Acrylic warping

[dave hensley]

Hi all,

I am working with .125" and .25" cast acrylic. I am cutting out several smaller holes in each piece and then cutting out an outline. Think of a 5"x5" square that then has several .5"x.5" cutouts within it.

I assume that since I am removing so much material, the heat from the lasering process is causing the acrylic to bend slightly so that it comes out bowed. I am using air assist, but was wondering if there are any tricks to prevent this - either during cutting or after. I thought I might be able to heat the piece once it's done and the sandwhich it between some boards to flatten it.

Any ideas?

[David Fairfield]

Its a real problem for me, too. Best solution I've come up with is set up the smaller pieces so they are inside a larger carrier sheet which is clamped down during lasering. Don't cut the small piece entirely out with the laser, leave little tabs holding it to the carrier. Then you can manually cut it loose. Or you can wait a while and run a separate file to cut the tabs, when the material is cool.

If a lot of surface engraving to the acrylic, sometimes it will still curl and sometimes weeks later! ugh

[paul mott]

Sounds like you are not fully supporting the piece when it is being cut perhaps ?

Paul.

[greg lindsey]

Dave, are you using some type of grid system, elevating the material off the table top, if not that may help. Also try cutting back on the power or increasing the speed. Please list what type of equipment you are using in your profile, this helps us to give you better advice when we know what your working with.

[Dee Gallo]

A looong time ago, I read about someone putting it in the freezer to make it really cold before cutting... I wonder if this really works? Or helps?

[dave hensley]

Thanks everyone!

Paul - I am cutting the pieces from 12x24 or 12x12 sheets and have those laying on my cutting table. Shouldn't that be enough support?

Greg - I assume elevating the material would allow airflow thus keeping it cooler?

David and Dee - I'll try both techniques and see how they work.

[Doug Griffith]

How about sequencing the holes so the material has time to cool. After one is cut, jump to the farthest one away and cut that one and so on. Like using a torque wrench on a cylinder head.

[Mike Null]

Chances are that a cutting grid would solve your problem. I suspect the the heat and trapped hot air beneath the work are causing the warpage.

You can get a grid here. and@en-gravs.com This is the email for Adam Desemone.

These are the ones I used to sell so I know they work.

[dave hensley]

Doug - I've not heard of sequencing before. Is that a manual process or something I should be able to do with Corel or my laser? I have a VLS 3.50.

Mike - I assume you meant to provide a link?

[Dan Hintz]

Dave,

Turn off vector sorting, then make sure the order of your vectors in the file is how you want them to cut (use "Move to front/back"). The tab suggestion is a good one.

[Doug Griffith]

Doug - I've not heard of sequencing before. Is that a manual process or something I should be able to do with Corel or my laser? I have a VLS 3.50.

Sequencing is just my jargon for controlling the cut order and direction of vector paths. You'll have to do this manually either using layers, color mapping, or building in the correct sequence from the get go. Oh, and any optimization in the driver should be disabled.

[dave hensley]

Thanks! That makes sense.

[Dick Jordan]

The object cut order can be specified by using the "Object Manager" docker.
When you open this docker, you will see each object listed for each layer.
The cut order is from bottom to top as they are listed within each layer.
Simply drag each object up or down in this listing to establish the order you want them cut.

[Scott Shepherd]

I'll go against the grain here and say none of that will solve your problem. Materials have stress in them. Some have more stress in them than others. Any product that is pushed through rollers or pressed will have stress on the faces of the material. It's an area where the molecules of the materials have been squished against each other (squished- a highly technical, scientific term I picked up along the way).

When it's in it's natural state, the material is fine, but as soon as you break that surface, the warping begins because you've removed a part of the material that had stress in it. The only way I know of to remove the stress is to stress relieve the material prior to cutting it. You heat the material up and all the molecules return to their normal spacing.

This is a very bad problems in materials like brass, so it's a known issues that machinists have dealt with for years.

My bet is if you stress relieved the material and then cut it, it would stay flat. However, I don't believe you'll take raw material like that and end up with a flat product.

I could be wrong, but that's my belief of the problem and solution.

[Michael Kowalczyk]

Or you can go to www.macromonster.com and get "shelbys object & tab creator. That is of coarse if you are using CorelDraw X3 or X4. Can't tell from where I am sitting since you do not have it in your signature. I just bought it last night to have the option when I need it.

Doug, sequencing is not just your jargon. (Sorry didn't mean to bust your bubble) It is used in Artcam Pro and other CAD/CAM programs. I use it all the time so I can control the order in which the parts are cut.