milling a shpere

[gallzer]

Hey guys

Can anyone help me i'm trying to mill 6 concave half spheres into a block of aluminium.

The radius of the sphere is 29.609mm
I'm using a 12.7mm ball nose cutter

I'd be very grateful if anyone has a heidenhain conversational program which could help me.

Thanks a lot Gallzer

[Ben_Kristek]

hey, do you have any 3D model drawings of the shape? you could put it through a post processor and generate the G Code

sounds like you might have to m/c half of the object, then make some kind of form to hold it then machine the secound half of it

you might need to make a clocking hole in your form to

does this help?

[greg b]

Hi mate i have a brigeport with a heidenhain 2500 controll and it has conversational on it, if you download a manual off heidenhains webb site it will give you a good idea how to do what you need.I dont know whether this helps or not but when i machine two stroke combustion chambers in my mill i use a form tool and interpolate the hole to size you just have to experiment a bit with speeds and feeds to illiminate chatter i hope this helps a little regards greg.

[Kiwi]

Is this more like what you want?
I drew the path and got BobCAD to generate the code for a Heidenhain 355 Bridgeport Conversational.
As I have never used a Heidenhain, I don't understand the logic.

L X+0.0000 Y+0.0000 Z+2.5400 R0 F5998 M
L Z+0.0000 R F02. M
L X+22.3754 R F20. M
CC X+0.0000 Y+0.0000
C X+22.3754 Y+0.0000 DR+ R F M
L X+22.5603 Z-0.6918 R F M
CC X+0.0000 Y+0.0000
C X+22.5603 Y+0.0000 DR+ R F M
L X+22.7238 Z-1.3890 R F M
CC X+0.0000 Y+0.0000
C X+22.7238 Y+0.0000 DR+ R F M
############
L X+1.4313 Z-29.5649 R F M
CC X+0.0000 Y+0.0000
C X+1.4313 Y+0.0000 DR+ R F M
L X+0.7160 Z-29.5980 R F M
CC X+0.0000 Y+0.0000
C X+0.7160 Y+0.0000 DR+ R F M
L X+0.7160 Y+0.0000 Z+2.5400 R0 F5998 M

[gallzer]

thanks kiwi

this program looks good to me, i was hoping to get some sort of formula, so that the only change in the program for a different semi sphere would be the radius in one line and the calculation would work out the rest of the program.

[Kiwi]

When the path is the tool tip path, a formula for this is quite complicated because the cutting point on a ball-nose changes as it moves around the sphere arc and therefore is not a simple offset of the sphere arc.

[Geof]

Originally Posted by Kiwi When the path is the tool tip path, a formula for this is quite complicated because the cutting point on a ball-nose changes as it moves around the sphere arc and therefore is not a simple offset of the sphere arc.

Can you make a simple sketch to show what you mean. I have convinced myself that if you developed the formula to make the center point of the ball nose cutter trace out a hemisphere the hemisphere that was cut would simply be larger by the radius of the ball nose.

[Kiwi]

Geoff
Sketch attached showing the tool path using tool tip.

[Geof]

Thanks Kiwi. I took your picture and put the path of the center of the ball nose on it and this does follow a simple semicircle. I also converted your picture into a plan view of a full circle and the cutter path which shows that the path of the ball nose cutter down the sphere is the same as the path of a regular cutter around a circle.

And I am confused. Your path looks correct; you program the tip of the tool to follow a complex curve. But my path looks correct; you program for the center point to follow a simple curve.

Perhaps the problem is your head is pointing in a different direction to mine . Literally; so we cannot see things the same way.

[Kiwi]

Geof
I'm confused about your confusion. (offcourse I'm down here in NZ doing this upside down.)
I think the path can be generated using the centre of the ball nose which would make generating a path much simpler.
I wrote my generator program using VB because I needed programs for a cutter I made which has round tips.

This may be of interest.
http://www.cnczone.com/gallery/showp...00/ppuser/1117

[Geof]

Originally Posted by Kiwi ...(offcourse I'm down here in NZ doing this upside down.)..

From my point of view not quite upside down; closer to sticking out sideways .

[Kiwi]

Geof
Had a play and wrote a VB program calculating on the centre of the ball nose and then deducted the cutter radius from the Z figure. This certainly made the math a little simpler.

Gallzer
A calculator program attached. Only produces ISO code as I don't understand the Heidenhain language.