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Acrylic Plastic Sheets or "Plexiglas" - Its Uses, Handling and Cutting

From hockey rink barriers to fish tanks... from shatterproof glass replacements to skylights... acrylic plastic sheets have countless uses around the home.  Here are some tips to make the most of this marvelous product!  This article (with slight modification) courtesy of San Diego Plastics. Full credits at the end of this article. (Please note that plexiglas, often misspelled "plexiglass", is a trade name for acrylic plastic.  They are exactly the same thing!)

Characteristics of the material

Plastic sheets made of acrylic plastic are half the weight of glass, are impact resistant, are not affected by the elements and have a useful temperature range from -30 degrees F. to 160 degrees F.  These qualties make it an ideal replacement for glass in many situations, especially where glass breakage is an issue.

Cleaning Acrylic Plastic Sheets...

Wash with mild soap or detergent, with plenty of lukewarm water, dry with soft cloth or chamois. Grease, oil or tar can be removed with hexane or kerosene. Solvent residue should be removed by washing immediately.

Do Not Use window cleaning sprays (unless recommended for acrylic plastic), scouring compounds, acetone, gasoline, benzene, carbon tetrachloride or lacquer thinner.  These solvents and cause permanent damage to the surface of the plastic, making it appear "frosted".

About the Paper or Plastic "Masking" Film on Acrylic Sheets...

All quality acrylic plastic sheeting is covered with a thin film on both sides.  This film protects the plastic from minor scratches that can occur during transportation and installation.

Generally speaking, when working with the material leave the paper masking film on the sheet as long as possible. Except for intricate detail work you should remove the masking only when your project is completed.

Working with acrylic plastic sheets

Things to definitely do...

  • Do not remove the thin plastic masking until absolutely necessary.
  • Use metal cutting saw blades and drills which are specifically made for acrylic sheets. 
  • It is essential to use sharp tools when trying to cut acrylic plastic sheets. 
  • Overheating can cause cutting blades to load up and become dull.  So always use cooling (water or oil) when cutting plastic over 1/8" thick or drilling plastic over 3/16" thick.
  • Wet the material before cleaning.

Things to NOT do...

  • Use saw blades with side-set teeth. Saw teeth ideally should be ground with 0° of rake and be of uniform height and shape.

How To Cut Acrylic Plastic Sheet

Cutting with a knife or scriber

Acrylic sheet up to 3/16" thick may be cut by a method similar to that used to cut glass. Use a scribing knife, a metal scriber, an awl, or a utility knife to score the sheet. Draw the scriber several times (7 or 8 times for a 3/16" sheet) along a straight edge held firmly in place. Then clamp the sheet or hold it rigidly under a straight edge with the scribe mark hanging just over the edge of a table. Apply a sharp downward pressure to break the sheet along the scribe line. Scrape the edges to smooth any sharp corners. This method is not recommended for long breaks or thick material.

Cutting with power saws

Special blades are available to cut acrylic. Otherwise use blades designed to cut aluminum or copper. Teeth should be fine, of the same height, evenly spaced, with little or no set.

Table and circular saws

Use hollow ground high speed blades with no set and at least 5 teeth per inch. Carbide tipped blades with a triple chip tooth will give the smoothest cuts. Set the blade height about 1/8" above the height of the material. This will reduce edge chipping.

When using a hand held circular saw, clamp the sheet to the work surface and use a length of 1x3 wood to distribute the clamping pressure and act as a guide for the saw.

Feed the work slowly and smoothly. Lubricate the blade with soap or beeswax to minimize gumming from the masking adhesive. Be sure the saw is up to full speed before beginning the cut. Water cooling the blade is suggested for thicknesses over 1/4", especially if edge cementing will be performed.

Saber saws

Use metal or plastic cutting blades. The blades you use to cut acrylic should never be used for any other material. Cut at high speed and be sure the saw is at full speed before beginning the cut.

Hand saws

Good results are possible, but very difficult. Be sure the acrylic is clamped to prevent flexing. Flexing at the cut may cause cracking.

Routers and shapers

Use single fluted bits for inside circle routing and double fluted bits for edge routing. At the high speeds at which routers operate it is critical to avoid all vibration. Even small vibrations can cause crazing and fractures during routing.

Drilling Through Acrylic Plastic

For best results, use drill bits designed specifically for acrylic. Regular twist drills can be used, but need modification to keep the blade from grabbing and fracturing the plastic. Modify the bit by grinding small flats onto both cutting edges, so the bit cuts with a scraping action. If the drill is correctly sharpened and operated at the correct speed, two continuous spiral ribbons will emerge from the hole.

Finishing Cut Edges of Acrylic Plastic Sheets

The cut edges of plastic sheets can be both rough and razor sharp.  Easing the edges makes handling easier and safer... now and if the sheet is ever removed from its mount!!

Scraping

The first step in getting a finished edge is scraping. The back of a hacksaw blade is perfect for scraping. Simply draw the corner of the square edge of the blade along the edge of the acrylic.

You can also use a utility knife.  Draw the blade across the each side of the cut edge with the blade tilted  in the direction you are moving.  You don't want to cut into the plastic sheet, just to knock off the high spots.

Filing

A 10 to 12 inch smooth cut file is recommended for filing edges and removing tool marks. Do not move the file back and forth... file only in one direction or you may chip the plastic. Keep the teeth flat on the surface, but let the file slide at an angle to avoid putting grooves in the work.

Sanding

If necessary, start with 120 grit sandpaper, used dry. Then switch to a 220 grit paper, dry. Finish with a 400 grit wet/dry paper, used wet. Grits as fine as 600 may be used. Always use a wooden or rubber sanding block.

When removing scratches be sure to sand an area larger than the scratch. Sand with a circular motion, and use a light touch and plenty of water with wet/dry papers.

Almost any commercial power sander can be used with acrylic. Use light pressure and slower speeds.

Polishing

Final polishing will give acrylic a high luster. Power-driven buffing tools are recommended without exception. Buffing wheels are available as attachments for electric drills.

A good buffing wheel for acrylic consists of layers of 3/16" carbonized felt, or layers of unbleached muslin laid together to form a wheel. Solidly stitched wheels should be avoided.

The wheel should reach a surface speed of at least 1200 feet per minute. Speeds of up to 4000 feet per minute are useful for acrylic.

Acrylic should be polished using a commercial buffing compound of the type used for silver or brass, or you can use a non- silicone car polish that has no cleaning solvents in it.

First, however, tallow should be applied to the wheel as a base for the buffing compound. Just touch the tallow stick to the spinning wheel, and then quickly apply the buffing compound.

To polish, move the piece back and forth across the buffing wheel. Be careful not to apply too much pressure. Keep the work constantly moving to prevent heat buildup.

Never begin polishing at the edge of the sheet. The wheel could easily catch the top edge and throw the piece across the room or at you.

Forming and Bending Acrylic Plastic

Bending acrylic plastic sheets

Acrylic sheets can be heated to make them pliable. It will become rigid again when it cools. Never heat acrylic in a kitchen oven. Explosive fumes can accumulate inside the oven, and ignite.

A strip heater is the best tool to form acrylic. This tool will only form straight line bends. Buy one from your acrylic dealer. The strip heater will heat just the area to be formed.

Heat the sheet until it begins to sag at the bend line. The bend should be made away from the side exposed to the heating element. Sheet thicker than 3/16" should be heated on both sides for a proper bend. Use forming jigs or clamps for best results, and wear heavy cotton gloves when handling heated acrylic.

Forming other than straight line bends will generally require specialized equipment and jigs.

Joining Acrylic Plastic Pieces Together

Solvent cementing is recommended for joining acrylic. There are two techniques for solvent cementing... capillary and dip or soak... which dissolve the contact surfaces to join the acrylic pieces.  A third method is viscous cementing, where dissolved acrylic is used as the cement.

Note that the descriptions below may not be sufficient for all circumstances and some experimentation with the materials may be needed for the amateur craftsman to make perfect joints with this material.

Edges should be smooth for the strongest and best looking joints.

Capillary cementing

Capillary cementing of acrylic sheets

This is the most popular method for joining acrylic edge to edge. However, this method will not work at all unless the parts to be joined fit together PERFECTLY.

Make sure the parts fit properly. Then join them with masking tape or clamp them in a form to hold them firmly in place. It is important that the joint be in a horizontal plane, or the cement will run out of the joint.

Apply the cement carefully along the entire joint. Apply from the inside of a box-corner joint, and on both sides of a flat joint. A needle-nosed applicator bottle is recommended. The thin cement will flow into the joint through capillary action and form a strong bond. Maximum bond strength will not be reached for 24 to 48 hours.

Soak or dip cementing

This is suggested only for THICK joints. Stand the edge to be glued in a tray of solvent (dip tray) for about twenty seconds. Remove the acrylic from the dip tray and allow excess solvent to run off.  Immediately put the softened edge of the acrylic against the piece to be attached. Do not apply excessive pressure... just allow the solvent from the first piece to soften the second. After 30 seconds, increase the pressure so the edges make strong contact, which also should force out any air bubbles. Clamping is recommended for this part.

Though clamps can be released after thirty minutes, full strength might not be reached for a few days.

Viscous cementing

Viscous cements are used for joints that can't be cemented with capillary or soak cementing, either because the joint is difficult to reach or because the parts don't fit properly. Viscous cement is thick and will fill small gaps. It can make strong transparent joints where solvent can't.

You can make your own viscous cement by dissolving chips of clear acrylic sheet in a small amount of solvent. Apply a small bead of cement to one side of the joint, join the pieces, and tape or clamp in place until cured.

Our appreciation to San Diego Plastics, Inc. at http://www.sdplastics.com for allowing us to reproduce this article.  Since 1986, San Diego Plastics, Inc. has been one of the best sources of plastics for business and personal use in The American Southwest.