Precision Cutting
Today I started a series of tests to see if a quantitative relationship could be developed to understand how a nominal dimension cut size in software translates into actual dimensions in flat wood. In other words, how much material is lost due to burn and charred dust that makes the cut dimension LONGER than the size indicated in the software design. I found that for a 1 inch block, the gap inbetween the cut-out block and the frame cut around it is about 1/32 inch. Knowing that the laser cut performance varies in the vertical and horizontal directions, I designed a series of 5 blocks for each dimension. The dimension being varied changes by 0.01 inch incrementally (1.39 , 1.38, 1.37, 1.36, 1.35 inches) for a nominal 1.4 inch horizontal. The verticals are varied also by 0.01 inches starting at 1.14 inch to 1.10 inch for a nominal 1.15 inch design dimension.
First, I tested various combinations of power and speed to see whether (a) the cut makes it through wood 3/16 inch thick, and (2) how much char burn dust is created along the cut edges.
This is a Boss Laser LS-2436 150 Watts and 4 inch focal length.
#1 35% power and 25mm/sec speed cut
#2 30% and 25 mm/sec no cut
#3 25% and 25 mm/sec no cut
#4 20% and 15 mm/sec cut
#5 15% and 15 mm/sec cut
#6 12% and 15 mm/sec no cut
#7 12% and 10 mm/sec no cut
#8 12% and 5 mm/sec cut
I assessed which combination of speed and power processes cuts with the least char debris by visually inspecting the sides and wiping all four edges of each cut-out block against the cotton terry cloth pictured below.
To my eyes the 15 mm/sec and 15% power produced the best results.
So, when I set my parameters to 15/15 and ran my series of 10 test blocks, I was surprised to see that none of them had full cut-throughs! As you can see from the photos though, burn lines are evident to different extents on the backside of the wood, suggesting that the power only needs to be increased a bit to achieve full cut-throughs.
What could possibly explain this? Two things that I can think of:
1. There is warping/unevenness in the wood and the metal bricks holding the wood in place are successful to different extents in keeping the wood perfectly flat. Differences in flatness will affect the ability of the auto focus to work properly and thus affect the cutting strength. I will try to use more bricks to keep the wood flatter.
2. I made a mistake and did not match the laser frequency in the g-code files between the single (125 kHz) and multi-block designs (20 kHz). So I went back and resaved the multiblock deign with a 125 kHz setting and will cut the test series again.
To be continued ...
First, I tested various combinations of power and speed to see whether (a) the cut makes it through wood 3/16 inch thick, and (2) how much char burn dust is created along the cut edges.
This is a Boss Laser LS-2436 150 Watts and 4 inch focal length.
#1 35% power and 25mm/sec speed cut
#2 30% and 25 mm/sec no cut
#3 25% and 25 mm/sec no cut
#4 20% and 15 mm/sec cut
#5 15% and 15 mm/sec cut
#6 12% and 15 mm/sec no cut
#7 12% and 10 mm/sec no cut
#8 12% and 5 mm/sec cut
I assessed which combination of speed and power processes cuts with the least char debris by visually inspecting the sides and wiping all four edges of each cut-out block against the cotton terry cloth pictured below.
Wiping char dust on cloth to find the cleanest cut
To my eyes the 15 mm/sec and 15% power produced the best results.
So, when I set my parameters to 15/15 and ran my series of 10 test blocks, I was surprised to see that none of them had full cut-throughs! As you can see from the photos though, burn lines are evident to different extents on the backside of the wood, suggesting that the power only needs to be increased a bit to achieve full cut-throughs.
Front and back sides of a series of unsuccessful cut-throughs on 3/16 inch wood
Click to see Video clip of laser in action
Front
Back
What could possibly explain this? Two things that I can think of:
1. There is warping/unevenness in the wood and the metal bricks holding the wood in place are successful to different extents in keeping the wood perfectly flat. Differences in flatness will affect the ability of the auto focus to work properly and thus affect the cutting strength. I will try to use more bricks to keep the wood flatter.
2. I made a mistake and did not match the laser frequency in the g-code files between the single (125 kHz) and multi-block designs (20 kHz). So I went back and resaved the multiblock deign with a 125 kHz setting and will cut the test series again.
To be continued ...
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