Educa's BigFoot

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Re: Educa's BigFoot

Postby dirktheeng » Sat Dec 31, 2011 2:54 pm



it will lower the energy density of the beam on your optical components and make them run cooler... not a problem with these lower power lasers though and even if it is with 80+ watt lasers, it is almost cheaper to get better mirrors.
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Re: Educa's BigFoot

Postby educa » Sat Dec 31, 2011 4:23 pm

OK then its not of good use for me.


I was thinking of also mounting a red laser pointer to see where the machine will start engraving.
Instead of using a beam combiner (expensive + 1 more step to align + some power goes lost with such a combiner) I would mount the laser pointer onto the moving laser head and let it point down.

Then I can use the red pointer to point to the working table and if I know the offset between the laser and the real laser beam then my software can calculate the difference and start cutting at the exact place where the pointer was previously pointing to.

Price for this all: $5 or so
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Re: Educa's BigFoot

Postby BenJackson » Sat Dec 31, 2011 8:04 pm

This guy had a clever solution for the 2.x laser: http://danielbauen.com/make/index.php/l ... n-extra-m/

Basically a pivot arm that drops a laser down between the CO2 tube and the first mirror when the lid is open:

Image

Personally I am avoiding any additional weight on the laser carriage (it needs to accelerate very fast for engraving) so I haven't done anything like you describe. I've actually been considering the "knife edge mirror" technique that's described in another forum post.
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Inline red laser pointer

Postby educa » Sun Jan 01, 2012 7:27 pm

That looks like a nice solution.

Maybe I should consider something like that.
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Laser power and engraving

Postby educa » Sun Jan 01, 2012 7:37 pm

Here I am again with a dillema.

The always returning dillema of HOW MUCH laser power to put in your machine.

I do know that 80Watt will be a lot more powerfull then 40 Watt, but I also have the following problem.


I intend to make the software for the machine myself. That is I want to make my own sort of cnc controller which accepts gcode + a subset of my own to define engraving.

The software will run on windows machines, but communicate through (probably) and arduino to some electronics.

I want my software to be able to both CUT and ENGRAVE in the same session.

For example a few posts ago in this thread you see my dragon image. This dragon is made out of vector engraved lines + vector CUT lines. Or course in real life I would first engrave and then cut.
But.... cutting is preferably done at full power and engraving possibly not.

So, at what power setting should I do engraving?

I intend to use the PPI technique for cutting, but isn't it so that for engraving you have to provide both very short pulses and secondly turn the power of the laser way down?



It's still not crystal clear to me how this exactly works. The Power supply has both a TTL High and Low input, but also a way to setup laser power by an analog voltage.

Does this mean that if I control with an arduino, it is best for me to connect 1 output pin of my arduino to the TTL Low (or is it high) and then connect the arduino through some DAC to that 5V analog input on the PSU to control laser power?

If for example I use a cheap 8bits DAC (or even an R2R ladder) then I could setup the voltage to the laser PSU in 256 steps (0->5 V in +- 0.02V increments) and in case of a 40 Watt laset I would control the power from 0->40 in 0.15 Watt increments.

Is that how it works? Or does such a PSU not react to 0->5 but to a smaller range of voltages? Maybe there is a minimum voltage needed to shoot a laser at all ?
I would really appreciate if somebody could xplain this a little.

Thank in advance,

Bart
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Re: Laser power and engraving

Postby awesomenesser » Sun Jan 01, 2012 7:56 pm

educa wrote:...
If for example I use a cheap 8bits DAC (or even an R2R ladder) then I could setup the voltage to the laser PSU in 256 steps (0->5 V in +- 0.02V increments) and in case of a 40 Watt laset I would control the power from 0->40 in 0.15 Watt increments.

Is that how it works? Or does such a PSU not react to 0->5 but to a smaller range of voltages? Maybe there is a minimum voltage needed to shoot a laser at all ?
I would really appreciate if somebody could xplain this a little.

Bart


Yes that would be how it works there is a minimum turn on but you could calibrate the software to add that offset.

One recommendation I would not use and arduino to power for your custom controller. I would recommend an FPGA, AVR32, XMOS or just about anything else faster than an 8bit AVR. Also depending how you do it you might have issues with the speed of communication from the pc to the micro controller. MACH3 which transfers the direct pulses has to use custom realtime drivers to be able to achieve those speeds. I would recommend that you just transfer (USB to RS232) your gcode and engraving information to the controller and it handle the pulses to the motors. I have many projects which transfer from a custom c# windows application through usb to a FTDI FT232RL chip which then outputs TTL 5V serial data for transfering data to a AVR32 (I have a little information on my site http://robertgivens.com/mediawiki/index.php/SyncPOV_Software).

This is a large project to undertake and I look forward to seeing the results.
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Re: Laser power and engraving

Postby BenJackson » Sun Jan 01, 2012 8:05 pm

educa wrote:For example a few posts ago in this thread you see my dragon image. This dragon is made out of vector engraved lines + vector CUT lines. Or course in real life I would first engrave and then cut.

I think when you say "engrave" most people are going to think of raster engraving (rapidly sweeping back and forth to produce a bitmap).

When you make vector lines like your dragon it's just like the cutouts except for the power and speed.

educa wrote:But.... cutting is preferably done at full power and engraving possibly not.

You may want less than 100% power even for cutting. Something thin like paper, for example. With an 80W tube more things will be "thin" for you than for me.

educa wrote:Does this mean that if I control with an arduino, it is best for me to connect 1 output pin of my arduino to the TTL Low (or is it high) and then connect the arduino through some DAC to that 5V analog input on the PSU to control laser power?

TTL low and high are identical and just for convenience. Yes, you will want analog control of the IN terminal. A DAC isn't really necessary. An AVR can easily PWM that pin fast enough.

Also only some of the voltage range is usable. On my laser it doesn't fire below 0.5V and full power is about 3V. It's also nonlinear. About half the power is between 0.5 and 1V and the other half between 2 and 3V. See the graph in my buildlog.
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Re: Educa's BigFoot

Postby educa » Sun Jan 01, 2012 8:21 pm

ok if the avr can pwm this fast enough, then its 1 DAC saved in the wallet.

When I say ENGRAVE I really meant raster engraving. thats why (in the case of my dragon) I specially mentioned vector engraving.

In the photo's above the dragon is cut on the edges, but the vector engraving lines are also cut quite deep, but I suppose with the right settings (and probably with some PPI tricks too) I could make the laser MARK the wood without cutting in it ?

In the end I would like to make a machine which can engrace (be it raster of vector engraving) some pattern on wood and then cutout the contours in 1 machine operation, so the machine will switch between engraving and cutting in my software.
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Re: Educa's BigFoot

Postby TLHarrell » Mon Jan 02, 2012 2:48 am

I've been using BOTH raster and vector engraving. On my machine, when vectoring MDF, I set to about 2% and 100% speed. You can see the results of both on the fin parts shown in this other post (sorry for cross posting, but I didn't want to upload the photo again) http://www.buildlog.net/forum/viewtopic.php?f=16&t=751&p=6828#p6828
40w Full Spectrum Engineering 5th Gen Hobby 20"x12" w/ Rotary Engraver
South San Francisco Bay Area - Sales and Support Representative for Full Spectrum Engineering
408-47-LASER - Skype: whitelightlaser-thomas - Facebook: White Light Laser
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Stepper motor power

Postby educa » Mon Jan 02, 2012 11:44 am

It looks very good. I allready saw that rocket lamp by the way, thats a very nice creation.

I have another problem.
For my machine I will use ball bearing linear rails. These are quite thick and very strong things, but I wonder about the motor to drive these carriages.


Please let me make some calculations and if I'm wrong please correct me.


The motor I will use is a nema23 3.1Nm stepper motor.
So technically speaking this motor would be able to hold 0.316112026kg (316 grams) at a distance of 1 meter.

My pulley is a 20 tooth 5mm pitch pulley, so 100mm around = a pitch diameter of 100/PI = 31.83mm or 0.03183 meter. So the pulley would be pulling the belt at a distance half of that = 0.01591 meter

1/0.01591 = 62.85, so I assume I then get a pulling torque of possibly 62.85 x 316 grams = 19860.6 grams or 19.8606 Kg


Can I then safely assume that my motor will have no problem at all to pull my bearing block ? I think that I need less then 1Kg of force to make the bearing block slide in horizontal direction.

Hopefully my calculations are correct.
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