Disabling all Z rapid during plunges (Feed Height not working like expected)

[probinson6061]

Hey everyone.

My shop has a knee mill with a 2-axis Prototrak CNC system. If running a .NC program, when it encounters a Z(x) position command, it prompts the operator to manually set the new Z height, then it continues the program.

We recently subscribed to F360 and I'm running into a roadblock, where I can't get the CAM to do plunges from clearance height without it splitting into multiple Z position commands (e.g. rapid down from clearance height, then G1) - which results in lots of extraneous operator prompts.

It seemed like setting Feed Height equal to Clearance Height would do the trick. Feed height "sets the height that the tool rapids to before changing to feed/plunge rate to enter the part". This implies that if it's set equivalent to clearance/retract height, then it wouldn't rapid at all, and simply start at feed/plunge rate.

The weird thing is, when this is engaged, it doesn't disable rapids. Instead, it now "rapids" from clearance height to top height using G1 at horizontal feedrate, which is baffling.

For example.

If feed height is disabled, a plunge will look like this:

G0 X0.1 Y-0.1033
Z0.1 (first op, initial position, clearance height)
Z0 (rapid to top height)
G1 Z-0.4 F42.02 (plunge at plunge feed)

When I set feed height to clearance height, I hoped it would look like this:

G0 X0.1 Y-0.1033
Z0.1
G1 Z-0.4 F42.02 (plunge from clearance in one move. feedrate is irrelevant, move is manual)

But if I set it up like this:

I get this:

G0 X0.1 Y-0.1033
Z0.1 (first op, initial clearance height)
G1 Z0 F126.06 (plunge to top height at horizontal feedrate?)
Z-0.4 F42.02 (plunge into material at plunge feed)

That doesn't seem like intended behavior. But it also seems like a bit of a 'hack' in the first place.

Is there some cleaner way to disable Z rapids? Either with configuration in CAM, or in the post?

Thanks!

The test part is here, but there's nothing special about it. this happens in multiple parts: https://a360.co/3tx6snK

[seth.madore]

Just to clarify; your machine has servo motors on the X&Y, but fully manual Z, is that correct?

[probinson6061]

Correct.

I get that it's a niche feature for CAM, but we've moved all our other programming to f360 and it seems like a really minor catch if F360 can't do no-rapid/no-multiple-feed-Z output. 

[seth.madore]

What post processor were you trying to use?

[probinson6061]

The "Acu-rite Millpwr 3" post, which is the controller on the machine. I didn't think it was post-specific, the behavior/bug of 'horizontal feed in the place of plunge rapid' occurs in any post I pick.

[seth.madore]

What does your machine do when it encounters a Z move, just prompt the machinist to manually move the Z axis?

In your "I hoped it would look like this" comment above, is that exactly what you are looking for?

[probinson6061]

Yes. Whenver it comes across a Z(x), It stops, prompts the operator to move the axis, gives a clear distance-to-go, then continues when the operator continues a cut.

The 'issue' (or, lack of feature), is that with F360's native behavior, it seems to always generate two separate Z lines for a downward motion - a rapid to top height, then a plunge-feed to bottom height. Configuring feed height equal to clearance height implies it would eliminate the rapid. But instead, it still splits up the plunge into two position commands.

My example might have been made less clear because of the program start, I'll edit it real quick.

[seth.madore]

Would this suffice?
At the beginning:

N25 T1 M6
N30 S7639 M3
N35 M8
N40 G0 X0.1 Y-0.1033
N45 Z0
N50 Z-0.4
N55 G1 X0.1905 F126.05
....
....

At the end:

...
...
N290 Y1.55
N295 X1.2877
N300 G0 Z0
N305 M9
N310 M2

[probinson6061]

Well, I can't edit it seems. Instead, I added a second feature to the demo part to hopefully make it more clear

Default behavior:

(start of program)
G0 X0.109 Y0.1033
Z0.1
Z0 (rapid to top)
G1 Z-0.4 F126.06 (plunge)
--XY gcode omitted--
G0 Z0.1 (rapid retract, feature complete)
(2D Pocket2 2)
X0.577 Y0.2411
Z0.1
Z0 (rapid to top)
G1 Z-0.6 F42.02 (plunge)

It's the rapid to top lines, the Z0 commands, that I tried to get rid of. But setting feed height to clearance height still injects Z0 position commands that move down to top height at horizontal feed (126), instead of rapid.

G0 X0.109 Y0.1033
Z0.1
G1 Z0 F126.06 (Z0 to top height)
Z-0.4 (plunge to bottom height)
--XY code omitted--
G0 Z0.1 (retract)
(2D Pocket2 2)
X0.577 Y0.2411
G1 Z0.1 F126.06
Z0 (Z0 to top height)
Z-0.6 F42.02 (plunge to bottom height)

[probinson6061]

The goal being something that does look 'exactly' like this:

G0 X0.109 Y0.1033
Z0.1
G1 Z-0.4 F126.06 (plunge from clearance height to cut depth, one line, ignoring top height)
--XY code omitted--
G0 Z0.1 (retract)
(2D Pocket2 2)
X0.577 Y0.2411
G1 Z0.1 F126.06
Z-0.6 F42.02 (plunge from 0.1 to cut depth, one line, etc)

[probinson6061]

I can understand why it's a weird ask. For 99% of machines out there, it really isn't a problem to have a Z1->Z0->Z-1 plunge at the same feedrate. It would be invisible to the operator and the machine would run through it smoothly. And it could make things clearer from a readability standpoint. But for these 2ax machines, that Z0 in the middle isn't superfluous and halts the program.

It was really easy to configure mastercam to eliminate that, and do straight Z1->Z-1 plunges. I was just surprised that F360 didn't have it. I could see it just being something that this CAM engine wasn't designed to do - it's more modern software, and nearly all machines are 3axis CNCs.

[probinson6061]

I missed your reply while writing my own, sorry.

I don't think that solution is reasonable, that implies starting and rapid-ing over the part at stock height. It does sidestep the issue, but by eliminating clearance height entirely.

I think I was mistaken about one claim though. It appears that, setting feed height to clearance height does eliminate a downward Z rapid, but it is replaced with a vertical lead-in. The lead-in and horizontal feedrate were identical in the demo tool feedrates, so I didn't notice.

The closest I can get right now is this:

G0 X0.109 Y0.1033
Z0.1
G1 Z0 F90 (move from clearance to top height with lead-in feedrate)
Z-0.4 (plunge with lead-in feedrate)
X0.107 (horizontal cut, a lead-in?)
X-0.1905 F126.05 (switch to horizontal feedrate)

Which is odd, since lead-in is disabled in the operation, and also shouldn't be relevant for a Z move, right? You would expect a plunge feedrate.