technical question about getting from plans to laser cutting

[Scott Richlen]

So, how do I get from the root and tip rib drawings on plans all the way to the proper lofted ribs written in the proper language for a buddy of mine to laser-cut the ribs for me?  I'm sure there are multiple steps to this process, but I don't have any idea of what they are.  And since I don't know the basic steps, I'm not sure what to ask in "search" to get an answer to this, so can someone provide the basic steps and where to look for additional information?  How do I get there from here?

Thanks,
Scott

[George Truett]

Scott, first of all, you need to ask your friend what type of file he needs to cut from.  I have dealt with several laser cutters, for Alex at AKM I provided CAD files, .dxf format.  Lately, Rob at Balsa Workbench has cut some things for me.  For him, I draw what I want in CAD and then print to PDF, Rob works from the PDF file.  I can show you some examples if you need.

[Dave Rigotti]

I think Scott is looking for how to get the intermediate ribs into CAD for laser cutting?

[George Truett]

If that's what you need to do, it becomes somewhat more involved.  The first thing I do is have the plans scanned into tiff or jpeg format, that way I can grab pieces out of the drawing.  For PDF files, I use PDF Xchange editor, that gives me the ability to manipulate the drawing a lot more than any free PDF Viewer.  Since the Imitation is already out there as a PDF, you can start with that file.  I use the snapshot tool to get the part I want, rib or whatever and then I paste that into my CAD program (DraftSight).  Once I have it pasted in, I trace the part as a poly line.  After tracing, you delete the image you pasted in and you're left with a CAD version which you can now scale and edit to get what you want. 

[Dan McEntee]

       If you are talking about the wing for the Imitation, Mike Griffen did a run  of kits for it. I think he had RSM do the laser cutting, so some one should have already done the hard work and have a file for cutting them. Just find out who, and then how many rib sets you would need.
   Type at you later,
   Dan McEntee

[Mark wood]

I think Scott is looking for how to get the intermediate ribs into CAD for laser cutting?

In CAD it involves lofting method of some sort. There are airfoil programs around that can do the job such a Profili and compufoil. I use niether of them as I have a full suite of Autdesk products at my disposal.

Scott

In terms of doing the lofting of ribs for you friend, It can be either simple or more complicated depending on the root and tip airfoils. If both are the same section and the spar can taper, it is a simple matter of simply scaling either one up or down as a percentage of the initial chord to the local chord for the rib location. If the airfoil sections are different from root to tip then the method is more complicated. How I handle that task is to create a surface of the wing and then cut sections at each rib station. Each the sections will result in the intermediate airfoil. I don't work in solid modeling tools but they have a similar function.

It takes a fair amount of time and effort to create the required files to make a wing rib set for a laser cutting job. In reality, for a one off airplane, it is much less effort to simply use the method of making two templates from the plans and do the stack and sand method. I know we tend to think the that the CNC and laser machines are so great but they aren't well suited for the simple single run projects. Sometimes they are because it is the only way we can make the part wanted but for the most part, the machines are best for production.

[George Truett]

I forgot Mike had done the Imitation, that would certainly be the easiest thing if he's willing to share.  You could always consider foam wings or the Lost Foam system, then you only need root and tip.  Profili is pretty easy to use and not horribly expensive: http://www.profili2.com/eng/default.asp

[George Truett]

Scott,  I traced the Imitation Ribs in DraftSight real quick to get an idea what you will have to work with.  I scaled the tip rib to the same size as the root and they are almost identical, the only difference may be in the tracing.  I usually only trace the top and then mirror it so I have perfect symmetry.  I went fast for now and traced the entire rib so that could explain them not being exact.  If they are in fact the same, only scaled, lofting is simple, you just scale the ribs down in order of how many you want.  For example, you want 16 ribs, just scale so each rib is 1/16" less overall then the one next to it.  It's easier than it sounds, sketch it out first to be clear in your mind.

[Steven Kientz]

look @ Rsm under building supplies, additional laser cut ribs.
Steve

[Mark wood]

I might would add, that for a reasonable fee for my time, I would be willing to do the CAD work for you.

[ericrule]

The suggestion about asking the laser guy what file format he uses is the best advice you have received so far. Most of the lasers in use today use a controller from Ruida Corp. This controller converts the drawing into a code that the laser machine can read. Most of the people with these machines have also obtained an app from Ruida that allows them to automatically convert AutoCAD dxf or dwg files. Check with your preferred laser cutting to determine what he uses.

If you are asking how to create the ribs using the root and tip ribs then either use 3D AutoCAD or something like Compufoil. Either program will produce accurate AutoCAD drawings of each rib. Once you enter the wing details (# of ribs, location of first rib, length of wing panel, sweep, rib thickness) the programs will create each rib and also provide you with a wing panel drawing showing the proper location for every rib.

If you are looking for a set of ribs for the Imitation just contact Mike Griffin and ask if he will allow you to use the AutoCAD file he owns. I created that file and it has all of the ribs plus other parts drawn in AutoCAD. You can also ask Mike if he will give permission for Mike Hanson at RSM Distribution to cut the parts for you.

Hope this information is of assistance to you.
Regards
Eric Rule

[proparc]

Requires Lofting capability. Welcome to the world of 3D CAD. Compufoil can do it. Autocad, Inventor, Fusion, Solidworks etc.

[Scott Richlen]

Thanks guys!  Lots to think about.  Not sure what my next step will be.

[ericrule]

Yep Milton. That "lofting" exactly what it is called. Although I have known you for years I forget what an expert you are in AutoCAD. My Bad!
Eric Rule

[phil c]

If you aren't planning on doing a lot of this I use a fairly simple method in a fairly simple CAD program.  Unless you are in the business of drafting learning how to use the CAD program can become a life in itself.
Get a drawing or coordinate list for the airfoil.  The exact airfoil is never attained unless you have some really powerful software and tools and CNC machine the whole surface down to +/- 0.001.
Not being able to do that, place the spars on the airfoil drawing.  Trace curves between the LE, the main spar, any auxiliary spars, and the trailing edges.  Most of the cutting software will not choke on ordinary curves or polylines which are  easy to work with.  Get it as exact as you can.  With the coordinates you get pretty accurate easily.  Trying to trace from a drawing can take more time to get a smooth, representative airfoil by pulling the control points for a curve around.

Lay out a top  view  and a front view with the correct root and tip dimensions.  Draw each rib, getting the dimensions directly from the top and front views.  Position the spar(s) in respect to the airfoil centerline or true chord for non-symmetrical airfoils.  Copy the curves from your original airfoil drawing and stretch them to fit where they belong between the LE, spars, and TE.  Voila, one rib done. 

Foam wings only require a root and tip templates.  These, depending on the foam cutter, will usually be several inches from the root and tip so make allowance for this.  Foam cutting also require making an allowance for the wire kerf.  Some cutting programs will allow for that, but it's a mixed bag on a tapered wing.  The kerf wider at the tip, so the best bet is to set things up with minimum taper and set the wire temperature, and cutting speed to just just the root of the wing with no drag marks or rounded corners.  If you can cut REALLY slow you can get the kerf down to twice the wire diameter.