Hi,
I fairly recently started using continous four axis toolpaths and find the the A axis units (in degrees) is a pain.

For instance if I wanted to put a thread on a shaft I might do so like this:

g1 a3600 x-15 f5400

the a 3600 means rotate 10 times ie 3600 degrees, the x-15 means the pitch is 15/10=1.5mm, and f5400 means that the cut speed is 5400 degrees per minute, being
150rpm, the max speed of my fourth axis.

Note that might also mean that any of the linear axes are under the current Feed Rate of 5400 mm/min, which is ludicrously fast for a linear axis to cut, in metals anyway.
The linear axes are coordinated so the max speed of the A axis effectively 'throttles' the linear axes, but given that F is modal any successive linear moves could conceivably
take off at 5400mm/min and crash.

Lets imagine the units for a rotary axis were in Radians then the Gcode would become:

g1 a68.82 x-15 f942.3

where 68.82 is ten revolutions in  radians (10 x 2.PI) and 942.3 is 150 rpm ( 150 x 2.PI)

Should a subsequent linear move be attempted at the prevailing Feed Rate it would be 942.3mm/min, which is a far more acceptable rate for a metal cutting machine.

I use Fusion which can post either radians OR degrees so I could very easily have all my rotary axis Gcode in radians if only Mach4 would recognise radians
as a rotational unit. If Smurph or Brian or Goomba is listening.....can this be done easily?

Craig

Hi,
I've just noted a typo in my post.

150rpm is 54000 degrees/min....not 5400 per my post.

It just goes to show that degrees are numerically unwieldy, and mistakes happen.

Craig

craig do you use the 4ax as rotate that need calculate kinematic or only as curve surface?

You can specify the "counts per unit" for your rotary axis to the appropriate value for one radian of movement. That should work reasonably well in the real world but with these considerations:

1)This will inherently be an approximation because for any reasonable gearing setup the value will include pi as a part of the computation and pi is an irrational number.

2)The concept of "rollover" in the Mach4 configuration probably assumes that the value to be declared to be the rollover point is 360, as in degrees.

One alternative approach would be to make your unit of measure be one full circle so as to avoid the irrational number issue.

Hi Steve,
yeah that makes sense. I'm limited to what Fusion can do, namely Radians or Degrees....unless I hand code everything!

At the current time I don't use roll-over anyway, so whether its keyed to 360 or not may not matter.

I will have to give a bit more thought into the consequences of a non-rational angular unit. Its usually the case that I'm the irrational unit! 

Craig

Hi Katz,
I'm using a rotary toolpath to make parts, in most cases the Gcode is ex Fusion. Some simple and specific tool paths I write by hand, but mostly CAM.

Mach4 Toolpath Window does a rubbish job of four axis display. I have seen on the forum a guy whom had written 'four axis kinematics', not that his interpretation
is what I'd describe as kinematics, but none the less he had a very credible tool path display to show for his efforts.

I'm already working on a fifth axis, I have the gear reducer already, the servo is ordered and paid for and on its way from Hong Kong as we speak, and I'm waiting on my local
steel supplier to cut a piece of 150mm 4140 steel shaft for me to make the C axis platter. A wee windfall on the income front will also mean that I can order the laser cut steel parts
I need for the trunnion table, I was going to have to wait until next week after I've been paid!

I'm thinking that once I get into five axis then even a decent four axis toolpath display is going to be of limited use.

Craig

Do your have photos of toolpath display for 5 axis that you would like to see? ( Toolpath not simolation )

Hi,
well no, given that I don't yet have five axis I have not got any code yet either.

Craig

at least we start test/run our 5 axiss
https://www.youtube.com/watch?v=UXt1g4M9-FE
actualy if you count also the tool magazine and Dust hood  and 2 servo on gantry its 8 axiss

Katz,

Very nice.
What do you use to make the G-Code?

Bill