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  • to our lapidary-ists

    I know we have a couple jewelers and lapidarists around here so:
    We have a couple small geodes that I'd like to polish up. I've been going around the web looking at how this is done. Most seem to talk about vibralaps. Now, never having seem one run it would seem that they are "basically" an upside down palm sander with a pan attached to it to hold the grit and stone. I know thats an over simplification of the device but it seems to be pretty accurate.

    Would a heavy based, excentrically mounted shaft, vibrated pan device be something that a HSM could make and get good results with for non-commercial use?

    Any advice?

  • #2
    I've been in on the making of one of these.
    Start with a heavy flat round plate driven off center on a bearing (underneath), tie a rubberband on to a pin on the underneath side. Anchor the rubberband. plate may need to run inside a fence to keep geode from falling off. Apply sandpaper to start, finish with finer grades and then polishing media. Vibratory stroke is defined by how far off center plate is driven and speed of motor doing the driving.

    Good luck, Kurt
    KurtSimmons

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    • #3
      Thanks, I didn't think about the rubberband to keep it from spinning. I found some pictures of some simplier ones that showed more detail.

      I found a site where a guy shows all the lapidary tools he's made. Not bad stuff.

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      • #4
        I have a 24" vibrolap.
        Picture a 150# orbital sander, on its back.
        theres a sheet metal fence that keeps the splash down, & the tray has a lipped edge to keep teh geodes or material from falling off., just slowly step the grit from rough 80 grit down to a fine pollish. Its pretty fun, but very time consuming, requires alot of cleaning bettween steps. Not jsut the machine, but the geode its self, one little partical of grit, from a previous step can haunt you in a polishing step.

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        • #5
          I read online where one guy said to save all your bar soap scraps. Leave them in a tub with enough water to turn them into a paste. Spread the paste into the geode and let it dry. After a grinding session you wash the soap out and no grid can get trapped in the crystals.

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          • #6
            <font face="Verdana, Arial" size="2">Originally posted by brunneng:
            I read online where one guy said to save all your bar soap scraps. Leave them in a tub with enough water to turn them into a paste. Spread the paste into the geode and let it dry. After a grinding session you wash the soap out and no grid can get trapped in the crystals.</font>
            Thats a great idea, i have alwas just bagged teh out side of teh geode in a sandwich bag with tape & that has kept 90% of the outside clean. Im thinking ill goto costco & look for some cheap paste hand soap. thanks for the tip.

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            • #7
              <font face="Verdana, Arial" size="2">Originally posted by brunneng:

              I found a site where a guy shows all the lapidary tools he's made. Not bad stuff.[/B]</font>
              Would you mind posting, or sending me a link? Sounds interesting!

              Thanks
              Van, from the Colorado high country

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              • #8
                Here's one, I'll have to find the other one I found.
                http://www.agatehouse.co.uk/lapid1.htm

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                • #9
                  I was heavily into lapidary work about 10 years ago on a semi-commercial basis (geodes, bookends, agates, slabs etc.)

                  (1) The vibrating tray is one option, but I don't recommend it unless you have a large number of items to polish, or want to get into this hobby. Most commercial
                  (Beacon, Lortone etc.) polishers have large, ie. 24+ inch trays, but there was a small 12" model sold at one time. The larger units used a 1/6 HP motor and an excentric weight which was a piece of bar stock. The tray needs to have a flat bottom, which can be scored or dimpled to hold the grit. (You can pour some epoxy into a pan with a rounded bottom to get the flat surface.)

                  The three steps are (a) Rough grind with 80 grit SiC for about 4 days. (The grit gradually breaks down.) This step must remove all saw marks. You need to inspect, and recycle if necessary. (Surface should be very uniform.) (b) grind with 600 grit for about 1-2 days. (c) Polish on a piece of carpet in the bottom of the tray with aluminum oxide or cerium oxide polish for about 2 day. The commercial units come with 3 trays. You don't need a lot of grit. About 2 tablespoons for a large lap.)

                  The geodes need to be protected from chipping, and I made a bumper from felt weather stripping which was stapled around the edge of each geode. I put shaving cream in the hollow to facilitate subsequent cleaning. Also, the trays can never be allowed to dry out. I usually added glycerine or antifreeze (ethylene glycol) (This is poisonous to small pets, especially cats, so don't use it outside of an enclosed shop.)

                  As indicated, it is imperative that successive steps are not contaminated with grit from a prior steps. You need to scrub extensively between each step with a stiff brush. The used grit will clog up a sewer line in a hurry, so the first step is to hose the trays and items off outside, and then do a second scrub with a stiff brush and detergent.

                  (2) If you are polishing only a few items, try a belt sander to remove the saw marks etc, again 100 grit, and 600 grit. Polish on a cotton or muslin buffing wheel. A disk sander will also work. (A woodworking sander may have too high a speed and burn the disks.) SiC sandpaper is available in diameters up to 12" with a sticky back. (you can also put this on a lathe faceplate, and use your lathe as a polisher.)

                  (2) A rotary lap is another option and is the most time and cost efficient. The diameter of the lap plates should be at least twice the diameter of the geode, with no protruding bolt or arbor in the center. The plates can be made of cast iron, or a soft material such as copper. Aluminum does not charge well with SiC and has a tendency to grab. (Wood has presumably also been used, especially for polishing, but I have no experience with it.)

                  Bob

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                  • #10
                    Bob
                    Use Propylene Glycol - it is non-toxic and safe to use around kids and pets. If you cannot find any Amsoil makes a very pure PG, but it is over priced.

                    I used to Diamond saw the geodes with a constant feed (Screw drive, not gravity like most) saw and would follow up with diamond powder on a copper or tin lap. Does a beautiful job. Try it on a test peice before committing a large (expensive) geode to it.

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