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ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324)
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December, 1993 • • •
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Fourth in a series for Dimensional Stone magazine
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Product Manager
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Marc Poirier
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AUTOMATIC EDGE POLISHING
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DIAMONDS:
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POLISHING STONE WITH • • • • • •
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TECHVIEW
abrasive technology, inc.

2. Polishing with diamonds: Automatic edge polishing
Almost all stone fabrication shops in the USA have table saws for edge polishing machines must be large, complex, and expensive
dimensional cuts, and most have a radial arm polishing ma- in order to do the work. Costs in the range $100,000 are common
chine. This equipment, along with right-angle grinders and some for purchase, transportation, installation, and acceptance trials.
workbenches, enables the shop to process most jobs. Abrasives
A typical scenario The manufacturers of edge polishing machines have tradition-
Up until recently, a large job was seen as the opportunity and the ally recommended the use of silicon carbide abrasives, and this
means to invest in an automatic edge polishing machine. This, it is still true. If the newer models perform better than the older
was reasoned, would allow the shop to execute the contract ones, it’s because they are more sophisticated. The working
quicker and easier than with manual equipment. Just as impor- parts are better designed. The frames are sturdier. And there are
tant, the new edge polisher could be amortized on a single more polishing stations—up from four or six to at least seven
contract. and sometimes as many as twelve.
The reality often turned out to be quite different. Almost as soon It is possible to polish granite in four steps with silicon carbide
as the edging machine was selected and installed, both the abrasives, but only by hand. Working manually, a craftsman can
operator and the owner realized that there was more to polish- stay on the piece with a particular grit size as long as needed
ing edges than the salesman and the sales literature covered. until the surface of the stone is ready for the next step. He can
also adjust the pressure on the work.
Endless adjusting and fiddling would be required to make the
With an in-line edging machine, however, the work is continu-
unit perform. Despite all the care and attention, the finish might
ously in motion. The amount of time available at each station is
vary considerably from day to day and even from piece to piece.
adjustable to some degree, but quite limited compared with
After endless trials and tribulations and considerable downtime manual operations. The pressure exerted by the polishing heads
the job would be expedited by putting on more craftsmen with can be adjusted, but only by shutting down the machine. A four-
hand-held equipment. The edge polisher would begin to gather or six-head machine, then, is severely limited in terms of grind-
dust. After several months, it would be moved out of the way to ing times and pressures.
a remote corner of the shop and simply abandoned. The whole True, the work can be passed through a second or third time
experience, with all its wasted time and effort, would be chalked using different sequences of grits, but the chance to increase
up to experience. production, the reason for buying the machine in the first place,
The new scenario is lost. Even more time is lost resetting the machine for each of
the many varieties of stone that go through a shop in a given day.
Shops still purchase automatic edge grinders as part of large
It’s no wonder that older machines are often considered incom-
contracts, but the level of awareness of the problems and
patible with modern shop requirements.
requirements for its use has increased considerably. The word
has finally gotten around that the purchase of an inadequate The newer machines are quite different. Some are computer-
piece of machinery is simply a waste of time. Today’s buyers not ized, and resetting for a different stone is as simple as calling up
only want assurances of performance, they also understand that the right program. All have additional polishing stations. An
ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324)
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3. eight-head machine, for example, can perform twice the work of finish and extends the life of the
a four-head machine at a given belt speed and can be fitted with diamond disks. Typically, pressures
twice the number of grits. With silicon carbide abrasives, the of 0.5 bar-1.5 bars are most com-
new machines work much better than the old ones. They work monly used for straight edge pol-
even better with diamond abrasives. ishing.
Today
The aggressive character of dia-
Diamond disks made specifically for edge polishing machine are mond disks also allows the work to
readily available. They have the proper attachment mechanism, be moved through the machine at a
and they can be used to replace silicon carbide disks on a one- faster rate. Increases in speed of 25% for granite all the way up
for-one basis. to 100% for softer stones are normal and common, depending on
The advantage of diamond disks lies in the fact that the dia- the finish desired. Linear speeds of 3-9 feet per minute for 3/4"
monds are much more aggressive and hence grind faster and material are typical.
more consistently. Because the time available at each of the
polishing heads is limited, diamonds can do far more work than Diamond disks also allow thicker-than-normal pieces to be edge
silicon carbide. polished to the same surface quality as thinner pieces.
Any machine that operates successfully with silicon carbide Water
abrasives, will operate faster with the use of diamonds. More- The right amount of water in the right place is important. The
over, diamonds will produce a better finish than silicon carbide grinding occurs inside the machine, away from the operator’s
can, especially on granite surfaces. sight. Most operators believe that if there is ample flow of water,
An older machine gathering dust in a corner can often be made to the point of deluge, an adequate amount is brought to the
productive by equipping it with diamond disks. work surface. This may not be the case. Care must be exercised
to ensure that the water is directed to the right place and that the
Disk use
diamond disks themselves have sufficient water on their work-
Diamond disks are available today in a variety of sizes, grits, and ing surface.
construction.
Popular sizes for the fabrication shop are 5" and 6" diameter. The water must be uniformly dispersed onto the surface of the
Some special uses require 4" disks, but they are rare. Grit sizes disk as well as on the stone. Lack of water will translate into rapid
commonly range from the coarsest #30 to very fine #8500. deterioration of the diamond disks, and burn marks on the disk
Typically, grits of #50, #120, #220, #400, #800, #1800, and #3500 surface will be noticeable. Periodical examination is the best
are most commonly used for processing marble as well as way to make sure there’s enough water and that it’s being
granite surfaces. directed to the right places.
All diamond polishing disks are resin-bonded. All disks are Bullnose capability
furnished with a snail-lock of attachment, making them quite The very sophisticated newer machines that use computers,
rigid. This rigidity produces a polished surface that is straight positioning sensors, servo motors, and oscillating frames per-
and true. mit the processing of arced edges, i.e., bullnose, as well as
Many owners of in-line polishing machines have successfully traditional straight edge polishing operation. The diamond disks
experimented with a disk consisting of a steel plate having metal- required for bullnose work differ from standard polishing disks
bonded diamond segments welded or brazed to its working used for straight edges.
surface (see drawing). The segments are very similar to those on
In terms of surface area, the amount of contact between the disk
the circumference of diamond saw blades.
and the stone is quite different. Straight line polishing offers
When used in the first polishing station on the machine, this good support for the disk and by the full edge of the stone. By
cutting head can remove large quantities of material, including contrast, bullnose polishing results in a straight line contact,
saw marks. It also does a good job of truing the edge straight and thereby increasing dramatically the pressure on the disk face.
at a right angle to the top surface. Resin-bonded diamond disks
are not suited for such heavy work because they aren’t as Experiments are underway to adapt traditional disks with a
aggressive. cushioning feature to bullnose work. This would allow the
diamond disks to better follow the surface contour. Neverthe-
Machine adjustments less, it seems more likely that the tool that will ultimately prove
Pressure settings on the machine should be reduced when best suited for this operation will be rigid and equipped to
operating with diamond disks. Because the diamonds are more withstand the tremendous operating pressures. In either case,
aggressive than silicon carbide abrasives and do not require water is most critical to this operation, and attention to this
high pressures. The lower pressure ensures a more uniform detail is imperative.
ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324)
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4. Single-head machines advantages, however, clearly favor diamonds—less grinding
Single-head machines offer another alternative for edge polish- time, improved production rates, better finished surfaces, longer
ing. They have many of the same operating parameters as the disk life—and add up to improved profitability.
multi-head models with the added advantage of allowing the For automatic polishing, the advantages of diamonds include:
operator to observe the work being processed. In addition, they
offer the flexibility to set up a variety of shapes, such as round • Raising the throughput and quality of any machine
pieces like table tops. They are also attractively priced. Their simply by replacing silicon carbide with diamond disks.
disadvantage lies in the fact that the grits must be changed after • The option of using the first station for heavy material
each polishing step. Diamond disks are adaptable to single-head removal.
machines to the same extent as multi-head machines.
• The ability to successfully polish very hard stones.
Costs • The prospect of returning older, less capable machines
On the basis of materials only, diamond polishing tools are to profitable production.
significantly more expensive than silicon carbide. The overall
ABRASIVE TECHNOLOGY, INC. 8400 Green Meadows Dr. Westerville, OH 43081 USA (614) 548-4100 Fax: (614) 548-7617 1-800-964-TECH (8324)
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