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Fig. 5. . . . . . . . . . . . . ... . . . . . . . . . . . . . .. .. . . Fig. 6

   Fig. 5. - The grinding head shown here is a sturdy dual unit. Since grinding wheel are changed often the two wheel unit is preferable. More about the use of the grinder and the slab rest will be given in the article.

   Fig. 6. - Tools used often in making stone pictures. They will help materially in the production of a good workmanship picture. They should be used frequently. Measure, don't guess.

   Fig. 5 is a close-up of the dual grinding head and the slab rest. The grinding head is firmly bolted to a good work table as vibrant prevents sound workmanship. The wheels must run true and also be without vibration. A wide deep splash pan is desirable. It will enable easy access and changing of wheels. The slab rest is made from a piece of plywood 1 inch thick by 4 inches wide. It is strongly fastened at each end to pieces of 2 by 4 inch stock. To prevent the slab rest from tipping either forward of back a piece of wood ½ by 2 by 8 inches is nailed to the bottom of the 2 by 4 uprights. Two pieces of stainless steel are clamped with small C clamps to the top of the slab rest. They should be allowed to overhang the front edge of the slab rest by about three-eighths of an inch. The rest is high enough so that the top surface of it, including the stainless steel, just comes up to the center of the grinder arbor. A small level should be used to be sure. The stainless steel should be thick enough not to bend down the front edge. About 18 gauge, or one-sixteenth inch thick piece will do. The slab rest fits snugly against the outside of the splash pan and rests on the work table. Before starting to grind on a piece of stone I take off as much of the excess material as I can on the trim saw. It is at this time that the stone is ground (if necessary) to the exact thickness of 3.5 mm., approximately one-eighth of an inch. If grinding is needed the side of a course 80 wheel, using plenty of water, will do the job very nicely. Use the vernier caliper4 to check the thickness. Place the cutout paper pattern on the slab and mark around it with a sharp aluminum pencil. If the piece of stone that is being fitted has a concave edge, that edge is usually ground first.
   Six inch wheels are used for much of the grinding. A wheel with the rounded cutting face that will best fit the curve is selected, see Fig. 9. Always grind the stone with its finished surface up. In grinding concave edges the slab rest is shoved towards the wheel until the wheel has cut its way into the stainless steel about one-fourth of an inch. This will provide support to the stone around the side of the grinding wheel. The 6 inch wheel, because of its curvature, will undercut .0026 inches on a one-eighth inch slab. It will do this if the slab rest is exactly even with the center of the grinding arbor. The .0026 inch undercut is not very much, about one-half the thickness of a hair on your head, but that little bit is important. It will allow the upper edge of the fitted piece of stone to touch first and still leave a bit of space underneath for the epoxy to do its work. It is necessary that the epoxy not all be squeezed out. An invisible point can be made by this method and it will hold. As the grinding wheel wears down the undercut will be more than .0026 inches, this results in the adjoining slabs humping up at the joint. To compensate for an error of this kind a thin wedge is inserted under each end of the slab rest, where it rests on the work table, so that the top of the slab rest will incline slightly toward the grinding wheel. All of that sounds a bit complicated but it solved a minor problem and the finished piece was the better for it.

Fig. 7

   Fig. 7. - This drawing shows the steps involved in the making of the "Wood Duck" bill. There are five pieces in the bill and I was cemented together a piece at a time to make up a unit. The bill unit was then cemented to the Plexiglas backing. It was allowed to extend over the backing by the one-sixteenth of an inch as is mentioned in the article.

   There are times when the pieces of stone to be ground are extremely small, such as the pieces of the bill of the Wood Duck and the tiny feathers on the under side of the wing. The pieces are too small to hold in the fingers. The pencils held with erasers down and as shown in Fig. 10 will get the job done. The stainless steel top of the slab rest must be practically touching the grinding wheel for firm support. It is possible to grind pieces that measure as small as one-sixteenth by one-fourth inches by this method. By loosening the C clamps the stainless steel top of the slab rest can be moved about as need be.

Fig. 9

   Fig. 9. - The grinding wheels most usually used will have their cutting faces similar to the ones pictured. They will take care of practically every grinding job. The wheels range from one inch down to one-eighth inch in thickness. Sometimes a special shape is needed as at B. This wheel was used to do just one job and that was to cut the curved openings in the upper part of the Wood Duck leg. In this special job the slab had to be fed toward the wheel in a curved manner. Needless to say such sharp pointed cutting faces would soon be worn out of true shape if they were to grind out the full cut. Rough out as much as possible first. A careful use of the trim saw will cut away much of the excess. Wheel D has a diamond rim about one-fourth inch deep and was kept for sharp inside corner work. Shaping of wheel edges must be done with a diamond tool dresser. Fine-grained Aloxite wheels serve admirably.

   Now let us take a specific part of the "Wood Duck," the bill, and follow through the steps in its construction. The bill, with its five parts, is completed as a unit and then cemented to the Plexiglas. The drawing in Fig. 7 starting at the upper left with parts A and B and going on to the finished bill at the lower right, show how the stone pieces are trim sawed, then ground to fit, then cemented to the adjacent part and finally ground to finished size. I started by cutting parts A and B from the drawing, using the small pointed scissors. Trim saw the black petrified wood, part A, somewhat larger than the pattern that we have just cut out of our full size working drawing, and grind only the curved edge of A. The one-fourth inch wheel, marked H in Fig. 9 was used for grinding the concave curve on part B since the curve is of short radius. All convex curves are ground on a wheel such as E in Fig. 9. When the fit is as near perfect as could be made, using the test box Fig. 8 to be sure, the two pieces are cemented together. Fig. 11 shows the method. The epoxy was left to cure for 48 hours because the cemented unit had to go back to the grinding wheel. Then the patterns were placed on the cemented unit, drawn around with the aluminum pencil, and ground to the finished shape. Use rubber tipped pencils, for as many of you know, a grinding wheel turning at 3000 R.P.M. can administer a beautiful manicure in just about nothing flat. After this first two piece unit is complete, trim saw part C and proceed as has been just explained. After all five parts of the bill have been cemented together and the edges have had their finished grinding, the entire unit is cemented to the Plexiglas. It is to extend over the edge of the backing one-sixteenth of an inch.

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Fig. 8. . . . . . . . . . . . . ... . . . . . . . . . . . . . .. .. . . Fig. 10

   Fig. 8. - The box has a 25 watt frosted light bulb I it and it is a valuable aid in the make up of the smaller units. The box is made of half inch plywood. It measures 6 x 6 x 7 inches. A piece os sanded Plexiglas is fastened to the slanted top of the box. A strip is cemented to the lower edge of the box top to prevent the stone slabs from slipping off. While testing for accurate grinding, dry the two stones and place them together as shown in the picture. Light will shine through if the fit is not good. Strive for a fit that will keep the light from showing through. It will take some careful grinding. If you can achieve a joint that is near perfect it will be invisible in the finished intarsia.

   Fig. 10. - The duck intarsias could not have been completed without this very simple but valuable asset, using pencil erasers to hold small pieces while grinding. Look for them in surplus stores.

   I have been asked frequently to explain how it is possible to grind the very thin pieces of stone that I have used in so many places in the duck intarsia. For example: the thin white datolite in the top of the Wood Duck head; the yellow line of stone at the upper end of the bill; in the feathers of the Baldpate and the shadow lines in the back of the Baldpate and in many other places. It is not possible to grind the stone pieces to the thinness required by themselves. They must be cemented, in greater thickness to the adjacent piece first and then ground to the thinness desired. Fig. 11 shows how the primary feathers in the Baldpate got their quill cemented in place. The hade quill strip was a bit less than one-eighth inch wide when cemented to the swirl agate. After the epoxy has cured for 48 hours the jade will be ground down to 0 thickness at the tip end of the feather and to such a size as is wanted of the thick end. After the quill has been shaped the other side of the feather is completed and then cemented to the quill. The completed feather is then ground to fit in its assigned place and cemented to the Plexiglas.
   From here on to the finished picture the procedure is essentially the same. I worked downward and out to the wing tips. Most of the pieces were fitted individually .If the Plexiglas backing, with the partially completed picture, is held up in front of a frosted bulb of about 100 C.P. the individual pieces may be fitted very carefully. Units of more than 6 or 8 pieces are not recommended, for it is difficult to keep the units optically flat. The result will be an uneven surface and a wavy picture. To eliminate the unevenness the entire picture would have to be lapped down to a flat, this in turn, could open up the joints.
   We finally come to the last step, the lapping and polishing. It was done by hand in my intarsias. The photograph Fig. 12 show the equipment needed. The heavy base block is 2 inches thick. It is plywood, about 20 inches square and was made from a surplus piece of countertop with a Formica finish. The edges of the block have been painted to keep pout moisture. The small Plexiglas clips, held in place by two screws, are used to hold the intarsia firmly in place on the block during lapping and polishing. The one pound grinding block is stone and is rounded on top for convenient holding. The Formica surface makes a thorough cleaning between grits (200-400-600) an easy task. The picture must be removed between grits to thoroughly clean the surface and edges of the intarsia and to clean the block. A spatula is eased under the edge of the Plexiglas and carefully lifted. If the picture does not lift easily just loosen a clip or two. A felt pad and cerium oxide are used to put on the semi-gloss finish. Ample water, of course, must be used in all of the lapping and polishing. The amount of time needed for this last part of the project depends to a large extent on just how carefully the slabbing and grinding was done. It is quite important, as has been mentioned earlier, to maintain uniform thickness of the stone pieces used. If sufficient care was exercised in the proceeding steps the hand lapping and polishing will be relatively quick and easy.

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Fig 11 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Fig 12

   Fig. 11. - The soft wood block, with pins, waxed paper and tack hammer provides a convenient method of cementing together the pieces of stone that make up a unit. The unit is later cemented to the Plexiglas back. Several of the wood blocks may be used at one time.

   Fig. 12. - This is the simple equipment needed in hand lapping and hand polishing.


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