4th Axis slower than a snail <resolved, inverse time>

[DanielCA92563]

Hi all,
I just recently connected a DYI 4th axis to my G0704 CNC conversion, it seems to be working well other than when engraving on a cylinder the federate is slower than an injured snail. It doesn't even look like it's moving but I know it is since after about 40 minutes, my cylindrical engraving outcome looks good. I believe that in mach3 there use to be a setting to tell it the diameter of your part and the software would adjust the feed rate, wondering if there is a similar setting in CNC12?


Positional stuff works great, rotation of the a axis (set along the X axis) is speedy. I've adjusted my max rate, fast jog, and slow jog (20K, 10K, 4K, deg/min, respectively) to where I think it should be. I'm using fusion 360 for cam and Swissi's postprocessor.

It's really not a problem- I just need to be patient. Just wondering if anyone has run into this.

[eng199]

Sometimes another axis will limit the rate in a multi-axis move.
Are X, Y, or Z hitting a limit on acceleration or maximum rate?

[cnc_smith]

Please post a report and the G-code file you are using. We can look at the g-code to make sure Fusion 360 is posting the rotary feed rates correctly.

[Gary Campbell]

You also have the option for 4th axis to use G93 (inverse time) mode if F360 supports that.

[DanielCA92563]

It's a small test engraving around a 1 inch cylinder, I set the feed rate to 4 IPM, I measured the actual rotational speed, seems to be 6 degrees per minute. I'm not sure where rotary feed rate is set.
I uploaded the gcode and report but here's an example from the Gcode:
N1290 G0 Z0.6
N1295 X0.1481 A0.245
N1300 X0.112 A2.182
N1305 G1 Z0.5394 F10.123
N1310 Z0.496
N1315 X0.0867 F4.
N1320 A4.7
During above moves, going to A4.7 degrees, rate seems to be 6 degrees per minute which is really slow.

BUT at the end of the code (below) when it positions to drill into the 1 inch round stock at opposite ends, A90 to A-90 moves are really fast.
N18925 X0.1211 Y0.2081 Z0.4575
N18930 G0 Z0.7
(Drill2)
N18940 G28 G91 Z0.
N18945 G90
N18950 M9
N18955 T44 M6
N18960 T11
N18965 S1800 M3
N18970 G54
N18975 A90.
N18980 M8
N18990 G0 X0.175 Y0.
N18995 G43 Z0.65 H44
N19005 Z0.55
N19010 G98 G81 X0.175 Y0. Z-0.07 R0.52 F3.6
N19015 G80
N19020 Z0.65
(Drill2 (2))
N19030 G28 G91 Z0.
N19035 G90
N19040 A-90.

Seems like there should be a setting for 4th axis rotary to adjust rotational speed based on the radius of the stock to give you a surface feed rate at the circumferance that is close to your desired feed rate, in my case 4ipm.

[cnc_smith]

It's a small test engraving around a 1 inch cylinder, I set the feed rate to 4 IPM, I measured the actual rotational speed, seems to be 6 degrees per minute. I'm not sure where rotary feed rate is set.
I uploaded the gcode and report but here's an example from the Gcode:
N1290 G0 Z0.6
N1295 X0.1481 A0.245
N1300 X0.112 A2.182
N1305 G1 Z0.5394 F10.123
N1310 Z0.496
N1315 X0.0867 F4.
N1320 A4.7
During above moves, going to A4.7 degrees, rate seems to be 6 degrees per minute which is really slow.

The post from Fusion 360 is wrong. The post needs to post degrees per minute for any rotary move with a G1 not a feed per minute. Fusion 360 would give the correct degrees per minute base on the diameter that you are cutting with a G1 move with the rotary. When there are not any rotary moves the feed rate will be in inches per minute.

[cncsnw]

Also see the combined feedrate calculation method in http://www.cncsnw.com/4thHowTo.htm.

If your postprocessor cannot calculate combined feedrates (inches and degrees per minute), then you might have better luck asking it to use inverse time (G93).

[DanielCA92563]

Awesome, thank you all for the help.

[DanielCA92563]

UPDATE:
I used the "FANUC- Inverse Time and A-axis" postprocessor and engraving on a cylinder worked perfectly. It uses G93 as you guys suggested. Thanks again.

[cnckeith]

thanks for reporting back!