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Working With Acrylic Part 1: Cutting and Finishing

Copyright © 2007 by Davis Multimedia, Int'l. All Rights Reserved.
As Printed in September 2007, Volume 33, No. 3 of The Engravers Journal
Photos courtesy of Rohm and Haas Company, Philadelphia, PA.

   For many years, wood, flexible plastic engraving stock and metal have been the dominant materials used to fabricate signage, awards and gifts. Acrylic has also been a mainstay in the recognition and identification industry for quite some time, but recently, this versatile, sophisticated plastic has surged in popularity to become a fashionable material for everything from desk accessories and trophies to interior architectural signage. Indeed, acrylic awards now represent a major category of unique and laser-friendly awards.
   The marketability of acrylic merchandise has never been greater. Customers are attracted to the sleek, contemporary look of acrylic merchandise. The unique qualities of acrylic are ideal for customers looking for something other than traditional signage, awards and gifts.
   Today, acrylic is used to fabricate just about any product imaginable. It’s a popular choice for awards such as trophies and plaques, and for gift items such as desk accessories, key chains, coasters and jewelry boxes. Acrylic is also commonly used for all types of signage, ranging from desk nameplates to directory signs, and products such as control panels and badges.
   As an engraver, you have several options in terms of offering acrylic merchandise to your customers. Several industry suppliers offer prefabricated acrylic blanks which you can purchase and engrave in-house (see EJ’s R&I Directory™ for a listing of suppliers). As another option, you can purchase sheets of acrylic and fabricate blanks yourself. While this may not be practical for every job, the ability to cut and finish acrylic can be an advantage in certain situations, e.g. for rush jobs, for one-of-a-kind custom pieces, etc. In addition, in some cases, fabricating acrylic blanks may be more economical.
   One of the advantages of acrylic is that it is easily fabricated. Acrylic can be cut into different sizes and shapes and, by using a few simple techniques, it can be finished to a professional quality look. This article, the first in a three-part series, examines the techniques you can use in-house to cut and finish acrylic blanks.
What Is Acrylic?
   Acrylic, which was first commercially introduced in 1938, is a thermoplastic (heat sensitive) material composed of methyl methacrylate monomers. It is sold under various trade names, including Plexiglas (Rohm & Haas) and Lucite (DuPont), and is used to manufacture everything from plaques, desk accessories and key chains to formed parts for internally illuminated signs, skylights and aircraft windshields.
   Acrylic is a popular material for a variety of applications due to several notable characteristics. This material has extreme optical clarity – better than glass – and exceptional weatherability. It can also be easily rotary engraved, laser engraved, screen printed, etc., to add lettering and designs for award, gift and signage applications. And, as mentioned, acrylic is easy to cut and form.
   Acrylic is available in prefabricated, finished blanks or you can purchase acrylic by the sheet in various thicknesses. Acrylic is available in transparent, translucent and opaque formulations and in a variety of colors. Jade acrylic, for instance, has a slight green tint to it (resembling green jade glass) and is currently very popular for a variety of applications. Other options include front or reverse engravable acrylic and mirror acrylic in silver as well as other tinted mirror colors.
   The two most common manufacturing methods for acrylic are cell casting and continuous casting. In the cell casting process, liquid acrylic is poured into a cell/chamber having plate glass walls. The liquid acrylic is then cured with heat and pressure. Cell cast acrylic is available in a wide variety of sheet sizes and thicknesses. Cell cast acrylic has superior optical clarity and is usually solvent weldable.
   Continuous cast acrylic is created by casting liquid acrylic between continuously moving stainless steel belts which exert the necessary heat and pressure to cure the acrylic. Continuous cast acrylic often does not have the same degree of optical clarity as cell cast acrylic and it frequently cannot be solvent welded.
   In general, cell cast acrylic is easier to work with. This type of acrylic tends to cut cleaner and cement better than acrylic sheets produced by other manufacturing methods. For this reason, you may want to specify cell cast acrylic when purchasing sheets to fabricate in-house.
   With a few tools and the proper techniques, you can cut acrylic sheets in your shop on an as-needed basis. In the following discussion, we will look at several different methods for cutting acrylic.
Cutting Acrylic
   There are several methods that you can use to successfully cut acrylic sheet. Which method you choose typically depends on the job, e.g. whether you are making straight, curved or oddly shaped cuts.
   Before performing any cutting operation, however, there are some tips to be aware of that will help produce the best quality results. First, do not remove the paper or polyethylene masking from the acrylic before cutting. This masking helps prevent scratching due to sawing or handling. Additionally, the masking provides a handy area to sketch your layout. For example, if you are cutting an oddly shaped piece of acrylic, you can pencil
the shape directly on the masking and use it as a template when cutting. If the masking has already been removed from the acrylic, it’s a good idea to “remask” it with a paper masking material or masking tape.
   Secondly, always make sure the work surface and the area you are working in is clean, e.g. free from material chips, dust, etc. Material chips in particular can cause poor quality cuts, e.g. if they lodge underneath the acrylic, adhere to the saw blade, etc.
   Scribing & Breaking – This method is one of the easiest ways to “cut” acrylic as well as being one of the most economical. With this method, you score the acrylic sheet with a scriber and then break it along the scribed line.
   The scribing and breaking procedure is only suitable for jobs involving straight cuts in acrylic up to 1/4" thick. The minimum cutoff width that you can achieve is approximately 11/2".
In addition, this method is best suited for small quantity jobs.
   The tools suggested to successfully scribe and break acrylic include a straightedge, a 3/4" wooden dowel and a heavy-duty scribing tool. (Scribing tools can be purchased from acrylic manufacturers.)
   The first step is to draw a line on the masking material where you wish to cut the acrylic. Using the straightedge as a guide, score the masking material with the point of the scriber. Next, place the cutting edge of the scribing tool against the straightedge and pull it across to score the acrylic (Fig. 1). In general, you will probably need to do this five or six times for 3/16" thick acrylic; 1/4" thick acrylic usually requires seven to ten passes.
   Once the acrylic has been scored, position the scribed side of the sheet over the wooden dowel. Place one hand on each side of the acrylic and push down (Fig. 2). The acrylic should easily break along the scored line.
Sawing – Sawing is the most common, most precise and most practical method for cutting acrylic sheet, particularly for large quantities. Most power saws are suitable for cutting acrylic, although the type of saw you use will depend on the type of cut you wish to achieve.


Figure 1: Using a scribing tool to score acrylic. Figure 2: Breaking the acrylic along the scored line. Figure 3: Using a sabre saw to cut acrylic.

Circular Saws
   A circular saw is a good choice for making straight cuts in acrylic, e.g. to produce square and rectangular blanks for items such as plaques, desk nameplates and signs. Circular saws can generally be used to cut acrylic of any thickness.
   The most common circular saws include table saws, radial arm saws and portable saws. Whichever saw you use, a carbide-tipped blade with many teeth is recommended for the best results. Carbide-tipped blades produce a superior cut in acrylic, as opposed to steel blades, which means you will spend less time edge finishing the cut pieces. For the best results, purchase a good quality carbide-tipped blade (even though they may cost a little more) and use it only to cut acrylic. When the time comes to have the blade resharpened, make sure the person is a professional and knows how to resharpen blades for acrylic. In addition, if you will be using a steel blade, use one that is especially designed for cutting acrylic.
   Cutting acrylic with a table saw is a straightforward and, usually, trouble-free process. Before performing any cutting operations, make sure all work surfaces are clean and free from material chips and other debris. Set the blade height on the saw slightly higher than the material. This will minimize chipping during the cutting operation.
   To cut the acrylic, hold the sheet firmly against the worktable and feed it through the blade. For the cleanest cut, do not force the material; rather, feed it slowly, allowing the saw to cut freely. Also, to prevent chipping the corners of the acrylic, reduce the feed rate at the end of the cut.
   If you will be cutting acrylic with a radial arm saw, be sure to firmly clamp the material to the table to prevent it from sliding. Also, the adhesive residue from the masking material tends to build up on the saw blade, causing it to become dull and sticky. To prevent this, occasionally wipe the blade with oil.
   Another option for cutting acrylic is to use a portable circular saw. This type of saw does not have the stability of bench saws so it is a good idea to clamp the material to the worktable before cutting. When using a portable saw, set the blade depth slightly greater than the thickness of the acrylic. To provide additional stability, position the line to be cut as close to the edge of the worktable as possible. Since using a portable saw requires guiding the saw by hand, you may also want to use a straightedge as a guide to ensure a straight cut. When cutting, do not force the saw through the material; rather, use a slow, steady feed rate.
Jig Saws, Sabre Saws and Band Saws
   These types of saws are used for making curved and/or irregular cuts in acrylic, e.g. to profile circles, state outlines or other unusual shapes.
   Jig saws are well-suited for intricate curved cuts in relatively thin sheets of acrylic. For the best results, use a blade with at least 14 teeth per inch. The advantage of using a jig saw is that you can cut a shape out of the middle of a material sheet, i.e. you do not have to cut a path starting at the edge of the material. To do this, drill a hole in the area to be cut. Then remove the blade from the jig saw, insert it through the hole and reattach the blade to the saw.
   A potential problem that you may encounter when using a jig saw is that the blade does not clear the chips very well. This can cause the material chips to heat up and soften, and they sometimes weld in the slot cut behind the blade. To avoid this, always use a slow, steady feed rate. If the blade stops cutting freely, back the material/blade out and clear the chips. Also, always hold the sheet firmly to the work surface to prevent the material from vibrating.
   A sabre saw is a type of hand-held saw (Fig. 3). While this type of saw does not offer as much control as a bench saw, it’s still suitable for making both curved and straight cuts. For optimum results, use a blade with 14-32 teeth per inch.
   Before cutting with a sabre saw, clamp the acrylic sheet firmly to the edge of the work surface, allowing the portion of the sheet to be cut to hang over the edge. A straightedge is useful if you will be making straight cuts. Simply clamp the straightedge to the material and run the base of the saw along the edge of the straightedge. In addition, position the saw as close to the edge of the work surface as possible when making straight cuts. This helps to avoid vibration and possibly cracking the acrylic. As with any sawing operation, use a slow feed rate and light pressure.
   A band saw is another option for making both curved and straight cuts (Fig. 4). The blade on this type of saw consists of a continuous metal loop or “band.” As such, a path must be cut to the area of the sheet to be shaped. A blade with at least 10 teeth per inch is recommended when cutting acrylic with a band saw. Set the tension on the blade tight enough so it does not slip but with enough slack so it does not stretch. When cutting acrylic with a band saw, always use a slow feed rate.
Sawing Tips
   Regardless of the type of saw you choose to use, there are a few general tips to keep in mind to make cutting acrylic a successful operation. First, always make sure your work area is clean. Excessive material chips can lodge underneath the acrylic sheet, “gum up” the saw blade, etc., prohibiting you from achieving a good quality cut.
   In some instances, you may want to use a coolant/lubricant. Friction between a saw blade and the acrylic can cause heat buildup, which can cause the material to melt. Heat also causes stress which, in turn, causes crazing. In some cases, crazing may not be immediately visible on the acrylic, i.e. after cutting and finishing the acrylic, you may see a series of fine cracks develop on acrylic that has been “stressed.” Mineral oil, silicone-based lubricants or a couple of squirts of WD-40 are all suitable coolants for acrylic.
   As mentioned, slow feed rates produce the best results. Never force a saw through acrylic. Also, if you are working with unmasked acrylic sheets, place masking tape or another suitable masking on top of the acrylic to avoid scratching.
   Finally, always observe all safety precautions when using a saw, e.g. properly utilize safety shields, wear eye protection, etc.


Figure 4: Using a band saw to cut acrylic.

Edge Finishing
   The next step in fabricating acrylic is the finishing stage. Sawing acrylic tends to leave saw/tool marks along the cut edges that may be objectionable for many applications. In general, the goal is to achieve a highly polished edge finish. If you will be cementing an edge of the acrylic to something else, e.g. another piece of acrylic, the goal is to achieve a flat edge (this will be discussed in detail in a future article).
   Achieving a highly polished edge finish generally requires two to three separate steps: 1) scraping (optional), 2) sanding, and 3) buffing/polishing. Note: If you have several cut pieces of acrylic to finish, it’s easiest to finish them at the same time. For instance, you can hold several pieces in a vise and scrape, sand and polish them simultaneously.
   Scraping – Scraping the edges of cut acrylic is not always necessary but it may reduce the time you spend sanding, which is the next step. Scraping acrylic is particularly effective for removing saw/tool marks that are unusually large and/or deep.
   In order to scrape the edges of acrylic, you need an appropriate scraping tool. A piece of hacksaw blade or tool steel will work for this procedure. In either case, the tool should have one edge ground to a 90 degree corner as opposed to a knife-like edge.
   Scraping involves using a special technique to avoid rounding the edges or corners of the piece. First, clamp the piece in a vise. To avoid scratching or gouging the acrylic, place protective wood blocks or some other protective material on either side of the acrylic when clamping it in the vise.
   Next, place the scraper at the far end of the piece (away from you). Holding it at a 45 degree angle, pull it toward you (Fig. 5). Use firm, steady pressure, but don’t use excessive force. Also, try to keep the scraping tool flat, rather than rocking it from side to side, to avoid rounding the edges. Continue to scrape the acrylic until any deep and/or large tool marks are smoothed over.
   Sanding – The next step in the edge finishing process is sanding. The sanding procedure should remove any remaining saw marks or imperfections along the edges of the cut acrylic. The goal here is to achieve a flat, smooth, satin finish.
   Sanding can be done either “wet” or “dry.” Wet sanding, which involves using water, is usually faster but it does require the use of a sanding machine. And with odd-shaped pieces, a sanding machine may be difficult to use.
   If you will be dry sanding, it is usually best to sand by hand vs. using a sanding machine. Sanding by hand reduces the danger of heat generation which, as noted earlier, can cause the acrylic to craze.
The sanding procedure involves using progressively finer grit sandpaper to achieve the desired smooth finish, e.g. 80, 120, 220 and 320 grit sandpaper in that order.
   To sand a piece of acrylic, first secure it, e.g. in a vise. When sanding, remember that you want to avoid generating heat so avoid sanding too rigorously. For convenience, attach the sandpaper to a sanding block and use back-and-forth movements. As noted, it is a good idea to use three to four different sandpaper grits to achieve a smooth finish.
   Buffing/Polishing – The buffing/polishing stage is essentially a continuation of the sanding process. Whereas in the sanding stage the goal is to achieve a smooth, satin finish, the goal in the buffing stage is to achieve a high polish.
   There are two common techniques used to polish edges of acrylic: hand buffing and flame polishing. Of the two, hand buffing is usually the preferred choice. To hand buff acrylic, you need a buffing wheel and buffing compound. Buffing wheels are made of cloth, e.g. soft cotton. A popular buffing compound for acrylic is standard jeweler’s rouge. The buffing compound serves to polish the acrylic and prevent the wheel from “burning” the acrylic.
   To polish the acrylic, apply the buffing compound directly to the wheel and then move the edge of the acrylic over the wheel. Note: It is important to buff only the edges of the acrylic and not the surface. Buffing the surface can affect the clarity of the acrylic, i.e. it may turn cloudy. After polishing the edges, remove any excess buffing compound with spray polish and a soft cloth.
   Flame polishing is another method for edge finishing acrylic. This method involves using a torch (usually an oxy-acetylene welding tool) to polish the edges with heat. In layman’s terms, the torch vaporizes the material surface. However, hand buffing is usually preferred over flame polishing because the flame polishing technique produces heat which can adversely affect the acrylic, i.e. heat causes stress which causes crazing.
Flame polishing is generally only suitable for edge finishing acrylic thicker than 1/4". The flame on the torch should be wide enough to cover the edge in one pass. Also, before flame polishing, be sure to peel the protective masking off the acrylic.
   The flame polishing process takes skill and experience. You need to use a fast, horizontal sweeping motion along the edges of the acrylic to avoid burning or yellowing the acrylic. If you have several pieces of acrylic to finish, you can make this process a little easier and faster by finishing all of the pieces simultaneously. For example, you can stack and clamp the pieces together and flame polish them at one time. In general, flame polishing requires special techniques and experience in order to produce quality results.
Conclusion
   The ability to cut and finish acrylic can be useful skills to have. These procedures allow you to create professional quality acrylic blanks in-house on an as-needed basis. In some instances, it may be more convenient to order acrylic blanks directly from suppliers; but in others, you may save both time and money by purchasing acrylic sheets and fabricating them yourself.
   Cutting and finishing acrylic does take time to master. The information presented in this article should help you get started but experience is also key. The next article in this series goes a step further and examines drilling/hole cutting operations and techniques for joining/attaching acrylic. Watch for it!

 

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