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Thread: 2.5D or 3D?
09-02-2010, 11:31 AM #1
2.5D or 3D?
I'm still not clear what the difference is between 2.5D and 3D. If I wanted to engrave a circle into an inclined plane, is that a 2.5D or a 3D function?
09-02-2010, 11:52 AM #2
2.5d is basically positioning in 2d then drilling with the third axis
3D is all 3 axis interpolating together ie moulds or your inclined circle
09-02-2010, 12:49 PM #3
Here's the definition of a 2.5D part I like best-
If you place the part on a flat table and look down at it from the top, every machined surface on the part is either parallel to the table surface or at 90 degrees to it.
You can have pretty complicated parts that fit this description and thus can be made with 2.5D design tools, they can have pockets, shelves, cutouts, shoulders, ledges, etc., all with arbitrary outlines and still be 2.5D parts.
One thing to keep in mind is that a 2.5D CAM tool will typically generate tool paths that don't limit themselves to 2.5D motion, ie they will use ramped plunging and helical paths when it makes sense, but the final completed part will fit the 2.5D description.
09-02-2010, 02:20 PM #4
So if I have a 2.5D mill, do I need to run it with a 2.5D CAM tool? Will a 3D CAM tool work, or will it be somehow incompatible with the mill? Can a 2.5D setup create, say, a hemispherical pocket?
I'm still a bit confused as to whether the 2.5D/3D limitation is part of the mill itself or just a software modification ..... people talk about upgrading a 2.5D mill to 3D and swapping out hardware to make this happen. Is there something in the servo drivers that makes the difference, etc?
Also, I was thinking about getting Rhinocam2.0 (a bit of a shot in the dark since I'm so new to CNC) since I was told I could design everything on the laptop, and Rhino would ultimately create a Gcode file that I could dump into the mill with little or no modification. But doubts keep creeping in as I hear other stories about additional software being necessary to manipulate the Rhino output before it is truly ready to run. Any ideas on this?
09-02-2010, 02:39 PM #5
Unfortunately from my understanding a 2.5D mill is a more limiting than the limitations of typical 2.5D CAM software. I believe your 2.5D mill can not have the spindle be moving in the up/down Z direction if either of the X or Y axes are moving and unfortunately this is pretty restricting.
Rhino would be overkill if you are working with a 2.5D mill. Rhino is powerful for designing complex 3D shapes but its not so hot for 2.5D designs as it takes a lot of rework when you need to make design modifications and its human interface is fairly "unique".
I'd start with one of the free 2D CAD packages. I've used the SolidEdge one, its a pretty powerful parametric style design tool but it does take a while to get comfortable with it.
Solidworks has also just introduced a free 2D CAD package that is also apparently pretty good.
Take a look at SheetCAM from SheetCam homepage for a CAM tool. I think it may have a configurations setting to specify you have a 2.5D machine (otherwise it will using ramping and helical toolpaths that won't work on your machine). Its a solid package but its pretty affordable (I think around $250. now) and they have a demo version.
09-02-2010, 02:50 PM #6
And "Here's the definition of a 2.5D part I like best ...... " ..... to dissagree with.
You can doo a lot more than that with a 2.5 mill. You CAN cut in X/Z and Y/Z to create inclines or even rads.
It does NOT have to only be a 2 axis position and then drilling setup.
A 2.5 axis can NOT move all three at the same time. It CAN move ANY 2 at the same time. (May require a G code for "plane designation" to achieve.)
As for the inclined circle - that would be 3 axis.
And for the CAM - I wouldn't have the first clue.
Think Snow Eh!
09-02-2010, 03:11 PM #7
2.5D is any 2 axis moving at the same time, then the .5D positions for the next 2 axis movement, be it XY, XZ or YZ. as others have said i can cut domes, sphears ramps and even complex 3d parts with 2.5 axis CAM. a planer cut in x or y direction is 2.5 but if i planer at an angle say 45 degrees then it is 3 axis machining as is the circle on an angled face, XYZ moving at he same time.
09-02-2010, 03:18 PM #8
The restrictions on 2.5D machines are pretty different from the restrictions on 2.5D CAM tools, the description I gave only applies to the CAM tools.
Born2, if you have a 2.5D machine, definitely make sure that any CAM tool you are looking at can function with the machine. I believe the SheetCAM tool I mentioned will, but I'd definitely check with developer. He'll also be able to tell you if there is a post processor for your machine, typically if not he'll create one for you if you can supply him some example G code that was generated for the machine.
09-02-2010, 03:59 PM #9
Then that means a 2.5 D machine can't thread mill, correct???
What about helical interpolation on cleaning out a hole?
Thanks for asking this question. There are somethings about this that I have been wondering about, myself.
09-02-2010, 04:13 PM #10
Can a 2.5D machine be upgraded to 3D by swapping out some of the electronics, or do the all electronics have to be totally replaced? One of the programs I want to run is Vcarve, and I believe it occasionally requires all three axes to be in motion at the same time.
I was told that 2.5D could run any two axes in a non-linear manner (say cutting a circle) while the 3rd axis was moving simultaneously but restricted to a linear motion. Has anyone else heard this? This is a Milltronics machine if that makes any difference.
09-02-2010, 04:33 PM #11
Milltronics offers really good support even on their older machines. I'd call them and give them the model number and ask them what the restrictions on your machine are.
You can ask them about any potential ways to upgrade it to full 3D, but that may not be practical anymore, if the control was 2.5D its got to be pretty old.
Unfortunately likely the only way to upgrade it to full 3D would be to retrofit it with a new 3D controller, but to be candid, unless you have way more time than money it would be more cost effective to sell that machine and buy another one that has a more modern controller.
09-02-2010, 04:47 PM #12
Sounds like I better get hold of Milltronics in the morning. They advertise being PC based and easily upgradable so I guess I'll find out. I have heaps of time and don't mind the effort swapping out controllers.
And I do thank everyone for the replies, I've learned a lot in a very short time!
09-02-2010, 05:42 PM #13
Also, I'm getting the impression that all the good software is written for full 3D machines, and that 2.5D has pretty limited support any more.
09-02-2010, 05:50 PM #14
So.... a 2.5 axis mill can only move 2 axis at once, I've never run across that.
However I have a 1978 Wells Index with a Bandit control on it sitting out here that will do a 3 axis linear, but not a 3 axis helical move. It will do an arc, but only in 2 axis. So what is that... 2-11/16 axis? or is it 3 minus a qwata axis?
09-02-2010, 05:52 PM #15Then that means a 2.5 D machine can't thread mill, correct???
What about helical interpolation on cleaning out a hole?
How does helically interped "cleaning" differ from thread milling? You explain that - and then maybe I can answer that question.
I was told that 2.5D could run any two axes in a non-linear manner (say cutting a circle) while the 3rd axis was moving simultaneously but restricted to a linear motion.
Can a 2.5D machine be upgraded to 3D by swapping out some of the electronics, or do the all electronics have to be totally replaced?
Think Snow Eh!
09-02-2010, 06:14 PM #16
Ox, not sure what you mean by a "control" issue. Does that mean a simple board swap makes the difference between a 2.5D and a 3D machine? Or do you mean the difference is simply in the software? Or something more? Sorry if I sound like such a dummy, but I've been bitten too many times 'cause I didn't ask all the seemingly basic stuff.
Last edited by borne2fly; 09-02-2010 at 09:07 PM.
09-03-2010, 04:43 AM #17Does that mean a simple board swap makes the difference between a 2.5D and a 3D machine? Or do you mean the difference is simply in the software? Or something more?
Control = 'putor.
Think Snow Eh!
09-03-2010, 05:47 AM #18How does helically interped "cleaning" differ from thread milling? You explain that - and then maybe I can answer that question.
Looking back at it now, the machine ran down in Z. Made a cut from the outside in ( kinda like a record player) then went back down in Z and repeated. After the cleanout, it would make a final pass around the outside dia of the hole.
Really I guess this would be a phony helical interpolation.
09-03-2010, 07:02 AM #19
2.5D thread milling on Denford Triac
I have a Denford TRIAC CNC mill and it is a 2.5D machine, i.e. it does not cut under parts. There is a definition earlier which seems to fit very well - whatever you can cut from the top looking down onto the table. I would need a 4th rotary axis in order to be able to cut all around the part and produce a true 3D cut.
Regarding thread milling - have a look at this:
YouTube - Thread milling
My machine can have all 3 axes x,y,z operating concurrently - so I wasn't too sure that 2.5D defines only 2 axes that can be moved at any one time.
It does get rather confusing as you can get machines that have multiple axes but can only cut in 2.5D!! i.e. the part can be positioned any how but the machine will only be able to cut from the top.
09-03-2010, 07:34 AM #20
This entire discussion is controller hardware/software specific.
In particular, there are 2.5D controllers that will do threadmilling (but not general helical milling) via some special code added on (sometimes at extra cost.)
So whether *your* controller can do thread milling and the like is specific to the controller - it may have "special stuff" for special cases.
(By comparision, a full-on 3-axis let along simultaneous 5-axis controller doesn't need special thread-mill or helical routines, it's just a standard command.)