Acrylic Haze

[Linda Creatore]

Hi Folks,

Hope someone can help me out here. I tried to find this in the forum, but no luck...am sure I'm probably just missing it. So please forgive if this has been asked before:rolleyes:

1) I just cut some 1/4" acrylic. I am getting a haze developing on the uncut/unrastered areas. It doesn't come off...I'm thinking it is caused by heat.

I am using a Epilog 45w 24tt; running at recommended settings of:
cutting at 12speed/100power/4500ppi
raster at 100speed/60power/600dpi
air assist used in both vector and raster

Should I be using air assist with raster as well as vector?

Usually takes two passes to cut through...I think that's pretty good?

2) Also, any suggestions on the best acrylic to use? Cast or extruded? I know one is supposed to be better for vectoring and the other better for rastering, but I can't seem to keep them straight:D Can most acrylics be used in laser? Are there any brands, etc. that should be avoided?

3) What about cutting mirrored acrylic....any problem here with reflection back into the optics?

4) How about cleaning up the acrylic/polishing it? Has anyone tried the Novus Polish (?) (I think that's the right name:rolleyes: ) Or is there anything cheaper that would be good?

5) I know I read in one of the posts about having to be careful about the protective covering containing PVC!!! How are we supposed to know if the cover contains PVC?

6) Does anyone know if typical sandblast mask contains PVC. I have some of the green and the white sandblast vinyl, and some thicker rubber mask, as well as clear vinyl mask. I was thinking of using them mask for color fill work on pieces (since my compressor is on the fritz and won't be putting out the big bucks anytime soon....thought I might be able to use my mask in the laser)

Okay, I'm done....for now!:) :rolleyes: :D

I thank all of you ahead of time for any help....thanks!

Linda

[James Stokes]

The haze is caused by the smoke coming off the acrylic, leave the paper backing on when cutting will stop this.

PPI is to high use half that. Leave the air assist off on raster, less clean-up.
Cast works better for rastering, extruded works better for cutting.
No chance of problem cutting the mirror acrylic,non issue.
For cleaning Novus polish is the only way to go.
Some sandblast stencil is made with pvc. Hartco is one that is. Anchor and 3m are not. Most vinyl sign matierial is pvc.

[Rodne Gold]

You should use air assist at all times barring when it might make stuff float away (like cutting small pieces of paper), it removes lasered by products and does a lot more besides.
2 Passes to cut 1/4" is a problem , yoo will have endless hassles doing a 2 pass cut as the melt that is produced with the first cut resolidifies and has no where to go anyway. The second cut will compound the haze problem and you will end up with a far messier cut than a single pass , we cut 8mm and 10mm with a 30 watt laser , 1/4" is only 6mm. Focus on the surface of 6mm and then raise the table about a 1/3rd of the pex thickness for a better cut - dont do this for engraving. Large solid areas of engraving will actually benefit by a small amount of defocussing the beam as you will get a smoother surface , you can drop dpi to 300 for this to make it take about 1/2 the time , but you will have to increase power to get the same depth as if you were using 600 dpi.

Cast acrylic is less stressed than extruded but will be very bad in terms of thickness tolerance , it "frosts" better than extruded. Extruded deep engraves better (cleare - a lot better for reverse paint fills) and cuts with a slightly more polished edge , its cheaper , its incredibly stressed and it is uniform in thickness. The laser stresses acrylic badly , clean it with meths or a solvent and you WILL have stress cracks appearing - soapy water is fine generally , hot soapy water , naptha does work (zippo lighter fluid) as does benziene - but neither are safe and benziene is carcinogenic. You can use a plastic polish too - like novus
Cut mirror from the back side of the mirror , engrave it in reverse that way too. No danger of any reflection. Be aware some mirror is extruded and is generally even more stressed than plain extruded. Shiny gold and silver vinyl which is generally polyester vinyl is safe to use , but then so is paper based self adhesive vinyl application tape which is cheaper and far easier to remove (just wet it and it rolls off)
DO NOT FILL acrylic with solvent based paints , you WILL have problems especially if reverse filled - the acrylic WILL stress crack.
You would only cut acrylic with the protective layer - you would not engrave it and even if it does have PVC , you will have no problems as there is so little chlorine etc released it wont or shouldnt matter if you do it now and again.
To see whether acrylic is extruded or cast , light a small piece , cast wont drip molten flaming balls and it burns with a smokey and crackly flame , extruded burns silently and drips.

[Linda Creatore]

Hi,

Thank you both for the replies! Great info...this will really help!!

Rodne, in one of your other posts, you mention using gilding wax to fill acrylic. I have a lot of Gilder's Paste, so I think that is what you are talking about? Then you say to clean up excess with turpentine. Isn't turpentine a solvent...and will cause stress cracks? I know it's not going to be put directly on the filled area (chuckle) but I'm assuming at least a smidgen will get in there. This isn't a problem?

What is perspex? where can I get a bender?

Can you recommend a source for 1mm UHI and for mylar vinyl "(the shiny gold or silver - no need to use expensive "laser" vinyl)" and paper based vinyl application tape?

Again, thanks so much! I am sure I'll have more questions...this forum is GREAT!

Linda

[Rodne Gold]

Turps is not the same type of volatile solvent as thinners , methyl alcohol . acetone etc , the paste is wax based and the turps disolves it.
Perspex is the brand name for acrylic
Benders should be available from suppliers of plastic fabricating machinery or from the supplier of your acrylic , search for acrylic line bender or the like on google , Im not in America , so dont know the suppliers there. 1mm UHI or the like should also be avaialble from acrylic or plastic suppliers

The vinyl stuff is available from tons of places , go to your local sign shop to find out where they get theirs or just beg a few pieces from them.

[Linda Creatore]

Thanks Rodne, I'll check out those places!
Take care,
Linda

[Kate Raap]

For cutting 1/4" acrylic on the laser I always put masking on the bottom side and use a spray water bottle to wet it down. This gives it a very clean edge, clean cut and no haze. The mask that I use is just the thin paper mask that is used on vinyls. To clean the edges I use Novus and an old clean t-shirt (as someone else mentioned.) I like the Acrylite acrylic. Seems to laser the best for me. I can't remember the maker off the top of my head, but at there website they have a sample pack you can request. It's called a magik pack or something like that. All the acrylic is laser cut and they have some great stuff to check out in there.