REDUCING BURN MARKS ON WOOD

[namara]

HI,

I am looking for ideas on how to reduce burn marks on birch plywood,
during cutting a flame appears which is pulled by the air extractor leaving
burn marks on the wood.
Lowering the current or increasing the speed prevents a flame from appearing but then the laser is not strong enough to cut properly.

i integrated a tube taped to the air outlet on one end with the other end on
the opposite side of engraving space facing the outlet.
i thought this would make the flame stand up and not be pulled in one direction,but the tubing outlet had no effect.

im wondering if some sort of tape over the wood might work or even lightly wetting the wood!!,?,

[Melody-gweike]

HI, Namara,

You can try changing to a larger power air compression.

Melody

[Gary Cooper]

hi there we are having the same problem with birch plywood in 1.5 3,4,6mm thickness it is getting a flame and the char and burn marks are bad we have a 100w reci laser and have tried various speed and power settings

but for the 4,6mm ply we have had to use speed of 6 and power 95/100 and for the 6mm we have had to drop to a speed of 3 and same power to cut but leaves the edges very chared and but which leaves the project unsellable

so really need some help with some solutions to the problem as trying to make 3d puzzles/models and at the moment cannot sell them to anyone...

any good solution would be great

cheers

gary

[herby08]

Hi gary
pretty unusale with 100W that you have to go so high with power I use a 40W CO2 tube and can cut 4mm bamboo with 80% power and 5mm/s speed.
do you use air assist? very importand for cutting woodto avoid excessiv flame!
now you are sure your mirrors are all adjusted right ( beam center)
do you have the right distance between the wood and the head lense.
greetings
walt

hi there we are having the same problem with birch plywood in 1.5 3,4,6mm thickness it is getting a flame and the char and burn marks are bad we have a 100w reci laser and have tried various speed and power settings

but for the 4,6mm ply we have had to use speed of 6 and power 95/100 and for the 6mm we have had to drop to a speed of 3 and same power to cut but leaves the edges very chared and but which leaves the project unsellable

so really need some help with some solutions to the problem as trying to make 3d puzzles/models and at the moment cannot sell them to anyone...

any good solution would be great

cheers

gary

[epilotdk]

Gary, what kind of ply are you using? Some types will char and flame regardless of what you do because of the glue used. It has to be proper laser grade plywood.

[Gary Cooper]

hi there we are using birch plywood BB grade the 1.5mm seems to cut ok at speed 30 power 65/70 but the 4 and 6 mm it is charing and burning and when done and you touch it get all over your hands and then in turn get on surface and cannot get it off and to be honest i thought the 100w reci would eat through it like butter.

but as described in previous post have to slow it right down to speed 3 on 6mm power 95/100 to just cut through it

smiliar with the 4mm just having a nightmare with it at the moment and feel like sending the laser back to be honest....

the mdf is a bit better 9mm we can cut @ 13 speed but once again full power

we are making sure the lens are clean and focus we are using a 53 lens which was supplied with the laser as was told this was a mid range to engrave and cut most things.....

we also have air assist that come with the machine so really confused... as when they are selling the machines they give the hype that it will cut through most things i.e 20mm acrylic 10mm MDF etc etc also have aindustrial water cooler on the 100w reci laser tube....

but to be making such a mess of thin stuff like 4mm & birch plywood... it does the acrylics and hardboard etc very well....

so if anyone can help would be great

[Gary Cooper]

Also just to add to the post we have a 1200x900 bed and top left corner where the laser is strongest we can cut the 4mm @speed 15 power 95/100 at the bottom right had corner where the beam has to travel the longest we are down to speed 5/6 same power....

now i understand the phyhics of a light beam but we are losing nearly 50 or 60% of the power that does not seem right to me....

example if we was cutting a job the size of the bed at 15 by the time it got to the other corner the job would not be cut on that side and if we use the lowest settings it will burn the job at the top left far too much

i would of thought that if you make a bed size that big the laser should be able to cut the whole job. i know we would lose a little power as the beam is travels to the longest point but not that much surely......

[Exsecratio]

Hiya Gaz,

If it's B&Q type ply (BB) then its going to be close to useless, it has a mineral type glue that will flame and scorch no matter what you do. Hindleys do decent ply but if you need bigger sheets drop me a direct line and I'll send you a list of UK suppliers.

Air assist is *god* of wood cutting, loads of clean, dry air...a routine 15 psi is good, 20psi is better but that will mean a good quality compressor is required.

Piston direct drive compressors are pointless, not only are the noise levels above what the HSE will allow (by a big margin) but they will also burn out, something like a belt drive 3hp twin cylinder is great, or a Clarke SSHHH or Bambi if you need things to be extra quiet.

The cutting issue could be down to an out of level table, check the drop from the gantry to the bed all over the face of the table , more than 0.5mm and you will have trouble.

best wishes

Dave

[Gary Cooper]

i there dave i bought it from a proper timber merchants so it is not from B&Q not saying that it is any different but i did tell them what i was doing with it and they gave me prices for the a/ab and bb grades... so i thought it was ok.... as for the air assist i must admit it is just like a little pump that come with it nothing like you are talking about maybe have to look into that but would it give me much better results and would i still have to sort laser plywood rather than birch plywood... also we have had them down as the table was 2/3 mm out and they sorted that...

could you please give us the supplier you use for the wood
many thanks

[Exsecratio]

Hiya Gaz,

Try Totton Timber or DH Timber and ask for laser grade (Low formaldehyde)

Hindleys Ltd
908 Ltd
Hobarts

all do good grade laser Ply,
where abouts are you in the UK, if your close enough drop by and I can show you what set up I'm using, on ply on my 80 watt it runs at 26mm PS on 4mm with little or no staining, zero flame and a light brown cut edge.

best wishes

Dave

[70cyclone]

About the only use for the air pumps that come with most of these lasers is to add air bubbles to your fish tank. I have my lasers plumbed into my shop air and can adjust the flow for any application.
Table level is very important for a bed of that size otherwise your focus is all over the place. You should see very little if any attenuation from on corner to the next if the system is properly aligned and focused.
Another issue usually overlooked is the smoke/debris plume. You do not want the plume to just float up into the beam path, any particles in the beam path will reduce power. I have added fans and such to force the plume back and down to the exhaust so it does not interfere with the beam path.

[Gary Cooper]

could you send some photos of your set-up just to get an idean of where the fans are etc and also what air pressureare you using and is that accross the board with all materials or do you have to adjust everytime...

many thanks

Gary