Program takes roughly three times longer to run than it should

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29 Apr 2020 23:05 #166161 by adouglas89
Ok, so I made a simple program in fusion 360, and it says machining time is 3:30 approcximately. When I actually run the program it takes more than ten minutes to complete
The maximum axis speed is limited to 1500 mm/minute while the program specifies 2000 mm/minute. However that does not account for most of the difference. I will try to post the program and link to the fusion file in the comments.

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29 Apr 2020 23:10 #166163 by adouglas89
a360.co/3f5AAfZ

there is the link to the fusion file. the stepconf files are sort of locked in the other computer there, idk if they would be any use anyway.

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30 Apr 2020 07:18 #166195 by tommylight
The specified machining time does not account for G0 moves and the time it takes for the Z axis to go up and down, so on a slow machine as yours, it will take longer than the estimate.

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30 Apr 2020 12:13 #166210 by adouglas89
I thought of that and tried putting in the setting to not use g0 moves, but instead only use high feedrate moves, at the same 2000 mm per minute. It makes essentially no difference.

I'm pretty sure fusion does take into account z axis move time, it would be a pretty serious flaw if it does not, although I have not tested it

In any case none of those things could account for a factor of three difference. The machine must be moving more slowly than it thinks it is, which is a problem I must resolve as the feed rate etc has to be reasonably accurate when cutting steel etc.

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30 Apr 2020 13:36 #166215 by adouglas89
Ok so I realized that even though the maximum rate was set to 1500 mm per minute, the velocity display said 790 mm per minute.

I assumed it was due to the max pulse rate. The max speed displayed by Linux CNC should reflect the actual max speed but whatever.

So I changed the encoder step count per revolution from 2048 to 512, assuming it would then be able to move four times as fast, if the pulse rate is the limiting factor.

Now it moves at 1425 mm per minute according to the velocity display.

Ok.

I will keep working on it.

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30 Apr 2020 13:50 #166216 by adouglas89
Ok so I went back to stepconf and updated the max speed on each axis from 25 mm to 100 mm per second. The max speed indicated in the display on the sliders for jog speed and max velocity is 6000 mm per minute, so that must be where they are derived from. The actual max velocity is 3190 or something, per axis. So problem basically solved although it's pretty messy business. There should be better diagnostics available really...

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30 Apr 2020 14:20 #166221 by tommylight
Linuxcnc will show you how much time it takes at the rate that is in gcode, file>properites menu will shot time also, but again only for the feed rate.

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01 May 2020 13:57 - 01 May 2020 14:01 #166317 by Todd Zuercher
I wasn't able to look at what your file looks like, but for some milling files the machine's acceleration times can make significant differences in what the actual milling time is, especially on machines with low accelerations and high feed rates. The machining time estimate in Linuxcnc does not make any allowance for machine accelerations, and none of the run time estimators in cam programs I've used do either, other than sometimes adding a time percentage to the estimate as a fudge factor. The result is files that have lots of changes in direction with short moves can have the actual milling times be wildly different from their estimated time. (I have never tried Fusion360.)

Be sure that the feeds specified in your files are within the capabilities of your machine and the feed rate limits you programed into your ini file.
Last edit: 01 May 2020 14:01 by Todd Zuercher.

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01 May 2020 15:11 #166332 by bbsr_5a
also the effect of G61 vs G64 P0,1
did make on plasma a 30% decrease in Cutting time

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