have it on the saw within about 5 minutes.  With the silicone and epoxy it's 24 hours.  I use the gel super glue and an accelerator which I buy at a wood workers supply store. Both the rock and the block are cleaned with 91% isopropyl alcohol before gluing. It is detailed in the following post: http://lapidaryforum.net/group/index.php?topic=1859.msg14588#msg14588

Hope this helps.

Jerry
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peruano

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Re: Clamping round rocks
« Reply #2 on: January 03, 2017, 05:13:24 AM »

There are many variations on the gluing rocks onto the stub strategy.  I use wood stubs (2x2 is most common but bigger or smaller depending on the rock) and wood glue (Elmer's, Gorilla, or generic, no matter), a 24 hrs setup time, and saw away.  To remove I just use my miter or hack saw to saw just next to the rock.  The sliver of wood and glue that remains will soak off in an hour or two and leaves a clean rock.
I reuse wood blocks all the time - after I cut a new edge with the chop saw to remove the oil surface and allow them to air dry a week or so. and have no problems with rocks releasing (except when wood glues are subjected to freezing temps before totally setup). 
The glue on to a stub is a great strategy for small beach cobble that you might be tempted to cut by hand but will do a better job on if you cut in while its clamped in a vice.  So, I sometime clamp a special pebble even if I'm only going to make one or two cuts from it.  I used to try to soak the entire stub but that took much longer and sometimes was never ending because the water couldn't penetrate deep enough to reach all the glue.  Enjoy.
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nwbeachrocker

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Re: Clamping round rocks
« Reply #3 on: January 03, 2017, 06:57:31 AM »

Thanks for the effort in the details provided.  Much appreciated.
As a carpenter I have lots of wood hanging around, often too much.

I wonder if anyone has used the plaster of paris method, with multiple small rocks embedded in one block of p.o.p.?
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hummingbirdstones

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Re: Clamping round rocks
« Reply #4 on: January 03, 2017, 07:17:44 AM »

We've never used it, but folks in our club do.  Vince is really good at hand slabbing rocks, so we've never had to use it yet.  I think if we had gobs of small cobbles to slab, it would be the expedient way to do it, though.  Basically Vince will hand slab small, good rough on a small saw to save material.
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Robin

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Re: Clamping round rocks
« Reply #5 on: January 03, 2017, 09:54:46 AM »

About a year ago I picked up the leftovers from a rock sale. One bucket had a block of cement in it. What it looks like is that the guy took a bunch of nice, but small, stones and put them in the cement then sliced it. POP would probably work better and be easier to get the stone out of later.

I have some large, softball sized, geodes/thunder eggs to cut. I'm going to experiment with wedges. Probably won't work, but I'll try.
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finegemdesigns

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Re: Clamping round rocks
« Reply #6 on: January 03, 2017, 11:42:24 AM »

Use 1 or 2 of these to start:

Gator Saw Clamp



Then after you have 2 halves use one of these to start slabbing.
It also comes in a smaller version for smaller chunks of rough.

http://www.ebay.com/itm/MEDIUM-ROCK-CLAMP-for-12-to-24-slab-saws-Holds-end-cuts-hard-to-hold-rocks-/232192661397?hash=item360fc2d795:g:b1UAAOSwmmxW6XL~
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peruano

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Re: Clamping round rocks
« Reply #7 on: January 03, 2017, 02:23:27 PM »

There is no doubt that the Plaster of paris will work.  I'd suspect that you might end up fouling your cutting oil pretty quickly with what could turn into more P of P in the bottom of your saw.  Slab saws run on distance of vice movement and adding to that distance by surrounding the cobble in more matrix seems to be lengthening the cutting process.  I can stub up 20 or so cobbles in one afternoon and spend the next afternoon cutting them as thin or precisely as I choose and I'm guessing with a bit more control over orientation than with their being embedded.  But that's just the way I got started doing it and other ways can work just as well or better. 
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Ranger_Dave

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Re: Clamping round rocks
« Reply #8 on: January 03, 2017, 03:15:34 PM »

Could that Gator Clamp be clamped in saw clamp?
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jerrysg

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Re: Clamping round rocks
« Reply #9 on: January 04, 2017, 11:11:54 AM »


I reuse wood blocks all the time - after I cut a new edge with the chop saw to remove the oil surface and allow them to air dry a week or so.

I'd rather not risk the fingers on cutting a fresh surface on the chop saw with a 4" piece of wood.  That's reaching the limit of my chop saw clamp.

After a lifetime of woodworking as a hobby with all my fingers intact, I'll pass.

Jerry
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Jhon P

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Re: Clamping round rocks
« Reply #10 on: January 04, 2017, 12:31:36 PM »

You can buy an 8' 2x4 at Home Depot for a few bucks and cut it into 4" pieces and you have 20 or more pieces. I use gorilla glue, tried epoxy but it didn't hold the the wood for some reason. I will cut a flat spot with my 10" tile saw. Geodes I have an assortment of wedges I cut from 2x4, you have to make sure it is jammed around the rock good or you will be buying a new blade. I have thought about buying or making a geode clamp.
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olgguy

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Re: Clamping round rocks
« Reply #11 on: January 04, 2017, 01:35:56 PM »

Yep , the plaster works too. I used tile grout, but it scored the jasper as it cut.
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olgguy

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Re: Clamping round rocks
« Reply #12 on: January 04, 2017, 06:11:16 PM »

Automotive 'bondo" works too, and you can saw it off with a carpenter's saw.
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Ranger_Dave

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Re: Clamping round rocks
« Reply #13 on: January 04, 2017, 10:25:23 PM »

A geode clamp is what I'm looking for. That gator clamp, at $36 each, and you'd need two, is a bit pricy. I need something to hold the round geode, cut as close to the middle as possible. Gluing to a board or something leaves glue or plaster that would be a mess and not very attractive. Wedges look to be about the best so far. Maybe my welder friend down the road can make me something similar to that gator clamp?
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olgguy

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Re: Clamping round rocks
« Reply #14 on: January 05, 2017, 06:50:38 AM »

Here is the other clamp the guys were talking about. Normally you use the short end, with a cut face in the notch, but some times the long side works.
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