Need Help!- Programing a parabola on mill

[roger_e]

Hey,

I needed to hollow out a parabola like the inside of a flashlight, or an egg shell.

Material is aluminum, part size about 18mm tall and 20mm square

I have got the formula for the parabola I am not quite sure on the syntax for the G-Code...

I was going to run it as a seperate operation(really the third operation)...or the other option was to get a tool ground to the right shape and just run a drilling cycle.

Programming seemed like a good idea...

Thanks

[Roger Hamlett]

What you don't say, is what sort of focal length the parabola is going to have?.
Thing is that at long focal lengths, relative to the diameter (high focal ratio - say over about F/8), the difference, between a parabola, and a sphere, is basically unmeasurable at any normal 'mechanical' scale. In fact to the limits of what a milling machine is likely to achieve, the difference will be below the working accuracy, probably out to something like F/4. So you only have to worrry about it being a parabola, as opposed to a sphere, if you are working to relatively low focal ratios.
There is no 'inbuilt' G-code, that is going to give you a parabola. Your simplest programming route, would be to have the unit on a rotary table, and program a circular cut, while rotating the table. Then repeat this, but with a fractionally deeper centre, using a smaller diameter cut. Effectively cut a circle, then deepen this in the middle with another smaller radius circle, and then deepen this again with an even smaller circle.

Best Wishes

[Pres]

Are you cuttine the concave (inside) or convex shape?
(that affects cutting tools, chip removal, lead in, etc)

Of course, there are a number of ways to do it, depending on the coefficients of the parabolic equation and your tool rigidity/accuracy.

If it's a male part then you could make a series of circular interp cuts using a starting point that's constructed from the equation.
e.g. assume the parabola is in the z-x plane, pick a starting
z value to be machined, determine the surface normal and
move out that vector by the ball cutter radius and subtract
the cutter ball radius for a starting Z value.
Similarly, for the starting X value it would just be the surface point adjusted by the surface normal vector times the cutter radius value.

Also, the X value would be used for the starting value of a full circle cut - using circular interpolation.

Essentially, this would generate a bunch of decending circular cuts that follow a parabolic shape.

Hopefully, I made the above explanation understandable.
One picture is worth a 1k words, but it would take me
awhile to draw up one that is meaningful.

Hth & good luck,
Pres

[mscir]

Hi,

I wrote a freeware program that calculates parabolic curves for any depth, diameter or number of steps, you can read about it or download it here:

http://mscir.tripod.com/parabola/index.htm

It may be possible for me to modify the way the program saves the coordinates so your mill software could read the file correctly. If this sounds good please send me a data file that shows exactly how to format the (x, y) coordinates in the output data file. The more details you can provide the better. If you have already programmed a parabola and can send me the coordinate file that would be very useful.

Best Wishes,
Mike

[jetpig1]

Form tool would be expensive. If you know the equation, you could create the geometry simply in a program like Rhino, and generate surfacing G code in a CAM program. Tolerance of the surface would be your biggest issue -Geo

[twoartistic]

I could write the code for you cheaper than you could buy the tool, if you can give me the following;

1 parabolic curve cross section as a dxf or dxb

2 size of ball end tool you want to use

3 horse power of your spindle, flood lubrication or dry machining

4 controller you are using or (I could write as simple g-code for you to import)

5 Metric or inches for code

6 where x0.00, y0.00 is on your machine in relation to the table

7 where you want to clamp your block to the table, and where the hold downs clamps are to be located

8 size of block you are going to cut this out of

9 working height of your z-axis

10 Do of want z0.00 to be the top surface of your block, or the top surface of your table.

Best Regards
twoartistic@gmail.com

[Kiwi]

Attached is a program which I wrote some time ago. Not sure if this is of any use.