20 Years in the Making...

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FSE Laser Beam Divergence

Postby trwalters001 » Sat Mar 05, 2011 11:29 pm

I finally fired up the laser today. It's the 60W model from Full Spectrum Engineering.
No problems at all. It measured 60W with my Ophir laser power meter. Beam diameter at the laser is about 3/16".

Since I've been in laser-light-show mode for a long time, I wanted to see what the beam divergence was on this laser.

The large black circle in this picture is the beam hitting thermal paper 58.5 feet from the laser.

Divergence Front.JPG


I shot the laser at my concrete basement wall for about 30 seconds and then found the warm spot by feeling of the wall. :shock:
I then taped a piece of thermal paper over the spot and fired the laser for about 5 seconds.
The brown area in the middle of the spot is where the paper started to char.
This picture is of the back of the thermal paper, showing the charred area.

Divergence Rear.JPG


The spot dimensions are 2.75" wide and 3" tall. There seems to be an area above the main spot that's affected by rising heat.
I used 2.75" as the beam diameter for the divergence calculation.

The calculated divergence is 3.65 mR. That seems a little high, but I don't have the specs on the laser. (Henry - you want to chime in?)

So, the farthest my cutting head can get from the laser is about 11 feet. At that distance, the beam diameter will be about 0.67". That is for the entire spot.
If I use the diameter of the charred area (1") to calculate the divergence, the spot size at 11feet will be 0.34".

The reason I want to know this is because the entry hole for my cutting head is 0.4" in diameter. It looks like the beam will be larger than the hole and may cause ghosting like hoda113 is reporting on his system.

We'll just have to see...
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Re: 20 Years in the Making...

Postby bdring » Sun Mar 06, 2011 12:37 am

Check my entry 10/5/2009 buildlog entry here...

http://www.buildlog.net/cnc_laser/build ... l#LogStart

I measured a lot less...1.4mRad
Bart
"If you didn't build it, you will never own it."
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Re: 20 Years in the Making...

Postby trwalters001 » Sun Mar 06, 2011 3:36 am

I plugged my numbers into your calculator and got the same divergence.

It may be that at that large of a distance (58.5 feet) that I have to use a different spot diameter. The entire spot is 2.75" dia., but the charred area in the center is only 1" in diameter. If I use the 1" spot as the final diameter, the divergence is 1.157mR.
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The Perfect Air-Assist Pump

Postby trwalters001 » Sun Apr 03, 2011 5:19 pm

Hi All,

I've been wondering what I was going to use for my air-assist pump. Some folks are using diaphragm-type pumps like air-brush compressors, some are using Sleep-Number-Bed pumps, some are using air-mattress pumps.

All of these either pulsate, have low flow or are loud (or combinations thereof.)

I had an epiphany... I've been using the perfect pump every night for years... a CPAP machine!

The pump is quiet, doesn't pulsate, delivers quite a bit of air into high static pressure, and filters the air it blows.

I didn't want to use my CPAP machine for the laser, so I found one that was no longer used. It works perfectly. LOTS of air, clean, smooth flow and quiet.

Keep in mind that (in the US) these machines are obtained by prescription only. That's why you don't see them for very long on ebay (the ad gets pulled.) Craigslist, however, is a different story. There are several for sale in the Atlanta area, but they're a little pricey. $99 was the cheapest I found. A lot of times, people will try a machine and not like it, so they stop using it. That's how I got mine. A freebie from a friend.
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Re: 20 Years in the Making...

Postby macona » Mon Apr 04, 2011 7:06 pm

I personally like about a lot more flow than one of the normal pump can put out delivered to my nozzle. Helps immensely with charring and does create a cleaner cut. Downside is it can blow stuff lightweight around but adjusting the pressure regulator helps.

The big 80w machine we had at work came with a small diaphragm pump and it was a joke compared to running it off of shop air. Gauge pressure around 25PSI but with hose restrictions I dont know how many CFM it was using.
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Re: 20 Years in the Making...

Postby swaggs21 » Fri Jun 15, 2012 2:02 pm

Tim,

What are your rapids and cutting speeds on the X with the belt drive?

I am researching a couple of different systems drive systems, and have seen some belt drives that will go up to 10m/s :shock:

I would like to run cutting speeds in the 3600-4200ipm range, which would be a stretch with a stepper motor without some insane gearing and probably a fair loss in resolution.
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Re: 20 Years in the Making...

Postby trwalters001 » Fri Jun 15, 2012 3:12 pm

Hi swaggs21!

Glad to see you here!

You wrote: "I would like to run cutting speeds in the 3600-4200ipm range" (this equals 1524-1778 mm/sec)

Uh... are you sure about that?

A belt-drive system can definitely run that fast, but you're not going to cut anything unless you've got some SERIOUS laser power.

I cut regular poster board at 75mm/sec at 80% power on my 60W system. I cut 1/8" acrylic at 15mm/sec.

When I was getting my machine tuned up, I saw it run (X-axis) at 1500mm/sec. The problem with those speeds is acceleration and deceleration times and distance. It take quite a bit of both to sling around a 70" long gantry. Also, the forces acting upon the hardware are brutal. If you slow down the gantry quickly enough, it's pretty much a "bang." I don't like that part...

So, I've got it set so that the acceleration and max speed on the X-axis are much higher than the Y (gantry.) However, the system is speed-limited by the slowest axis.

Let me know if your speed request was in the correct units...

Tim
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Re: 20 Years in the Making...

Postby swaggs21 » Fri Jun 15, 2012 3:21 pm

Typing/Brain fart.

Engraving speeds.

I just got a quote from PBC for a 68" belt-driven linear actuator for $1700.

Yeah, that isn't going to happen :o
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Re: 20 Years in the Making...

Postby steppenshoe » Fri Jun 15, 2012 9:21 pm

Hey swaggs and twalters. Swaggs what are you doing here, laser and 3D print time I guess!

Loving the system twalters!

DT
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