Peter Braroe wrote: > Hello all! > > I am new to the list but have been checking out the project for quite a > while. I am thinking about building a ultralight aircraft by 1) designing a > 3D object 2) Making real by CNC in foam 3) building skin in > epoxy/fiberglass. Much like a surfboard! Stringers and such would of course > be needd. They could be pre-added to the core. > > The thing is, a BIG machine CNC would be needed. Does anyone have experience > building such a big CNC machine? It would need to work object several meters > large. Preferable up to 4-5 meters. > > I am thinking some serious welding is needed for a solid frame but how to > make suitable sliding rails that are long? And are there tooth belts that > long? Perhaps a cograil? How to maintain minimum play? I am sure all these > problems are solved since i have seen big sailboats beeing protyped on TV, > but how to make a DIY version? > > Ideas anyone? > > Peter
Cutting foam makes things easier since the machine doesn't have to be extremely rigid. But it will still be a very expensive project. I suspect cost is somewhat proportional to the volume of the work envelope. So a machine that can work 5 meter parts isn't 5 times as expensive as one that works 1 meter parts, but somewhere between 25 and 125 times as expensive. There are all kinds of creative possibilities for reducing the size, but first you need to define your requirements in some more detail. How much accuracy are you looking for? Achieving 0.01mm over a 5m workspace would be extremely expensive. Even 0.1mm would be hard to do cheaply. If your tolerances are closer to 1mm, things get simpler. How many axes do you need? A three axis machine is usually simpler and less expensive than four or five axes, but smooth curvy airplane shapes might be hard to do with three axes. How big does the workspace really need to be? Does it need to be a 4 x 4 x 4 meter cube, or can you get away with one or two shorter dimensions? For example, wings are long, but only moderately wide and not very tall at all. Where will you be building this machine? A machine that can cut objects that are 4 meters tall might require an 8 meter ceiling - it won't fit in your garage. If you have a suitable space (such as a small hanger), an interesting possibility would be a cable hexapod. EMC2 is capable of running such a machine, although configuring and homing it is non-trivial. A cable hexapod can be very inexpensive per cubic meter of workspace compared to anything else. The tradeoff is limited accuracy and limited rigidity. Alex has made a (tabletop sized) version with three cables: http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Alex_Joni's_Toy Alex's tripod uses three cables to define a point in space - for machining, you need to control both the location of the tool-tip (a point) and the orientation of the spindle. That requires six cables. But it can be done - the original NIST version of EMC did it in the late 90's. No matter what approach you use, such a machine is a non-trivial engineering exercise. It sounds like you aren't afraid of big projects (an airplane is a big project). Just make sure you know what you are getting into. Regards, John Kasunich ------------------------------------------------------------------------------ Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are powering Web 2.0 with engaging, cross-platform capabilities. Quickly and easily build your RIAs with Flex Builder, the Eclipse(TM)based development software that enables intelligent coding and step-through debugging. Download the free 60 day trial. http://p.sf.net/sfu/www-adobe-com _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
