Help! Profile to 3D CNC cutter

[Jscheehl]

I am new to autocad and have version 2010. I am hoping to get better at using it so i may begin using it to draw items to cut with my cnc router. I am trying to use it to cut out the ribs and stringers for an RC airplane but cant get the stringers to work quite right. I have figured out how to displace the ribs along the y axis at the correct interval and can see them fine when i select them as an individual item to move them and save as an individual piece of the plane. I am trying to draw several lines from the closest circle to the farthest. I want it to follow the curve that the side of the airplane has. I would like then to select just that line and put it on a 2d draw space to dimension it then load it to my cam software to cut out from a piece of balsa. any help would be great. I can kinda get a spline up there but when i look at it from the front, the line isnt straight. If you can imagine an ice cream cone, with a large circle at the front and small in the back. I am trying to draw sections of the sides of the cone going straight from the front circle to the back and forming the shape of the cone down the side. This is really hard to explain. Thanks in advance.

[kencaz]

A screen shot would help us out a lot... I think I follow what your trying to do but still...

 

KC

[Jscheehl]

K. let me see what i can do.

[Jscheehl]

Ok i don't have autocad here at work but here is the basic concept of the stringer/rib design. The ribs are each cut out of balsa and are positioned in order from largest to smallest from the front of the aircraft to the rear. The spacing between the ribs is a fixed dimension. The stringers intersect with each rib and run the entire length of the aircraft. The curves of the aircraft are defined by the way the stringers intersect with the ribs. This image shows almost exactly what i am trying to draw with the exception that the stringers are perfectly straight. Keeping the stringers straight keeps things simple but also makes a very straight, not as modern or aerodynamic fuselage. I am able to draw the ribs and move them to where they resemble the aircraft, but when i try to draw the stringers by making a spline intersecting each rib it does not turn out at all the way it should. the stringers should be about 1/8" thick and 2 inches wide or so and the lengths and curve change from stringer to stringer. Where the stringer intersects each rib, it should be oriented perpendicular to whatever angle the outboard edge of the rib happens to be. not sure if any of this makes sense but im trying. LOL. Thanks again.

[MikeScott]

I sense some lofting is required.

 

Also.. Those stringers ARE curved in one direction, and then rotated, because the ribs aren't the same size.

[Dana W]

I think the OP's ribs (actually formers) are going to be spaced and sized so that the stringers are not curved, thus achieving a more flat sided, cone shaped, rather than bullet shaped fuselage. The stringers are still going to be rotated, though.

 

I dunno nuthin' bout 3D AutoCAD, but I could build ya a RC plane with no plans and my eyes closed (well, maybe an occasional peek):wink:. I'll be interested to see the finished product fly.

 

I would suggest laying out the four main stringers (longerons) first, the ones running along the center lines of the top, bottom, left, and right surfaces, and which are on the 90 deg points of each former. In order to get to this stage, I would have to have at least two longetudinal 2D sections of the fuselage, vertical, and horizontal. I would place the longerons first to define the fuselage outline, then place my formers. This would give me accurate height and width for the formers and attachment points for the longerons.

 

Don'tcha just love the way airplane parts are named after French girls. We will say hello to Ms. Nacelle and Ms. Empanage later.

 

After I have that done, I would draw an elevation of each former with the additional stringers arrayed around them. But, I suppose 3D software makes shortcuts for all of this layout work, or does it?

Edited August 23, 2010 by Dana W

[Jscheehl]

I have the plans for the plane in PDF format and would love to see an example or have to try to explain how i can make it using autocad. The 4 main longerons are certainly easy. i have the crossection view giving me the shape of those and they do curve making a very smooth looking plane. the part i cant get is all the stringers in between each of those 4 main longerons. I would like to have them spaced depending on the load they will be carrying. so along the sides of the plane further apart and closer to eachother at the tighter radius curves.

[Dana W]

I have the plans for the plane in PDF format and would love to see an example or have to try to explain how i can make it using autocad. The 4 main longerons are certainly easy. i have the crossection view giving me the shape of those and they do curve making a very smooth looking plane. the part i cant get is all the stringers in between each of those 4 main longerons. I would like to have them spaced depending on the load they will be carrying. so along the sides of the plane further apart and closer to eachother at the tighter radius curves.

 

You can attach the pdf file to a post here if you would like to, but I think they may be copywrited material, so decide wisely. There is not a huge market for model airplane plans and the people who draw and sell them are a touchy lot. If you have a scanner, just scan the pertinant section of the plans in to a 300 dpi jpg, and post that.

 

I may have missunderstood you. I thought you wanted to flatten out the fuselage side curve form a bit to make it simpler to build.

 

These plans must be from some sort of kit. Plans for a cut it yourself plane would include a pattern for each former. Most kits have pre-cut formers, so you don't need the patterns.

 

Like I mentioned, I would not have a clue how to draw the plans in 3D preped for CNC machines. If I were to draw them, and I have drawn a few, I would do it in 2D, because I am an old school builder who prefers to cut and glue by hand with everything pinned down to a copy of the plans on a workboard.

 

One way to locate the intersections of the stringers on the formers is to orthographically project them from the longetudinal section drawing, once it is copied into AutoCAD, to a face on elevation view of each former.

 

This really looks like a whole lot of 2D drawing needs to be done in order to determine some of the unknown details, before starting to create solid parts.

 

I only jumped in here because I love RC model planes. (I don't have any of my aircraft plans on the computer. They're all on paper. It's the "Cobblers Kid's Syndrome".) I should stand out of the way until you have questions or issues with the design itself, but there are RC forums for that.

Edited August 26, 2010 by Dana W
tried 3 times to spell copywrite rite, uh right.

[Jscheehl]

The loft Command works! it looks great! thanks for the tip. I copied all the formers (ribs) and aligned them all to scale, i drew a line from the center of all of them as the path and did the LOFT command and it looks just the way it should. Now for the question, is it possible to look at the newly drawn fuselage in the 3d or 2d wire frame view and convert all the lines that the loft command drew into individual poly lines, arcs, or splines??

[MikeScott]

The Explode command should break those down for you I think.. (I have old autocad with no lofting, so I can't verify that). However, that may also stop the item from being a 3d solid.. which you probably don't want.

 

For a 3d view, you could type in 3dview. If you're not seeing a wireframe view, you need to change your "shade" options..

 

Eventually, what you're probably going to need to do with it, in terms of getting it ready for CNC..:

 

You'll have to use "set UCS to face" ..select the face you want, and then "set view to UCS". I'd then copy the part (3d or otherwise), using the "copy with basepoint" function, and paste it into a new drawing so that it's isolated, and flat to your view so that you can lay the part out on your blank.

 

There's other ways to achieve that, but this'll get you started, and my experience with CNC files from DXF has taught me to use a new file every time, just to keep the file clean before it goes into your cam system.

 

Then go back to your original file and do the same with the next piece.. and add it to the part file you're creating. When you're done, use the "Purge" command to drop out any nonsense that might be unusued in the part file.

 

The ideal format you want to save it in (assuming your version of AutoCAD can do it) is a DXF version 12.

[Jscheehl]

I dont mind it not being a solid. What im looking for is the wireframe so that i can grab each piece, place it in its own file and get it ready for CNC. Ill give the "explode" command a shot. Im hoping that i can grab hold of all the individual pieces, lay them flat and have them cut out ready to glue together. Kind of like the 3d wooden puzzles that you can buy, each piece is cut with a notch that fits into a notch on another piece. Is this possible using autocad? I have version 2010.

[MikeScott]

Yes, you DO mind it being a solid.. your DXF to N-Code for the CNC machine will likely require it.

 

Plus, a solid is just a solid view of a wireframe.. if you explode it, it'll be a series of lines, and likely not usable by your Cad/CAM software.

 

What you want is to "SEPARATE" the solid, so you end-up with the separate 3d pieces. Try using the "separate" command. If that doesn't work, you'll need to use the slice command. I'd help you with the usage of that command, but from what I understand, it's changed since my version of CAD.

 

As far as the "puzzle piece" concept, you can do that to a certain degree.. it depends on the cutting tools you use. you'll need to allow for the width of the cutting tool between each part. So you'd need to separate the parts a bit in your "nest".. which is to say, the wood blank you're going to cut the parts out of, is what you lay the pieces down inside of.

 

You can buy nesting software, but there's nothing for AutoCAD as far as I'm aware.. AutoCAD will help you get to DXF, but you typically need CAD/CAM software to position the parts in your nest.. Nesting software permits you to maximize how many parts you can get on your nest.

 

I use CAD to size/shape my products, and then import the resulting DXF file into my CAD/CAM software to make the actual nest, and select which tools to run and how to run them.