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Can't cut plywood

at first I thought it was the machines limitations but know I think I have messed something up. I have tried cutting two different types Baltic and red oak both 3mm. Settings started at 100% 10mm/sec 30 passes. This would cut about half way through. Then I broke down and upped the laser to 2.2 amps with no visible change in results. I have checked the focus step by step several times and I think the beam is as narrow as possible, the cuts are almost razor thin. I have now wasted 4 boards of each. Any help would be appreciated as I just read a post where Juergen cut 4 mm plywood in 4 passes At 350mm/min which I believe is 5.8mm/sec.

Comments

  • Where did you get the plywood and what type is it? If it's a low grade they will often have knots in the wood(sometimes only in the middle layer) that you won't be able to cut through. If it's a strange type(aircraft, marine, specialty) they can add extra stuff which will make it difficult/dangerous to cut.

    You might want to try first cutting either cardboard or soft non-ply wood to establish a base-line. If those aren't within normal cutting speeds you might want to revisit laser focus.

    http://en.wikipedia.org/wiki/Plywood#Grades
    http://en.wikipedia.org/wiki/Plywood#Types
  • I have been purchasing from a specialty wood shop here in called Exotic Wood ( http://www.exotic-woods.com/index.html ) They have types I have never heard of. My local building suppliers having nothing thinner then 1/4. So the first attempt was on Red Oak I am not sure of the grade but I would guess A/b or A. The second attempt was with Baltic Birch grade B/BB. Both of these were 3mm.

    I can cut paper and card stock easy enough and like I said the lines look tight. Last night I tried again with the CRV file that was left by Dominic for the Melbourne map (Really cool project btw). I used card stock and I basically etched the paper but if I change the settings for two passed it cut it out no problem but left light burning/charring. I figure that could be rectified had I used the same paper as him or changed the settings instead of the quick up the passes fix. Unfortunately I am not home so I couldn't say how thick the stock was which really doesn't help though it is thin enough to go through my printer. I will get that information in a couple of hours.

    I also tried to see how the Phone Stand Business Card stand would cut using 3mm instead of the 2.5mm as his settings should almost, I would think, cut through the wood given that we are both using birch though his is 2.3mm thick. This is after I rechecked the focus which again seems to be pin head size. The results were less then stellar. the notches where the stand hitches to were etched at best. Meaning they looked light brown instead of black as i would expect a real cut to look like. I can upload a picture later.

    I can't imagine it isn't safe to take a picture of the focused laser and upload it as well. I will put it near the notch on the focusing widget to give it a relationship (can't think of the right word atm). I will also go and talk to them about there softest plywood.
  • edited June 2015
    In my experiences plywood takes many more passes than solid wood to cut even when it's high-quality plywood. The 2.3mm birch phone holder business cards I made aren't plywood, they are solid untreated birch.
  • Hi Derrick

    I have made good experience with putting something under the wood at the edges, so there is an airflow possible under the wood. So smoke can get out another way and does not have to go through the laser-module in which it will disturb the laser-beam.

    Just pay attention to cut the inner parts first and the outline of the part as the last cut.

    Dominic
  • Just saw the vacuum like container that was used to house the map making laser. (Sorry to many new names to track). Will build this up this weekend. Currently I have my work sitting on cork but after reading a couple of peoples post looks like I should make something that allows more airflow.

    Gabe thanks for the info I will see if i can source some and try that.

    Below are the pictures the focus one I am including but it didn't photo well it looks like my focus is about 5 times larger then it is in reality. i just thought if some one compared this photo to one taken from their (roughly 2-3 inches) the comparison might tell me about my focus. meaning if they look the same in a picture then I am focused.

    Not going to put the others up as until I try again with better air flow there is really no point.
    focus.jpg 1.4M
  • edited June 2015
    Taking a picture of the dot is hard. The bleed is crazy.

    Here is my best pic of the dot when I VERY first enable the laser through safety glasses(I have two pairs of glasses).
    LaserDot

    I seem to have misplaced my focus tool... oops
  • It is not possible to get an accurate idea of the true focus shape without looking through the safety glasses.

    Derrick's pic should look very similar to Gabe's when photographed through the glasses.

    Light spill makes it too difficult to accurately gauge without the glasses.
  • Hi Derrick,

    I also had problems with cutting through plywood in the beginning. I noticed that the wood layers would cut easily in one pass but the glue layers would take 10 to even make a dent and then afterwards I had lots of charing on the edge. I tried with the G2 lens and it just burnt more. I tried with more amps and still not the effect I was looking for.

    Then I finally found a supplier that sells laser compatible plywood. It uses a light glue in between layers that does not char so easily and cuts fairly well. Now 6mm of ply are as easily cut as the 1.5mm of the standard plywood.

    Regards,

    Arne
  • Hi Arne,

    This is excellent information.

    We have also obtained a small sample pack of laser "approved" plywood from our local Trotec supplier and will be testing it very soon.

    Can you share any more details of the wood name, brand etc so other users can source it for themselves?


  • Ja,
    Here is the website that offered the laser approved plywood:
    http://www.shop-01.de/cgi-bin/sv1/shops/s000778/index.cgi?aktion=artikel&ps=6618&subid=11327
    They do Poplar and Birch.
    The Poplar is tested and the results are already in the spreadsheet.
    https://docs.google.com/spreadsheets/d/1Z5cy-z8XW8XLOGNaC4WRI_AFFluJn5Tk5GJi0e3ocxQ/edit#gid=0
  • Woot! ordering!
  • I ordered this http://www.amazon.com/gp/product/B00IXWKH1Y

    Interesting blog about obtaining laser plywood http://n-e-r-v-o-u-s.com/blog/?p=6042
  • We make our own ply wood by bonding thin laminate sheet oak with diluted PLA glue. Similar glue to Resin W.
    To date I have only considered rotary tool cutting (0.8 - 1.5mm) which is considerably quicker than laser cutting.
    However, most folk here don't have a rotary tool CNC machine, they have a laser cutter/engraver.
    We bought Emblaser for the engraving jobs on our products.
    I now understand why the test patterns I cut didn't burn through. (See my postings in FR V Power).

    View our products at http://belfastbeardcompany.com
  • edited July 2015
    We are testing the Nichia NDB7K75 laser diode. We are pumping 3 amps through it and getting around twice the cutting power than with the standard Emblaser diode.

    Still a way to go with full testing, but it is looking very promising.

    The first drawback with this diode are a slightly increased kerf size (which can be compensated for with cutting). The second is the cost. It's laser unit will be over double the cost of the existing laser unit.

    We are cutting standard hardware store 3mm ply at 400mm/min in 2-3 passes with this diode. This is compared to 8 passes at 400mm/min with the standard diode on the same wood batch.
  • John,

    Cool website and products. Makes me want to grow my beard out!

    The combs you rotary cut have the added benefit of not having the black charred edge that would result with laser cutting.

    Interesting that you laminate your own ply. We really respect companies that make the call that what's out there isn't good enough or suitable and decide to make it themselves.
  • edited July 2015
    I just did a test with some Revell 1/8" (3.1mm) Birch 3 ply with our air assist on our EmBlaser. The laser diode is the stock NDB7875 and the driver is set to the 1.8a default. I set the laser's focal point .05" below the top surface, ran 10PSI air pressure to the air assist and I was able to cut clean through the plywood in 3 passes at 8 IPM (203.2mm/min). I imagine if I pumped more amps to the diode, it would most likely perform and cut better, but I want our laser diode to last a long time.

    The top and bottom surface did not char or even discolor, but the cutting area below the top surface on the sides did darken some, which is to be expected from torching the wood.

    I tested the kerf width by cutting out a .500" (12.7mm) square in two passes at 2 IPM (50.8mm/min) The first pass almost cut all the way through, but with the second pass, the piece just fell out. It measured .494" (12.54mm) across it, so the kerf width is .006" (.1524mm) .
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