Laser Cutting and Engraving May Be Closer Than You Think

laser warningI've often written about getting acrylic parts cut at Metrix, the local hacker space.  It's awesome to have a panel cut where, if you've measured carefully and made an accurate drawing, the holes are the right size and shape (like D-holes for switches and pots) and everything lines up.  You may be thinking "That's great for you, but what about me?  There's not a hacker space anywhere near me."

I made a discovery.  Many trophy shops have lasers these days to make plaques for trophies and awards.  In fact, engraving is one of the things they do all the time, so they may do a better job than a hacker space!  The trophy shop about 2 miles from my house did a superb job for me when I wanted better quality engraving than I got at the hacker space, and it was cheaper too.  They were happy to work with the file I supplied to cut and engrave my panel.
I also found an awesome material to create an instrument panel – Rowmark Metalgraph Plus. This is an acrylic material with a thin metal-like surface over a black core.  When it's engraved using a laser or rotary engraver, you end up with black markings on what looks to be a metal panel.  The material is available in 1/8" thickness, which will be suitable for small instrument panels.  The panel pictured is about 4" x 6".  It's available in 1/16" thickness too, which you might use to create a custom lid for a project box.
I'm also looking at Gravograph's Flexilase.  This is a thin (0.01") two ply material with an adhesive back.  It can be laser cut, and engraving exposes the core color just like the Metalgraph.  Imagine this as a faceplate over the metal panel of an enclosure.  Machine the metal with a Dremel tools, drills, files, nibblers or other means, and then hide the imperfections with a laser-cut faceplate.  Pretty slick. 


Creating Files for Laser Cutting / Engraving

You must create a drawing of the panel you want to have cut and engraved.  I use Visio for this but there are a number of programs that can be used, such as Inkscape. To determine the cutouts for switches, display bezels and other components, a good place to start is the manufacturer's data sheet.  A suggested cutout is usually given.  For items without a data sheet, a digital caliper is a good investment.  Decent calipers can be purchased from eBay or Harbor Freight for less than $20.  If you're measuring something for a mounting hole, be sure to leave some clearance.  I'm terrible at estimating the proper amount of clearance, so I open the caliper a bit until the clearance seems adequate without being sloppy and use that size.
digital caliper
Laser cutting leaves a lot of stress in the material, so you should avoid stress risers like square corners and holes that are so small you have to force the component in.  Round corners of holes slightly to eliminate the stress riser.
Draw the laser cut lines with hairline-width lines.  Don't fill any of the shapes to be cut out.
The text and any lines you want engraved should be done in a different color; say black for the lines you want cut and red for the items to be engraved.  Explain this to the laser shop.
When the drawing is complete and checked, save it as an SVG (scalable vector graphic) – this format seems to be easy for most shops to use, but check to see what they prefer.  Also, make note of the exact size of some object in the drawing, say the overall panel size, so the shop can check for any scaling errors in converting file formats.
A Few Hints
Laser cutting leaves a lot of residual stress in the panel.  Do not use isopropanol alcohol to remove laser debris from the panel!  Doing so will result in instant cracking and crazing of the panel.  Warm water and dish soap work well to clean up a panel.  This picture below shows crazing on a 1mm panel after alcohol was applied and the panel gently flexed.
 image copy copy
Acrylic (Plexiglass, Perspex) is a great material for laser cutting.  Avoid PVC as chloride is released during cutting which is hazardous to both you and the laser.  ABS should be avoided as well – most shops won't cut it because of the smell during cutting.  Thin (3mm) plywood is a common choice for laser projects, but the edges will have a burned appearance.
The edges of a laser cut piece are not square because of the beam characteristics.  If you stack a number of pieces, the result will not be a smooth edge. For a full description of beam characteristics, click here.
image copy

Posted: 2 years 4 months ago by Baldor #16943
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I never thougt of trophy shops. Thanks!!

There is a rule for the clearance of screw holes: 10% bigger. So, a hole for an M3 screw should be 3.3mm, for an M6, 6.6mm, etc. For laser cutting this isn't a problem, but if you have to drill, is not practical. So, I use D+0.25mm for M2,M3 and M4, D+0.5mm for M5, M6 and M8, and D+1mm from M10 uppwards. This is aplicable to all round holes, not only for screws. See a chart.. If you want a thigter fiting, use D+0.25 for all.

For other shapes, is better to forget ISO tolerance tables, since you only need a loose fitting. Just use dimension+0.25mm for small shapes, like slide switches, and dimensinon +0.5mm for bigger shapes. If you are confident with your measurements and the precision of the cuts, just use dimension +0.25mm for all.

Also, you must know if the cut is made over the center of the line you drawn, or if it's compensated to the inside for the laser width. If the cut is over the line, you will have a bigger cut, and you must compensate in the drawing (just an offset to the inside of the shape of half the cut widht.)

I'm a mould designer by trade, and used to work with much, much thigter tolerances. If you need a tighter fit, just ask. (Whithin the capabilities of the laser machine and your measurement tools)
Posted: 2 years 4 months ago by Jon Chandler #16944
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Here's a picture of the assembled panel.

Posted: 2 years 4 months ago by Baldor #16945
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Posted: 2 years 4 months ago by GM_Mike #16946
Posted: 2 years 4 months ago by davekr #16987
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I tried engraving award plaques and trophies several times in the past. But never got a satisfactory result. Last week I went to a shop named Hoult-Hellewell in Scarborough to engrave in one of those plaques. They use laser engraving technique. They did a great job with the perfection I will never make, if I try it myself unless I own a laser engraving machine.

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