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View Full Version : Problem Engraving and Cutting Clear Acrylic Sheet



Ric Taylor
04-03-2012, 8:32 PM
I'm having trouble engraving and cutting clear acrylic sheet. I'm getting some blow-off residue on the surface that looks a lot like smoke residue after engraving wood, except it is a frosted clear color. This is on 1/8 sheet acrylic, and it remains next to both engraved and cut lines.

After experimenting to find the right settings, this is what I am using: engraving 100/40 and cutting 15/85/5000. This is with the exhaust fans running and with air assist running. I got similar results after trying again with the air assist off.

I haven't had this issue before with acrylic. Does anyone have any ideas or suggestions?

Thanks,

Ric

Doug Griffith
04-03-2012, 8:39 PM
If you haven't had this issue before, then maybe the acrylic is extruded. Extruded engraves more clear than cast and stinks a bit.

Frank Corker
04-04-2012, 6:15 AM
Ric, I agree with Doug, it doesn't sound like you have cast acrylic there. Cast acrylic smells sweet, when bent it will snap easily. Extruded stinks, when bent it will flex. There is a noticeable differences.

Mike Null
04-04-2012, 7:41 AM
I agree that you probably are using extruded acrylic. The smoke cannot be removed unless you spend enough time on it to buy new material.

So far all the cast I've bought has paper protective covering while extruded has plastic.

Chuck Stone
04-04-2012, 7:44 AM
I'm no expert, but from your description it sounds more like
what happens when I accidentally pick up polycarbonate instead
of acrylic.

Martin Boekers
04-04-2012, 10:15 AM
If it yellow ish marks, I agree with Chuck. You may want to check to make sure that your Air Assist is
working and pointing in the right direction. I have had the tube get bumped and knocked of "course"

Ric Taylor
04-04-2012, 11:26 AM
I appreciate all of the comments so far, and my responses are a mixed bag. The plastic was given to me by a friend, so I wasn't able to look for specifics while purchasing. The brand is Plaskolite.

It is paper-covered, which would indicate cast. The engraving is nicely frosted, which would indicate cast. However, I pulled the paper out of the trash and printed on it I did find a small arrow with "extrusion direction". I guess that would indicate extruded.

With the paper covering, I just assumed it was cast without reading the small print.

Ric

Doug Griffith
04-04-2012, 11:32 AM
When we get plastic sheet extruded for us, we can specify which protective covering is applied. I wouldn't trust the paper=cast / plastic=extruded method.

Glen Monaghan
04-04-2012, 4:05 PM
I have had this before with the extruded acrylic. My experience was that small items could be wiped clean if done immediately, but the "fog" seems to set up or harden fairly quickly and doesn't wipe completely off after a very short time. You can use a paper or tape mask if the engraving design is amenable. I've had good success using Novus #2 polish to clean it up but, again, easier to do ASAP after engraving.

-Glen

Ric Taylor
04-04-2012, 7:55 PM
Well, I took the suggestions to heart and made the presumption that the acrylic was extruded. I went to a plastics dealer and bought some more 1/8 acrylic and was assured that it was cast. After discussion with the owner, I'm convinced he knew what he was talking about, and I showed him a sample of my problem. I brought the new acrylic home and did more testing, with the same results. The "fogging" appears around the cut lines, while the engraved lines seem to be ok.

I've attached a pic. It's hard to photograph, but you can see the fogging around the cut areas. The cut edges are all pretty nicely polished (the photo is a close-up which shows more detail than when viewed naturally, the edges really do look good when viewed naturally) except on the left edge there are 4 tics, I don't know what caused those tics.

I tried different settings, 15/85/1000 and 15/100/1000 with identical results.

Does anyone have any more suggestions? I really don't want to get bogged down hand polishing each piece, especially if I receive a large order from a customer.

Many thanks,

Ric

Ric Taylor
04-04-2012, 7:59 PM
Glen,

Many thanks for the input. With the test pieces I did wash them and wipe them clean immediately after the laser stopped, and now I'm sure I'm working with cast acrylic.

I'll try again with a tape mask. I think the fog is on both the top and the bottom (mostly on the top), so I guess I'll have to try masking both sides.

Thanks,

Ric

Richard Rumancik
04-04-2012, 8:10 PM
I think what you are getting is just the PMMA (acrylic) vapor condensing on the surface of the plastic. Acrylic turns directly to a gas when lasered; if the air assist and exhaust system does not take it away and it condenses on the part, it will cause it to frost. When I cut acrylic I always mask both sides; then if marking is needed I remove the paper from that side alone. I prefer to keep the paper/mask on as long as possible.

It just takes one spot of acrylic vapor to spoil a part. Although it may be possible to polish it out, I find that trying to save parts usually costs too much in labor.

Doug Griffith
04-04-2012, 8:17 PM
Engraving front to back might be worth a try to help minimize the haze.

Dee Gallo
04-04-2012, 9:57 PM
I just did a bunch of cast acrylic ornaments today and as soon as they came off the laser bed I threw them in the sink and covered them with water. This was to loosen the paper backing on the complex snowflake shaped pieces (I leave it on the back only) ... which normally are hard to peel clean. Two things happened: the paper backing came off VERY easily and there was NO fog left on the pieces from cutting. I normally have to clean them with DNA. I can't believe I never did this before, since I've made many hundreds of these... I only tried it because I had a kid helping me and wanted to make her peeling job easier... it always works for me when I'm working on plastic mah jong tiles so I figured why not clear cast?

cheers, dee

Kenneth Chan
04-04-2012, 10:46 PM
You can also try to mask it with a wetted A4 paper - soak a sheet of A4 paper in water and then place it onto the acrylic. The wetted paper should help to absorb the residue

Mike Null
04-05-2012, 9:27 AM
Lower your ppi/dpi/hertz setting on the cut mode.

On cast acrylic I clean this with dna. I leave the paper on most jobs.

Dan Hintz
04-05-2012, 10:34 AM
You can also try to mask it with a wetted A4 paper - soak a sheet of A4 paper in water and then place it onto the acrylic. The wetted paper should help to absorb the residue
I always suggest against methods like this. Water is a great absorber of CO2 wavelengths, so you're adding one more layer of variability to your settings... this can have a major effect when working with materials that are sensitive to proper settings. The substrates perceived settings change as the paper dries out.

Mike Null
04-05-2012, 10:38 AM
I concur with Dan's points on this. I do not even use wetted paper with glass.

Ric Taylor
04-06-2012, 6:48 PM
Thanks to everyone for your suggestions. I have used the information and have solved my problem.

Regards,

Ric

Ric Taylor
04-06-2012, 6:50 PM
Thanks, Doug. I almost always engrave front to back. That is one of the first tricks that Roy Brewer taught me when I first got my machine.

Ric Taylor
04-06-2012, 7:01 PM
Hi Dee,

Thanks for the water-soaking idea, it did help the paper come off easier.

I'm interested in your comment about using DNA for cleaning. I use DNA for many things around the house, but whenever I use DNA around acrylic, it immediately causes cracking on the edges that have been cut.

For cleaning off adhesives and removing tape, I use a product called Motsenbocker's Lift Off 2 (pic attached). I discovered this product while helping to remove duct tape from windows after a hurricane. It dissolved the adhesive easily, greatly simplifying the job. It feels a bit oily when working with it, but as soon as it dries there is no residue left. The bonus is that it left the windows spotless with no streaks. It works great on acrylic. I get mine at Ace Hardware.

Regards,

Ric

Richard Rumancik
04-06-2012, 8:30 PM
Ric, if you search old threads you will find a few opinions on the use of "DNA" for cleaning acrylic. Some people swear by it for cleaning acrylic, others have poor results. There are a few reasons: DNA is not a "unique" formulation. It could be comprised of various types of alcohols, with 30-100% concentration. Also different brands and formulations of acrylic (also cast vs. extruded) react differently. If I look at Acrylite FF (extruded) and Acrylite GM (cast) I see that the data sheets tend to give "no resistance" or "limited resistance" designations for ethyl, methyl, and isopropyl alcohol. Since I use mostly Acrylite products I do not use alcohol. Can you get away with a quick wipe of low-concentration alcohol? Maybe . . . but I'd rather not take risks on a finished part.

The edges are much more sensitive than engraved marks. So you might be able to clean an engraved mark as long as the DNA does not contact an edge.

Doug Novic
04-08-2012, 12:12 PM
Do a lot of intricate acrylic work. We use transfer paper for top masking. Immediately after cutting we put them in a bowl of Krud Kutter. Everything lifts off easily and the acrylic comes out shiny.228977

Ric Taylor
04-09-2012, 3:11 PM
That's a very nice ornament. Is it a file that you would be willing to share?