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Mach 3 - G93 4th Axis Speed Incorrect
« on: October 15, 2021, 05:19:41 PM »
Good afternoon.  After searching and racking my brain for a couple days I thought I'd come to the experts to see if you can help me solve my problem.

A quick basis:

Machine - We have a 3 axis router table with a 4th axis rotary.  It started as a CNCRP machine several years ago but we've since upgraded to TeKnic ClearPath SD's and Thomson screws all around along with a host of other structual frame modifications.  It works very well and is generally a workhorse in the shop - we do large composite molds and run times frequently reach into the 12hr realm with no issues.  We've recently added a custom built 4th axis for rotary work, also running an ClearPath SD motor.

Control - Mach 3, version 43.062, running on an independent/dedicated XP machine and the smooth stepper.  We are using a portion of the CNCRP plug and play controller but all the stepper drivers got eliminated with the ClearPath upgrade as the motors have internal drivers.

CAM - Fusion 360 with the generic post processor and the rotary set along the Y.

Issue - The rotation rate of the rotary is too fast when cutting at a prescribed speed.  I've been trying to nail the issue down and have programed a simple 6.366in circle and am doing two passes around it at F20 as a simple check.  So, it should take a full minute to do a full rotation.  In actuality, it is doing a full rotation in about 15 seconds.

I am running things via inverse time, G93, and when it's doing the rotation the feedrate on Mach 3 says 360 which I am assuming means 360 deg/min as would be logical and correct.

I've gone into the toolpath menu and enabled A rotations and use radius for feed rate.

I've gone into the settings tab and have the A rotation radius set to 0.0001.

It is worth noting that the 4th axis is moving the correct amounts.  Test cuts verify the rotation is correct - both MDI tests and test CAM out of Fusion.  It's just spinning too fast.

I'm pulling my hair out trying to sort this out and would love some input to help me fix whatever I'm missing.  Many thank you in advance.

Thank you,

Lee

>>> Test G-Code I'm running >>>

(TEST - BASE R2)
(T1  D=0.25 CR=0. TAPER=45DEG - CHAMFER MILL)
G90 G94 G91.1 G40 G49 G17
G20
G28 G91 Z0.
G90

(ROTARY1)
M5
T1 M6
S6000 M3
G54
G0 A-90.
G0 X0.0366 Y0.
G43 Z4.9013 H1
A-90.
X0.0248 Z3.3138
Z3.288
G1 Z3.208 F20.
X0.0242 Z3.2028
X0.0225 Z3.1975
X0.0195 Z3.1926
X0.0153 Z3.1884
X0.0104 Z3.1854
X0.0052 Z3.1836
X0. Z3.183
G93 A88.864 F2.0128
A267.442 F2.016
A270. F140.7099
G94 Y1. F20.
G93 A448.995 F2.0113
A627.809 F2.0133
A630. F164.2884
G94 X-0.0052 Z3.1836 F20.
X-0.0105 Z3.1853
X-0.0154 Z3.1884
X-0.0196 Z3.1926
X-0.0226 Z3.1975
X-0.0244 Z3.2028
X-0.0249 Z3.208
G0 Z3.3138
X-0.0368 Z4.9013

G28 G91 Z0.
G90
G0 A0.
G28 G91 X0. Y0.
G90
M30

Re: Mach 3 - G93 4th Axis Speed Incorrect
« Reply #1 on: April 05, 2022, 08:08:57 PM »
Gentleman,

Just bringing this back up to the top to see if anyone has any input.  I know I'm not the only one running Mach 3 with a 4th axis and others have had plenty of success.

Any thoughts as to what I'm missing?

To add to the discussion, when the CAM does a movement that requires a rotation and a gantry move, it doesn't move in sync.  What I mean by that is say I cut an opening normal to the surface at A0, Y0 and then move down the tube 30in or so to cut another opening at A300, Y30.  It should rotate smoothly while the gantry travels down the tube such that it gets to A300 and Y30 at the same time.  What happens in actuality is the rotary smoothly rotates while the gantry moves, pauses, moves, pauses, moves, pauses until it finally gets to A300, Y0.  The machine does get to both points at the same time but it is not a smooth motion.

I have do a lot of 3D contour work where all three axes are moving concurrently and never have problems.  Something with the rotary is preventing it from kicking out the right thing.

Thoughts?

Thank you,

Lee

Offline TPS

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  •  2,508 2,508
Re: Mach 3 - G93 4th Axis Speed Incorrect
« Reply #2 on: April 06, 2022, 02:48:56 AM »
have you tryed to use MDI for testing with simple commands like:

G90 G1 Y30 A300 F200 ?
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.
Re: Mach 3 - G93 4th Axis Speed Incorrect
« Reply #3 on: April 06, 2022, 10:05:55 AM »
TPS, thank you for the response.

I just tried it and I get a smooth coordinated motion with both the rotary and the gantry arriving at the endpoint at the same time.  No issues.

Thoughts?

Offline TPS

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  •  2,508 2,508
Re: Mach 3 - G93 4th Axis Speed Incorrect
« Reply #4 on: April 07, 2022, 02:02:48 AM »
i have seen in your sample G-code that you are using G93 with a-axis moves.
don't know wether this ay cause the problem, never used G93 and an a-axis.
i think it will be try and error to figure out what causes the problem in G-Code,
because this simple G1 move in MDI showed that it is basicly working.
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.

Offline BR549

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  •  6,965 6,965
Re: Mach 3 - G93 4th Axis Speed Incorrect
« Reply #5 on: April 07, 2022, 03:33:34 PM »
Are you using both A axis correction AND G93 at the same time ???. Are you using G61 or G64 ??

Just a thought, (;-) TP