I'm working with a company right now that is assembling a very large 5 axis machine. The too head pivots in two axes and and it is mounted on a gantry slide to create the 5 axes. The final drive at the head is via wide toothed belts - HTD type of similar.
The head is a yoke type design - supported on both sides of the pivot and the gearbox and servo motor extend through one side of the yoke and spin the other member via the toothed belt which is probably 3 inches wide. Think of a driven U-joint for a car or truck. Part of it looks a lot like that but much bigger. The joints are supported on two sides. This machines bed length is about 25 feet long by about 12 feet wide and I believe there is about 8 feet under the tool. It is very massive machine since it is designed to be able to provide a tool tip pressure of 5 tons in any direction. The gantry frame is heavy boxed steel sections. It all runs on linear square rail bearings that are very large - about 2" square. The pivoting head mechanism is at least 3 feet square in size, approaching 4 feet. This machine spins a tool but it isn't a cutting tool... that's about all I can say about it since I signed my life away with NDAs at this place. My point is that if they can use toothed belts for the final drive on a machine this big, I'm sure they can be used for a smaller machine. Dave On 4/6/2011 5:54 AM, andy pugh wrote: > On 4 April 2011 05:30, Sven Wesley<svenne.d...@gmail.com> wrote: > > >> I need to make a tilting head 4-axis, further on also rotating to get the >> 5th axis. Before I start making parts, has anyone already made a similar >> machine or own one and would like to provide some details? >> > Chris (I think) has a tiny little 5-axis mill, but I am not sure how > well his design would scale up. > http://www.youtube.com/watch?v=1EYaM4FkASA > > It seems to me that if you engineer it like a lathe headstock with big > taper rollers then the rotation is relatively easy to achieve. (and > co-axial drive to the spindle seems like it ought to work if you do > not want to swing the motor). > The problem I see is finding a suitably stiff and backlash-free > actuator mechanism. I don't have much feel for how stiff toothed belts > would be in this application. Chris' mill has the cutting tip very > near the axis of rotation, which will mitigate this problem somewhat. > > My mill has an adjustable-angle head, and I have pondered whether I > could make a "sandwich" drive to go between the clamping surfaces, > possibly based on a large-diameter crossed-roller bearing (if one ever > appears at a good price) > > You might find a harmonic drive on eBay which would be a good start. > > Another solution might be a drive mechanism which in "invented"[1] at > a previous employer which uses a large internal gear with 3-4 more > teeth than an external gear. The external gear has an anti-rotation > link (preferably a flexure, but peg-in-slot might work), and is held > tightly in mesh with the inner gear by a rotating, eccentric, housing. > There are a lot of teeth in mesh, so it is stiff and low-backlash, and > the effective gear ratio is the tooth difference divided by the tooth > count, so 50:1 or so is pretty easy to achieve. Drive to the eccentric > is the "right side" of this ratio, so can probably be a conventional > spur or bevel drive. > > [1] Almost certainly not for the first time so I don't mind describing it here > > ------------------------------------------------------------------------------ Xperia(TM) PLAY It's a major breakthrough. An authentic gaming smartphone on the nation's most reliable network. And it wants your games. http://p.sf.net/sfu/verizon-sfdev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
