2.5d or 3d

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danimal
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Re: 2.5d or 3d

Post by danimal » Sun Jun 15, 2014 1:19 pm

3D is moving all three axis at the same time creating a path with varying values on all three axis. 2.5D is moving 2 axis (maximum) at a time through 3D space, while the z axis remains in a constant position. From a software perspective, the program needs to be able to analyze and measure the surface of an object and define a tool path to follow it in 3D. 2.5D is much simpler in that you define a set of constraints in the shape that you want and it draws the tool paths off of those constraints stepping down vertically.

So if you need the program to take a model and build a tool path off of it you will need 3D, if you need to build parts with simple outlines and pockets 2.5D will work just fine.
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WillAdams
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Re: 2.5d or 3d

Post by WillAdams » Sun Jun 15, 2014 2:07 pm

One thing which I've suggested as an improvement for a 2.5D workflow is to take advantage of the G-codes for switching the plane used for arcs:

G17 Select the XY plane (for arcs) --- this is used as a typical default

These would allow one to cut pockets w/ rounded bottoms:

G18 Select the XZ plane (for arcs)
G19 Select the YZ plane (for arcs)

Similarly, one could alter the Z positions for each point as one descends in a spiral and get a more rounded cut.
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Gadgetman!
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Re: 2.5d or 3d

Post by Gadgetman! » Mon Jun 16, 2014 9:43 am

A good definition for 2.5D seems to be:
Anything you can carve with a tool that is always at the same angle to the material worked on.

A bowl can be a 2.5D object as long as you accept that the outside is a vertical cylinder.
If you want the outside to keep approximately the same profile as the inside, though, you're out of luck.
(You can flip it over and consider the inside and outside two separate 2.5D objects, though)
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cvoinescu
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Re: 2.5d or 3d

Post by cvoinescu » Tue Jun 17, 2014 1:25 am

Gadgetman! wrote:A good definition for 2.5D seems to be:
Anything you can carve with a tool that is always at the same angle to the material worked on.
That's the definition of machinability on a 3-axis mill (as opposed to 4-axis or more). For 2.5D, the consensus on the other thread agreed more with:
danimal wrote:3D is moving all three axis at the same time creating a path with varying values on all three axis. 2.5D is moving 2 axis (maximum) at a time through 3D space, while the z axis remains in a constant position. From a software perspective, the program needs to be able to analyze and measure the surface of an object and define a tool path to follow it in 3D. 2.5D is much simpler in that you define a set of constraints in the shape that you want and it draws the tool paths off of those constraints stepping down vertically.
In other words, if your object can be described by a number of 2D curves or surfaces, each of them with a depth, it's 2.5D (read that as 2D + constant depth). If the depth of the features varies continuously, it's 3D. Some 3D objects can be made on a 3-axis mill, some require more axes, some can not be made by milling at all.
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glendresser
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Re: 2.5d or 3d

Post by glendresser » Tue Jun 17, 2014 1:44 am

Another option for making simple, 'organic' type shapes without actually getting into 3D modelling programs is to do a simple gradient in a drawing program and then import it as a heightmap in you CAM software. Here's a simple gradient, imported into CAMBAM (Draw -> Surface -> From Bitmap), and a resulting bowl shape.
You don't have as much control as you would in a 3D program, but I've been using it for some quick-and-dirty marble run designs and I've been impressed with how well this approach works.
Screen Shot 2014-06-16 at 7.26.29 PM.png
Screen Shot 2014-06-16 at 7.26.29 PM.png (157.27 KiB) Viewed 620 times
To me, 2.5D will always be anything that's produced on a 3-axis CNC without any rotating (manual or automated) or anything, but it definitely seems like there are multiple interpretations, so probably a good idea to be aware that it could be used in either context.

Woodworker
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Re: 2.5d or 3d

Post by Woodworker » Tue Jun 17, 2014 2:10 am

Thank you, I will have to give that a try. I normally just need simple shapes and this might be the solution.
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Marty M.
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Re: 2.5d or 3d

Post by Marty M. » Tue Jun 17, 2014 8:52 pm

Auarhau wrote:If you try that approach, I think a large ball-nosed end mill would make life easier. But for anything other then testing and goofing around I would use a proper 3D cam if I needed to make this kind of geometry 8-) I hear good things about meshcam, but haven't tried it myself yet.

I've been using meshcam for drawings I make in Rhino and would say the last revision of the version I have has been pretty flawless, They have a new version but for what I do, I'm OK with the older one.

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