---Thread Files---

Bulk Slabbing of Nodules


The numbers at the beginning of each message refer to the Issue number and the message number. Thus, 73-5 is the fifth message in Digest Issue #75. The name in parentheses at the end is the actual file name of this thread file in the Archives

17-3
Hi all:
One of the duties performed in the production of Fischerstone involves taking nodules of Snake Skin Agate, from the size of your first down to golf ball size, and slabbing them. Current process includes blocking this material in 1/2 gallon milk cartons with plaster patch as the bonding medium. The use of Almag oil as the coolant has it's detrimental effects, such as the cutting residue forming an unusual sludge that doesn't settle out as one would expect with other carrier agents.

Thanks to Peter Rowe, the ability to reclaim some of this captured oil is derived through the use of paper bags. Question to you commercial cutters, or hobbyests who have experience in bulk slabbing, would you describe the technique you use? Results? Pros and cons. I am interested in reevaluating my S.O.P., incorporating as much knowledge as you are willing to impart.

Thank You in advance

Vincent
Vybtl@aol.com
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18-3

As a saw matrix, I have found Portland more satisfactory than Plaster of Paris because PoP must lose water in order to gain compressive strength while Portland USES water to cure. I like Type III (High Early) Portland because it can be locked in the saw within 36 hours after casting. It is far stronger at 36 hours than PoP at 2 weeks (full dry). Since you can't use aggregate (sand) in the Portland, I use the acrylic latex "Acryl-60" (ThoroSystem Products) as an internal plasticizer which also enhances adhesion to the rock being slabbed. Mix 1 part Acryl-60 with 3 parts water as the liquid portion and figure 3-1/8 fl oz liquid per 8 fl oz "cup" of dry Portland. For mixing, measure the rock volume by water displacement and subtract from the molded volume (takes 2 inches head space to fit our saw to cut 100% of the rock). Vol yield is (appx) 11.3 cu. in. per "cup" dry Portland. The mix should "slump" less than applesauce but soft enough to be able to poke it down easily around the rock. Be sure to record the vertical height of the rock to mark on the finished block to aid in setting the saw.

The molds are made from 1/8 inch plexiglas- One plate is permanently bonded upright (exactly) to a base plate. A variable rectangular "case" is then made from three more upright plates at mutual right angles. These are offset laterally (to fit the dimension of the rock at hand) and a hobby hotmelt gun seams the plates to each other and to the base plate, forming a leak proof joint. The rock should be oriented with the saw kerf in mind. The rock, if small, may have to be anchored to the base plate with a bit of clay or dbl sided carpet tape to keep it's position when the portland mix is loaded. Be sure to "poke" the mortar around the rock, filling clear to the corners. Pure Acryl-60 latex can be painted as a primer on the rock to enhance adhesion. If multiple rocks are embedded, it is better to "stack" with a tad of plumbers epoxy holding apart in a vertical position, rather than side by side because the blade often wants to "jiggle" when going from one rock to another leaving an edge saw mark. I have mini-mold sets to handle special small (down to 3/4" diam.) stones for stable use on a fine cutting saw (manual feed).

The assembly can be peeled apart after about 18 hrs. The hotmelt glue will float free of the plexiglas if placed in a dishpan of moderately warm water. I recast and reuse the hotmelt just because it takes several sticks per assembly. The plexiglas pieces will last forever and are totally adjustable for face rectangle. A milk carton is easy but can leave excess mortar around the rock, leading to needless "sludge" being cut into the oil.

Regular Portland works ok, too... but let it cure for at least 3 days. White Portland is smoother and about as fast as High Early but twice the cost. Regular Portland is half the cost of High Early, about $3.00 per bag (trivial $ per rock). Acryl-60 is about $10 per quart but cheaper by the gallon.

George Butts

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18-4

If it was me, I might consider a gang saw. If you are doing that much slabbing and everything is blocked, you can do 4-5 slabs in one pass. And from the size of your workpieces, you would need a 6" & 10". This would not run into that much money. I would say 3-4 manufactures in Idar-Oberstein, Germany would have them on the shelf stock. You can even find equipment there to cube it. All kinds of state of the art equipment. I also would use sintered blades, if you are not already. Larger initial capitol outlay but Lower cost in the long run. You have Edus, Winter & Lux as the three main manufacturers there. But you will find even the hardware stores there carry
automatic cutting machinery, cobbing hammers, diamond blades,...the works. The whole town is a lapidary city. If you go in September for the annual show, all the equipment will be on display.
Mark Liccini

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19-3

Being a novice and faced with the same problem, I tried setting the nodules in a piece of clay, let it harden a bit, then let the clay hold the stones as I cut. It was a matter of "doing the best I could with what I had" but it worked OK.
Sue
s-cyr@usa.net
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20-7

Hi George:

Very comprehensive explanation of your proceedure, thank you very much. As I've got a couple of blocks worth of test material to run, I'll give your recipe a shot.

[[I use the acrylic latex "Acryl-60" (Thoro System Products) as an internal plasticizer which also enhances adhesion to the rock being slabbed]]

I'm assuming here that this additive will be found in the Paint section? One of the other difficulties with the process I use, is the losing of the end cuts, which more often than not are a little more than end cuts. The gist
of your formula leaves me with the impression that the nodules to be cut will literally be "glued" into the matrix. Have you experienced a significant loss of end cuts during the cutting process, or do you find that these hold in place regardless of shape? Without exception, all of the Snake Skin nodules that I cut are very much smooth and rounded detracting from any adhesion properties that would normally exist in a surface that is uneven.

[[The mix should "slump" less than applesauce but soft enough to be able to poke it down easily around the rock.]]

Opinion time. While building up the molds, what's the detraction from doing a dry stack inside the mold to evaluate quantity of material to be stacked and layout. Place the stones in the order to be fit inside mold. Mix brew, pour in enough to fill mold about 1/4. Dip future slabs into remaining solution to allow total coverage of material, then stack into mold as per laid out in dry run. Stack till stone pokes out of goo, pour more, stack more till container is full. This method would guarantee fewer air pockets, allowing better adhesion between forthcoming matrix and rock. What drawbacks do you see from this?

[[Pure Acryl-60 latex can be painted as a primer on the rock to enhance adhesion.]]

Should this happen at such a stage that the latex painted on the stones tacks up, or is a fresh coat, then directly into mixture acceptable?

[[A milk carton is easy but can leave excess mortar around the rock, leading to needless "sludge" being cut into the oil.]]

Something else disliked about using the Plaster Patch, is it's inability to hold it's own form. Sounds to me that this Portland method will keep it's own shape with out any external assistance. This would allow the stripping
of the carton from the molded stones decreasing swarf that is introduced into the cutting fluid. By the way, what type of cooling fluid do you use? I'm currently running with Almag oil, which could be a thread all it's own. The
estimated costs for your method are acceptable. If it proves to provide a higher return on the number of slabs that I can achieve, the returns will overcome the increased investments.

Thank You George! This is exactly the reason this list exists. I only hope that I will be able to help someone else as much as you've helped me!

Mark: Thank You as well for your thoughts of the gang saw. Unfortunately, I can hardly afford to pay attention, therefore the thought of putting several saw blades on one arbor makes my check book run yelping into Yvonne's purse. I am willing, but the placement of the decimal point is heading in the wrong direction. When I get serious about making Fischerstone beads, then it will be taken into consideration. But that's another thread.

Thank You again Mark.

Oh Hale, Thanks to you as well! I was supposed to be working on my "other" website this evening! {:-{

G'nite All!

Vincent King
Vybtl@aol.com

(Hale's Note: Thoro Systems Products home page is found at :
http://www.hsc-ss.com/thoro/about.htm) Product pages follow. hale)
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21-5


While some small pieces of rough are very difficult to hold in a vise for even 1 cut, most can be held for that first cut. If you can hold it for one cut, you don't really need to set it in cement, Plaster of Paris, or anything else. Once you have a flat surface (and assuming that your saw doesn't leave huge, rough gouges in the surface) you can glue each flat surfaced piece to a wooden block with waterglass, sodium silicate. Just spread a little on the wooden block, plop your rock down on it and go to bed. Next day you can saw to your heart's content. If your wood block is square, the last slab you cut should be just as true as the rest of them.

The last slab can be removed from the wood by soaking in water for several days. I day to dry, 1 week to unglue is just about right for waterglass.

I bought my waterglass at the Wal-Mart pharmacy for $2.58 a pint. A pint should last me several years.

Incidentally, waterglass is strong enough to hold very substantial sized rough that is difficult to put in a vise, as well as the small stuff.

Herb Luckert
Phyllis.Luckert.3@nd.edu
221 Marquette Ave
South Bend, IN 46617
219-282-1354
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24-7

In Digest #18 (msg3), I outlined the gist of embedding a rock in High Early Portland / Acrylic Latex using a Plexiglas (or Lexan) variable-sized mold to produce a saw-friendly "cube". This technique is faster and stronger than plaster of paris embedding.

In Digest#20 (msg 7), Vincent had some further questions:

[[I'm assuming here that this additive will be found in the Paint section? One of the other difficulties with the process I use, is the losing of the end cuts, which more often than not are a little more than end cuts. The gist of your formula leaves me with the impression that the nodules to be cut will literally be "glued" into the matrix. Have you experienced a significant loss of end cuts during the cutting process, or do you find that
these hold in place regardless of shape? Without exception, all of the Snake Skin nodules that I cut are very much smooth and rounded detracting from any adhesion properties that would normally exist in a surface that is uneven.]]

Acryl-60 is a professional level product and should be found where High early Portland cement is sold. We have a building supply yard where bulk sand, brick etc is available where it is sold by the quart, gallon, 5gal (? 55gal drum). Sometimes a savvy DIY store will have it. The Thoro site mentioned by Hale) is excellent and www.hsc-ss.com/thoro/w&d_prod.htm has a FULL data sheet (.PDF image) for Acryl-60 as a download option.

I leave 2" waste above the rock which is held in the saw
jaws. I cut slabs until the trace remaining is of no
further interest. ALL of the rock is available, encased
in cement, extending beyond the carrier vise. The big saw
is an 18" Highland Park. I'm sorry I don't know the oil
brand. It was last purchased in a return deposit 55gal
drum and was poured off into 5gal pails which say "floor
cleaner" or some such today.

I also cube out medium sized rock to be cut on a water cooled 10" Beacon Star manually using a .040 diamond blade. For fine work, a 6" .012 LapCraft Dia-Laser on a high speed Beacon Star will cut quite small stones embedded in
the same fashion, scaled down, of course, typically 1"x1"x3". Finer blades work ok but I tend to be a fine motor klutz and too chicken to use the .006 & .004 blades manually.

I suggest setting up a mold for just one of your nodules and giving it a try with the formula I outlined. Be certain the nodule is absolutely free of loose material as the Portland is moderately alkaline so tends to scour any hard adherent clay or such. If adhesion is too low for you, step up the ratio of Acryl/water to 1:2. If this is too low still, go back to 1:3 ratio and after mixing the mortar and just before pouring make a "neat" mix of
pure Acryl and Portland which coat as a primer on the nodule. At 1:2, I have some difficulty removing the cement "rind" from the slabbed piece and I think you can get the bond "too good"!

Note that Acryl-60 is designed to interbond stone aggregate with portland. For me, I just paint the rock with Acryl-60 when I place it in the mold. I go on to mix the mortar so the coating is about tacky half-wet when I add the mix.

[[Opinion time. While building up the molds, what's the detraction from doing a dry stack inside the mold to evaluate quantity of material to be stacked and layout. Place the stones in the order to be fit inside mold. Mix brew, pour in enough to fill mold about 1/4. Dip future slabs into remaining solution to allow total coverage of material, then stack into mold as per laid out in dry run. Stack till stone pokes out of goo, pour more, stack more till container is full. This method would guarantee fewer air pockets, allowing better adhesion between forthcoming matrix and rock. What drawbacks do you see from this?]]

Sounds ok to me. But Portland firms up rapidly when not stirred and there is an ultimate time of 10 to 20 minutes when the mix will stiffen too much to handle.

A few further additions to my original post-

Fluid portion of 3-1/8 oz per cup of dry portland depends on packing... Have extra Acryl/water mix available. A finished yield of 6-1/4 fl oz per cup of dry portland used is also "ballpark" depending on packing.

I measure ingredients as well as the rock volume in fl oz. I measure the mold in cubic inches and I use:

fluid oz = (cubic inches)x(0.56)
and
cubic inches=(1.8)x(fluid ounces)

as conversion factors.

To determine the rock volume, I drop it into a can brim full with water. I capture the spillage and measure the displaced volume.

To hold the plexiglass sheet sides in place while seaming with the hot melt gun I use steel cubes and high strength magnetic buttons (rare earth 1"x1/8"...35Lb pull) pkg of 5 for $8.95 from Lee Valley Tools 1-800-871-8158,
item 99k32.13.


..gtb
gtbutts@infinet.com
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28-4

George:

Write the book and I'll buy a copy, autographed of course. Thank You for the advice. When testing is complete on my end I'll let you know how it works with the Almag Oil. Sump cleaning time, yuck %-p

Vincent
Vybtl@aol.com
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53-5


Hi Hale and all.

My name is Bill Collins and I have a comment and a question concerning slabbing.

I have collected many geodes and various small globular agates over the years but could never cut them because the saw vices would not hold them and they were so round that they could not be glued up to a chunk of board secure enough. I got a bright idea and tried it. It worked like a charm and have since found that many others have used the same or similar technique.

Save some of the square milk/orange juice containers (Half-gallon size work great). Mix some mortar mix (or plaster of paris -- I used mortar mix) and place alternate layers of mix and rocks-to-be-sawn into the containers (cut the tops of the containers off first to make it square). The cement will surround the stones (try to orient the stones in the cement so as to get the proper faces cut) and lock them in position. After setting up about a day, just put the container with the rocks into the vise and start slabbing. Better results will be obtained by marking on the container where the cuts should be made in relation to the rocks. Of course the containers are destroyed as you cut but are easily replaced.

Question: The above procedure makes a horrible mess of the oil/lubricant in the saw tank. I would therefore recommend that it only be used immediately before changing the oil or lubricant) unless -- does anyone know of a way to clean the oil so that it may be reused? I have heard that there is a simple way but I don't know what it is. help ????

Bill Collins
rockhead@erols.com
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(Ed. note: Bill, this topic was discussed back in Issues 17 throu 28, under the subject title: Bulk Slabbing of Nodules. I just checked the Archives for Index-47.txt file, which is an index of all topics in the first 47 issues, and find that items in this thread appeared as follows, where 17 is the
Issue No., and 3 is the Item No.:

Bulk Slabbing of Nodules: 17-3, 18-3, 18-4, 19-3, 20-7, 21-5, 24-7, 28-4

Bulk slabbing was discussed in these items, as was how to clean up oil. See Welcome letter or the note at the end of any issue for how-to instructions for accessing the Archives. If you want more information on oil cleanup after reading these, send a query to the digest. hale)

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end (BulkSlabbingNodules.txt)



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ClampingRocks
11/22/1998