Engraving Acrylic with a Laser

Things I have Learnt about Engraving Acrylic with a Laser

I have recently acquired a LEGO Star Wars T-16 Skyhopper. It’s one of my favourite ships from Star Wars. The tri-wing design reminds me of my very favourite ship: The Lambda-class T-4a shuttle which Vader moves about in. The T-16 is barely on screen, but in A New Hope you can see Luke play with a model Skyhopper when he’s hanging out with the droids. You see one flying later in the Special Edition version of the original trilogy.

LEGO T-16Anyway, it’s a cool model and it deserves to be displayed with a little pizzazz. I have made a fairly shabby prototype tonight using some laser cut acrylic which I bent using a heat gun. I need to refine the process a little to perfect it, but it’s definitely a viable method. I used a couple of largish bits of steel that were lying around as blanking plates to direct the heat and this was the result:

LEGO stand prototypeI need to experiment with the heat gun timings, as the acrylic became far too pliable and ended up distorting. There are also bubbles in the acrylic now. My plan was to glue a 4×2 LEGO tile to the top plate. In V2 I think I will engrave a section for this to slot into, and I think I’m going to add a ship identification label to the large base too. There may well be an eBay/Etsy market for this kind of thing if it comes out well.

The dimensions of the base plate are 100mm x 100mm with a corner radius of 10mm. It feels very sturdy laterally and it will be more than enough to support the 220g model.

Here’s a PDF of V1: v1_t16_stand_CS6.pdf

Flight Stand V2

I had melted the original stand because I thought it would take a lot more heat to soften the acrylic – I took a guess and heated it for 20 seconds. Way too much! Using the Bosch PHG 600-3 at BuildBrighton it would begin to soften enough to bend after 4-5 seconds. On V2 the bend was a lot more successful, and instead of bending using heat gloves I formed the stand around a piece of decking plank with a rounded edge. On V2 I also engraved the name of the ship ‘T-16 Skyhopper’ and the fictional company that builds that model: ‘Incom Corporation’. I also added a engraved rectangle on the top of the stand 32.5 mm x 16.5 mm – 0.5 mm longer and wider than a 4×2 stud LEGO tile. Iwill hopefully be able to glue one into the stand to affix the to model later. Unfortunately, I didn’t mask either of the engravings, so ended up with a frosty, smoke-damaged engrave.

Flight Stand V3 (using V2 PDF)

flight_standsI went down to the hackspace today to create what I thought would be my final version of the flight stand. I used some masking tape to stop the smoke damage from the engraving and I raised the acrylic a few mm above the honeycomb to aid the smoke extraction.

The cut quality was affected far more by the masking tape than I had expected – I assumed the laser would just power through it, but the cut is noticabley lower quality around the masked section. Oh well, I forged on…2015-05-22 23.51.04The bend went well – I am clamping the piece to a wooden forming block with rounded edges, then laying two wooden blocks parallel with a 5mm gap to direct the heat to the desired part of the acrylic. The acrylic gets very warm, so I am using a heat proof welding glove to push the section down once it is heated (I am trying to push as far away from the heated bit as possible, as I have imprinted the glove’s rough texture into the acrylic before). I had a small storage crate filled with warm water to dunk the acrylic this time – it set in the desired postion much more accurately than before (on Thursday I had run through the main hackspace room and run the prototype under the tap…)

So, at this point I had a well formed stand with the masking tape still applied. The engrave is certainly much cleaner, but the masking tape was more difficult to remove (melted glue?) and there was residue left in the openings of the letters. Next to the sink we have a bottle of isopropyl alcohol for cleaning the laser cutter, I’ve used this stuff in the past for cleaning printers and it is safe to use on most plastic, so I thought nothing of it and cleaned off the masking tape residue. Job done.

Except… when I got home I looked at the stand in daylight there were loads of little cracks extending from each of the letters on the engrave. I didn’t remember them being there in the workshop, so I went back and did a couple of engrave tests on acrylic – I cleaned two with isopropyl and two with warm water. The ones with the alcohol developed the cracks, the other two didn’t. It would appear that the IPA caused this and a bit of research confirmed it: StackExchange Chemistry.

I’m going back tomorrow armed with all this knowledge to make the perfect flight stand!

Flight Stand V4 (using V2 PDF)

This is the final one. I masked the engraving using blue painters tape and the residue was much easier to remove with washing up liquid and water. After heat forming the acrylic I super glued a 4×2 stud LEGO tile into the engraved cut-out on top of the stand. I gave the ship a more nose down look, to make it look like the pilot is targetting womp rats on Tatooine.

2015-05-27 10.27.07Engraving is sharp and distinct.

2015-05-31 13.42.57The final nose-down look.

TL;DR – List of things to remember about engraving acrylic on the laser…

  • Use masking tape over the area that will be engraved to stop smoke damage (consider upping the power or lowering the speed if cutting through this area too).
  • DO NOT clean the residue with isopropyl alcohol
  • For 4mm clear acrylic from hackspace stock (Plastic People?) the cutting/scanning speeds were 10mm/s @ 40% cut and 100mm/s @ 40% scan. This did overcut slightly, so power could be reduced or cut sped up.
  • There are two types of acrylic: Extruded and cast. Cast creates a white ‘frosty’ surface when engraved. Extruded has a lower melting point and does not produce the same contrast when engraved, but produces a nice finished edge when laser cut, due to the melting.

Here’s the final PDF for you to cut, if you so desire: v2_t16_stand_CS6.pdf