Laser cutting Question

[Robert Bonenfant]

Lowes and Homedepot offer builder grade plywood, great for the every day contractor but not so great for lasers. Also if you check the thickness its not true 1/2" plywood. I would talk to a few lumber yards and see what they have instock and what they can order.
As I stated above, a go to plywood for Lasers and Routers is Baltic Birch - Its offered in a verity of Thicknesses and is available through out the US. We go through pallets of it each month and it always cuts well, We get a few hard spots every so often but what do you expect its from Russian :-)

Monograms are a pain to cut, make sure you cutout the middles first and then make the second order the outside.

[Bert Kemp]

like everyone has said 100 watts is really not enough power for 1/2 inch big box store plywood. this plywood is not designed for lasers. Go online and find some good BB grade baltic birch from Woodworkers source, woodcrafters, Rocklers and try that.
Why does it have to be 1/2 inch? If I were doing that I'd cut 2 pieces from 1/4 and glue them together. JMO

[Bill George]

Could be attributed to being low grade Lowe's plywood?

I would try to switch over to 3/8 and plain wood not plywood if you can. I dont think anything 1/2 inch is going to be something you can realiably do. Like Dave said, its the glue. So many good suggestions here!

[Mike Null]

Read again what Steve says:

As a general rule, you aren’t going to cut 1/2” thick wood with a 100w laser. The focal band of a 2” lens is 1/8”. When you try and cut 1/2”, the beam goes out of focus and the power density drops drastically. The beam diameter exiting is probably .060”-.090” wide.

You need to understand the capabilities of your equipment.

[John Lifer]

I'll speak to the grades of ply. DO NOT by underlayment from ANY of the big box stores. It has very hard and a LOT of glue that is probably an epoxy based. I can cut great and then hit a spot and laser won't even dent it at power needed to cut thru the clean areas. I've found my local HD to have decent Baltic Birch (marked as such) at 3 and 5mm thickness that is flat and easy to cut. Three layers. Thick center ply and two thin veneers. Not 5 layers, nor 3 that are roughly same thickness. Look for thick center and thin surface veneers. Those will cut well and Yes, double to triple the cheap ply costs...... But well worth it.

And Half inch MDF is impossible with my 80watt. Charred Mess. I have a bunch of 6"x96" pieces I create as scrap from my other projects and it just sits. Guess I could engrave rather than cut couldn't I? Anyone have project that uses 6" x MDF in half inch? Just ends up as jigs when I can use it.

[John Blazy]

Lowe's 1/2" ply could be glued with exterior grade glue which resists cutting, might not be tho. Baltic Birch (buy through cabinetmakers supply plywood companies) is generally regarded as best for laser, and some specialty laser grade birch is available.
Although 1/2" is maxing out practicality, just figure in two passes with the laser, and it should be fine, but plan on ordering a mini saw blade for your dremel to cut the uncut areas. I cut 1/4" BB all the time, and have gotten pretty good at cutting the uncut areas with my dremel fitted with a 1" DIA blade.

Now the reason you need to check mirror alignment is this: When the laser cutting head is closest to the laser (usually deep left corner) and say your beam is visually dead center on the mirror, but maybe .030" off center (which you can't tell by eye), then when the laser is cutting close right corner (farthest from actual laser tube), then that .030" is magnified to maybe .120" off center. Hope you get the picture here. My bed is 36 x 48, so alignment is important all across whole bed. So check beam center with tape at all four corners and adjust accordingly.

Another unique issue on large bed lasers is that there is such thing as beam spread. I removed the cover and the first mirror on my laser to shoot it into my shop for cross cutting 4 x 8 sheets of acrylic (long story, mounted a mirror / lens assbly cantilevered off wooden arm - look for my thread on it), and tested the beam DIA across ten ft, then twenty feet, and the spot grew to 1-1/2" DIA at 20 feet. This is why laser mirrors are larger in DIA than the effective beam spot, to catch all the photons when farther away.
When my laser hit the mirror dead center on my cantilevered arm, the whole black housing got really hot, proving that residual beam spread photons were hitting the mirror mount armature.