including drilling & cutting glass

Rev. ... 2003-01-19, -21,-23; -02-24, -10-01, -12-11, 2005-06-26, 2007-06-12, -08-18
2008-01-06, -03-14, 2009-01-11, -12, -02-20 (layout)

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Glossary Center
Coldworking is what is done to glass after it has been annealed (which may be in the middle of further hot working, as with graal.) The purpose of this page is to provide illustrations of some of the techniques. I am not strong on coldworking, doing only the basic work listed below.

Broken glass can be glued. High strength clear glues, some cured by UV or placing in the sun, are available at many hardware stores.  The crack will always be visible.
No, it can't be done. Hitting a glass object with a torch will crack it.  So to keep from cracking the glass while heating, it has to be heated very evenly all the way across. In theory, this could be done in a kiln over a few hours. Then, in theory, the heated item could be melted with a torch by someone using one of those silver heat suits.
Scratches normally can not be polished out unless they are so slight that they do not catch a finger nail.  The abrasion and polishing for deeper scratches leaves the surface dipped and noticeably changed.
Nicks and chips places can have the edges smoothed rather easily.  A diamond nail file will work, but for a rounded edge, black emory cloth wrapped around a pen or dowel is available in fine and finer grits that will take off sharp edges and corners and leave a fine frosted line that is usually not noticeable. 2009-01-12

INTRO - Coldworking as a skill is completely different from hot glass furnace work. Where there is enough work, some artists will find a person who does cold working cleanup for hire. A studio doing enough output will hire a person just for coldworking.

All the operations that involve grinding, blasting, carving, etching, cut glass, or polishing are considered coldworking. This page also includes drilling and cutting flat glass, which are not usually considered coldworking, since they normally require only moderate skill and standard tools. Stained glass assembly is not normally considered coldworking, but is a separate discipline, as is beveling flat glass, although that involves most of the same skills and machinery as coldworking.

Non-decorative coldworking tasks include smoothing the edges of the punty mark, grinding the bottom flat for proper standing and signing the piece. Decorative methods include cutting, etching, blasting and polishing. Painting is not normally considered coldworking but is a separate operation. However, note that applying color with enamels may be intermixed with coldworking, graal involves painting a partly finished piece, carving away some of the paint, then heating and further encasing the work.


on glass leaves a frosted white surface. [Here we are talking large scale grinding.  The small head grinding tables for shaping stained and fused glass are for removing material.]  If a clear polished surface is required, several additional steps are normally needed to remove the large scratches, then the finer scratches, and then finally all the haze. Grinding may be done with stones, diamond tips or wheels, copper disks and abrasive and assorted other methods. Grinding glass requires water cooling. Sometimes the water carries the grinding grit or it may be done with a wheel with diamonds embedded in the surface.
The steps of shaping glass, from Beveling by Isenberg
Roughing - Taking the basic glass, cut to the general outline, and removing most of the glass that needs to be removed, using 80-100-120 grit on the horizontal wheel or a 100 grit diamond vertical wheel (120 grit is twice as fine as 80)  On the horizontal, the trough of grit should be full and mucky, stirred up with the fingers while working.  Grit on the roughing wheel can be reused.  In smoothing and polishing, a bubble can be seen through the glass, indicating where the glass is touching the tool.
Smoothing - This uses, in the book, a stone wheel, horizontal or vertical, either natural or aluminum oxide. The horizontal wheel has a 4 degree pitch.
Semi-polishing - using a cork wheel with pumice or smaller faster turning fiber wheel with imbedded 600 grit silicon carbide abrasive to remove any defects - ripple - and haze from previous steps. Pumice is applied with a sponge from a 50-50 mix with water. Shape cork with a rasp while spinning.  Dress a fiber wheel with a piece of wood.
Polishing -  done with a felt wheel, wet with cerium oxide sponged on and embedded with a scrub brush.  The goal is wet hot flow of the surface.

The final step in preparing glass that has been ground or cut if the desired result is a clear transparent surface. After finer and finer grinding has brought the surface to an even light grey etch, increasingly fine compounds are used to remove the last scratches, commonly emery, pumice, and cerium oxide.  Felt and cork wheels should move at 700 surface ft per minute per on line discussion.  (See also: Cut Bottle Edge Treatment)
Abrasive or so-called sand (which should not be used so as to avoid silicosis) blasting involves sucking more or less fine abrasive into the air stream from an air compressor and using this flow to carve or etch the glass. Normally done with film masking on the glass to prevent damage to nearby areas that are to remain clear. Blasting requires a substantial air compressor - usually several horsepower with tank - and is normally done in a temporary (plastic sheet) or permanent box or room to contain the abrasive material for use and draw off the fine powdered glass and abrasive. A respirator should be used when needed.
Is the carving of details on glass.  Kinds in complexity of tools and skills:
Diamond Point - A pencil-like tool with a diamond chip on the end is used for making dozens/hundreds of small marks on the glass surface.  As more marks are made, the image is whiter and the other areas appear darker or shadows just as printed half-tone pictures are made of small dots.  Requires patience and artistic sense to translate picture to image. Glass Engraving, Tools and Techniques seems a good site
Small Diamond Bit - "Dremel" type high speed tools can be used for engraving glass. This book covers it in detail.
Abrasive "Sand" Blasting - With a mask, fine details and half tone images can be done, but it is not considered the highest quality choice.    "For more information on high speed engraving equipment go to:   I have used the Paragraphics tool and was impressed.  The three books that I would recommend are: "A Beginner's Guide to Glass Engraving" by Seymour Isenberg, "Glass Engraving Pattern Book" by John Everett and "Engraving Glass; A Beginner's Guide" by Boyd Graham.  These books can be order from Barnes and Noble Booksellers." 2003-01-21
Stone Wheel - Stone wheel engraving is done with (obviously) stone wheels, which may be rather large, mounted on stands for .... 
Copper Wheel - requires a special lathe to mount the tools.  The actual cutting is done with abrasive applied to the wheels and the lathe allows rapid changing of the wheels, each of which is mounted on its own stem.  A worker may change the tools many times each hour.
Forming a frosted surface on the glass for the purpose of defining all or part of the design or for changing the texture of the surface. May be done by abrasive blasting, application of acid containing cream or liquid, by copper wheel or stone engraving or by diamond point scratching the surface. Etching can be done with hydrofluoric acid which is extremely dangerous to use as it quietly and, initially, non-painfully penetrates the skin and begins destroying the bones and skin. Less risky creams are on the market which should still be handled with care.
involves removing considerable glass, including cutting away good portions. A blown piece may look more like a skull after such work. Carving may be done with a heavy fine blast, thin diamond wheels or other effective means of removing glass.
Cut Glass (note difference from Cutting Glass)
normally involves thick glass and shallow V-shaped cuts, the traditional cut crystal being a standard. Traditionally cutting is done with copper wheels of various sizes with added abrasive. With a heavy lead glass, the cut can produce a brilliant sparkle effect after polishing.
"Creations of a surface of small planes or facets by using a grinding wheel." GMOM
Drilling Glass
Drilling glass is always done with plenty of liquid, either flowing or a lake retained by a ring or dam of clay. There are 4 kinds of drills for glass and a web site but prices seem a bit high.
1) A prism bit 2) a spear bit, 3) wire bit, and 4) a core bit.
A prism bit is a chunk of hard steel with a pyramidal point (flat sides, sharp edges) that can drill small to medium holes. Normally only used in a drill machine. Search words "Prismatic Glass Drill"
Sample of a prism bit for drilling glass.
A spear bit looks like a flint spear with a fairly blunt end. Possible to use in hand drill, awkward to start - skitters. Search words "Spearpoint Glass Drill"  Critical to using this bit is slow steady pressure as the tip grinds through the glass.  It goes much faster once the sides are grinding the hole larger. Only one likely to be found in hardware stores. Spear point bit for drilling glass
A wire bit is a hard wire coated on the end with diamonds for use in a high speed (Dremel) tool. Search words "Diamond Plated Miniature Flat-Tip Drill" Diamond tipped wire bit for small holes
A core bit is a can shaped cutting surface mounted on a shaft. The cutting may be done with diamonds imbedded in or soldered to the edge of the can, or it may be grit poured in the liquid around the bare metal (brass or steel) cutting edge. Search words "PLATED DIAMOND DRILLS" Must be used in a rigid tool, not in a hand drill.
Drills and bits are available from CRL
Sample of core bit for drilling glass
Hi Mike,  (E-mail 2008-03-14)
I ran across your site and thought I'd add my own tricks to the stew.
Back in the days when making your own helium-neon laser was all the rage, one of the requirements was that of cutting a precise miter in the ends of the laser body to receive the Brewster windows. I think the angle was pretty steep--about 27.5 degrees, but I'm not certain.
At any rate, the way we did it was with a hacksaw and a blade made of copper (no serrations, just sheet copper) and a slurry of automotive valve-grinding compound. It's not fast, but it results in a very smooth and accurate cut with no chipping.
An old workshop book that I have from the 30's mentions that one can drill a hole in plate glass using a standard HSS drill bit in a drill press and a slurry made of equal parts camphor and turpentine. You can't allow the drill bit to break through--you use a sharp triangular file to finish bringing the hole through to the other side.
At any rate, for whatever it's worth, you have my two cents.
Best regards,
Chuck Guzis
Eugene, OR
  To drill glass, especially larger holes, it is vital to have a drill press, even a small one, and a method of turning the bit fairly slowly, either a speed control or belts on larger drill presses.  Venders of bits will tell you the recommended RPM.   Around the site of the hole build a dam of plastic clay, the oily kind used by kids that comes in colors - red, blue, green - not Sculpy.   Water will be put in the dam and the hole drilled through the small lake.  The bit should be withdrawn every once in a while to cool the leading edge and the bottom of the cut (and reintroduce grit when using metal core bits without diamonds.)  The goal is to keep the glass from getting so hot it cracks from thermal stress.  If the back of the glass is accessible, the other side of the cut should be covered with clay to keep the lake from draining through.  If it is not, then when the water does drain through, the bottle, hollow block or shape should be filled with water.  If the piece is small enough, it may be possible to put in a bowl of water that covers it to the top.  If the task is to be done often enough, it may be worth building a tank to keep from fiddling with the clay.
   The glass dust ground out by the drill is not good to breathe.   While wet, it does not cause problems.  Swirl the water to pick up the sludge and pour it through a scrap rag and throw the rag and glass out rather than letting it dry and pouring the dust around. 2003-01-19
  Having written that over four years ago, I finally got around to drilling a pair of largish holes today (2007-06-12) when I needed them.  The project is an indoor fountain using parts I have purchased over the years and put aside, often in frustration. These four pictures show the results of drilling and the assembly of the fountain.
  The bowl was drilled upright, adding about an inch of water and a tablespoon of medium grit.  The glass bowl was placed in another bowl, which happened to have wax in the bottom (see below for support) and about an inch of water was put in that.  The shape of the bowl naturally caused the grit to settle in the cutting area and the slots in the bit whirled the water.
  It was easy to hear when I had to raise the bit, every 10-20 seconds, to let in cooling water and more grit - the sound of grit cutting and brass turning without grit is distinctive.  Because I was applying fair pressure, perhaps more than I should, there is shallow breaking away on the exit side, but not as much as the picture suggests as part of what you see around the hole is the flat that was ground on the bottom of the bowl long ago.
Drilled bowl example
Drilling the glass plate was a bit more exciting.  The glass, as you see, was roughly cut from a broken piece of 1/4" tabletop glass found at the curb.  I did not care to invest the time in making it perfectly round and it wasn't quite big enough anyway.  I also found I needed a path for the cord so one flat was required.
  A plastic wash basin was placed on the drill press platform, a piece of wood added to put water under the glass and protect the basis when the drill broke through and enough water was added to put a half inch across the glass.  A heavy metal ring cut from fence post tubing and about an inch high was placed around the hole and the grit from the previous job poured inside.
  Again the process was apply pressure, listen for the change and watch for binding, raise the bit to let the water in, go again.  The ring could have been sealed, but I just held it with my hand.  Enough heat was generated to make it distinctly warm.  I think the shape of the wood support, a small block with a large hole drilled in it, was a mistake and a grid or other support that let more water in the bottom would have been better.  I paused while drilling to let everything cool and relieve impatience.  When it broke through again there was flat flaking away from the hole, perhaps 1/64" deep. 
Drilled plate glass example
Both holes were ground lightly with a wetted pointed grindstone.
The picture at right shows the first assembly.  The small pump (with a frustratingly heavy cord) is suction cupped to the bottom, a short length of PVC pipe with notches for the cord and to let water back in is placed around the pipe. A short extension tube of plastic and brass brings the pumped water up.  The glass plate goes over the tube, rests in the PVC and fits snugly in the bowl.
Fountain setup with drilled plate
Here the glass bowl has been placed over the tube, black river rocks have been placed around the bowl on the glass plate, water added, and the pump turned on.  The pump has a lever to set flow rate.  The rate was annoyingly high the first time I tried so the water made too much noise.   I disassembled it all, cleaned some stuff again, changed the setting and reassembled for a more satisfactory burble. I also added some glass marbles and weight to the rocks.
The stainless bowl is a bit mechanical and the power cord is irritating.  A pottery bowl would be more organic and taking steps to hide the cord would be nice. 2007-06-12  Added images of fountains -06-27
Overflow bowl with rocks in larger bowl
Cutting Glass
is done by putting a deep continuous scratch in the surface of the glass then starting a crack usually at one end of the scratch and working the crack along the scratch. Straight cuts may be worked by laying the scratch line on the edge of a surface and pressing down on the unsupported part or laying the glass at the cut on a dowel and pushing on both sides. More complicated cuts can be tapped to crack them; many older glass cutters have a ball on the end for the purpose.  For more control, a dowel rod may be placed under the scratch and the glass pressed down on either side, so it can't be pushed further than the diameter of the dowel or dropped to the floor from the edge. This site from a maker of cutting tools offers some excellent advice - they don't want their tools blamed for poor technique!  Pliers exist with soft jaws that have a ridge on one jaw and valley on the other, so that when the valley is placed above the scratch and the ridge below and the plier handles are squeezed, a controlled cracking occurs.
Thick glass, 3/8"-3/4" requires a different cutting wheel and tapping to break usually starts in the middle with a heavy ball tapper. 2008-02-26, 2009-01-11
The common glass cutter has a hard carbide cutting wheel on one end, slots for chipping glass edges on the side and a ball for running a crack on the other.  Also sold without ball. About $4.  Standard angle of cutter edge is 124° for thin glass. Also sold with sharper angles for thicker glass - 135°, 142° that really help. These cost more. glass cutter, standard metal wheel, ball end
Cutters with a chip of diamond on the end range in price from $5 to $60.  I have one at the lower price and one about $30 and they appear to work the same for me.  Warnings were given that a diamond cutter is harder to control, but I have found that not true. Glass cutter with diamond tip, low cost
 After observing a man cutting 1/2" plate at a specialty glass cutting and table top making place, I quickly realize that for thick glass a heavy tapper helps.  The top one with a 3/4" ball costs over $58 from CRLaurance, so I cast one from lead and a couple from brass. Short handle length is to fit my modest glass cutting tools storage box and a longer heavier handle would improve balance. 2008-01-06, 2009-01-11 Tapper for thick glass, $58 at CRL
Lead & brass home cast tappers

After observing an expensive tool for controlled cracking of thick glass that involved a heavy bar with two hold downs and a screw drive to apply pressure from underneath so the glass does not have to be turned over, I decided to make my own version for the thick plate glass I am cutting for water features. Instead of the large features, Glass cracking tool from C-clamp, wire and angle.I would turn over the glass and apply pressure with a C-clamp.  To focus the pressure, but do it in a soft way that would be less likely to harm the glass, I would use large 9 gauge aluminum wire.  I cut a short length of hard flat angle iron (brown in the picture) and Marine Goop glued two carefully straighten aluminum wires to the top about 2" apart.  I then took a longer piece of wire and Gooped it to the swivel pad on the clamp (cleaning all surfaces before gluing.)  It would be easier to handle in several ways if the wire on the clamp were glued to the fixed jaw, but I quickly found that some breaks at angles to the edge could not be accommodated that way.
In use, the angle iron is positioned so the wires straddle the scratched line and the C-clamp is positioned and snugged down.  The long "handle" on the clamp wire is aligned with the scratch (not shown in photo.)  Pressure is then applied by turning the C-clamp handle until the crack runs, usually explosively.  With only two days experience, I am running much straighter lines and being able to do breaks within an inch of the edge of the glass where gripping was awkward before.  I put the wires 2" apart to handle splitting pieces that narrow.  I believe that wires further apart (3-4") would allow more control, bending the glass near the edge to start a crack without running it across the glass in a pop. 2007-09-22
Cutting bottles


This list copyright Mike Firth 2000 and of copyright holders quoted.

Glass Cold working DRAFT 10/28/96


Subj: Hot Bits #34
Date: 96-12-26 18:10:24 EST
From: Divas II
To: MikeFirth
In the latest Hot Bits you mentioned an interest in cold working. How to Work in Beveled Glass by Anita and Seymour Isenberg is an excellent reference book complete with pictures. The process used in cold working hot glass is the very same as used to bevel glass, except easier since you're normally grinding the surface flat rather than at an angle. I switched from silicon carbide to diamond pads a year or so ago and am absolutely delighted with them and, hopefully, will never go back to grit. You are welcome to try them out your next trip to Cowtown.
Thought I'd drop a note to Lori Hultman, sounds as though she needs some more encouragement.

Subj: Re: Cold working Glass
Date: 96-11-04 13:02:59 EST
From: (JC)
To: mikefirth (MikeFirth)

On 2 Nov 1996 21:08:32 -0500, you wrote:

> Since I have been unable to find a book that details the steps in cold
>working hot blown glass, having asked companies who supply the material
>and several experienced teachers of glass blowing, I am going to write a
>section for my Virtual Glass Book on that topic. I would appreciate any
>notes or comments from people with experience in this area (who presumably
>learned by watching) and any references to (or copies of) articles or
>books that discuss choices in detail.
> Cold working of blown glass is all the steps of removing glass that are
>done by grinding and blasting. The most common activity is flattening the
>bottom to remove or reduce the punty mark. Other activities include
>grinding flats for optical effects on paperweights, grinding though opaque
>surface color to reveal the inside, removing glass to leave a pattern,
>sculpting the glass (like jade is carved), and shaping the glass so it can
>be glued to other pieces of glass or other materials.
> The basic steps are easy to put down, but details (like how smooth the
>grinding must be for the polishing to work) and problems (like
>overheating the glass or the grinding plate) come from experience. For
>some kinds of work, the steps are the same as sandblast etching while for
>others they are the same as beveling plate glass.
> I would also like to hear from any experienced person who would be
>willing to review the chapters when they are done.

>Mike Firth, Hot Bits Glassblowing Newsletter


Try contacting John Bingham, 2810 Industrial Rd, Santa Fe, NM 87505 505-471-2621.
Ask him if he has any copies left of the "Hot Glass Information Exchange".
It is a compilation of a conference we all held here in Boulder in 1979. It may be
somewhat out-dated, but is still a great resource AND it has an article about Glass
Grinding with some great drawings of grinding equipment.
James Clarke

[From the guy with the 10 machines.]
> >I would also be interested in any "How To" or instruction manuals about
> >beveling.
there are, or were, anyway, two books in print on hand beveling (I've searched far and wide for
other book on the same subject, for years, by the way, to no avail...)

one was written by Vincent Fox (of Fox Stained Glass Studios, Indianapolis, Indiana, and the other book published by Chilton, and written by Sidney and Anita Isenberg (I forget the name of the Fox book's publisher right now, but Fox himself may've published it, or it was a VERY small publishing house). Both are called "Glass Beveling", far as I recall... Vince Fox may be dead by now...It may be that neither is still in print anymore, but a search by a competent used book store ought to yield you a copy of one or both - seems to me they were both in print and being sold, uhhh, 10 or 15 yrs back or so...I own copies of both, but they're not for sale...sorry

> In addition, I would consider building the equipment myself
> >if I could obtain plans to do so.
that's too complicated to address here (I've built some of my own, and some for other beveling studios, too, and also refurb'ed/re-configured, and repurposed other beveling machinery), but see my site when it "goes up"... The Fox book, BTW, goes into rough parameters, optimum wheel speeds in surface feet per minute, and other tips generally toward that end, and the Isenberg book, while serious, is more "chatty hobbyist" in outlook, and omits all sorts of technical details/specs'/info ....

COLDWORKING Rev. 12/15/96
Mike Firth
Draft subject to correction and review

Coldworking of glass means two things. One is coldwork in general, that is all the grinding, engraving, carving, blasting and etching that might be done with glass after it has been annealed to room temperature. The other is more specifically the grinding and polishing of flat surfaces on previously hot worked glass.
All of the many general coldworking techniques can and have been used on hot glass forms: Abrasive blasting and acid etching take away one lay of color to reveal another. Engraving, etching and blasting put frosted designs on clear glass. Carving and blasting leave fragile portions of glass raised above the solid body of the glass. All of these techniques are used on other kinds of glass, including stained, fused, and cast glass.
But the coldworking that has to be done by virtually all hot glass workers1 is the specific coldworking: removing glass from one or more parts of the blown body to leave flat surfaces that permit the glass object to stand on a table, permit the viewer to see inside in an interesting way, or permit the glass to be glued to another piece. The process usually involves removing a moderate amount of glass (1/16" to 1/2") and then polishing the frosty flat surface to optical clarity. Coldworking is done with several basic tools: flat wheel grinders, belt grinders, and buffing wheels. Additionally, rotary or oscillating laps may be used in some cases. Vertical grinding wheels could be used, but the curved surface created is not usually desired. All grinding and polishing of glass is done wet, with a water drip or other water feed. Water removes the glass fragments but also keeps the glass cool so that it does not crack from stress due to local heating.

The most basic equipment is a flat wheel for grinding and two thick buffing wheels for polishing, although it is possible to grind on a flat steel or glass plate. A flat wheel grinder is not difficult to build and since similar equipment is used in lapidary work, is available from several sources. Plans and a list of sources are at the end of this section.

In a better equipped shop, there will be several grinding wheels so that course grit does not mix with finer and cleaning of wheels is unnecessary and so that a wheel is available for each of the steps in polishing. An alternative to wheels is a belt grinder, which is said to remove glass quickly while staying cool. Unfortunately, building one is difficult and sources are limited. Belt sanders from other sources (e.g. woodworking) are difficult to modify because they almost always have direct drive motors at the bottom where they will get wet. Belt sanders ready to go from lapidary sources will start at over $475 for a small unit (about 3" x 9" grinding surface.)

The latest change in equipment is the use of diamond grinding wheels and diamond plates which mount on wheels. Diamond grinding is said to remove glass more quickly than other grinding methods while leaving a smoother finish that may need less or no polishing. Diamond polishing is done at a higher speed than other forms, but a good flow of water is vital, not only because heat will build up faster in the glass at the higher cutting speed, but if the plate gets too hot the material holding the diamonds to the plate gives way and the diamonds are lost.

Technique - In summary, a coarse grinder will be used to remove the bulk of the glass as quickly as possible without overheating the glass. This is followed by any needed detail grinding, rounding edges, removing bumps, etc. One or more finer grinds will take out the large scratches and prepare the piece for polishing. A succession of finer polishing compounds will be used to produce an optically clear surface.

First Grind - If you have never worked glass before or if you are working a wheel that you have never worked before, always test the wheel with a well annealed fairly heavy scrap piece before doing any serious work. An abandoned paperweight may be a good choice. The first thing to check is whether if the machine is stable and doesn't tip from leg to leg. Check power connections for safe wiring, working with water and random electricity can be a nasty combination. Power up and check that the wheel seems in balance and the motor and wheel are moving smoothly. Turn on the water and check for good grit pattern and water flow. Begin your test by touching the chunk of glass to the wheel and listening to how it sounds. Faster than anything you can see, you will be able to hear changes in speed and grinding. Move from the rim to the center. Try various locations to see whether pressure on the wheel tends to stall the motor or make the belts slip. If the latter, see if an adjustment can be made.

Make a serious cut by applying pressure about midway center to rim and learn how much glass the wheel takes off. Try cuts nearer the center and at the rim. Get a feel for how much cutting is being done along with how the wheel sounds and how the glass vibrates and pulls while being cut.
Check the temperature of the piece and work with increased water flow if needed. If using grit, adjust the grit flow so it is not wasted or skimped.
It is not totally necessary that the wheel rotate dead flat, but it certainly makes working more comfortable. If when you try to touch the glass to the wheel it clearly touches and skips, then the wheel is not perpendicular to the axle. The amount should be very slight to none with a commercial wheel or one ground by a machinist. It may be more on a hand built machine. If possible adjust the position.

Remove bulk of glass - Two great risks occur when removing the bulk of glass:
1) that the glass will become overheated and crack and
2) that the grinding wheel will grab the glass by suction and fling it across the room or just onto the floor. Overheating is avoided by providing plenty of cooling water, feeling the glass while working, and not pressing too hard. Many people also feel that working glass within a day or two after it has come out of the annealer increases the risk of breakage. Suction is avoided paying attention, keeping a firm grip on the piece, providing comfortable rests for the arms, and perhaps adding anti-suction lube to the cooling fluid.
Two different formats are used for rough grinding, on a flat wheel or on a vertical belt. The flat wheel may use a flat iron or steel disk on which water is dripped along with grinding grit or the wheel may have a thin plate added which has diamonds fixed to it. Plans for a flat grinder are in the appendix.
The belt grinder uses a belt with grit on it. A belt grinder has the advantage of running much cooler. If properly constructed, it will produce as flat a surface as a disk. Unfortunately, the need for drums that are properly aligned to hold the wide belt mean that making one is out of the question for most people. Purchase cost is $***
On the disk grinder, the process begins by setting the water flow so there is a small continuous drip with a grit grinder and a small continuous flow with a diamond plate. When the machine is running the flow should evenly cover the wheel in either case. In the drip/grit system, normally the drip falls first into a shallow V tray in which grit has been placed and the drip carries the grit. Not much grit is needed, so normally things are arranged so the water falls on one side of the V, drains along the edge of the grit stacked on the other side and carries grains of grit with it.
With the wheel turned on, the person doing the grinding should sit (or stand depending on wheel height) comfortably next to the machine, holding the piece in both hands with arms extended.
There should be a flat edge or additional support to brace the elbows during long grinds and with heavy pieces.
Normally, heavy grinding is for either (or both) of two purposes: leveling the bottom so the piece will stand upright and stable or removing glass from one or more faces of the piece. In either case, it is important to try to start the cut as close to parallel to the final surface as possible. If this is done, there is less risk of cutting beyond the final surface or of leaving a rounded edge. It allows early determination of the balance of the piece in the hands, which allows a better feeling for
position while working on it. Observing the early and progressive grinds lets the worker see the final shape form and change it if necessary. And when working the bottom, with a good level test surface nearby, the upright positioning of the piece and even its ability to stand up can be tested early in the process.

Detail Grinding - Edges

Sources of cold working equipment
Covington Engineering Corporation, 715 W. Colton Ave., P.O. Box 35, Redlands CA
92373-0006, 909-793-6636. Wet belt sanders, grinding wheels, laps, bevellers, motors, parts for
grinders, grits, diamond disks.

Plans for a flat wheel grinder.


Contact Mike Firth