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Tech view edge polishing
Tech view edge polishing
Tech view edge polishing
Tech view edge polishing
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Tech view edge polishing
Tech view edge polishing
Tech view edge polishing
Tech view edge polishing
Tech view edge polishing
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  1. 1 ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324) • ••••• ••••••••• ••••••••• •• • • ••••••••• •• • • • • • • ••••••••• •• • • • • • • • • • • ••••••••• •• • • • • • • • • • • • • • June 24, 1994 • • • ••••••••• •• • • • • • • • • • • • • • • • • • • • • Presented at ITSE, Anaheim, CA. • • • • ••••••••• •• • • • • • • • • • • • • • • • • • • • • • ••••••••• •• • • • • • • • • • • • • • • • • • • • • • ••••••••• •• • • • • • • • • • • • • • • • • • VP Engineering and Quality • • • • ••••••••• •• • • • • • • • • • • • • • Robert W. Evans, Jr. • • • • • • • • ••••••••• •• • • • • • • • • • • • • • • • • • • • • • ••••••••• •• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • THE ONLY WAY TO GO • • • • • • • • ••••••••• •• • •••••••••• • • • • • • • • TOOLS: • • • • • • • • • • • • • • • • • • • • • • • POLISHING WITH DIAMOND • • • • GRANITE & MARBLE EDGE • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • TECHVIEW abrasive technology, inc.
  2. Granite & Marble Edge Polishing Conclusions Robert W. Evans, Jr., VP Engineering and • Following the optimum operating parameters can result in over Quality, Abrasive Technology, Inc. B.S.M.E., Ohio State University. a 70 % increase in productivity above current field practices (1.7 times current). Mr. Evans has been with Abrasive Tech- nology for four years. His prior positions • Annual sales revenue increases from a single operator can include Director of Engineering and Quality exceed $600,000 in over half the cases when switching from typical at TRW and Sr. Project Engineer at Gen- current practices to more optimum levels. eral Motors Engineering Staff. • Following the optimum operating parameters can result in an Abstract improved finish and minimize reworks. Conventional polishing of granite and marble edges has • Following the optimum operating parameters can result in less been done by hand. While this has changed somewhat with the operator fatigue and thereby improve output. advent of automatic finishing machines, it is still very much a hand finishing technology. The addition of power tools to aid the finisher • Both granite and marble can be effectively polished with dia- has made the job less fatiguing but still very much a hands-on art mond tools. form like process. Further, the control of the operating parameters • Polishing marble with diamonds and water reduces respiratory varies widely between technicians. Surface finish quality also dust concerns for both the polisher and those in the work area.. varies considerably between individuals and their selected tools. Today, craftsmanship continues to reign supreme in the area of • Shops doing 3/4" and thicker edges on a regular basis would do edge polishing. well to select 3 inch diameter tools. They need to maintain their current force level on 3/4 inch edges and press harder on 1 1/2 inch The relatively recent addition of diamond pads for power edges (from 7.7 pounds up to near 15 pounds). hand tools has made the job easier, particularly for granite edge polishing. However, finish quality, while easier to achieve, still • Current hand polishing practices can be easily modified to varies a lot because of inconsistency in operator techniques. Also achieve the optimum levels. there is a general lack of working at the optimum levels of feeds and • Following the optimum parameters can result in significantly speeds for the diamond-granite polishing interface. faster delivery times without additional work hours. This paper presents the results of two years of work focused upon the diamond-stone polishing system with a particular focus upon power edge polishing by hand. The data was collected across a wide variety of stone fabrication shops and their operators. This FAST FORWARD? »» was a field based study that was quite revealing. Practical If you are in a hurry, you can skip the next sections suggestions are given to assist the practitioner in producing a and get right to the recommendations starting with higher quality finish in less time. This is done by focusing upon the paragraph labeled "Traverse Speed" on p.6. operating more closely to the optimum parameters for diamond tools. 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. Discussion Abrasive Technology, Inc. is a major manufacturer of supera- brasive tools for a wide range of industries. In an effort to assist its customers and the stone fabrication industry, it has con- ducted a product development program focused upon the pol- ishing of stone using diamond tools. An earlier paper entitled, “Granite and Marble Polishing With Diamond Tools - The Ulti- mate In Efficiency and Finish”, was presented at Stone Expo in March 1994. It discussed the use of diamond tools to polish large flat surfaces. The, then current, industry practices were exam- ined and the test results from both laboratory testing and field validation runs were presented. It was shown that more detailed attention to operating parameters can result in an outstanding finish in less time and with more productivity than had been possible before. Practical field guides were presented for setting up the polishing system to achieve the correct contact pres- Photo B sures, surface speeds, water flow rates, traversing velocities and The special platform and data acquisition system were trans- head overlaps. This paper expands upon the previous work and ported to a number of stone shops. Each available operator was addresses the issue of correct application of diamond tools asked to polish a granite edge and a marble edge using his when performing edge polishing of granite and marble stones. normal tools and techniques (ref photo C). The approach taken was to design and build a special polishing platform. This platform would need to measure and record the forces and times being used by an operator for each grit, over a variety of stone types. This platform had to be portable since all the data was to be collected from polishing professionals in their own shops, on their own stones, and using their own tools. A three axis Kistler dynamometer was procured. Its high fre- quency capability made it especially suitable for this work. The dynamometer was attached to two square plates (one above the dyno and one below). In this way, the bottom plate could be fastened easily to a bench top. The stone could then be placed on the top plate and clamped in place (ref photo A). Any forces applied to the stone would then have to be transmitted through the dynamometer, thereby producing an electrical signal pro- portional to the actual force being applied to the edge of the stone. Photo C No attempt was made to influence each person’s style and technique. Each stone was their selection from their own yard. The stones polished are shown in Table 1. STONE TYPES EVALUATED GRANITES: • BLUE PEARL • BLACK ABSOLUTE MARBLES: • WHITE CARERRA • VERDI ALPI • BOTTICINO Photo A The electrical signals were sent to amplifiers and then into a two Table 1 pen strip chart recorder (ref. Photo B). The entire system was The power tool was their own choice and from their own quite portable and the strip chart records provided adequate equipment inventory. A list of the power tools used in shown in resolution over the anticipated operating range (approximately Table 2. 0.5 pounds resolution). ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324) 3
  4. EDGE POLISHING TOOLS USED DURING EVALUATIONS TOOL SPINDLE TYPE STONE POWER BRAND TYPE DIAMETER (in.) SPEED USED ON SOURCE 1 BOSCH BELT SANDER N/A 2,700 FPM MARBLE ELECTRIC 2 PORTER CABLE BELT SANDER N/A 1,550 FPM MARBLE ELECTRIC 3 MAKITA 9218-PB 4 2,000 RPM ANY, BUFF ELECTRIC 4 FLEX ORIGINAL LW1503 4 3,700 RPM GRANITE ELECTRIC 5 NIKKEN WS-5 3 2,000 RPM GRANITE AIR 6 NAT.DETROIT DSQ 5 10,000 RPM MARBLE AIR 7 NIKKEN WS-7 4 4,000 RPM GRANITE AIR ADJUSTABLE 8 MALTABO 4 4,000 RPM MARBLE ELECTRIC ADJUSTABLE 9 ALPHA 4 2,000 RPM GRANITE ELECTRIC Table 2 The abrasive tools they used were theirs to choose, and again, from their own inventory. All machine settings such as RPM and water flow rate were their choice. Consequently, there should not have been any issues regarding lack of familiarity with how to perform the work successfully. Photo E nies were quite open and willing to give of their time with their Most operators chose to have the stone laying horizontal and to best people. Due to the production focus and the art or craft polish the vertically oriented edge by pushing in lightly. This orientation toward edge polishing, there has been a general lack orientation is shown in photo # A, above. One shop chose to of data collection and virtually no systematic testing for better place the slab vertically and to polish the horizontally oriented methods and a more complete understanding of the polishing edge with a slight downward pressure (ref. Photo D and E). This process. This is in spite of the fact that most of the companies seemed to provide some advantage to the operator in consis- visited could benefit in a significant financial way from a more tency of loading and minimization of fatigue. Further, he avoided optimized and consistent approach to edge polishing. water in the face with this setup. Data format The forces from the dynamometer were output as lines on a moving strip chart. A typical sample of the strip chart record is shown in Figure 1. The upper line, labeled “grinding contact force”, is the force being applied to press the tool into the stone. The lower line, labeled “tangential force”, is the force being produced from dragging the tool across the stone. It is in the same plane as the edge being polished. SINGLE GRIT BLACK ABSOLUTE GRANITE AND DIAMOND TOOLS OPERATOR TECHNIQUE AS OBSERVED Photo D General observaions GRINDING CONTACT The average operator had 3.9 years of experience in edge FORCE (INTO STONE) polishing and nearly half had over 5 years of experience. One (LBS.) operator evaluated had 16 years of experience. There were wide differences in technique, choice of operating parameters and finished product appearance. There were also large differences in the time to perform a polishing sequence. The majority of the granite edges had to be redone because of cosmetic appearance TANGENTAL issues. This has to be very costly in both time and materials. FORCE (ALONG EDGE) There was a surprisingly strong reliance upon post polish finish- (LBS.) ing techniques other than buffing. Chemical “coatings” of many types are in use. Levels of commercial acceptability varied widely. Some operators were much more skilled with one stone than another. Years of experience did not seem to completely predict polishing skill. It seems that training efforts could be STONE strengthened with a focus on consistency of technique and TANGENTAL FORCE Figure 1 selection of more optimum operating parameters. Most compa- CONTACT FORCE ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324) 4
  5. A graphical analysis of the data is shown in Figure 2. The average titled “Granite & Marble Polishing With Diamond Tools - The value was taken from an "eyeballed" best fit line drawn over the Ultimate in Efficiency and Finish” and is also available from data. The max and min values were similarly taken for each trace. Abrasive Technology, Inc. The values were recorded in tabular form across each operator, For White Cherokee marble and both Charcoal Black and Ma- on each stone, and for each grit used. hogany granites, a test plan was developed using statistically SINGLE GRIT based Designed Experiments. Variables evaluated included abra- BLACK ABSOLUTE GRANITE AND DIAMOND TOOLS sive types, bond systems and associated characteristics, and OPERATOR TECHNIQUE AS OBSERVED operating parameters. The output characteristics were stone reflectance, depth of color, overall appearance, and tool wear. 17.0 Tests were conducted almost continuously over a 24 month period. The tooling formulations were developed in response to GRINDING CONTACT AVG. = 11.0 lbs. the output characteristics initially measured. Progressive im- FORCE (INTO STONE) provement was incorporated into each succeeding level of tool 0 (LBS.) RANGE = 13.5 or + 6.75 lbs. design and testing. The various stones’ finish sensitivities to 3.5 both small and large changes in the operating parameters were also quantified. 3.0 Each of the variables, surface speed (SFPM), load (LB), water SIDEWAYS AVG. = 2.0 lbs. flow rate (GPM), traverse speed (FPM), pass overlap and the FORCE (ALONG EDGE) 0 number of passes required were varied over a considerable (LBS.) RANGE = 2.6 or + 1.3 lbs. range during the test program. A table of optimum values was 0.4 published which, when used, produced significantly better re- sults than any other levels tested. We recognize that field condi- tions are often less than optimal. Also, production equipment STONE often lacks the adjustment and control features necessary to SIDEWAYS FORCE obtain the table values exactly. However, three things can be CONTACT FORCE Figure 2 stated definitely. First, deviation from the table values detracted Field testing summary from the optimum finish and productivity numbers we achieved during testing on the specific pieces of White Cherokee marble, Table 3 below shows some summary statistics from the field work Charcoal Black and Mahogany granites that we used. Second, no we conducted on granite. The values shown are brought into one is using THE exact pieces of stone that we used. Conse- practical focus in the section “Implications For Edge Polishing”. quently, some changes in operating parameters may be useful. Previous work key relationships However, the table values represent a well tested and proven set of parameters for a starting point when polishing stones in this It is important to compare this current round of field data with range. Third, care must be taken when changing parameters. We the previous work. This comparison will assist in achieving a found interactions between parameters that significantly af- more complete understanding of where the current practice of fected finish. An interaction between load and water flow rate, edge polishing resides and where it needs to go in order to be at for example, would mean that at light loads, water flow should be a more optimum level. low for optimum finish, but that at heavier load water flow To that end, this section is a series of brief excerpts from the should be high to maximize reflectance, a reversal or interaction. previous work by the same author on the use of diamonds in the The reflectance values obtained during testing are shown in polishing of both marbles and granites. This excerpted paper is Figures 3 and 4. FIELD TESTING - GRANITE DATA - 3/4" THICK, 12" EDGES AVERAGE TOTAL AVERAGE TOOL PERIPHERY LOAD POLISH TIME NUM. OPER YEARS TOOL DIAMETER SPEED APPLIED MAX MIN LOAD TIME PERGRIT GRIT EDGE . EXP. GRANITE TYPE (in.) RP (sfpm) (lbs) LOAD LOAD RANGE (sec) (sec) STEPS STYLE ID 1 A 6 BLACK ABSOLUTE DIAMOND 4 2,000 2,094 6.4 10.0 2.0 8.0 574 82 7 FLAT 2 B 5 BLACK ABSOLUTE DIAMOND 4 2,000 2,094 4.9 8.0 3.0 5.0 289 41.5 7 FLAT 3 C 2 BLACK ABSOLUTE DIAMOND 4 2,0002,000 2,094 2.8 4.5 0.5 4.0 424 60.6 7 FLAT 4 D 0.5 BLACK ABSOLUTE DIAMOND 4 10,000/4,000 2,094 10.5 22.5 0.5 22.0 981 140.2 7 FLAT 5 E 0.5 BLACK ABSOLUTE MIXED 5/3 10,000/2,000 13,090/2094 1.5 4.0 0.5 3.5 534 76.2 7 FLAT 6 F 6 BLACK ABSOLUTE MIXED 5/3 2,000 13,090/1571 5.9 18.0 1.0 17.0 548 49.8 11 DEMI BULL 7 G 0.5 BLACK ABSOLUTE DIAMOND 3 3,700 1,571 8.0 15.0 3.0 12.0 232 29 8 FLAT 8 H 2 BLUE PEARL DIAMOND 4 3,700 3,875 13.4 20.0 7.0 13.0 285 40.7 7 FLAT 9 I 16 BLUE PEARL DIAMOND 4 3,700 3,875 9.9 15.0 5.0 10.0 261 37.3 7 FLAT 10 J 0.3 BLUE PEARL DIAMOND 4 3,875 13.6 17.0 8.0 9.0 386 55.1 7 FLAT AVG: 3.9 7.7 13.4 3.1 10.4 451.4 61.2 MAX: 13.6 22.5 8 22 981 140.2 16 0.5 MIN: 0.3 1.5 4 3.5 232 29 TOP HALF AVG. 82.8 Table 3 ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324) 5
  6. WHITE CHEROKEE MARBLE TECH SHINE™ PADS & DIAGLO M™ COMPOUND operational parameters. However, after several shop visits, we just could not resist trying to help improve their practices. After 100 the operator had polished an edge in Black Absolute granite, we 90 showed him the strip chart graphs of his work (ref. Figures 1 & 80 70 2).We explained that a smoother, more steady motion would REFLECTANCE 60 help eliminate the somewhat wavy appearance he had produced. 50 While it was not severe enough to reject the stone from a 40 commercial standpoint, it was noticeable under a reasonable 30 examination. Also, the edge had some lightness (lack of depth of 20 color) in a streak running over a good portion of the length of the 10 0 edge. We suggested that a closer examination of the stone after 30m 50 120 220 400 800 Buff the 120 grit would help prevent this problem in the end. He GRIT SIZE agreed to use an air gun to dry the stone after the 120 grit and to Figure 3 not advance to the next grit until all of the 50 grit scratch pattern CHARCOAL BLACK & MAHOGANY GRANITE with TECH SHINE™ PADS & DIAGLO X™ COMPOUND had been removed. Finally, we suggested that he was spending too much time and not getting the higher quality results possible 90 from spending less time at more optimum levels. Specifically, an 80 increase in contact pressure and a decrease in traverse speed 70 across the stone with fewer passes should help achieve the 60 REFLECTANCE optimum finish in the minimum time. He agreed to try this 50 approach on the adjacent side of the same stone he had just 40 polished. The change in method is shown for the same operator, 30 20 grit and stone in Figure 5. 10 0 SINGLE GRIT 30m 50 220 600 800 1800 Buff Amb.Temp. BLACK ABSOLUTE GRANITE GRIT SIZE AND DIAMOND TOOLS Figure 4 OPERATOR TECHNIQUE AFTER TRAINING We have found that the two most significant variables for con- trolling polishing results are the contact pressure on the stone and the tool rotational velocity. Water flow is important. Further, it is clear that the number of passes the tool makes over a single GRINDING CONTACT spot on the stone is important. Of course, the proper values will FORCE (INTO STONE) be different for different tools from different sources. Also, we (LBS.) know that stone varies widely. However, for a given stone, the two key variables that the producer can control are the load on the stone and its resultant contact pressure and the surface feet per minute being produced by the motor RPM and the diameter of the tools. The optimum contact pressure for both marble and granite was found to be 9.5 psi. The optimum surface speed for marble was found to be 850 SFPM and for granite it was 1400 SFPM. The optimum water flow rate was found to be 0.5 GPM. The optimum traverse speed was found to be 5 FPM. The optimum number of passes for marble was found to be 2 passes while for TANGENTAL FORCE granite the optimum was 4 passes. The diamond grit sequence (ALONG EDGE) (LBS.) commonly used in the field for granite is 50, 120, 220, 600, 800, 1800, and 3500. For marble, the sequence is 50, 120, 220, and 400. Implications for edge polishing The differences in technique and associated times to polish, along with the high frequency of reworks greatly reduces pro- ductivity. We estimate that in half the cases, over a 70 % increase Figure 5 in output per operator can be achieved if techniques are opti- The analysis of the data is shown in Figure 6. mized for first time acceptance and standardized for consistency between operators. This 70 % increase number initially came The dramatic change in technique was achieved after a brief five about when we decided to attempt to train a polishing technician minute discussion. The quality of the final finish was signifi- to more closely duplicate the practices that had worked so well cantly improved to a level well above “just commercial”. This in the large flat surface work we had previously conducted. Our shows that a little training can be quite effective when properly original plan was just to observe current practices and quantify focused and delivered. ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324) 6
  7. SINGLE GRIT produce 75 lineal feet of polished granite edges per shift using BLACK ABSOLUTE GRANITE AND DIAMOND TOOLS the “after training” optimized method. For estimating purposes, OPERATOR TECHNIQUE AFTER TRAINING we used a six foot counter, 0.75 inches thick, of granite, with a flat polished edge being sold for $500. Using the productivity num- bers above, the improved method would yield 5 additional 17.0 counters out the door per person per shift. That translates into GRINDING $2500 per day in increased sales revenue or $600,000 per year per CONTACT FORCE AVG. = 14.5 lbs. person! The benefits from this change in productivity are in (INTO STONE) (LBS.) RANGE = 4.0 or + 2.0 lbs. three areas. First, more sales mean more profits. Second, in- 13.0 0 creased output per labor hour means a more competitive shop, getting more jobs and winning the jobs it really wants to win. Finally, and perhaps most importantly today, an optimized operation can promise quicker delivery times and meet its commitments more easily. Of course, each stone is different, and each operator’s current practices are different. These numbers do not include the additional operator setup times that go with 2.0 this increased output. Also, the favorable impact of reduced or SIDEWAYS AVG. = 1.8 lbs. FORCE 0 eliminated reworks has not been included in the estimates. Our (ALONG EDGE) (LBS.) RANGE = 1.0 or + 0.5 lbs. data suggests that elimination of reworks may yield another 33% 0.4 improvement! In any case, savings per operator will vary. How- ever, the data and field experience clearly show that a tremen- dous gain in productivity is possible when using diamond tools properly. Figure 6 Traverse speed: A comparison of the “as found” method and the “after training” The optimum traverse speed is 5 feet per minute (FPM). For method is shown in Figure 7. practical purposes, an operator should be moving the power tool across the stone edge in a smooth motion that covers 1 foot CYCLE TIME COMPARISON TWO METHODS - ONE GRIT every 12 seconds. It may be helpful to mark off 1 foot sections BLACK ABSOLUTE GRANITE AS FOUND with masking tape and counting “one thousand and one, one thousand and two,....one thousand and twelve” for a while to help get the correct idea of an appropriate traverse rate. Number of passes: Granite requires four passes and marble only two passes. A pass is defined as moving from one end to the other. The operator would then move at the same speed back to the starting point. 15.0 cm This would be the completion of two passes. When polishing = 112.5 sec granite this sequence would be repeated again (a total of 4 START FINISH passes). Surface speed: AFTER TRAINING • Smoother motions This parameter is somewhat more difficult to manage. Each • More consistant pressure • Less total time operator seems to have his/her own power tool preference and each manufacturer’s power tools operate at different speeds. Some tools are speed selectable while others are of a fixed RPM 10.9 cm design. The other variable that effects surface speed is the = 81.8 sec START FINISH diameter of the polishing disk. Most shops are operating with either 3 or 4 inch disks. Considering the importance of surface speed, it will pay big dividends to the operator that takes a little Figure 7 time to optimize this parameter. From the previous work, the The charts were run at the same speed during the tests. There- optimum value for granite is 1400 sfpm while that of marble is 850 fore the difference in lengths of the two lines represents the time sfpm. The nomograph below (Figure 8) shows the interplay saved per grit when converting to the more optimal method. between the diameter and the spindle speed and their effect This saving represents a 37% increase in finished edge footage upon surface speed. While it may not be possible to hit the for this one operator! This operator was still using too much time optimum values exactly, the closer you get to the optimum the to achieve the optimum polish. We found that half of the better the results. Knowing the tool diameter and the handpiece operators tested can produce an average of 43.3 lineal feet of RPM, draw a straight line connecting the two values. Where the polished granite edges per shift using their current methods line crosses the surface speed line is the speed this set up will when excluding setup times. The same operators can each produce. An operator can either adjust the RPM via the manufac- ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324) 7
  8. turer provided dial or select another power tool with a more favorable RPM in order to achieve a more optimal surface speed. 4 INCH DIAMETER TOOLS CONTACT AREA ANALYSIS Of course, changing the tool diameter selection can also be an effective way to optimize surface speed. In some cases, changes CENTERED ON STONE in selection of both the hand tool and the disk diameter may be required to obtain optimum levels. NOMOGRAPH FOR OPTIMIZATION OF SURFACE SPEED (SFPM) HAND EDGE POLISHING 3/4" 1 1/2" 5000 4500 4000 3500 OFFSET ON STONE 7000 3000 6000 3/4" 5000 2500 1 1/2" 4000 OPTIMUM 2000 3000 FOR GRANITE 1900 5 2000 1500 4 1500 • 1400 1000 3 900 800 700 • OPTIMUM FOR MARBLE 1000 1100 Figure 9 TOOL SURFACE HAND TOOL becomes polished. If the stresses are too high, the excess DIAMETER SPEED SPEED pressure helps to break the diamond tool’s bond prematurely (IN) (SFPM) (RPM) and tool life suffers. Table 4 summarizes the contact area and Figure 8 force considerations for three tool sizes. Contact pressure: CONTACT PRESSURES AND APPLIED FORCES The issue of contact pressure relates to four variables. The first FOR SELECTED TECHNIQUES variable is how hard the tool is pressed onto the stone. This is EDGE CONTACT AREA FORCE REQUIRED FORCE REQUIRED TOOL CONTACT AREA expressed in pounds of force. The second variable is the gross TOOL FORMULA DIAMETER (in.) THICKNESS (in.) CENTERED (sq.in.) FOR 9.5 PSI CENTERED OFFSET (sq.in.) FOR 9.5 PSI OFFSET contact area over which the load is distributed. This is measured (lbs.) (lbs.) SUPER-DIASHINE™: in square inches. The third is the percentage of the contact area 3 3/4 0.763 7.2 0.983 9.3 3 1 1/2 1.712 6.3 1.768 16.8 that is actually resin and diamond touching the stone. Finally, 4 4 3/4 1 1/2 1.039 2.200 9.9 20.9 1.169 2.412 11.1 22.9 because the edge is a narrow line and the polishing disk has a PRO-DIASHINE™: 3 3/4 0.812 7.7 0.680 6.5 larger diameter than the edge width, the geometry of the pad 3 1 1/2 1.646 15.6 1.519 14.4 4 3/4 1.232 1.7 0.961 9.1 orientation to the edge must also be considered. Figures 9 shows 4 5 1 1/2 3/4 2.575 1.405 24.5 13.3 2.237 1.039 21.3 9.9 some of these considerations graphically. 5 1 1/2 2.620 24.9 2.468 23.4 Stone is polished by the contact pressure between it and the Table 4 diamond tool. Imagine a 10 pound weight 1 inch square resting Figures 10 and 11 show this data graphically for the two most upon your hand. The weight does not cause you pain because the common edge thicknesses and for the two styles of tool position- contact area is relatively broad (1 square inch) and the load is ing (centered and offset). Based upon the field data, 7.7 pounds relatively light (10 pounds). This translates into 10 pounds per of load on the stone is commonly achieved. In Figure 10, we see square inch or 10 psi. If however, you then turn the weight up on that tool to stone centering and offset techniques on 3/4 inch edge so that the entire weight is pressing onto your hand over a edges produce little difference for the 3 inch Pro-Diashine™ (3p) 0.1 square inch area, your level of comfort just deteriorated and 4 inch Super-Diashine™ (4s) (around a 10-15% change). significantly. It is still the same 10 pounds but the contact area However, the 5 inch Pro-Diashine™ (5p) and 4 inch Pro-Diashine™ through which it is pressing on your hand is now just 10% of what (4p) produce a substantial difference in contact load require- is was previously. This new arrangement translates into 100 ments depending upon technique (up to a 30% change). This pounds per square inch (100 psi). It is the high contact pressures seems to suggest that an operator should select one approach or that break down the stone piece by piece. If the stresses are not the other and stay with it to enhance his/her consistency of load high enough, the stone does not become scratched and it never and resultant contact pressure. The 3 inch tools seem to be ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324) 8
  9. With loading being so important, the efficient shops need a OPTIMUM LOAD FOR 3/4 INCH EDGE POLISHING 6/94 rwe method to assist the polishing technician in periodic calibration 14 of his/her feel for the correct loading. One simple and inexpen- 12 sive way to accomplish this would be to obtain a bathroom scale. X 10 X X This scale could be placed in the shop in a standard and X 8 convenient location for a painless check on a scheduled basis. COMMONLY ACHIEVED LOAD The human memory for correct feel is somewhat weak and in LOAD (lbs) X 6 cent 3/4 offset 3/4 4 X need of frequent reinforcement. A "start of shift" habit could be 2 just enough to emphasize the importance of correct loading and 0 frequent enough to become ingrained. 3-S 3-P 4-S 4-P 5-P Water flow rate: TOOL DIAMETER AND TYPE Water flow rates are generally uncontrolled beyond “full on” and Figure 10 “full off” flow levels. Because the water tends to run off an edge much more so than off a slab, more water is needed in edge close to optimum contact pressures at the commonly achieved polishing. Too little water translates into shortened tool life and load. The 5 inch tools need an increase in contact load for either unwanted scratches from the stone swarf as a secondary abra- tool orientation, centered or offset (between 2 and 6 pounds sive. Too much water can cause tool hydroplaning and poor increase). In Figure 11, the tool to stone centering and offset surface finish or at least require a longer time to achieve a good techniques on 1 1/2 inch edges produced little differences for polish. We did not conduct a full investigation into the optimum any of the tools surveyed. water flow rate required when edge polishing. However, it seems apparent that some level would be more optimum than others. OPTIMUM LOAD FOR 1 1/2 INCH EDGE POLISHING 6/94 rwe Further, it is nearly impossible to determine what level is opti- 25 X X mum if there is no way to repeatedly obtain a given flow rate. X 20 cent 1-1/2 Also, there is a need to identify relative flow rates in order to be X X offset 1-1/2 able to arrive at statements such as “higher is better”. For these 15 X reasons and to assist all operators in setting up to the same LOAD (lbs) 10 COMMONLY USED LOAD levels, we recommend that the water flow rate be set by a control valve and gage placed before the hand tool. The valve on the 5 hand tool should only be used for full on and full off switching. 0 We have had good success with a relatively inexpensive flow 3-S 3-P 4-S 4-P 5-P TOOL DIAMETER AND TYPE meter and control valve assembly that is easy to set, gives numerical flow values and is consistent. The cost of the system Figure 11 is around $140 and it would be well worth the investment. However, the optimum contact loads required are well above what is typically used by skilled operators. Further, as the tool Summary diameter gets larger the required forces increase significantly. There are several key lessons to be learned from this work. For 1 1/2 inch edges, the case for 3 inch tools seems clear. The 1. Major productivity improvements (over 70 %) can be achieved operators need to increase their contact force by nearly 100% to from a more disciplined and informed approach to edge polishing. get to optimum productivity levels. They need to nearly triple 2. Annual sales revenue increases from a single operator can their current load when using the 5" Pro-Diashine™ (5p). For exceed $600,000 per year in over half the cases we observed these reasons, a shop doing both thicknesses of edges on a when switching from typical practices to more optimum levels. regular basis would do well to select 3 inch diameter tools. They 3. Rework can be greatly reduced by following a more consistent should maintain their current 7.7 lb. load on 3/4 inch edges and and optimum approach. A 33% increase in productivity is pos- press harder on the 1 1/2 inch edges (from 7.7 pounds up to 15 sible in over half the cases we observed. pounds). Figure 12 shows this for the centered technique for both edge thicknesses across the family of tool sizes and types. 4. Current hand polishing techniques can be easily modified to achieve optimum levels. OPTIMUM LOAD FOR CENTERED TOOL AT 3/4 & 1 1/2 INCH EDGE THICKNESSES 6/94 rwe 5. Shops doing 3/4" and thicker edges on a regular basis would do 25 X X well to select 3 inch diameter tools. They should maintain their X current 7.7 pounds of force on the 3/4" edges and press harder on 20 cent 3/4 X cent 1-1/2 the 1 1/2 inch edges (from 7.7 pounds up to 15 pounds). X 15 X 6. Following the optimum parameters can result in significantly LOAD (lbs) 10 faster delivery times because of the large increases in productivity. 5 CURRENTLY ACHIEVED LOAD Special thanks I want to extend my heartfelt appreciation to all those who so 0 3-S 3-P 4-S 4-P 5-P willingly helped to make this project a success. None of this TOOL DIAMETER AND TYPE would have been possible without the enthusiastic support of all Figure 12 who participated. Thanks team! ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324) 9
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