Darkly Labs Community

Any idea what I'm doing wrong?

Hi everybody, 

I just finished cutting my first complicated project, and it failed pretty miserably after about 10 hours of cutting. I’ve attached some pics below. It’s a picture frame with lots of silly cutouts. 

Top:

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bottom:

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You can see it cut through a couple places in the middle (two small pieces fell out), but mostly just scored through to the bottom here and there.

The material is 6-mm Baltic birch ply, cut 7 passes at 100%, pass depth of 1 mm, starting at 18 mm (6 mm material, 2 mm glass, 10 mm cutting mat) at 100 mm/min with air assist. Each pass took about 1.5 hours, and I ran them two at a time over three days, cleaning the lens after every 2 passes, and lowering the start height to match the progressive pass depth (i.e., two passes at 18 mm, two at 16, two at 14, one at 13). 

Any idea what I did wrong here or how to improve? Is this just the way it is with plywood, or am I getting the height or something else wrong? 

Thanks for any advice you can offer! 

Is it laser friendly ply? You’ll find lots of comments here about the difficulties of cutting plywood, usually due to trying to cut standard hardware shop ply. The adhesive layers can form a barrier to the laser beam, especially the marine quality ply. I tried one attempt  at cutting ‘expensive’ 6mm Bunnings ply, and it caught fire! Scary.

If you are in Australia, the ply from balsacentral.com.au is decent. Theres also plyco in Melbourne. Their laser ply range is pretty much in the same price range  as Bunnings evil plywood.

The other possibility is that your ply was slightly bowed or not flat, this will affect the beams focus and therefore cutting power too.

There’s possibly other reasons for not cutting right through, but these are the first two I’d be suspecting. Especially the plywood quality. I can cut clean  through 4mm balsacentral plywood using the same settings that won’t completely cut through Bunnings 2.7mm ply…

 

In addition to all the valid points that Chris raised, its possible that 6mm ply is on the edge of  the capability of the laser.

Since its ply anyway, I’d be considering doing it in 2 layers of either 3mm or 4mm ply. The total cutting time would be quicker and if its your own design it would be possible to stagger the positions where the two halves join up, giving you a stronger final result.

Hi Chris and Daryl, 

Thanks for the advice! I’ve had better luck with 3 mm, so layering may indeed be the way to go. The 6 mm sheet does seem to have a very slight bow, which I didn’t notice before and which could explain why the center was almost cut through but the edges were barely halfway cut. Some people in another part of the forum were using magnets to pull the sheet flat; I may give that a try and stick to thinner material. 

I’m not sure whether this ply is considered laser friendly, but I’ve read others having success with Baltic birch. I’m in the States (Austin, TX), and the wood is from Woodcraft, our main chain of woodworking stores. I went with the 6 mm because they didn’t have large enough sheets in 3 mm (they only had 300 x 300 mm), and I was hoping to cut this out of as few sheets as possible to avoid visible joints (and out of laziness), but that’s probably not be the best approach. I have some nice aromatic cedar (wth red streaks in the grain) that might be a more aestheticly pleasing fix anyway and may be easier to cut, but I’ve been hesitant to use the nice stuff until I know more what I’m doing! 

Thanks again for the responses! 

Laser cutting is a bit of a black art, if you want to cut say a 2.5mm deep slot in a piece of timber, then with a circular saw table or a router, you can set your tool height precisely and you’ll get that depth

. With a laser though its dependent on the material, the laser strength, the feed rate… you really do need to accept that you will waste a fair bit of practice materials before you find the ideal settings. And then once you’ve done that, you put in the good quality stuff that you want to use, and you find that those settings don’t work on that material and you have another piece of waste!

If you are working with a material such as card or thin ply then you will  have a wider leeway with the settings you use, its the thicker and denser stuff that is pushing the limit, and so is prone to more slight imperfections in material density, quality or thickness and so therefore  relies on more in depth experimentation.

Eventually though it all comes good…

Ha! Thanks, Chris! I don’t mind the trial and error, but it’s good to have some more experienced feedback to streamline how I tinker. I tried out the cedar this morning just to see how a solid wood differs from the ply, and holy lasers, batman! It cuts like butter and smells amazing (forgot to route the hose out the window for the first pass!). 7 mm thick in 3 passes at 300 mm/min.

I’m going to rework the frame file to cut on a narrow sheet instead of a huge one and use this (or a thinner strip) instead. 

As you have discovered Nathan, solid wood cuts much better than ply, generally.  I have been “playing” with the Emblasers for some time and work pretty much all with wood.  I have discovered that some timbers just wont cut no matter how many passes.   Cedar is probably my favourite for ease of cutting and I think softwoods do cut better.

I engraved and cut some drink coasters in cedar - see below.

 

 

Hi Daryl, what settings are you using for Cedar and specifically for that coaster, what was the thickness of the wood? Looks great and I’ve been thinking about what material to make coaster from.

Hi Richard,

I think the Cedar was 3 - 4mm thick. You will find Cedar cuts quite nicely and I think I’ve cut up to 5mm.  If you use engrave settings of 800mm/min at 30% power  and 300mm/min 100% 4 passes for cutting this will give you a pretty good ball park figure.  With all engraving on timber, for optimum results, post cleaning up the work with 320 grit sand paper will give optimum results.

Oh I also made a box for the coasters out of the cedar.

Thanks Daryl, appreciate the info.