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Tech view radial arm polishing

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Tech view radial arm polishing

  1. 1. 1ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324) • ••••• ••••••••• ••••••••• •• • • ••••••••• •• • • • • • • ••••••••• •• • • • • • • • • • • ••••••••• •• • • • • • • • • • • • • • • • • ••••••••• •• • • • • • • • • • • • • • December, 1993 • • • • • • • • • • • ••••••••• •• • • • • • • • • • • • • • Third in a series for Dimensional Stone magazine • • • • • • • • ••••••••• •• • • • • • • • • • • • • • • • • • • • • • ••••••••• •• • • • • • • • • • • • • • • • • • • • • • ••••••••• •• • • • • • • • • • • • • • • • • • Product Manager • • • • ••••••••• •• • • • • • • • • • • • • • • • • • Marc Poirier • • • • ••••••••• •• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • ••••••••• •• • •••••••••• • • • • • • • • RADIAL ARM POLISHING • • • • • • • • • • • • • • • • • • • • • • • DIAMONDS: • • • • POLISHING STONE WITH • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • TECHVIEW abrasive technology, inc.
  2. 2. Polishing with diamonds: Radial arm polishingThe broad majority of stone fabrication shops in the USA have time and higher pressures exerted by the operator. As fora radial arm polishing machine, used primarily to resurface granites, which are much harder, polishing is uneconomical,stone slab surfaces damaged through handling. Without this often impossible. Silicon carbide is simply incapable of cuttingmachine, a shop has to send the damaged slab to somebody else the granite surface without extremely heavy pressure. Somewith the machinery to repolish large surfaces. Radial arm polish- radial arm polishers are incapable of these higher pressures anders are not only great cost savers, they are quite rugged durable. those that are can be impossible to control.Most units in operation today were purchased anywhere from Let’s look at the mechanics of what happens. In manual polish-several years to several decades ago. The typical radial arm ing with right-angle grinders, the 4" diamond disks spin at 4000polisher consists of articulated arms supported from a station- RPM. The velocity of the outside edge of that disk is about 4000ary post. An electric motor drives a plate supporting the abra- feet per minute.sives by means of pulleys and belts. A handle permits theoperator to guide the whole assembly across the face of the Attach the same 4" disk to a typical radial arm polisher rotatingstone to perform the polishing operation. at 300 RPM, and the outside edge will be traveling at only 300 feet per minute. Even the standard 10" disk will have a peripheralAn acceptable polish on marble has traditionally been achieved speed of only 800 feet per minute. That’s better, but not nearlywith three or four grit sizes of silicon carbide bricks, followed by fast enough for optimum performance. Diamond abrasives re-a buffing operation. The resulting finish usually matches the quire much higher speeds. The hand-held, right-angle grinderfactory finish although the process is quite time consuming. yields a peripheral velocity of 4000 feet per minute, and thatIt’s a different story for granite. Most shops are unable to match should be the goal for a radial arm machine.the factory finish with a radial arm polisher and silicon carbide, The best option is to increase the rotational speed of olderand experienced shops will no long even make the attempt. machines with a different combination of pulleys. The motors onYet, it stands to reason that if granite be finished with a hand- radial arm machines have enough power to operate under asheld grinder and flexible diamond disks, the average shop much as 200 pounds of pressure on the abrasive block. Withshould be able to do the same thing with a radial arm polisher diamond abrasives, that power can be used to obtain higherand diamond abrasives. Indeed, it can be done, but some changes speeds because far less pressure is needed. New machinesare required. already have the option for high speedsMarble is easily polished when it is relatively soft. The silicon Todaycarbide abrasive, the slow 300 RPM speed, and the 100-200 The use of diamond abrasives on the plate of a radial armpounds of pressure—typical working parameters of a radial arm polisher offers new possibilities for the fabricating shop. Dia-machine—are adequate. monds are much more aggressive than traditional silicon car-Harder stones, however, begin to cause problems. Green marbles bide abrasives. They will perform as well on granite, and faror serpentine marbles require more work, usually in the form of faster on marble, And polish both with far less pressure. ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324) 2
  3. 3. Disk use 1. With hook and loop fasteners (e.g., Velcro) glued directly ontoFor rough work, most shops will use a flat steel plate to which a clean metal support plate.have been welded segments of metal-bonded diamonds similar 2. With a special adaptor and rigid plates designed for thisto the segments attached to circular saw blades. Such plates are specific purpose. One is required for each grit size.well suited to removing saw marks or taking off a flawed polish.Resin-bonded diamond disks don’t work as well because they The latter method (the single adaptor and the rigid supportaren’t sufficiently aggressive. plate) has distinct advantages:For polishing operations, the best choice is a resin-bonded, 10" • Optimum cushioning of the diamond for the longestdiameter disk made specifically for radial arm machines. These disk service life.disks range in grit sizes from a coarse #30 to a very fine #8500. • The proper rigidity for an even and perfectly flat polish.Most shops use #50, #120, #220, #400, #800, #1800, and #3500 for That rigidity also allows the polishing plate to extendprocessing granite. Marble polishing is less demanding, and the well beyond the edges and the corners of the work tocombination of #50, #220, and #800 grits usually yields the ensure a uniform finish over the entire surface.desired finish. • The simplest means of attachment for fast and easy gritThe technique of polishing with diamonds is not that much changes.different then the technique used with silicon carbide. Thestandard practice of overlapping passes and crosshatching is • Easy and hassle-free switch-over from diamond tothe same. The only real difference is that far less pressure is silicon carbide if it is necessary to use traditionalneeded. In fact, excessive pressure will shorten the life of a abrasives.diamond disk. For machines fitted with Frankfurt type abrasive bricks, all-For polishing marbles, a good flow of water is needed to flush diamond resin-bonded bricks may be used. They are made in theaway the abrasive cuttings. Adjust the water flow when using a same grit sizes as the 10" disks. Unfortunately, they cannot reachcoarse diamond disk such as #30 grit. The water coming off the to the corners of the slab with the same degree of success as thedisk should be milky, as opposed to clear or pasty. The water 10" disc configuration.flow rate that is right for that first, coarse grit will also right for Costseach succeeding grit all the way up to the finest. On the basis of materials only, diamond polishing tools areFor granite, the water flow should be a little less than it takes to significantly more expensive than silicon carbide. The overallmake the diamond disk hydroplane. That’s usually slightly less advantages, however, clearly favor diamonds—less grindingthan the ideal flow for marble, but consistency of the slurry is not time, improved production rates, better finished surfaces, longera concern for granite. disk life—and add up to improved profitability.The results with diamond disks are very predictable. Processing For polishing with radial arm machines, the advantages ofobstinate, tricky, and soft Negro Marquina marble, for instance, diamonds include:becomes a routine task, without even the usual variations in • The ability to resurface and polish harder stones,gloss over the surface of the slab. And, for the first time, granite including granite, to acceptable finishes.processing to a high gloss is not only achievable, but repeatable. • The ability to polish stones with variable surfaceWith marble or granite, polishing will be enhanced by buffing to characteristics and achieve a uniform polish.bring out the full gloss and depth of color of the stone. • Doing more work in-house and sending less work toAttachment better-equipped shops.Attaching the 10" disks onto the faceplate on the radial armpolisher can be done in either of two ways: ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324) 3

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