3d machining a twisted wire


(Idan) #1

Hey all, I recently came across a nice picture frame that had a decoration that looked like a twisted wire / wire rope / stranded wire along its edge and thought it might be fun trying to machine something like that. I modeled something basic in Fusion 360:

I didn’t get very far in the CAD department though. It seems like I’d want a Parallel toolpath with a constantly changing pass direction, as the tool advances along the circle. I’m not sure Fusion can produce something like that.

Can anyone think how to produce the necessary toolpath to get a decent looking result? Here’s how Fusion simulates the good portion of its Parallel:

https://a360.co/2HozQk1


(mikep) #2

The stepover is too big, and you’ll also need a smaller endmill to get the detail in the corners. Beyond that, it’s going to be really difficult to do the undercut.


#3

This is a tough one to get ideal results with any standard tool, but you can improve the result several ways.

First, rough with a larger tool leaving about 0.2mm (0.008"). Then run a finish with the larger tool, knowing that it will not get the finest detail. Then change to a smaller tool and run another finish pass with rest machining. Then a smaller tool yet and do it again. The finish passes should be run with a maximum step of about 1/8 the tool diameter for this kind of convex detail. (The geometry isn’t real hard, but a rule of thumb works OK here)

The strategy is the other thing. I would not use parallel here. There are a number of other options that will hide the scalloping better, or make it look like yarns in a rope strand. The Inventor (I think it is the same in Fusion… not on this computer to check) I would go for it the SCALLOP 3D tool. You can select the surfaces to touch (or avoid).

Another option would be the adaptive, but select ORDER BY DEPTH so the residual scalloping is roughly parallel to the stranding of your feature.

You could also do this using RADIAL strategy, from the center of the arc. The stepovers will then be roughly equivalent to flat machining rather than convex (the tool path direction will be across the axis of the curvature rather than parallel to it) reducing the scalloping effect.


#4

For giggles, I set up a similar piece. (I may run it later). I tried several strategies to see the result, and for a wire strand size of 5mm, three strands, twisted 8 full twists around a guide circle of 120mm (sweep tool), A good result shows with:

Rough with 3D adaptive, 3.2mm square end, leaving 0.2mm all around, fine stepdown 0.2mm
Second op SCALLOP, selecting AVOID for the rope (actually, touch for the flat surfaces) no stock to leave

Morphed spiral would do this as well

Third op is morphed spiral with 3.2mm ball end, AVOID the flat areas, and select rest machining fro previous op

Forth is Scallop with a 0.8mm ball end, same as previous operation. Morphed spiral would do it as well, but I didn’t like the pattern as much


(Idan) #5

Did you mean to include pictures? Can’t see any.


#6

I will add them later. Sorry about that. I am at work so didn’t do the screen shots, and we have enough of a slow network thst uploading isn’t practical from this location.


#7

Different site now so I have network that works.

Here are some screen shots. (note that the tool parameters- RPM, travel rate, etc are defaults. They need to be set for a particular job, material, and machine)

General setup for the machining operations

First op is an 3Dadaptive, leaving 0.2mm for finishing and fine stepdown of 0.2mm

Second op is scallop to level the flat areas and get into the corners at the base. This isn’t going to get everything due to the undercut required at some places. The undercut leads to some other finishing issues later, as well. To get a good final job, I should eliminate the undercut, either by projecting the profile to the surface or building out the bottom with a fillet. I chose not to bother here.

Note that this was done as rest machining, and 0 adjustment (to not ignore minor profile issues from the previous ops) I also selected the surfaces to touch.

Third op is with the larger ball end. It should only touch the rope feature. Again, set up using rest machining. Stepover is 1/8 of the tool diameter to minimize scalloping on the surface with convex curvature.

This is actually a pretty nice look (IMHO) as the finish looks a lot like the stranding of a rope. A little tuning or pencil work on the concave sections between the strands would tighten it right up.

The pecks at the meet to the flat surface are an artifact of the undercut at the meet. There are a number of ways to eliminate this (revise the model, force a small clearance by setting the bottom plane for the operation to be 0.001mm above the flat surface, etc) but, in this case, I don’t even know if it will be visible in the final product. The simulation tends to highlight these things.

The last op is another of scallop (The morphed spiral would also work here, but tries to maintain a roughly circumferential path, while the scallop op doesn’t worry about that. The less regular toolpath tends to hide a lot of small defects) The small tool gets a lot more detail and cleans up the grooves between the strands, but does have trouble getting all of the way to the bottom in some places due to the small tool needing to be short (the shaft and/or toolholder will collide, even at this scale. the 0.8mm ball end mill has about 2mm of flutes and 3mm total length to the shoulder)

note the stepover is 1/4 of the tool diameter. 1/8 would give a minimally better result on the convex, as the convex looks nearly like a plane to the tool this small. The extra time isn’t worth it. Also note the shaft and holder clearance. This provides another AVOID condition. The tool won’t rub or try to collide with stock or finished surface, and the tool holder (model your tool holder. Really. MODEL YOUR TOOL HOLDER. This is as important as modelling the tool) will be kept clear as well. I am not worried about the tool holder for this operation, so I didn’t enable it. These options do slow down toolpath generation.

The final sim looks quite good, except for the previously mentioned issues.

The primary thing would be to eliminate the undercut. If I cut the part, I will probably revise the model, as well as adjust the bottom height for the cuts with the ball end tools rather than using AVOID.