Scara based CNC plasma cutter?
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@droftarts said in Scara based CNC plasma cutter?:
I'm not sure if that makes it a SCARA or some other kinematic; @JoergS5 would know
Dear Ian, this is a serial scara with one axis being parallelogram-based in the middle. The parallelogram makes sure that axes stay parallel between begin and end of the construction (and the orientation, ie the XY rotational angle too). It is very similar to the 4 axis palletized robot type.Looking at it at a different position (YT at 8:03) at seems to be the 5 bar parallel scara type, with the two actuator starting points being at the same position and the endpoint being cantilevered.
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@Exerqtor I think the hardest part rearding RRF-conversion would be the manual tracing option. But that's just a feature, you won't need it.
Maybe there are options to run it on an SBC? All you need is to store each positional data on a button-click.
Can this be done with Duets CL steppers? -
@droftarts said in Scara based CNC plasma cutter?:
@Exerqtor Looks interesting! I've always wanted a plasma CNC...
This video shows the inside quite well https://youtu.be/qIk-UxMZ0U4?si=gMgWM8EIeHTX0FW0&t=191. I like how both motors are in the base, and it uses a linkage for the distal arm movement.Same thing here, but being short on space has held me back. But potentionally being able to build one with this small off a footprint using a ecosystem i'm used to would make me start doing it.
I'd think a Duet and 2x M23CL motors would work well. You would have to ask @dc42 if we could plot the position with the motors.
I figgure we would maybe need motors, since we would need a way to actuate the "Z-axis" lifting mechanism as well. I do suspect it would need to be writen a plugin or something like that to i interpret the motor position together with the kinematic matrix to get a idea of where the arm is in real life or something like that.
@o_lampe said in Scara based CNC plasma cutter?:
@droftarts Interesting video. It doesn't show much about the internals but it confirms my findings so far:
- shielded housing
- EMI filtered Mains socket
What I don't like is the small working area of a SCARA with regards to the weight of the plasmagun and stiffness of the airtube. You'd spend a fortune for decent bearings.
I've seen other plasma tables with PLA-printed H-bot frames. IMHO they will disintegrate in no time due to the intense UV-light.
I'm not even sure if one should use silicone-rubber belts?
Maybe I'm overthinking things: the plasma flame is mostly below the metall sheet.
With a dark colored water tank underneath the cutting table, we should be safe. (although I like the hinged cutting table, it won't have a water tank)EMI filtered mains socket is best practice to use anyways imo, and shielding the housing seems quite straight forrward (don't look like it's any "special sauce" inside the Arcdroid based on the video in that regard either lol).
I hear you, and if one have the room for a "convetnional" plasma table that would ofcourse be the way to go, but for me doing automotive and mainly smaller jobs i think the SCARA is more shop and usecase friendly.
That being mentioned, comming from the automotive industry myself my first thought for a "hub" for the SCARA arm(s) was to use some off the shelf "bolted" wheel bearings. They aren't too-too expensive, easy to mount and should be plenty stiff.
@JoergS5 said in Scara based CNC plasma cutter?:
@droftarts said in Scara based CNC plasma cutter?:
I'm not sure if that makes it a SCARA or some other kinematic; @JoergS5 would know
Dear Ian, this is a serial scara with one axis being parallelogram-based in the middle. The parallelogram makes sure that axes stay parallel between begin and end of the construction (and the orientation, ie the XY rotational angle too). It is very similar to the 4 axis palletized robot type.Looking at it at a different position (YT at 8:03) at seems to be the 5 bar parallel scara type, with the two actuator starting points being at the same position and the endpoint being cantilevered.
So this means the kinematics should be doable and configured as the "Cantilevered arm 2" in the docs, if i'm getting things right?
@o_lampe said in Scara based CNC plasma cutter?:
@Exerqtor I think the hardest part rearding RRF-conversion would be the manual tracing option. But that's just a feature, you won't need it.
Maybe there are options to run it on an SBC? All you need is to store each positional data on a button-click.
Can this be done with Duets CL steppers?That's what i'm currently and inseptionally view as the biggest hurdle too. My idea was to use a SBC to add some computing power and maybe a PanelDue i7 equivalent screen as an handheld.
The "simple trace" isn't something i think I would use too-too often, but the ability to move the machine Zera position around on the steel sheet by pushing the arm around manually to position it seems really valuable.
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@Exerqtor said in Scara based CNC plasma cutter?:
So this means the kinematics should be doable and configured as the "Cantilevered arm 2" in the docs, if i'm getting things righ
I am not sure where the actuators are located. If they are both at the starting point, then yes. If the second one is located at the left big hinge (of the video at 8:03) in the middle of the parallelogram, then one needs to think about whether the angles are the same, then maybe not.
It would help to see the red box below the arms opened. My guess is that both actuators are located there, because the parallelogram construction helps to place the heavy actuators away from the moving parts. An actuators placed inside the hinge would counter this idea.
The very tall arms the big hinge will result in high Z precision, this person knows IMHO how to make a good design.
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@JoergS5 said in Scara based CNC plasma cutter?:
@Exerqtor said in Scara based CNC plasma cutter?:
So this means the kinematics should be doable and configured as the "Cantilevered arm 2" in the docs, if i'm getting things righ
I am not sure where the actuators are located. If they are both at the starting point, then yes. If the second one is located at the left big hinge (of the video at 8:03) in the middle of the parallelogram, then one needs to think about whether the angles are the same, then maybe not.
It would help to see the red box below the arms opened. My guess is that both actuators are located there, because the parallelogram construction helps to place the heavy actuators away from the moving parts. An actuators placed inside the hinge would counter this idea.
The very tall arms the big hinge will result in high Z precision, this person knows IMHO how to make a good design.
I took some time and grabbed some screenshots of the video where the dude changes out the mainboard in a Arcdroid, here you go
Seems like it's pretty straight forward to me, 2 Nema23's with encoders to drive the kinematics and a standard Nema17 for the "z-axis" from the looks of it:
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@Exerqtor said in Scara based CNC plasma cutter?:
and a standard Nema17 for the "z-axis"
Looks like the Z axis works on a flex-drive. Keeps the weight off the arm, which is sensible. Looking at a couple of other videos, it taps off before starting each cut, but that doesn't strike the arc. I guess the same thing could be done to create a 'bed mesh'.
I don't know if the closed loop motors continuously track position, and update the Object Model, even when the motor is disabled; I don't see why they couldn't be, but I've asked @dc42. If they do, it would be quite straight forward to query the object model for the X and Y position as you move the arms around, for manual tracing.
Ian
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@droftarts
Yeah I've seen that too, i was thinking about maybe using the tip itself as a "switch", and have a beefy NO relay that physically breaks the connection between the controllboard and both sides of the "probe wires" when ain't doing a "bed probe" so that the board don't get fried when striking an arc.I'm interested in hearing what thoughts he have on it!
Having looked at couple reviews of the Arcdroid i'm not so sure it uses a flex drive to lift the tourch anymore tbh! It looks more like it's just a wire pulling up and depending on gravity and that small spring to aid it going down.
Look at this clip for instance, I can't see any threads to acuate the "head" up/down, just seems like a wire.
This video also gives a little bit of a tear down view of the machine from about 3:30.
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@Exerqtor said in Scara based CNC plasma cutter?:
i'm not so sure it uses a flex drive to lift the tourch
Same here, i guess it's a short leadscrew-stepper or similar.
Using a pilot-arc (pilot-spark?) to start the torch is a common way to extend life of the nozzle. Then tapping the base is used to set Z=0 only.
That pilot arc also works on rusty or painted surfaces.
Something you have to keep in mind when using the nozzle as endstop is: there is no guarantee for an electric contact from touching the surface.Using a waterbed has some benefits to consider:
- it collects the dust (no mess in the workplace and toxic gases are less of a problem)
- it eliminates almost all the sparks (sparks can fly upto 10 meters in all directions and they are very hot)
- it keeps thin sheets from warping
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Same here, i guess it's a short leadscrew-stepper or similar.
That makes more sense. Looks like a short motor with a longer box above it, so space for a leadscrew, to pull on a cable that goes through the tube to the tool head.
Ian
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@Exerqtor
I just had the idea to make a bed-slinger plasma table where the torch only does x-motions and the bed is the metal-sheet.
That way the waterbed could be very small and the bed frame could be hinged or foldable.
