Four axis routing is not much different that three axis machining. Instead of moving the router head across my table (X axis) the rotary axis rotates the work in minute degrees while the spindle travels up and down the piece in the horizontal and vertical planes. Y & Z axis) The good news is the software does all this work for us. All we have to do is build the files.
The trick is to know (and understand) what is happening and how it affects our design. For the most part (currently) we will build the designs as we always have. The key is both sides of the design must match or it will look funny was the design is wrapped around a center line. The join line needs to be invisible to be right The second factor to remember is that for 3D designs the further we get from the center axis the more things will stretch out as they are wrapped. The key is a little math to figure out circumferences and the like. I am sure there are formulas to calculate the amount of stretching that will occur at each distance from the center but I tend to do this by trial and error, learning by hands-on experience. It has been a lot of years for me since I did any math remotely like this. The good news is the internet and calculators makes finding the basic solutions to the math relatively easy these days.
Like all aspects of 3D design there is a definite learning curve and this is definitely a little trickier than flat work - but if I can get my head around it most should have no trouble with it after lots of practice and a little trial and error. Luckily I have a super sized garbage bin. I filled it often when I first started routing and I suspect that time is upon us one more.
For the balloon we want each section to pillow out as well as have the middle section much fatter than the ends. The cones will be routed and installed separately. It is just easier and quicker that way. Since the ends taper to almost point a lot of material and machine time would be used up for little effect by doing it in one go. I started the balloon with diamond vectors and a vector rectangle of the size I needed.
My block of Precision Board is 14" square on the end and 20 inches long. The balloon would taper to 6" diameter on the end meaning the circumference is 6" x 3.1416 The plate for the balloon would measure 18.8496" W x 19" H. Then I set to work. Everything would be done inside EnRoute.
I built a diamond shaped grid, making sure the corners of the diamond shapes went through the corners of the rectangle. I pulled these lines to the side and used the jigsaw tool to extract the diamonds as individual shapes, then deleted the lines. Then I used the offset tool to create smaller diamonds inside those. These would be the basis for the pillow shaped puffiness of the balloon.
Then I deleted the lines and lined everything up just right.
Then I drew an oval in the center. This is where the balloon will hook up to the hot air pipe from the gondola. The jigsaw tool was again used to trim the surrounding diamonds to fit.
Then I built the plate. The end diamonds were flat reliefs added to the original plate. Then I built the puffy diamonds in the center using the dome tool. I forgot to get a screen shot of that stage but it is pretty simple. At this point the relief is still flat with the puffy diamond pillows.
Then it was time to build up the center of the ballon to make it look like it was inflated. I knew I wanted a 3" high arch so I built a 3" x 19" box. I used this as a guide to create a curved vector line which would be used in the next stage - sweep two rails. I also created the two vertical vector lines that hug each side of the relief.
I used these lines with the sweep to rails function and got a mesh that looks like this.
Once I had added the mesh to the relief it formed the arch I wanted.
When I looked at it at this point I realized I had made a serious mistake. On reviewing my notes I discovered I had calculated the circumference incorrectly and for some reason had made the file only twelve point something high instead of the required 18.8496" It was a simple matter of stretching it out to size. I actually liked the shape of the diamond better and since I was in charge I made an executive decision to forge on ahead. I wouldn't have to start over.
In 3D view it looked like this. The end towards the viewer would wrap around to meet the other side and form the balloon shape I wanted.
To run the file on my new four axis MultiCam I tool path the file as I would any conventional 3D file in EnRoute. I used a half inch ballnose bit with a 50% overlap for the rough pass and a 3/8" ball nose bit with a 90% overlap for the final. All speeds were set at 300 inches per minute. The MultiCam software takes the G-code and converts it for the round axis automatically. Next week I'll show a movie of this file running on the machine.
In the mean time as a teaser I show you a wireframe simulation of the balloon as it will look when it is cut. (side view)
This makes me smile. Imagine where we will go from here...