Laser cutting clear acrylic sheet

What is clear acrylic anyway?

Back in the 1930’s, new plastics were being invented by boffins like they were going out of fashion – neoprene in 1932, polythene in 1933 and Perspex in 1934.

These newfangled materials found important uses almost from day one – in World War Two, flying machine cockpits were made of Perspex, while polythene was used to insulate components in the newly invented RADAR scanners on the South Coast of England, while neoprene was used to make synthetic rubber for tyres.

Today, Clear acrylic Perspex sheet hasn’t changed much and still offers near perfect optical clarity and makes for a great alternative to glass.  It is also, handily, very easily cut with a laser cutter.  On top of that it engraves beautifully and with a bit of care you can make some stunning point of sale display stands and even laser cut jewellery.

Clear acrylic sheet benefits from the following features:

  1. high gloss surface, which is exceptionally hard-wearing (though not totally scratch resistant)
  2. alternative finishes including frost acrylic sheets
  3. various thicknesses available from 1mm to 25mm
  4. easy to post form or bend with the application of a heat source e.g. hairdryer or heat gun (you can even put it in the oven but do remember to take it out before it melts everywhere!)
  5. it can also be vacuum formed with heat and specialist vacuum equipment to make small to medium sized items such as cups, chairs and even prosthetic limbs

In addition to clear acrylic, there are a variety of colours and finishes available including fluorescents and “edge lit” acrylics.

So is it Perspex or acrylic?

Perspex is a brand name which is used interchangeably with acrylic.  There are many manufacturers of acrylic sheet, but only one producer can call it Perspex.  Think of it like the difference between brand name prescription drugs and generic drugs.

In practice, there are slight differences in melting temperatures of acrylic between batches even from the same manufacture, and Perspex is generally regarded as a safe bet by laser cutters.  Some of the darker coloured generic acrylics in particular do behave relatively poorly in a laser cutter – “more melty” is a phrase which comes to mind.

How is acrylic sheet made?

There are two types of acrylic sheet.  Cast acrylic sheet is produced directly from what’s known as a monomer, a hot liquid squidged between two sheets of high quality glass.  The sheet is poured out in large batches from special ovens, with swimming pool sized water baths to cool things down in a large scale manufacturing process.  The sheets are then released from the glass and cut to standard sizes.

Extruded Perspex Sheet is produced from the acrylic polymer known as “Lucite Diakon”, in the form of granules.  The heated polymer is extruded under great pressure through what is basically a long slit, to form a sheet.

The main differences between cast acrylic and extruded acrylic are:

  • When laser cutting extruded acrylic , there will be a visible burr on one side, where the acrylic has melted but not vapourised
  • On laser cut cast acrylic there is almost no burr, hence the perception that cast acrylic is generally better
  • Extruded acrylic laser cut parts may look different depending on the direction of the acrylic extrusion
  • Laser engraved extruded acrylic has more tensile strength due to its composition, meaning it can be used in a rolling mill to apply a laser engraved texture to metals (e.g. in a rolling mill for silver jewellery)
  • Laser engraved extruded acrylic will appear more grey
  • Laser engraved cast acrylic will look whiter, especially noticeable on clear and dark acrylics

Handling acrylic sheet

As with many commercial sheet materials, acrylic sheet comes with a protective film surface.  This can be removed prior to cutting and engraving, although it’s generally much better to leave it on until the sheet has been processed.  You can laser engrave straight through the protective film.

Perspex comes labelled with a “display side”, but that’s more to do with logistics and human fallibility than any actual difference between the two sides.

Price of acrylic sheet

Although the oil price does directly affect the price of acrylic sheet, it remains an affordable, quality and readily available material to work with.

Generally, unless you specify when purchasing acrylic, you will receive cast acrylic, as it’s considered superior for most purposes, and generally a little bit cheaper.

Benefits of laser engraved clear Perspex

  • It looks great.  It’s quick and easy to cut.  It’s easy to handle.  It’s quite cheap.
  • Clear Perspex sheet has light transmission in excess of 92% – superior to all other thermoplastic sheet available and higher than that of glass.
  • Clear Perspex can be safely used outside and is backed by a 10 year manufacturers warranty against significant reduction in performance.

Drawbacks of laser engraving clear acrylic

  • Smell – fumes are quite pungent and filtration of the exhaust, or preferably extraction to the outside are required
  • Acrylic sheet does heat up during cutting if too many cuts are put too close together – this can cause cuts to fuse back together in places
  • Flash back from the laser bed can be an issue with inexperienced operators, causing the underside of the work to be marred, especially visible on jewellery and small items
  • Not so easy to recycle small amounts of waste, though specialist companies do exist to process it into coasters and place mats for example
  • In practice, bear in mind that harsh sunlight and driving wind and rain will affect that shiny new finish somewhat over time
  • It’s an oil based product 🙁