I am engraving 1/8″ extruded black acrylic to a depth of 1/16″. Using my Universal M300 40 watt it seems to require three passes, as doing it in one pass I have to slow it down to where there is melting. The problem is that the acrylic dust is collecting on the trailing edge of the cut, and seems to almost remelt and adhere to the edge of the raised part of the engraving. In other words, while I get a really clean cut with the vector cutting, the raster engraving leaves me with a ragged edge where the residue has glommed on to the sides. What can I do to avoid this? As it is I’m cutting about .02″ per pass. Thanks.
Leave the mask on or add a light tack paper mask if it doesn’t have one. Or cut if from the back side. (face down)
The mask protects the upper horizontal surface, but the accumulation is on the vertical cut surfaces. Cutting it from the back side doesn’t apply as the issue is only with engraving.
Are you using air assist? Strong air current may help sweep away residue before it sets.
Yes, I am using air assist and yet still the problem persists. Thanks for responding.
For what it’s worth, I have similar problems with acrylic. I’ve not been able to take a layer of material off cleanly. I’ve always got bumpynesss and the deeper I go, the worse it gets.
One thing I’ve wanted to try was to build in stages to burn. By giving visible stages, it makes the bumpyness less noticeable. The stages could contain any pattern you’d like. Cross hatches, halftone cells, “V” shaped… Basically, since if I can’t get it flat, is there a texture which would be acceptable?
Here is what I have done in the past, using CorelDraw 12 with my Epilog laser…..
Add a vector outline to your engraving. If you are doing letters for instance, add an outline to the letters (hairline width). If you are doing shapes and whatnot, it may take a little extra time to add the hairline outline, but it could be as simple as selecting the object then adding the outline.
Then engrave as you have been — three passes to build depth, then the laser will go into vector mode and trim up the outline. The only thing that will take time is to get the correct power and speed settings for the vector pass so you get the same depth of cut as the engraving. Once you do this once on a practice piece, write down all the details for use later.
Hope that helps.
Thanks for writing, David. I thought that would work, but the build-up was outside the outline of the letters, and vector cutting around the letters did not remove the residue. I have yet to try cast acrylic, though I don’t think that will make any difference. It seems like I need to somehow burn off the residue without it melting back on. I have bandsawed acrylic in the past, and had the cut reseal behind the blade because of this effect.
You need to use cast for this. And you need a new strategy for it. I do a lot of engraving for spin cast masters using pex where we take away a background and leave lettering standing up. Ideally you need a LOT of air assist in that you really want to cool down the pex and avoid “remelt” when taking away the background. You also need a registration system. The strategy is to engrave in a single pass and use the air assist whilst dropping dpi and ppi to about 300 (to much dpi and ppi will overlaps pulses and create heat affected zones. however dropping DPI will require more power or a slower speed to get depth), you will get a bit of edge encrustation. But it’s removable. You laser the item and then remove it from the machine. You use a brass brush with an abrasive household surface cleaner like Handy Andy and scrub away the residue. You will see the encrustation does largely remove. Now you put the item back in the laser (this is where a PRECISE registration system comes in. I’m sure you can find a way to do so depending on your machine) and you give the item a polishing pass. The polishing pass is a much lower powered higher speed pass over the existing engraving with the lens focused on the engraved background. This effectively “cleans” up the engraved surfaces and to some extent the edges and gets rid of the riffled surface to some extent. What’s actually important in this case is to very securely hold down the acrylic on the first pass. The heat of engraving makes the pex flex and buckle ever so slightly which does lead to deeper engraving over the surface as it does so. We use a layer of double sided mounting film under it and stick it directly to the table or some other subsidiary support. Whacking up air assist to some extent prevents a lot of flex as it cools the pex too.
Thanks, that is just the kind of information I was looking for.