Just joined, hobby level

[black5f]

Welcome! Mine runs on homebrew software too!
Tom

[cncgcg]

Hi Tom,
Thanks for the reply,
Have you ever tried a bowl shape?. I have been thinking about the trig for this for a while now. I remember seeing a G code routine doing something similar and it used Tan, but the way I visualise it you only need to mill repeated circle pockets moving inward with Z increasing down as it moves inward, which is also calculated with Cos or Sin and not Tan. Doing it this way makes it easier for me to also generate a scaled curve rather than a pure circular one i.e much deeper or shallower as required. If you look at my program you will see what I mean about scaling the arc.
By scaling I mean ellipse, it's just my word for it since the program produces elliptical arcs depending on the X,Y scaling. Can you follow me?
Here is the program, take a look at Arc, click the Arc button, drag the mouse in the drawing area to make the shape appear and scale X,Y to say 100, 45 and a sweep angle of 180 degrees. yes it's mm's, I got metrified years ago sorry

http://cnc-gcode-software.com/wp27

Gareth

[Jonathan]

At first it looks like just simple sin/cos ... but if I may there's one thing I think you might be missing out? When using a ballnose cutter, unless the cutter is kept perpendicular to the finish part's surface (impossible on a bowl without 5-axis) the cutter will cut more material off than intended. That's because the cutter is not a point, it has a finite diameter and the outer edge will cut more from the surface. It gets worse as the surface is steeper. This diagram will hopefully make it obvious:



It's a fair bit more difficult to work out the co-ordinates for that...

[cncgcg]

Hi Jonathan,
Thanks for the reply,
Very illuminating about it having to be kept perpendicular to the surface (impossible without 5 axis, as you said). I'm hobby level as I said, but it would have been fun trying to write it.
I think my idea, having looked at what you wrote, would result in a stepping effect, is that right?.
Is Tan necessary to roughly accomplish what I'd hoped for or can this all be done using Sin Cos alone?. I'm not into Tan...
Regards
Gareth