Lasercutting tool

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pjdestexhe
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Joined: Thu Feb 27, 2020 4:11 pm

Lasercutting tool

Postby pjdestexhe » Thu Feb 27, 2020 4:36 pm

Hi everybody!

I'm somewhat desperate. I want to build the frame of a robot using finger joints.

I followed a tutorial from Sliptonic (https://www.youtube.com/watch?v=0Mz6o9s ... gu&index=3), but he doesn't say a word about how to configure a tool/controller/Post processor.

The machine I will probably be using is an ML-W960 (it's from a fablab).

On this fablab's website, they say it only supports BMP, PLT, DST, DXF, AI and CDR files, so I'm not even sure I will be able to use my .ngc gcode.

They suggest using DXF files. I could export my document as a DXF, but then it wouldn't compensate for the kerf in the finger joints, and I couldn't use a dogbone dressup.

So I have two issues :
  • How to configure a tool/controller/Post processor for laser cutting ?
  • Can I output a DXF file instead of a gcode or how to make sure the machine will accept my gcode ?
Thanks !
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dubstar-04
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Re: Lasercutting tool

Postby dubstar-04 » Thu Feb 27, 2020 5:30 pm

The ML-W960 uses its own cam software to generate the machine code.

You won't need to use the path workbench.

Export your model as a DXF and open it in whatever software the machine uses, likely Coreldraw, autocad or Photoshop.

The machines are generally supplied with a plugin for the selected software.

Thanks,

Dan
pjdestexhe
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Re: Lasercutting tool

Postby pjdestexhe » Thu Feb 27, 2020 6:06 pm

Thank you! But then how to compensate for the kerf ?

All tabs in my model have the same width, be them pockets or pads. To compensate for the kerf I need pads larger than pockets, and dogbone dressup, so Path would be a good solution, any alternative ?
chrisb
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Re: Lasercutting tool

Postby chrisb » Thu Feb 27, 2020 6:13 pm

As dubstar-04 said, the postprocessor is integrated in the machine, so it should offer a possibility for compensation.
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sliptonic
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Re: Lasercutting tool

Postby sliptonic » Thu Feb 27, 2020 8:18 pm

Many times these machines are not compensating but simply running the laser ON the line. That means the kerf width of the beam is split between the two sides. So your 'slot' ends up 1/2 kerf larger and your 'tab' ends up 1/2 kerf smaller.

How tight is the tolerance you're trying to hold?
pjdestexhe
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Joined: Thu Feb 27, 2020 4:11 pm

Re: Lasercutting tool

Postby pjdestexhe » Thu Feb 27, 2020 10:06 pm

I don’t need a very good tolerance, I just want my finger joints to be tight.

Unfortunately I can’t make a lot of tests : I am a high school teacher, I will bring 4 students to a fablab this sunday afternoon, but otherwise I don’t have access to this machine. So I’m reading and training so that I can cut their project within a couple of hours as I won’t be able to make a lot of tests in one single afternoon... I’m ready to prepare a couple of ways to try prior to get there.

The ideal would be to produce a path compensating for the kerf and then turn it into a dxf so that the machine will just have to follow ON the line, just as when you cut a dxf produced with boxes.py. That’s why my first try was to use FreeCAD to modify a drawing produced by boxes.py as a DXF or an SVG, but I couldn’t find any way to do it.

The machine seems to be piloted by a software called LaserCut.
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sliptonic
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Re: Lasercutting tool

Postby sliptonic » Thu Feb 27, 2020 10:23 pm

Without cutting some test pieces it'll be very difficult to get the pieces to be 'tight' without being 'too tight'.

You don't say what material or thickness you're using but with 3 mm acrylic, the wall of the kerf isn't perfectly perpendicular to the face. The beam is focused at the final optical element so the kerf is ever-so-slightly beveled. I've found that parts can fit together loose one way, flip one over and the joint is tight. This will heavily depend on the capabilities of your machine so you really need test cuts if you want a good fit.
chrisb
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Re: Lasercutting tool

Postby chrisb » Thu Feb 27, 2020 10:32 pm

Lasercut seems to include a simple drawing program. It seems to have an offset function which can be used for the kerf compensation.
pjdestexhe
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Joined: Thu Feb 27, 2020 4:11 pm

Re: Lasercutting tool

Postby pjdestexhe » Thu Feb 27, 2020 10:45 pm

Thanks ! Of course I will cut test pieces, I would just like to prepare my project so that I only have a couple of parameters (kerf, speed etc.) to experimentally determine so that I can quickly adjust my files. I just want don’t want to wait for these tests before designing my plans on site while my students watch me and mess around...

I will try 6mm plywood for the frame of my robot and 3 mm plywood for the arm.

So any idea about how to turn a path into a dxf ? or is it just impossible with FreeCAD ? it seems to be possible with fusion 360 : https://www.youtube.com/watch?v=dKBxSx3Tv1k
pjdestexhe
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Re: Lasercutting tool

Postby pjdestexhe » Thu Feb 27, 2020 10:47 pm

chrisb wrote:
Thu Feb 27, 2020 10:32 pm
Lasercut seems to include a simple drawing program. It seems to have an offset function which can be used for the kerf compensation.
That would be great! Where did you find that info?