Ben's 2.x Laser Build

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Re: Ben's 2.x Laser Build

Postby naPS » Tue Jun 28, 2011 6:11 am

Which direction is your lens facing?
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Re: Ben's 2.x Laser Build

Postby BenJackson » Tue Jun 28, 2011 6:31 am

Curved side up.
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Mini ITX driver board

Postby dirktheeng » Tue Jun 28, 2011 11:46 pm

Ben,

How do you propose doing all the calcs and generating pulse trains with the mini ITX? Custom software? Do you have something in mind for open source to start from? I'm interested as I am only so-so impressed with grbl and would like something better.

Let me know.
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Reflections on the 2.x laser build

Postby BenJackson » Wed Jul 06, 2011 5:02 am

Bart's post about the black washer upgrade reminded me of my list of ideas/suggestions compiled while building:

  • Add a hole in the right front of the laser carriage for the air hose. This would be an easy mod for people to do if they knew it would be useful, but it's tricky once you realize how the air hose can interfere with your X and Y travel.
  • In concert with the above, switch to a right angle fitting for the air assist barb fitting. I actually sawed off all but one barb and used a ziptie to secure the hose. Again to try to minimize the air fitting stickout leading to reduced travel.
  • The air assist should have a deeper pocket at the top so that the setscrews can engage the locking collar of the mirror assembly rather than grabbing the threaded lens retainer (or grabbing right between them -- it's hard to tell)
  • The kit should include the 18mm to 20mm spacer for the lens. I keep meaning to cut one myself. Anyone have a drawing?
  • Dirk has a good list of minor adjustments to improve travel, like relocating the X endstop to the front and using button head screws in a few key places. Moving the Z motor to the bottom would also help quite a bit.
  • The right side door stop can hit the gantry end and really wrench it if you close the door with the gantry all the way back (farther back than the usable cutting area).
  • The table doesn't align that well to the cutting area. I think ideally the usable cutting area would be entirely within the open space of the table so that you can use expanded honeycomb and not have to do any cutting over the frame of the table.
  • The table brackets are well designed to avoid binding, but it would be nice if the table were really registered in some way to ensure squareness of jigs and the like. The Epilog I used had flip-down rulers that also formed a lip to register 0,0.
  • If expanded aluminum tables were popular I think something like a C-channel table frame would be much easier to work with than Misumi 2020 (plus it would eliminate the corner brackets).
  • It would be handy if the top skin behind the door was not pinned by the door hinges. It's a little fiddly to install the door, which discourages removing that back skin that gives good access to the top of the laser and the primary mirror adjustments. Perhaps notch out the hinge area in the skin and mount the hinge itself on spacers (which could be made out of alupanel as well).
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Re: Ben's 2.x Laser Build

Postby BenJackson » Wed Jul 06, 2011 8:46 pm

One more suggestion I forgot about:

The Y cable carrier should be turned around (so that the loop is at the front):
  • The air hose would then point straight out the back
  • The wiring would point toward the new interface board location
  • The air and electrical connections at the gantry end would face the back where they would not interfere with Y travel

I measured at one point and I think the current attach point would still work.
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Re: Ben's 2.x Laser Build

Postby bdring » Wed Jul 06, 2011 11:37 pm

Thanks for the list....

Carriage Hole - That sounds like a good idea. Have you done this on yours? I can add it to the drawing and get it with the next buy. I have about 25 left.
Right angle fitting - I'll give that a look when I work on the ideal hose hole location
Nozzle Deeper Pocket. - Sounds like a good idea. I have about 40 nozzles in stock though.
Lens adapter. - I have been meaning to try that. I really does not fit with the current kits, so it could be a separate item.
Dirk's Travel Log - I will addressing travel tweaks when Makerslide is ready.
Door Stop Issue - I might just switch to a single door stop.
Table Cutting Area - It sounds doable. Once all the travel issues have been worked out, I will look into it.
Table Squareness - The 2.x was never meant to have true 3 axis perfection. I had an upgrade for the original laser for this. Makerslide might give a simple solution.
More Honeycomb compatible. - I'll look into it. Misumi has a lot of options that would help.
Top Skin Removal - That sounds doable. Maybe open ended slots facing towards the door would allow the that skin to slide out when loosened. The hinges might hide the slots.
Y Carrier Turn Around - I need a visual on this one.
Bart
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Re: Ben's 2.x Laser Build

Postby BenJackson » Sat Jul 09, 2011 7:18 am

bdring wrote:Y Carrier Turn Around - I need a visual on this one.


Which part? I assume the benefits on the bottom are obvious since the wiring and tubing all wants to go to the back.

The issue on the gantry is that the X motor wire and the assist air don't want to go on the inside of the gantry plate on the front because the carriage will hit them (limiting X travel). If they simply bow out toward the front then they are pinched between the gantry plate and the front of the machine (limiting Y travel). Dirk solved this by folding the wire and tube back on itself immediately to stay under the X carriage and come out at the back of the gantry plate. My solution roughly follows the front edge of the gantry plate but angled to avoid interference. If the tubing and cables simply exited toward the rear (with reversed cable carrier) it would be no problem.

Another idea from looking at a pic of another laser: A 1/4" acrylic door would be self-supporting, simplifying the front frame and front skin. The handle would have to point up instead of forward.
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Re: Ben's 2.x Laser Build

Postby bdring » Sat Jul 09, 2011 12:43 pm

Sorry, I got the cable issue. I was thinking about something else. I agree and will be doing that soon.

I like the way the door works now. I'll implement your suggestion of making the rear top cover more easily removable. I will slot the front holes, so you loosen them and slide it out. The slots will be hidden by the hinge.

new_rear_top.JPG
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Graph of laser current vs control voltage

Postby BenJackson » Tue Aug 30, 2011 10:03 pm

I finally put a meter on everything so I could plot laser power vs V IN:

Untitled 1 - OpenOffice.org Calc 8302011 24142 PM.bmp.jpg


It appears to have two linear regions:
  • From 0.5V (below which it will not fire) up to 1.0V maps linearly to 0 to 50% laser power (assuming 20mA ~ 40W)
  • From 1.0V to 2.9V maps linearly from 50% to 100% laser power

One note from this for new builders is to be sure you've got a meter going before you turn the knob beyond halfway (2.5V) or you risk running too much power through the tube.

On top of this if you use PWM to drive V IN (from pin 14 or 15 on the parallel connector if you use Bart's board) there will be scale error to include since the parallel port voltage is used directly (rather than having it PWM the PSU supplied 5V for example). My parallel port at 100% output produces 4.43V at V IN. More than enough, but if you assumed 5V you'd be off by 10%. Some parallel ports will probably max out at 3.3V or less.

Rather than waste 1/3rd of my PWM range (and thus 1/3rd of my resolution) I should probably at least install a divider to bring 100% down to 2.9V.
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Re: Ben's 2.x Laser Build

Postby BenJackson » Thu Sep 08, 2011 6:35 am

When I first assembled the laser I hooked up a microcontroller to drive it. That let me do vector cuts (though the ergonomics were poor because I had no UI, just serial gcode access). The big problem was that it discouraged me from hooking up a PC controller because the first step would be unhooking the working setup and being unable to use the laser for a while. Plus component arrival order and general laziness had left me without limit switches so all that would have to be fixed.

Enter my vacation! Unbelievably my wife wanted to go somewhere for part of it so I haven't been able to devote it to laser hacking like a normal person...

But I do have EMC2 working now on an old PC. Some BIOS setup to disable hyperthreading, disable onboard sound, legacy USB, power management, and all those realtime-crushing things and I can get a 37kHz BASE_PERIOD which EMC2 can turn into 37kHz steps (its special parallel port driver has an auto-reset feature that enables one pulse per tick). That gets me about 470mm/s on X (8x microstepping) and I've tested up to 7500mm/s/s acceleration with no problems.

With the BIOS tweaking (same sort of things you'd do for Mach3) and the EMC2 live CD plus the included "stepconf" I think anyone could be doing vector cuts with EMC2 very quickly. The major difference for a laser builder (as opposed to end user) between EMC2 and Mach3 is that where Mach3 has almost unlimited flexibility of the GUI, EMC2 instead has almost unlimited flexibility of the internals. Take a look at this list of realtime modules: http://linuxcnc.org/docs/html/hal_components.html . Now consider that you can hook those together in any way you want. I fully expect I can implement an equivalent functionality to the Epilog "frequency" setting just with some work in the HAL file.

What I've got working so far is rastering based on an idea from the Hacklab (Toronto) configuration. An external script processes the image and feeds the raster information to the streamer module which executes logic in the inner loop via HAL config. Their version created a paired "gmask" and gcode file to execute together. My version just generates the info on the fly (by executing a custom M-code script) and executes a gcode subroutine to produce an arbitrary raster scanning pattern.

Here's my first result in wood (300 DPI in X, scan gap of 0.125mm or about 200 DPI in Y, about 80mm/s and about 20W laser power):
P1000098.JPG


Here's one letter under higher magnification (courtesy of a USB microscope by Celestron):
Image28.jpg
Image27.jpg
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