Anybody tried designing a rotary add on?

Mostly Printed CNC - MPCNC Hardware Development
41

I do not think the changing radius of the material is an issue.
But you would have to scale your design in the y-axis to fit a given radius of the wood.

-I think

42

If you imagine the outermost layer, unrolled, and laid flatā€¦ If you wanted that to be square, where 1mm in your drawing in x ended up being the same distance as 1mm of your drawing in y ended up being, then:

  1. Youā€™d have to compute your steps/mm based on the outside radius of the object spinning. Itā€™s a simple calculation, pi * diameter gives you one entire rotation, so:
    steps per rotation / (pi * diameter)

  2. If you want the deeper cuts to be aligned underneath the top layer*, then you donā€™t need to do anything else. The key (for me at least) is to think about how much the surface has to move to make a repeated cut. If the first pass is 5cm long, and that ends up rotating it 180degrees, then if the second pass was also 5cm (the drawing hasnā€™t changed) then the second cut would be 180 degrees as well. The cuts will end up being perpendicular to the surface. The distance the bit travels at the bottom of the cut will be smaller than the distance it travels at the top, and thatā€™s a good thing.

  3. If you donā€™t have the axis of rotation aligned with the x-axis, then the bit will enter the material at an angle, which is going to be bad for milling and will end up with strange results on multiple passes. Itā€™s probably not as big of a deal with the laser, but with the laser, it will have a hard time staying focused everywhere. Just thought Iā€™d point that out.

  4. If you have a material that isnā€™t a constant radius, then the design will be stretched/pinched when the outside radius changes.

This is completely wrong if what you want is to project the image from a single viewpoint. i.e. If you want an image that looks square when you look at it straight on. You can imagine cutting a design that you want to look correct from straight on, but will be stretched when looking at it with the blob rotated. For that, youā€™d probably want to do something to ā€œwrapā€ the design around the object, but it really wouldnā€™t even require a 4th axis, You would just have to adjust the z-axis and cut with the normal 3 axes. EstlCAM has a tutorial where they cut a design into the surface of a mouse. This would be more like that. Here that is:

  • I canā€™t think of a better sentence to describe that. But Iā€™m thinking the lower layers are just what you would have if you just cut a lot deeper the first time.
43

So then the g-code ā€œwrappingā€ software isnā€™t really necessary at all right? Itā€™s easy enough to set steps/mm with pre-processor gcode in Marlin. Wonder why no one does it this way if itā€™s that simple? I always figured the Z axis values had to be translated but after reading Jeffā€™s post , 3 times :), Iā€™ve become enlightened. The wrapping software is a convenience, but not necessary if all thatā€™s required is setting steps/mm for your stock diameter, connecting rotary stepper to X/Y axis, and maybe using a text editor to replace the X or Y moves with E moves in the gcode file. Oh well, the software to do this is done and Iā€™ve already made the changes to ā€œMarlinizeā€ it so no turning back nowā€¦ I do like the Estlcam wrapping on probed surface feature. The G-code ripper does that too but that only works with CNC controllers that support G38.2 probing codes, which I think will be added to future RC versions of Marlin.

44

jeffeb3,

Thanks for the thorough explanation !

My x-axis would be aligned with the rotational axis, and I would also be interested in having the layers radially aligned.

I would probably scale my design in the y-axis instead af changing the steps/mm ?

Have you published your designs anywhere ?

/thanks

45

FYI: I just uploaded my rotary to Thingiverse. Iā€™ll be posting the software and a brief write-up soon in case anyone is interested.

http://www.thingiverse.com/thing:1877336

46

Excellent, cheers,

I know how big a job it is, posting a documented design !

47

Thanks:) FYI: I just updated Thingiverse with a copy of the ā€œMarlin-Friendlyā€ version of G-Code Ripper. I was going to do a simple write-up but this is all pretty self-explanatory so Iā€™ll wait and see.

1 Like
48

I know it has been a little while since anyone has posted on this subject but I would like to pose a question to the group. If you were to comment out this line in the firmware;

#define PREVENT_DANGEROUS_EXTRUDE

wouldnā€™t you then be able to use the extruder as the 4th axis and have a true 4 axis router or am I mistaken? The reason I ask is that my ultimate goal would be to have x,y,z and e axis available for use in say milling a model of a crank shaft.

49

Hi, awsome project - Silverback94 - the GCodeRipper mod by Leo - use in gcode E stepmotor - so i think the firmware can interpretate this code. I thing we can use REPETIER FIRMWARE too.

Iā€™m wonder - Leo69 what soft you use to send code to firmware (CAM SOFT, something like LinuxCNC/ Mach3 - maybe freeware software) ? RepetierHost ? or you run from sdcard ? I think you use RAMPS/RUMBA board with arduino to stepper driver ?

I hope you write some of tutorial.
Second question is that GCode Ripper are in version 0.13 - you plan update ? or open source your modification ?

50

I know its been a while but I was curious if there have been any updates?