[namara]

Hi,

I am new to using bamboo plywood-- see attached images,

Attachment 195880

Attachment 195882

does anyone with knowledge about bamboo plywood know what the cause may be?,and how to prevent it?,

bamboo goes through a unique process to become plywood,gluing with the grain with the stalks laid out side by side,

I have heard of the possibility of there being air pockets which I thought was the problem at first

but then unlike with the rest of the cut area,the laser did not go through to the reverse over the charred areas!,

so now I'm thinking the charred areas are where the wood is harder for some reason and as I had the power up high at

low speed this result occurred,

thanks in advance,

Graham,

[Exsecratio]

Hiya Graham,

That's fill splash, it happens on regular plywood where voids are filled with a resin based filler (that is almost impossible to cut). The beam burns through the surface wood then hits a "hard spot" in the core with the pictured result.

No way round it sadly other than buying high grade materials and even then few if any suppliers rate the core of ply.

cheers

Dave

[namara]

Dave,

thanks for your reply, it's good to know what was happening,

Graham,

[herby08]

that's solved it was the focal length. some material need to have for cutting a different focal length as the lens normally has. in this case it is 49.3mm instead of 50.8mm
greetings
waltfl

[namara]

Yes Walt is right,
it turned out to be simply that the bamboo was too far from the laser,
Graham,

[namara]

there was more to the problem;

warning for anyone who also has this nozzle;

Attachment 196364

Attachment 196366

it is not suitable for thick pieces,-as it is blowing air directly down the cut, fanning the heat
that could cause charring,as was the case here,

this would not happen with an outside nozzle;

Attachment 196376

Graham,

[ozstockman]

I believe it has nothing to do with your lens or air assist. It seems you have this problem because you use cutting table with big solid areas made of metal. The beam needs some room under material but in your case when it is not going through the holes of your table it is reflected and goes the other direction, hits material from the bottom and generates of lot of extra heat.

[herby08]

yes you are right too, I am using 5mm SS rods and this gives clean cuts see picture. but the air assist and the right focal length are very important too.
there are always many factor counting. but the cone air assist blows the air around inside the lens housing and mess the lens up and if the other factor not right brings the charring too
greetings
walt

[ozstockman]

Hi Walt,

I have two machines with air supplied through the nozzle so it is pretty common to supply air straight to where the cut is. I have never had any problems with it and I cut a lot of MDF up to 18mm thick. In fact it even cuts faster if you have pressured air supplied this way. So based on my experience I would eliminate air nozzle problem.

Re the lens, if you can cut clean at one place and you cannot cut through with a lot of charing at the other place which is right next to excellent cutting spot I would not think of lens problem too. Unless your beam is not aligned or you have some problems with rails(may be some dirt stuck to it) or there is a dirty spot on your lens itslef. But these problems can exist just all together.
It can be also that the beam is not aligned and it hits the nozzle inside at some position on the table. If nozzle is made of metal and they usually all are the beam is being reflected for the inside nozzle wall. Sometimes it makes kerf thicker, sometimes it makes a ghost cutting line but it looses power and it looks similar to what you had.

The best way to check if that's the table problem is to raise your material 5-10mm above your table and try to cut the same job. If you do not have the same problem at the same place that for sure is caused by beam reflection.

[herby08]

hi
if you can cut 18mm MDF you have a bigger machine with a completely different setup and equipment ( bigger compressor, rails etc.) what is a totally other story.
what is here are the small K40W machines from china.
but I know from quite a few guys who wrote in the groups that they have the same problem with the nozzle type and even epilog machines come with the outside nozzle
you know we are talking about 1K machines not 10K
greetings
waltfl

[namara]

thanks for the input on your experience with the air assist nozzle ozstockman,
all I can say is that after making an outside air assist which has been blowing 50 psi the same problem has been encountered,
but I agree with Walt that the nozzle could be troublesome, but does not seem to be the cause of the charring,
there is nothing under the material,I have been using rails and the beam has been aligned when I was using the nozzle,
I tried the air at 80 psi and there was no charring but the pressure cracked the bamboo,as you can see could happen with the design,
the engraver is 40W to cut through this 5mm bamboo the settings were 60 power and 3 secs with 2 passes,
but going faster does not seem to prevent the risk of charring,
It is single ply as opposed to 3 ply bamboo so it could be an issue with the structure of the wood, I know its very hot after cutting,
I am going to try using the nozzle again with 50 psi and contradict what I said before that the air blowing directly downwards could be the problem,
it may be the solution with the increase in air pressure which I wasn't using originally,

[Exsecratio]

It's splash

Look at the wood grain

Look at the direction of the bad cut areas

Notice how the height of the burn is the same in one axis and is aligned in the other axis.

The only common denominator is the wood backscatter doesn't cause surface burning, it burns the underside of the wood not the top.

cheers

Dave

[Desmobabe900]

Hi, could you tell me what the wattage of your laser is to cut 18mm mdf also what power do you use? I have a 180 watt cutter and it struggles to cut 10mm moisture resistant mdf at 99.9% power. Many thanks desmobabe900

[Exsecratio]

Try Medite MDF, MR MDF contains formaldehyde resins and is a pain to cut.

cheers

Dave

[ozstockman]

I can cut through 18mm plain MDF on a 280W laser only. It uses 2 x 140W GSI DC tubes. I have never tried 18mm MR MDF but 15mm thick MR MDF does not seem to be a problem for the 280W laser.
The setting for 18mm thick MDF on the 280W laser are 480mm/m speed and 90% of power.

My other laser with a 100W firestar tube laser can do 9mm thick plain MDF at about 400-500mm/m and 100% of power. Sorry I cannot tell exactly what speed is because my LaserPro Spirit GX which uses 100W firestar does not show actual speed, just percentage of maximum. It's 1% for speed and 100% of power.

[namara]

all I can say is if anyone is considering using bamboo plywood make sure to use 3 ply or more,
after many attempts cutting on two separate sheets of 5 mm single ply the charring kept happening,
it is occurring on particular 5 mm wide stems that run the length of the sheet that are much harder,
it is not because of glue for mending cracks or wood filler,