I'm trying to get a certain effect, but I don't quite know how to do it with MoI. What I'm trying to do is "V carving". It's really more of a machining operation than a modeling operation, but I was hoping there was some way to do it in MoI. Here's what I'm talking about.

VCarve Pro is an application for cutting parts with a CNC router. In particular, it's used for carving shapes into 2D surfaces, like signs. If you draw an outline in VCarve Pro like this:



You can then "carve" it using a V-shaped router bit. The previewed result is like this:



Notice that the result is not simply an extrusion down into the surface. Because of the profile of the V-shaped bit, the edges slope inwards in a V shape, with a sharp crease at the bottom of the shape. I hope everyone can imagine how this shape gets carved. Things get more complex with more complex shapes. Here's another example:



And here's the carved result:



In this case, the sides of the cut are still sloped downwards in a V shape (they always are - because of the shape of the physical tool, it's impossible to do anything else), but the creases at the bottom are more complex.

No (finally) on to my MoI question: Is there a way to do something like V carving in MoI? I've come up with a couple solutions, but I was hoping someone here could point me towards a more elegant approach. I think for the simple example I have a perfectly good solution. I can make a diamond or triangle profile and sweep it along two rails that define the shape of the simple outline. The result could be boolean diff'ed against whatever surface I wanted to carve. But this wouldn't work for my more complex example.

For the more complex example, I first tried drawing my outline. Then I duplicated it and reshaped it to sort of make the crease at the bottom of the carving. Finally, I used the Loft command to join them. Here's the result:



I'm not quite happy with this approach. The crease at the bottom doesn't (can't?) have the same "branching" qualities that a V carving does. If I try drawing the crease I want with unclosed curves, the Loft command gives me very bizarre results. That's why I switched to using a modified version of the original shape.

The "branching" nature of the creases at the bottom of V carvings is really quite interesting and nice. If there's a way to reproduce this with MoI, I'd love some pointers. Even if I can't quite get that branching effect, if there's a more straightforward way than duplicating, reshaping, and lofting, that would be great too.

Thanks,
Mike




P.S.

I don't think this is relevant to my question here, but if anyone is curious about how the tool actually cuts this shape, here's a screenshot of the toolpath that VCarve Pro generated from my more complex outline:

Hi Mike, unfortunately it's quite a difficult problem I think...

The fundamental difference is that VCarve is able to approach it more as an accumulation of separate cutting passes, while in MoI you're trying to generate the end result with just a single construction pass...

Especially when you have branching structures it will be very difficult to try and replicate many stages of cuts in just a single surfacing construction.

It's also not going to work very well to try and make a single surface that tries to "turn on a dime" and fold back over itself like in this spot here:



For something like that you probably need to have some more separation into pieces there - stop the "main side walls" at around these spots here:


Then the corner area would be built separately, more as a cone-like surface for just the corner, sweep the top profile down along the red sides there to make a surface that collapses down to a single point for a pivot area like that. That will be how you'll be able to make things come down to a single sharp ridge line.

You'll probably have to be breaking it up into somewhat more pieces with some cone-like pivot areas to get it down to a single collapsed centerline like you want.

It's still going to be a rather difficult type of work though...

- Michael

Hi Mike, so maybe something more like the attached quick attempt (see attached 3DM file).

That's done by making the bottom ridge as an open curve, do not try to make it a squished down closed curve as that will be problematic in the squish area. Then various segments are done by lofting like this:


For pivot areas you would select this piece and run Sweep along the 2 adjacent edges to make those cone-like (by cone like I mean collapsing into a single point at the tip area) corner juncture areas:



- Michael

Some rough thoughts:

A 60 degree vbit is a cone. For each depth, there is a circle of a different radius.
If a maximum depth is selected, There is a circle, maxCircle, of maximum radius.

For two intersecting curves, using the Moi tantan circle, a series of largest circles can be created touching the upper curve,
and also touching the lower curve. If the separation between the two curves exceeds the maxCircle, the maxCircle would hug
the upper curve. The zDepth of the center of the circle is determined by the vBit angle.
The centers of all the tangent circles would create tipCurve, the path of the tip of the vBit.
Then sweep a line along the top curve and the tipCurve.

Repeat for the bottom curve if maxCircle is exceeded, and also form plane between tipCurve1 and tipCurve2.

(This is a rough "algorithm")

- Brian





I did locate a Rhino/Grasshopper reference: http://www.grasshopper3d.com/forum/topics/tangent-circles-between-2-curves

I have actually been using MoI for this very purpose recently.

I do have a program for V-Carving, aka Centre Line Machining, but for the mould I'm making it's not quite the right tool for the job.

MoI made it about as easy as is possible although it's still turned out to be something of an awkward task because of the fairly complex geometry.

The way I found to create V-Carve(ish) style toolpaths involves Sweeping an angled line (45 deg cutter in my case) around the shape so that intersecting surfaces are produced. When these surfaces are Trimmed with each other, the trim lines are extracted and used as the cutting path for the milling tool to follow.

In the attached file, I've imported some of the toolpaths that were generated by my V-Carving program, along with the characters they are derived from. The sample letter "F" has some Sweep surfaces around it, so it's possible to compare with proper V-Carving.

PS. Turn off Edges in my attached file to better see the comparison.
 

Martin.

Thanks for the tips, guys. Looks like I'll have to do some experimentation. It'll be fun to mess around with, anyway. I've had some luck breaking my complex shape into two curves and using them as two rails for a sweep. I'm not getting quite what you get with a router bit in a v carve, but it's similar in some ways. I think for me, the "cleanliness" of the model is more important than getting the same exact result as a v carve.

Martin, that's an interesting approach, to use the toolpaths in MoI. But I can't quite figure out how to trim the resulting surfaces. Any tips on getting the final result?

It's really a matter of splitting up the geometry so that separate fully intersecting surfaces are produced that are good candidates for Trimming with one another... it can and does get quite messy on screen, but is doable.

On the other hand, if all you really want to do is produce V-Carved shapes, then I would strongly suggest you buy CamBam and use the totally free and unrestricted V-Engrave plugin - it works a treat and CamBam is the most bang per buck of CAM software anywhere, anyway.

See here: http://www.cambam.co.uk/forum/index.php?topic=3513.0

 

Martin.

Here is a couple visuals of me fooling around with it...

I thought as Blowlamp and just used a Vcarving program to generate some gcode, then I converted the gcode to dxf and brought it into MoI. I could do a simple loft on the outer profiles of the toolpath and get the vcarve surface...



The second one is my "fake" vcarve. It's fake because the proper calculations for a vbit or specific tool, to rise and fall in the shape aren't attainable with my eye.. I just made a shape that looked kindof "vcarvy"... It does show the surface trimming thing that I think Blowlamp is referring to, though... I've attached a 3dm of the second method with the surface and the curves I used....



The file I posted is a little different than the video. The file has just a center morphed curve, rotated by "end" down to a depth. The 2 meet up, and are lofted and trimmed the same as the video...

MorphBetween2curve is a good trick ! ;)
http://moi3d.com/forum/index.php?webtag=MOI&msg=6373.1

Another file here.

In it, I swept the green curves around the magenta letters to make intersecting surfaces, which were then trimmed to leave those as shown.

The next step was to Copy & Paste the 'ridge' curves to make them into the orange curves placed at the surface intersections.

Finally, copies of the orange curves were mirrored below the surfaces to give the blue curves and it is these that can be used directly as toolpaths for an engraving style of machining operation.

If I'd modelled the surfaces to peak in the opposite Z direction it would have saved having to create and mirror the orange curves to get the blue ones, but I just find it a bit easier to do it this way.

Using a Tapered Extrude that trims at the peaks would be an easy & quick way for us to get the right shape, but this isn't possible due to the complexity of such a task.



Martin.