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Allan Wright
08-11-2007, 9:03 PM
OK, up to now I've been mostly engraving and cutting thin (1/16, 1/32) balsa and plywood. Today I started trying 3/16" balsa. Some pieces came out great, some under cut and some over burned on the back of the piece.

Due to the highly variable nature of the density of balsa, I even had some boards not fully cut in one area, and over burn in others. Over burn happens always on the light density wood. In some cases I even had to pull a piece out of the laser and spray it with a water bottle to keep the piece from burning.

I know I'm close to the right settings, as on medium density the pieces burn perfectly. Right now on a 35-watt machine I'm using 100% power and 42% speed, 2500 hz. Should I try to bring down the power in order to bring down the speed, up the pulse rate and speed, or change my focus?
The over burn has no relation to where the piece is in the laser, so I'm fairly confident that it's not a beam alignment issue.

Attached is an image of the BACK of a piece that over burned.

Stephen Beckham
08-11-2007, 9:26 PM
Allan,

I'm running a 45 watt epilog and I've too had problems with Balsa. Not quite like yours, it was just uneven burning. One thing I noticed is that you have the Pulse up pretty high. I run everything at 500 except for flexibrass (700) and Acrylic (max).

I cut most of my wood at 20/100/500 (speed/pwr) and then decrease speed from there. Since you're running 35 watts you may need to adjust your speed.

The interesting thing is that it looks like your backburn didn't happen where the honeycomb touched or did you have something holding the board up off the deck?

Eric Allen
08-12-2007, 4:20 AM
Yeah, that seems to be waaay too high a pulse. I've even cut back from Epilog's recommended 500hz and had good results down to 300. Too much power in too short a space really overdoes the wood.

Allan Wright
08-12-2007, 8:23 AM
Thank you both. Ill cut down (WAY down) on the PPM.

Yes I was using a grid.

I'll try again today on some tests.

Allan Wright
08-29-2007, 8:11 AM
I've cut down to 500 PPM, and that has improved things. I still get some overburn. Cutting from 600 dpi to 400 dpi also helped. What DPI do you normally cut your balsa at?

Getting more consistant wood from a new supplier (recommended by another laser cutter) also has helped.

One last question. When you back down to 300 PPM, do you have to increase your power consistantly or decrease your speed? I start to get 'perferated' wood unstead of cut wood at that pulse rate.

Dennis Perry
08-29-2007, 8:41 AM
Hi Allen try using transfer tape on the back it will eliminate the burning. I also cut at 200 dpi.

Dennis

Allan Wright
08-29-2007, 9:33 AM
I'll have to get some and try it. I cut a LOT of balsa, so the extra labor may be prohibitive, but for special projects this might be worth a try.


Hi Allen try using transfer tape on the back it will eliminate the burning. I also cut at 200 dpi.

Dennis

Mike Hood
08-29-2007, 7:36 PM
I cut balso and lite-ply most every day. Are you using a good steady air assist? and at what pressure?

Kim Vellore
08-29-2007, 8:19 PM
Allan,
Try focusing it to the bottom of the wood rather than the top. What I am thinking is if the beam exits at the bottom is wider it could ignite the sharp corners which burns the bottom, just a thought....

Kim

Allan Wright
08-30-2007, 10:02 AM
I'm using an airbrush compressor that I had. I can hear plenty of air coming out and it blows away debris (when there are loose bits that pop out). I believe the compressor is 30 psi, I'll have to check it.


I cut balso and lite-ply most every day. Are you using a good steady air assist? and at what pressure?

Allan Wright
08-30-2007, 10:03 AM
I will try this, might be just the ticket on the thicker balsa. Maybe this or focusing on the 'middle' of the wood. I'll try both.


Allan,
Try focusing it to the bottom of the wood rather than the top. What I am thinking is if the beam exits at the bottom is wider it could ignite the sharp corners which burns the bottom, just a thought....

Kim

Mike Null
08-30-2007, 10:34 AM
I can't set my air pressure that high but I wonder if a setting of around 10 psi might not "fan the flame" so much.

I'm only grasping at straws with that suggestion.

Allan Wright
08-30-2007, 1:41 PM
I'll see if I can dial back the compresser's PSI. Worth a try.

I did reduce the DPI and PPM frequency and that's helping quite a bit.


I can't set my air pressure that high but I wonder if a setting of around 10 psi might not "fan the flame" so much.

I'm only grasping at straws with that suggestion.

Allan Wright
09-03-2007, 1:43 PM
Since I get a lot of answers searching old threads, and in the interest of helping others. Here's what I have found works best for me for 3/32" medium-weight balsa:

35-watt Epilog Legend TT: 300 DPI, 475 Hz PPM, 95% Speed, 80% power

For hard balsa, I go to 90% power.

Allan Wright
10-25-2007, 7:50 PM
Revisiting this topic. I still haven't found any settings that work well for balsa with varying density. Settings for hard balsa really scortch the back of soft.

Allan Wright
10-26-2007, 1:00 PM
Last night I took quite a while making a bunch of tests again. Air, no air, different PPM settings, etc.

Finally it came down to me just sorting the balsa by weight, and using 3 settings for soft, medium and hard balsa. This means putting each balsa board on a gram scale prior to cutting, but at least I'm not wasting every 3rd board.

I'm sure with a higher wattage laser my sweet spot would be larger and I could probably get away with 2 or even 1 setting. This works for me with my 35 watt laser. I'm just documenting my results for those who hit this thread years from now doing a search.