How to mill an arc using X & a 4th axis ?

[Toymaker]

Using Mach3 with a rotary table as the A-axis, is it possible to mill an arc or helix where X & A are used to calculate the arc as shown in the video? In the video, I'm using the X-Y plane (G17) and this line of code: G2 X3 A2 R1, which doesn't work. Although "A" is rotated, the resulting cut is a straight line and not a smooth arc. Also, the Y axis is used to describe the arc, even though Y is omitted from the G2 line. If Y start point is "0", I can limit the amount of travel Y makes by inserting Y0 or Y0.0001, ie G2 X3 Y0 A2 R1, but the rotated cut will still be a straight line, and not an arc.

I'm self-taught in G-code, and I'm hoping that I simply don't know the proper way to use the forth axis; if there's no easy method I will be forced to use the math formula to find the length of an arc and set up a subroutine with an incremented arc length.

 

[MachineFun]

If I'm not mistaken, Mach3 can only do linear, so if you want to do arks you'll need to do hand coding or to use a subroutine. There's no other way to do it, unless you're planning on getting a new machine

 

[Toymaker]

If I'm not mistaken, Mach3 can only do linear, so if you want to do arks you'll need to do hand coding or to use a subroutine. There's no other way to do it, unless you're planning on getting a new machine

Thanks for the feedback. Seems like I need to blow the dust off my Trig text books; at least Mach3 can do all the basic Trig functions like Sin, Cos, Arc Tan , etc.

Mach3 can do arcs & circles, but from what I can tell, it only uses X, Y, & Z to do the blended arc calculations; I have not found an easy way to tell Mach3 to use "A" for the arc calculations. Interestingly, Mach3 allows me to omit Y and use A# instead, ie: G2 X3 A2 R1,....BUT, for example, if I've selected the X-Y plane (G17) the table motion uses X3 Y2 to create the arc, and rotates to A2 in a linear motion.

 

[weldmetenderly]

Mach3 can do arcs & circles, but from what I can tell, it only uses X, Y, & Z to do the blended arc calculations

I think this is what @MachineFun was trying to say. Unlike other models that can do arks with a rotary axis, the mach3 can't. One option is to break up the ark into incredibely short straight lines or use a software with rotary axis interpolation support.

 

[xerxes]

Using Mach3 with a rotary table as the A-axis, is it possible to mill an arc or helix where X & A are used to calculate the arc as shown in the video? In the video, I'm using the X-Y plane (G17) and this line of code: G2 X3 A2 R1, which doesn't work. Although "A" is rotated, the resulting cut is a straight line and not a smooth arc. Also, the Y axis is used to describe the arc, even though Y is omitted from the G2 line. If Y start point is "0", I can limit the amount of travel Y makes by inserting Y0 or Y0.0001, ie G2 X3 Y0 A2 R1, but the rotated cut will still be a straight line, and not an arc.

I'm self-taught in G-code, and I'm hoping that I simply don't know the proper way to use the forth axis; if there's no easy method I will be forced to use the math formula to find the length of an arc and set up a subroutine with an incremented arc length.
View attachment 32

Yeah, Mach3 won't blend arcs with the A-axis like you're hoping. Your best bet is to break it into tiny linear moves or script it with some trig and a loop.

 

[3vilgenius]

Yeah, Mach3 won't blend arcs with the A-axis like you're hoping. Your best bet is to break it into tiny linear moves or script it with some trig and a loop.

This is right, that's why you're getting a straight cut instead of a smooth arc. It still processes arcs in the XY plane, even if you leave Y out. Unfortunately, there's no simple fix for this.

 

[Kwanda_Rosman]

Wait, so Mach3 can't just do arcs on the A axis like it does with XY? I thought G2 and G3 handled any combo. Kinda wild it just spits out a straight line instead. Does that mean people always have to break arcs into tiny steps when using the 4th axis?

 

[Toymaker]

Wait, so Mach3 can't just do arcs on the A axis like it does with XY?

Correct.

I thought G2 and G3 handled any combo. Kinda wild it just spits out a straight line instead.

Mach3 cannot use A properly with G2 and G3.

Does that mean people always have to break arcs into tiny steps when using the 4th axis?

Breaking the arc into lots of tiny straight lines is probably the easiest method, and does produce very acceptable results for inside curves where the radius of the end mill helps blend & smooth the straight lines into a curve. For outside curves, you need a lot of very short straight lines to produce acceptable results.