Cutting 1/4" Acrylic tricks?

[donald bugansky]

Ok, You all have convinced me to toss the Lexan. I went to home improvement and purchased some 1/4" acrylic.

Are there any tricks to cut it cleanly without any stress cracks? I cut out "BELIEVE" and used some brake fluid (a local trophy shop guy told me he uses brake fluid for acrylic) to clean up the "stuff" left after the cut.

An hour later, I looked at it and it had stress cracks at the 90 degree intersections. I searched the forum and found Rodne's post on "Tips & ideas for lasers" (http://www.sawmillcreek.org/showthread.php?t=22369&highlight=stress+cracks) He mentions solvents can cause stress cracks.

Can you share the techniques you use to cut 1/4" acrylic?

Thanks

[Gary Hair]

1st tip - don't use brake fluid.

2nd tip - use acrylic cleaner

3rd tip - anything with solvent of any kind will cause crazing or cracking when you laser cut acrylic.

Gary

[Joe Pelonio]

Brake fluid??:eek:

Any solvent will do that to the edges. I never found a reason to use anything on the edges, they come out smooth and clean. I would leave the paper on, or replace it with transfer tape for easier removal, but with or without it the edges are always fine. If you do want to clean them for some reason use some inert product like window cleaner that doesn't contain ammonia.

if he uses brake fluid without the cracks, it must be some new kind, but that stuff is very corrosive, and will remove paint.

[Rodne Gold]

If you use cast and not extruded acrylic , your incidence of stress cracking will be vastly reduced.
Warm soapy water is the best cleaner of acrylic.
If you are getting melt mess , something is not right with your air assist or your way of supporting the piece or you are stripping the protective covering before cutting..the melt should eject right thru the cut.
I can tell you this , that doing a 2 pass cut is a bad idea as in the first place you wont get melt ejection and in the 2nd place you put too much heat into the perspex leading to extreme stress and often warping.

[Lee DeRaud]

Probably doesn't hurt to put a small radius on inside corners also.

[Dan Hintz]

a local trophy shop guy told me he uses brake fluid for acrylic
Two possibilities:
1) He uses it on items that were cast into the desired shape.
2) He was trying his best to prevent you from becoming competition.

Use the effect to your advantage :)

[Joe Pelonio]

You can use solvents and possibly even brake fluid on the face of acrylic, it's only the cut edge that's an issue. The heat from the laser (or flame polishing)
changes the molecular structure to make it vulnerable to the solvents.

[Martin Boekers]

Sometimes, the stress cracks won't show up for awhile, It's good they did in your case instead of weeks later in the client's hands.

Like the others said "no solvents"


Marty

[Gary Hair]

You can use solvents and possibly even brake fluid on the face of acrylic, it's only the cut edge that's an issue. The heat from the laser (or flame polishing)
changes the molecular structure to make it vulnerable to the solvents.

Not exactly. The heat from the laser, or flame polishing, tempers the acrylic and the solvent simply accelerates the crazing. The only ways to eliminate this altogether is to anneal the acrylic or use a non-solvent based cleaner.

Gary

[Andy Joe]

wow, i have never seen that before, i just run my edges real slow, with very low air pressure at nozzle and lifted of table to prevent laser beam from bouncing back up and i get smooth, clean, see through lines. Im glade i came across this post however, i have never heard anything about solvents or stress cracks, i dont even clean my acrylic before running. Maybe its time to start

[donald bugansky]

Anyone want to buy "slightly used" 32oz bottle of brake fluid?

I've got the message...toss the brake fluid.

I really like the suggestion of FIRE in another post.


Merry Christmas to all!

[Rodne Gold]

Fire is merely added heat and will make the stuff crack even more - apart from being an issue if you actually have a mixed engraving /cutting application having to avoid the engraving or possibly warping thin substrates.
The first place to start is to minimise and or eliminate the need for any cleanup and I firmly believe that air assist , elevation and protective coverings should allow you to laser and ship without intervention.

[Lee DeRaud]

The only ways to eliminate this altogether is to anneal the acrylic...Annealing is just heating followed by a controlled cool-down, right?

What kind of temperatures are required for acrylic? Is this something we can macgyver with a regular oven?

[Rodne Gold]

You can use a regular oven tho a thermofan is best , cast is 80c and an hour for every mm of thickness , extruded needs 70c and the same - 1 hour per mm thickness.
Air cool after