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Cutting Glass with a Water Jet: Article and photos by Jim Clark (The Hot Rod MD)


Story & Photos By Jim Clark (The Hot Rod MD)

Replacement flat glass for hot rod and custom vehicles has been produced by hand-fabrication for many years.  The process of handcrafting it is very labor intensive and the results dependent on the skills of the individual doing the work.

Sanders Reproduction Glass has been one of the primary providers of replacement glass for these applications and handcrafted most of the glass that they sold.  We profiled their process here at Hot Rod MD showing how they prepared and installed flat glass for the hot rod and restoration market.  Recently Peninsula Glass, a large supplier of glass products to the home, boat, RV and commercial markets, acquired Sanders Reproduction Glass.
They supplied tempered glass and other items to Sanders before and now that they have added Sanders as a division of Peninsula; they have eliminated most of the handcrafting.  They now cut most of the glass using a water jet; a more accurate process.  Here are some of the reasons why cutting glass with a water jet is more desirable.

Cutting Custom Car Glass for Your Vehicle

Glass, like almost anything in the automotive industry, is best when cut and finished by machines.  This is true for any type of car - classic car glass, hot rod glass, and antique glass.  No O.E.M. (Original Equipment Manufacturer) windows for cars built after 1928 have been handcrafted in the automotive industry, which includes vintage car glass installation.  Automotive glass has to be uniform to fit properly and for optimal strength.

Use highly accurate glass cutting machinery

To achieve this goal it is necessary to use a specialized water jet cutting machine.
This type of machinery has been used for many years to produce household and commercial windows.  It has also been used for advanced machining processes involving stone, metals and ceramics.


Until recently, this type of equipment has been out of reach for small companies producing custom glass for specialty applications.

Why you should care about the benefits of water jet cutting

There are really only three virtues that a glass company needs to practice to produce a superior quality window: accurate shape cutting, careful handling and consistent edgework.

Shape cutting

The CNC water jet is used to cut the basic shape.  This machine is accurate to 0.0001 inches...600 times more accurate than handcrafting!  Once the shape is in the computer and verified 100% accurate to the original pattern, all of the windows cut using that pattern from then on will be identical to each other.  That's not possible using traditional, handcrafting techniques.

The traditional technique of using heat and chemicals to separate the waste while cutting the shape produces stresses that accelerate de-lamination.  De-lamination occurs when the bond between the glass layers and the laminate loosen, causing them to separate.  This allows water and other contaminates to seep between the glass layers, destroying the window.  Water jets cut with a mixture of high-pressure water and abrasive garnet...eliminating the need for chemicals and heat.  This helps preserve the bond between the glass layers and laminate, and eliminates any chance of contributing to the destructive process of de-lamination.


Traditional methods of cutting, shaping, and edging auto glass require constant handling.  This almost guarantees that the glass will at one point be dropped, chipped or scratched.  Water jet cutting eliminates almost 90% of the handling...from raw glass to finished product.  Less handling means fewer mistakes, fewer scratches...and a much better product.


The traditional glass cutting process requires that the window be ground to its final shape and the edge "seamed" on a water-cooled belt grinder.  After the seaming process, the edge is gradually worked using progressively finer belts until the desired shape and finish is achieved.  This long, laborious process often produces chips, undercuts, scratches and an inconsistent shape.  With a water jet, the window comes off the cutting bed perfectly seamed and ready for final edgework.

Instead of a belt grinder, the use of a shape edger quickly machines an even, consistent pencil edge with no stress to the glass or to the operator.  Multiple passes quickly refine the edge and prepare it for polishing.  Using the shape edger produces a superior looking edge in a fraction of the time it takes to produce a "good" edge by traditional methods.

Grade of Glass

Sanders offers windows in two grades: Concours and Replacement.

Concours Grade

Concours grade windows are intended for car show & points competition automobiles: exposed edges are polished or Black Edged and the original manufacturer's sandblasted script (logo and date, sometimes referred to as the "bug") are duplicated to ensure an O.E.M. appearance.

Replacement Grade

Replacement grade windows are intended for daily use; street rods or antique cars that are not built for car show competition.  Exposed edges are machined to a satin finish rather than polished, no Black Edging is applied, and instead of the O.E.M. markings a D.O.T. script is applied.  This is an affordable alternative to the Concours grade without sacrificing quality.

Black Edging

Black edging refers to the process used to seal the exposed edges of laminated safety glass and was necessary in the early years of automobile manufacturing.  The term "black edge" is commonly used as a reference to a highly polished edge (which appears black); this is a mistake.  Polishing and black edging are two different things.  Although a highly polished edge appears "black", it is only a result of light reflection.

black edging

A true black edge will appear as a black band around the entire edge of an original window...and only if that window was produced prior to 1941.  This was done because early laminated glass often separated at the edges, allowing water and other contaminants between the panes.  The solution was an inlaid black sealant.  Advances in the laminating process rendered black edging obsolete in 1941, but Sanders Reproduction Glass re-discovered the process and is practicing this lost art for the detail oriented customer.

Sandblasted Logo & Date Scripting

Sanders is one of only a handful of glass shops licensed to reproduce the FoMoCo scripting and one of fewer still that use the authentic sandblast technique

scriptsMarkings or "scripts" identify the window manufacturer as well as certify its compliance with US Department of Transportation regulations.

AS-1 is required for all windshields and at least AS-2 is required for sides and backs.
AS-1 can only be made out of laminated safety glass while all other AS numbers can be either laminated or tempered, as long as they meet the minimum AS requirement.
Sanders sells only AS-1, Category II laminated safety glass or AS-2 tempered safety glass.
Because most states require a safety inspection prior to titling and registration, and to comply with Federal law, Sanders marks all windows with some form of script; be it an O.E.M. marking for a Concours window or a generic D.O.T. marking for a Replacement window.


Some glass cutters forget that many windows serve a function other than keeping the weather out: they are moving parts.  A properly finished edge reduces the friction between the window and the rail or runner, providing a smoother operation and cleaner look.
Sanders pencil grinds to a satin finish (Replacement Grade) or polish (Concours Grade) those edges that are exposed.  The result is that your window will look good and function properly.


Above is a sample of Sanders machine cut and satin finished edge.  A proper edge should have no chips or undercuts, and should be uniform.  This can only be accomplished using an edging machine

Glass Thickness

Sanders offers the following specialty tints of glass that they can cut and temper to your specification.  1/4" is the most common size for sedans, hardtops, coupes and station wagons.  3/16" is sometimes used in doors and 1/8" is commonly used for back windows (backlights) for convertible tops.


1/8" - (3mm)

3/16" - (5mm)

1/4" - (6mm)



Solar Bronze

Solar Gray

#31 Gray



Solar Bronze

Solar Gray



Solar Bronze

Solar Gray

#14 Gray

Solar Gray is the most popular tint for all around shading.  Solex is popular for windshields and the Solar Bronze and Dark Gray tints are popular for customs, hot rods and limousines.  The color for our laminated glass is in the laminate while our tempered windows have the color in the glass itself.  No stick-on/peel off tinting here

tintsD.O.T. safety regulations require windshields to meet the AS-1 light transmission standard of at least 70%.  Front vents and doors must meet the AS-2 light transmission standard of at least 40%.  All other windows can be darker than 40%.  Tinting laws vary state to state, so be sure you know what your state requires


Laminated Glass

Laminated Safety Glass provides impact resistance, occupant retention and security.
1)Impact Resistance: The principal feature of laminated safety glass is its performance under impact.  The laminate absorbs the energy of an impact and resists penetration.  Although the glass may break, the glass fragments remain firmly bonded to the laminate, minimizing the risk of injuries.  US DOT regulations require the use of laminated (AS1, Category II) safety glass for all automobile windshields.
2)Occupant Retention: Even if a window is broken, the interlayer can continue to safeguard the interior and its occupants, even during rollovers.
Security: Lastly, laminated safety glass provides resistance to forced entry.  Burglars often break windows to get to door and window handles; laminated glass can resist their intrusion, providing added security.

Flat Windshield & Tempered Automobile Glass

Tempered Safety & flat windshield glass provides high strength, durability, light weight and a unique breaking pattern (called "dicing") that produces harmless cubes.
3)Strength: The principle feature of tempered safety glass is its strength. Tempered glass can be four times stronger than normal annealed glass.  Its strength allows it to resist the impact of objects traveling twice as fast as would shatter annealed glass.
4)Durability: Tempered glass resists chips, scratches, stars and "bulls-eyes", making it very durable.
5)Weight: Tempered glass is produced from a single glass pane, eliminating the laminate and second pane of laminated glass.
Safety: Fully tempered glass shatters into harmless cubes when broken, eliminating the hazards of flying shards of sharp glass during accidents.  Most automobile side and back windows manufactured after 1955 are tempered safety glass.

Sanders Reproduction Glass offers flat glass windshields in laminated safety glass only and all other windows (doors, vents, quarters and backs) in either laminated or fully tempered safety glass.  Please call (800) 468-4323 or go to for further details.

Waterjet MD-2

Tempering is performed in this special oven that heats it to a high controlled temperature and cools it with a controlled airflow process.


Waterjet MD-3

Glass is held in special clamps that grip the glass without damaging the glass when sent through the tempering process.

Waterjet MD-5

The process begins by finding the pattern for the job from the more than 10,000 patterns stored in the computer system

Waterjet MD-7

Glass is positioned on the table on top of the support strips and indexed to the lower left corner establishing the starting reference point.

Waterjet MD-9

A nozzle with a focused jet of high-pressure water and abrasive garnet does the glass cutting.  Nozzle tip is not visible because it is hidden by the safety shield encircling it.

Waterjet MD-11

When the cut is completed a suction cup makes it easier to pick the finished piece up off of the table.  Item cut in this demonstration is a ½-inch thick glass tabletop

Waterjet MD-13

Multiple passes through the shape edger create an even, consistent pencil edge with no stress to the glass.  Machine is capable of processing small to very larges pieces of glass.


Waterjet MD-4

When tempered glass shatters it breaks into harmless cubes (“called dicing”).

Waterjet MD-6\

Joe Kemp then transfers the pattern from the computer to the control module of the water jet system

Waterjet MD-8

Glass is backed up with foam insulating material that supports it and prevents the jet spray from fanning out on the back side of the glass during the cutting process.  Fanning out would blast a pattern onto the surface of the glass.

Waterjet MD-10

Water jet nozzle travels through its X & Y paths during the cutting process regulated by the tower and carriage unit mounted onto the cutting table.

Waterjet MD-12

Mixture of garnet and water is washed off of the finished piece.

Waterjet MD-14

Finished glass is fed through a glass-cleaning machine that washed it with warm water and cleaning solution.

It’s always so useful when we can see the “inside operations” of a company and understand all that is involved in their business.   This was a great look inside the world of glass cutting and fabricating.

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