Concave machining with Mach 3

[Involute]

I'd like to machine a concave depression in a piece of 1/2" acrylic. The depression should be an inch in diameter, .125" - .250" deep, and round, but not a pocket. More like a section of a sphere. Is this possible with Mach 3 (and, I presume, a ball nose cutter) alone, or do I need a CAD/CAM package, too? I'm a newbie. Thanks.

Involute

[wjfiles]

Somewhere recently I saw an article on making lenses on a cnc machine.I think the code was there and this may be the type of program you could use.
There is an article on CNCzone about diamond turning that may help.
A search should come up with something useful.
Sorry I don't have a specific answer.

WJF

[turmite]

Try this one. Created in Rhino, cammed with Madcam. Use a .250 ball nose with the tip of the cutter sitting .500" about the surface. Center of the circle is x0y0.

You will want to edit out the g92 at the beginning and the g91.1 at the end. It is something I use that you probably don't need and it is already in my postprocessor.

Mike

[Involute]

Thanks! I'll give it a shot.

Involute

[DareBee]

This is all good, but I would like to know if Mach will create the code?
Art made a free LazyCAM (or something), will that do this?

[ger21]

LazyCAM is a 2D CAM package, but there is a way to trick it into doing this. It will require some work in a CAD program. You'll need to draw a series of circles for the toolpaths, each on it's own layer. You'll need to draw a side view to figure out where the toolpaths should be. In LazyCAM, you'll need to assign the correct depth to each layer.

Not the fully automated solution you're looking for, but it can be done.

[turmite]

Garry that is basically how I created the tool path posted. Madcam has a feature to do it automatically or maybe semi-automatically but I haven't used it yet. I just offset the distance from each curve the same amount, and then selected project curves. Madcam took over and did the tool path on the concave surface.

Involute to make life much simpler you are better off with a cam systm, especially if you intend to do any type of 3d work. I manufacture rifle stocks and pistol grips and the are all carved on cnc. There is simply no way possible for me to create a tool path as complicated as is needed for a rifle stock, much less do it in 4 axis.

You can do farily simple items like the example you requested help on even without a cad system, assuming you are fairly good in math. I'm not so I have to have my cad cam.

Mike

[DareBee]

Thanks for the info.
Someday I WILL build a plasma and use Mach.

FYI I believe FreeMill by MecSoft would do that program.

[ger21]

Originally Posted by DareBee FYI I believe FreeMill by MecSoft would do that program.

Yes, it will. If you have an .stl of your part.

I actually made some crown molding from MDF with freemill, which I wrapped in veneer.

[Involute]

As I was perusing turmite's file to get a sense for how it worked, along with the G-Code section of the Mach manual, I came across the G12/G13 codes for making a circular pocket (as I said, I'm a newbie). It occurred to me I could put one of these in a subroutine and call it a bunch of times with progressively smaller I values (radii). I could also progressively shrink Z to move the tool into the material. Done linearly, it would give me a conical, not spherical, recess, but good enough for a first approximation. And, in principal, I could go back and convert the Z function to something trigonometric that approaches a spherical profile. My problem is, I can't figure out how to do the "progressively smaller" part. In a programming language, you'd do something like x = x - .001, but in Mach I have to use parameters (I gather) for variables, and it seems they can only be assigned constants, not expressions, e.g. #1 = 5, not #1 = #1 - .001. Any suggestions? Thanks.

Involute

[ger21]

Originally Posted by Involute Any suggestions? Thanks. Involute

Download Alibre Xpress, and model your part. Then download a trial of MeshCAM to create the code.

[Involute]

Thanks for those two pointers. I'm downloading Alibre now. But, I was hoping for a simpler solution than getting up to speed on two new packages. Are you saying I can't solve this problem w/ G-code using the approach I've outlined? So much simpler if I could.

Involute