Laser power loss over distance

[powerfade]

I just completed building my laser table with a 4'x5' footprint. It has a 100w reci laser tube on it. I set up the bottom right corner as the home position, because thats what I am used to working with on CNC routers. Unfortunately I'm not getting the power that I should on the laser. When trying to cut 1/4" acrylic at 5mm per second, it maybe goes 1/16" deep. The alignment looks good. Does it make sense that a beam traveling approximately 8 feet to the laser head would lose that much power???

Specs:
100w Reci Tube laser
150w power supply
Water temp is maintained at about 66 degrees
PWM is 20000

Any ideas would be appreciated...
Thanks..
Chris

[Axeman]

Have you tried cutting at the closest possible position and made a continuous line moving away from that nearest point? That would confirm/deny your idea of whether or not the distance is making that big of a difference.

[powerfade]

I did move the gantry up the table where the distance from the laser to the focus lens was probably 4 feet and it didn't seem to make any difference.

[todmaerin]

I did move the gantry up the table where the distance from the laser to the focus lens was probably 4 feet and it didn't seem to make any difference.

Yeah, but did you try at Top-Left (assuming that's closest to the laser) and try cutting separate lines on each axis from there? Does the strength diminish along either line? It could be that you're just a hair off which just puts you further off the farther out you go. Given the size of the materials you'd need for that test, you could always sub a piece of masking tape on the air-assist head (again, assuming you have one.) Test fire on low power at two positions: Top Left Limit and Bottom Right Limit.

I suspect you'll see something similar to this:

tape.jpg (15.45 KiB) Viewed 3040 times

That's my crappy approximation of a piece of masking tape. The white hole represents the hole on the air assist. The red dot is Top-Left-limit (or closest to laser), the purple Bottom-Right-limit (furthest.)

I had enough problems with a small table, I couldn't imagine trying to align a table that large.

-Tod

Edit: Another note -- make sure that your table and cutting bed are perfectly level. If there's any slope away to the extremities, you could be de-focusing just enough to diminish power.

[powerfade]

Hey Tod.. Thanks for that. I had my buddy come over with his thermal camera last night and we were able to get it lined up and cutting nicely . It was mostly an alignment issue. So you were right. We used that method of the masking tape over the lenses and firing at low power. Worked like a charm.

I haven't put a beam expander on it yet, but I think that might be next.

Thanks.
Chris

[todmaerin]

Excellent news! I'm glad that you're up and cutting!

-Tod