Yesterday i tried my 4th axis for a real project for the first time. This post explains my difficulties experienced on this.
I use these cheap glue clamps made out of plastic all the time. Eventually they will break in the plastic somewhere. Until now i have made some handles out of plywood to replace the plastic by cnc and some handy work too.
One obstacle with making the woods handles is to make the groove for the spring. Now I can make such a handle with my cnc and have the groove made by the cnc to. Both handles for a single clamp are exactly the same.
I ran into several problems when making this handle.
- Creating the CAM operations.
It is much easier to make the CAM operations work together, for instance after the stock is rotated, if the zero point is at the center line of the rotating axis. In this exact case the stock dimensions are changing when the stock is rotated. If zero is not at the center, you need to take this into account for every CAM operation you create. If you place the Z zero at the A axis centerline, everything gets much easier.
- Zeroing the axes
I had more work aligning the zero point as i did not have the best probes for it. I’m my case it was either by eye or by using my z height probe in new creative ways. My conclusion is that i need to make some specialised probes for zeroing 4 axis jobs.
- 4th axis alignment
It turned out that my 4th axis was not in alignment after all. The t slots i made from curtain rails are fine, but the tail stock 4 holes in the base are to wide for the slot opening and as a consequence of this i chose smaller screws. I need to make it fit exactly so it won’t move sideways at all. Misalignment in the y direction causes the job to be milled offset on the two sides of the stock. You would not see this if you just mill ex. 0 and 90 degrees, but it clearly shows if you mill more sides than that.
- Stability
Having stock dangling in two tiny points is a weak construction in general. Milling speed therefore needs to be reduced. In my case i needed to reduce to one 1/3 feed speed to avoid chatter. The end result is a feed of 1000 mm per minute worth a 3mm endmill. This is not a problem for this hobby setup. It’s just a fact.
Let this be a lesson to you all 
