Does dropping the z depth on every pass actually make any difference

I have tried both options, 1.5mm thick, 15 passes no drop in z directions, also tried 15 passes 0.1mm drop every pass, cant make my mind up if it makes any difference.

Depends on your machine and or your focal length. Can’t say on a diode laser, but for CO2 it absolutely DOESN’T work for shorter focal length lens’. The sharper angle of the beam deflection makes the beam cone hit the side of the cut as you lower the beam into the work.

Thanks for the explanation, i am not convinced it makes any difference, and what you say makes sense

A longer focal length lens, say 4", has a narrower cone. Dropping the focal point on subsequent passes might gain you a little, but only until you start clipping the edges of your previous cut. The wide cone of a short focal length lens, say 1.5", will clip very quickly. If not the first drop, for sure on the next one.

Dave,
Yet again thanks for a very useful explanation, to be honest i did not think it was making much difference if any, i have tried using the focal test in LB but not had much success with it.
Certainly does not seem to cut plywood very well.
What is the best wood for cutting, i have read solid woods with close grain are better, like balsa and basswood, have also seen cherry, i am making cases for electronic projects so not that bothered what it looks like, can paint or stain, currently using 1.5mm plywood and laminating (gluing) them together, to make 3mm thick which is strong enough.
I have tried expensive “laser” plywood but does not seem to make much difference from standard plywood. From what i have read its the glue between the layers that the laser does not like.

Thanks again

Well, that would depend on your machine. First off, what kind / power laser is a Pro 3018? I gather it’s a diode laser. My knowledge is with an 80W CO2 laser so I don’t know how much help I can be. I have a VERY limited knowledge of the diode laser beam shape and lens system.

For me, unless I’m cutting my Premium MDF, soft woods like clear pine cut best. The lower the moisture and oil content the better.

‘Laser ply’ is what we in the trade call ‘solid core’ - two thin veneer faces on a core of MDF. MDF, due to it’s solid nature with the binders and high pressure that are used to make it is harder to cut than an equivalent thickness of timber. But, it’s predictable, repeatable and consistent, which is why it’s used.

It’s more expensive than equivalent thickness of ply because more processing is needed to make it.

Plywood comes in all sorts of grades and all sorts of glues are used to make it.

AA grade with an acrylic or phenolic glue is what is known as WBP (Weather and Boil Proof) and is clear of voids inside the plies - which is what you get with cheap ply and which can fill with glue and makes it very hard to cut. ‘Marine ply’ is made with high-grade veneers and phenolic glues - you gain on the lack of voids and the quality of the veneer, but phenolic glue is hard to cut.

For general purpose I use AA or AB baltic birch ply with a poplar core. Poplar cuts easily - it will catch fire with a laser - and the birch has a tight grain and is very ‘clear’, so not too much visible grain, no knots, etc.

If you are making something that is going to be viewed from both sides, you pretty much have to use AA. If it’s a one-face object, you can get away with AB or AC grade, which will have a good fine-grained face and a poplar or asian hardwood core and back side. I use a lot of that for signage, as it makes things like walnut and cherry and exotic hardwoods affordable.

As a comparison (NZ$, so the numbers won’t be relevant, but the ratio will) AC walnut I get for $52 a 8x4 sheet, where an AA sheet of walnut is nearly $180.

Solid timber is easier to cut, in theory, but less consistent and predictable. You have to cope with bowing and cupping, that you don’t with sheet goods. Less of a problem with small pieces than larger items like signs. I make earrings and buttons and such from 2,4mm walnut and back it on to ‘cover sheets’ - 1,5mm mdf used to protect pallets of plywood and MDF. I get them for free from my local timber merchant as once they unpack the pallet, it becomes rubbish that they need to dispose of. I back the walnut because it will easily split down the grain if it isn’t laminated. Effectively hand-making 2 ply.

If you bought a diode to cut wood, you bought the wrong tool. It does a great job of engraving, but I would use the spindle on your 3018 and cut it with a bit. If you really want to cut, you absolutely need to add air-assist. It will reduce the time to cut, significantly, and will give a better quality of cut. For a diode, a piece of metal brake line is a good nozzle - you can shape it and it’s easy to join with 3mm ID tubing.

I could go on for ages about wood - and in particular, ply. Where I live is rural and we have a lot of timber merchants and wood processing plants, so I have been able to pick the brains of the specialists. I would always recommend a proper timber merchant over a hardware place or online.

I keep them sweet with things like coaster, small signs, etc. and they treat me right. I get the same prices as bigger customers like builders and furniture makers.

If you have any specific questions about types of timber, I’m happy to help. There’s a great website with almost every species of timber, it’s characteristics, etc. - well worth a look.

https://www.wood-database.com

Wow,

Thank you so much for such a comprehensive reply, i agree about cutting using the cnc spindle, but i had problems with the software re programs / rewrites the firmware when i connect to the controller, took me ages to figure that out, i have to download GRBL firmware onto my controller when i switch to the laser software and change the spindle for the diode laser, which is why i was trying to cut with the laser, not the spindle, plus the laser is quiter and less messy, using it in a spare room in the house, so the wife complains about the mess and noise when i use the Milling spindle.
I am gettting very good results with 3mm plywood for strength, glueing 2 off 1.5mm sheets back to back, with about 15 passes on each sheet, takes hours to cut out, miniutes with the spindle.
i am adding an air assist, got the pipework , just need to figure out what sort of pressure is required, i have an airbrush compressor and a pump for inflating paddling pools, going to experiment with them, or i could buy a small compressor, but dont know what psi is best.

Airbrush pumps aren’t rated for continuous use - it will burn out/seize.

A 300-600L fishtank pump will work well for your setup. Vivosun is a decent Chinese brand.

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