Accurate modeling of machining operations?

[Anonymous]

In figure 1A, the grinding wheel has cut the workpiece along the indicated path.

But the software can not sweep a solid body, so in figure 1B the cut was made by sweeping the profile of the grinding wheel.  The resulting cut is missing the rounded end. I call this the ghost cut, the part of a cut made by a solid body that is not modeled by a planar profile.

In 1C, note that figure 1A was actually made by extruding the ghost cut as a separate feature.

  

In figures 2ABC, the grinding wheel follows a curved path. Again, the cut was modeled by sweeping a profile, then adding the “ghost” by hand.

  

These were trivial cases. In general, for arbitrary tools and paths, I have not the time nor ability to solve the ghost on my own.  Am I expecting too much?  The Modeling tools are for “mostly prismatic geometry” and Sculpt is for “when shape is more important than exact sizes.” I was hoping for a tool that could analyze exact details of tool, die, & workpiece interaction.

[etfrench]

Wouldn't you normally model the desired shape, then choose the tool and toolpath to create the shape? The simulation tool works fairly well and shows if the tool is removing too much or too little material.

[Anonymous]

Model shape first? Often, no. 

Once we made a scale model saxophone 50 feet high. The tone hole of a saxophone is the intersection of a cylinder and a cone.  This curve is an irregular saddle shape.  I didn’t “model a desired shape” to get that curve.  I specified the cylinder and the cone, the shape was what it was, and we worked with that.  I guess that’s the “desired shape.”  (Back then we modeled it with QBasic and plotted templates with asterisks on fanfold paper.)

Lets redefine the problem: we have a solid object of a particular (possibly complicated) shape, moving in a (complicated) path. We need a “hole” in some body that can accommodate the moving object.  (And we want a close fit – maybe it’s a novel progressive-cavity pump, or a pneumatic actuator with a non-linear motion.  Or a cam and follower...)  We have already stated the design intent: the body and its path.  The shape of the “hole” is a consequence.  So no, we would not design the hole first.  Maybe we will 3D print it, so there really wont be a “tool” and “path,” but how do we model it?

I know that’s an extremely general question, but Fusion can model very general bodies and paths. How to put the two together?

I hear what you’re saying about Simulation. That can tell me if the “hole” is OK.  But if it isn’t, I guess its back to Qbasic (well, C++) or maybe a die grinder?

(Just a thought – injection molding has a big advantage over 3D printing – you only have to use the die grinder once!)

[etfrench]

Sweep will work for both of the examples in your first post.

In the first example the path needs to be the path a single point on the cutter circumference will take.  The simplest way to draw the path would be to use the slot command (Either Center to Center or Overall) with the width equal to the diameter of the cutter. 

In the second the profile needs to match the arc where multiple points on the cutter circumference will move.

It would be interesting to see and hear a 50 foot saxophone being played   The tone hole would be trivial to model in Fusion 360.

When I have something hard to model in Fusion 360, I ask myself how would I do it on a drafting table.  That will usually point the way to modeling it in Fusion 360.