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Laser cutting but taking many passes

I recently got my 4w Emblaser A3 and got it up and running pretty easily.

The main thing I want to cut is 1/8"(3mm) plywood, 3-ply Baltic Birch currently.

I can cut it but I am needing 8 passes at 500mm/minute to make cut all the way through consistently, and even then there are a couple of places where it doesn't go all the way through.

I have tried refocusing many times, I tried changing up the # of passes and feedrate but I still seem to need 8.

I am attaching the bottom side of some test circles.

Can anyone tell if it just seems to be a focus problem or if there's anything else I might be missing?

The power is set to 3 amps.

Indications from Darkly were that they were able to cut a similar material in 3-4 passes.

Comments

  • edited December 2015
    Adam,

    Have you increased the maximum current setting on the Emblaser board?

    They type of ply wood you are using will make a very big difference. The combinations of wood types and adhesive affect cutting ability.


    We use a high quality ply which we purchase locally and found to work very well. Some people use 'laser friendly' plywood.

  • Yes, I set the maximum current to the maximum, 3 amps which I read was safe with the 4w laser.

    This is the plywood I'm using, it is advertised as great for laser cutting:

    http://www.amazon.com/gp/product/B013NT3OAC?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00
  • Can you please try a test cut with a feedrate of 350mm/min and 4 passes.

    Depending on the wood we usually work around 350-400mm/min for ply.

    We have been using 2.5mm ply recently because it cuts more easily and can be doubled up to create 5mm ply after cut.
  • I will give that a try and upload a picture tomorrow.

    I am having trouble finding 2.5mm (or 3/32" plywood) for sale online. Does anyone have any suggestions for the USA? Where do people buy theirs?
  • I tried some tests at 350mm/min at different numbers of passes.

    In the first picture below, in the top row of circles, from right to left they are 4, 5, 6, 7, 8 passes.

    You can see that 6, 7 and 8 all cut through.

    The second picture is me trying to cut out something larger at 8 passes and you can see the results. It is spotty.
  • Adam,

    We were experiencing things like this with the variation in plywood we were purchasing. Even things such as moisture content would cause a difference in the cutting ability of the laser.

    By going to 2.5mm we started getting very consistent results.

    That saving of 0.5mm in material made all the difference.

    Perhaps you may have more luck with 3/32" ply. This is close to 2.5mm and could possibly be sources from hobby aircraft supplier / stores.
  • I looked for 3/32" plywood and I can only find it through aircraft suppliers and it is about 12x as expensive, which is unfortunate.

    I did notice that the wood was bowing and that seemed to contribute to the ability to cut. Could you show your solution for holding materials flat?

    I also ordered aluminium honeycomb for under the material to see if that helps.
  • Adam, The ply bows due to changes in ambient Relative Humidity. It takes on and sheds moisture all the time according to local RH%. As the ply is being cut, it will dry the moisture content in the ply causing it to bow. My current solution - I have a piece of 18mm MDF cut to a larger area than the image area of the Emblaser. On this I have screwed in a grid of button head screws. This allows the ply to sit above the MDF surface on the screw heads. I then cut my ply all to the same size, again larger than the image area of the Emblaser. The ply is then held down with button head screws around its perimeter. This is a solution that I'm finally happy with.
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