How about 48" Z stroke?
Mach3 2010 Screenset
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
I have seen some CNC machines that are built for mold making that have very long, 12" or more Z travels.
It all comes down to the design.
Start by defining your work envelope. Then calculate the cutting force required for your work. Then design a gantry and Z axis that is stiff enough to withstand the cutting force.
Thanks to all for the feedback, pro and con.
Gerry does have a point, though. Router bits are relatively short and the more vertical the surface, the more difficult it becomes.
Sounds like I need more than 3 axes to achieve my overall objective.
How do I explain this... Your goal has to be as narrow top view "footprint" as possible so you can do typical 3d deep plunge toolpaths without having anything like a conventional router hanging out in the way. If you just take a typical 6" long bit in a traditional router, the achievable angle of approach for a deep cut is very limited.
So, make the sliding portion of the Z axis out of very thick wall ROUND tubing, and put a machined and balanced shaft with a collet system on the bottom, right thru the middle of it with high end bearings properly mounted on each end. This round tube can slide up and down on properly sized, conventional THK style bearings and rails, with the rails mounted on the tube for maximum travel. The new spindle shaft is driven by toothed belt and pulley from the very top, where whatever motor you pick to drive it is also mounted or clamped to the side of the tube.
Now if you have access to a really good machine shop, you could have the bottom foot or so tapered down, or slimmed down to narrower tube to minimize the footprint near the cutting tool. The linear rails start a bit higher than this narrow portion.
Some calculations have to be made or some good seat of the pants understanding applied when it comes to the size of this tube so it does not flex. If you were cutting foam plugs, this could be lighter duty. Again, you really need a thin profile of the spindle in order to get your longest bits to run along the vertical sides of what you are cutting without a router in the way.
I *think* I can visualize what you're describing, but a picture would be most helpful.
I happen to have a small machine shop (lathe, 48" mill, both with DRO) and am reasonably proficient.
More information (awaiting the flames)... I'm planning to use a heavy duty foredom tool with a shortened shaft (minimize shaft flex) in order to keep the tool head as small as possible.
I'm also investigating 4/5 axis solutions with automated path mapping that would keep the tool center line orthogonal to the surface. I refer you to the following doctoral dissertation Tool Path Generation and 3D Tolerance Analysis for Free-Form Surfaces (http://txspace.di.tamu.edu/bitstream...pdf?sequence=1)
One question... (Dammit, Jim. I'm a statistician, not an engineer). Will FEA software (a) generate vectors orthogonal to an irregular surface and (b) provide them in a usable file format?
I agree that this approach is highly ambitious, but it's piqued my curiosity and I feel compelled to follow it; at least as far as my skill allows.
Found a photo... weak, but the best I have. Its almost from before the internet era !
The idea was developed by a fellow I met named Dave...... Not something I "invented".
Notice that this was made specifically for FOAM plug cutting, and worked well. The spindle "footprint" is comparably non-existant with a long bit compared to a typical router. The main tube slides in a traditional round linear bearing, and the top is controlled via THK.
I believe this was a 2" diameter tube... may have been 2.5". Don't recall !
The shaft in the middle was NOT a simple home brew shaft... it did have to be properly hardened and balanced.