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Author Topic: MACH3 RAPID's: What determines the velocity?  (Read 385 times)

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MACH3 RAPID's: What determines the velocity?
« on: August 30, 2018, 04:29:30 PM »
So, having tuned my motors in Mach3 on my mill, whilst running a cut program, I noticed that my 'rapids' accelerate and move at a much higher velocity than the velocity I set in motor tuning.

Question: What dictates the speed of rapids? Is it some multiple of the velocity set for the axis? If so, what is that factor?

Bob T.
Re: MACH3 RAPID's: What determines the velocity?
« Reply #1 on: August 30, 2018, 05:06:47 PM »
Hi,
on Machs Motor tuning pages, its where you set the 'steps per unit'. You also set the maximum velocity
in units per minute and maximum acceleration.

These are the maximum Mach will drive that axis.

A move:
G0 X....Y....Z.... will move at maximum, being a G0 move or 'rapid'
G1 X.....Y.....Z....Fnnn will move to the nominated X,Y,Z location at a rate F units per minute. G1 is a 'feedrate move'
intended for cutting. If you nominate a feedrate F which is larger than the maximum in the motor tuning it will
go at the maximum not F.

Craig
My wife left with my best friend...
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Offline ZASto

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Re: MACH3 RAPID's: What determines the velocity?
« Reply #2 on: August 30, 2018, 05:38:51 PM »
I guess that the rapids in combined moves (X and Y simultaneously) can be higher than individual axis.
If your max feedrate is set to 1000 for both X and Y, the resulting velocity from X0 Y0 to X1000 Y1000 would be in vicinity of 1410.
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Re: MACH3 RAPID's: What determines the velocity?
« Reply #3 on: August 30, 2018, 05:47:23 PM »
Thanks Craig and ZASto. I'll have to think on this.

Although I haven't actually measured the velocity of the 'rapids' (G0's in a CUT3D cutfile I'm using. G1 is fixed at 12 tpi) they appear blazingly fast as compared to the maximum motor speed I have programmed in motor tuning. They have been a problem causing missed steps. As a workaround I've decoupled the Rapid and the Feedrate in the General Menu by unchecking the box. In that way I can moderate the Rapids independently of the Feedrate.

Bob T.

edit: I should clarify that in troubleshooting my missed step problem I have the Z and Y axis turned off. The only axis I've been observing is the X axis while running the cutfile, periodically pausing the program to check for missed steps (I marked the shaft and motor body with tape). Oh, and no there's no slipping of the couplers, etc. There is an area in the cutfile where there's some RAPIDS that cause the X axis to move, as I said before, blazingly fast.....
« Last Edit: August 30, 2018, 05:51:22 PM by injunear »
Re: MACH3 RAPID's: What determines the velocity?
« Reply #4 on: August 30, 2018, 05:59:03 PM »
Hi,
Quote
As a workaround I've decoupled the Rapid and the Feedrate in the General Menu by unchecking the box
That box is for having separate feedrate and rapid over-rides.

Rapids and Feeds are always separate. The modal F word sets the feedrate, modified by the feedrate over-ride if
enabled.
Rapids will go at the maximum permitted on the tuning pages or at some lesser percentage if the rapid over-ride
is enabled.

Craig
My wife left with my best friend...
     and I miss him!
Re: MACH3 RAPID's: What determines the velocity?
« Reply #5 on: August 30, 2018, 06:13:24 PM »
Yes, I am overriding the Rapid rate via the "BAR" on the Program Run screen (inside the FEEDRATE box) where I can click on the green bar for the RAPID and change it by percentage. That seems to control its velocity independent of the FEED rate I have selected. This only works if I decouple the two (FEEDRATE and RAPID) under the GENERAL Tab.

The cutfile has the FEEDRATE set to 12 (I set this parameter in CUT3D) and if I don't uncheck the aforementioned box under the GENERAL TAB, the RAPID status bar always shows 100%....However, 100% of what parameter though is what I question. My first thought was the same as you guys say, 100% of the maximum velocity I set in motor tuning but like I said, my eyeballs tell me the RAPID seems to be far faster than the maximum I have set in Motor tuning.....
Re: MACH3 RAPID's: What determines the velocity?
« Reply #6 on: August 30, 2018, 08:05:16 PM »
Hi,
Quote
That seems to control its velocity independent of the FEED rate I have selected. This only works if I decouple the two (FEEDRATE and RAPID) under the GENERAL Tab.
Thats normal.

Quote
the RAPID status bar always shows 100%....However, 100% of what parameter though is what I question
That means 100% of the maximum axis velocity in that axes motor tuning page.

Quote
100% of the maximum velocity I set in motor tuning but like I said, my eyeballs tell me the RAPID seems to be far faster than the maximum I have set in Motor tuning.....
Then you will have to measure it with enough accuracy to diagnose the fault. Just as a matter of interest what is
the velocity you have set? What units are you using?

Craig
My wife left with my best friend...
     and I miss him!
Re: MACH3 RAPID's: What determines the velocity?
« Reply #7 on: August 30, 2018, 09:34:29 PM »
 I have my STEPS PER at 4000, my microstep at 1/4. The native STEPS (no microstepping) is 1000 = 1 inch. I have the velocity set to 120 and the accel to 24 (20%).....

I'm 100% that it is I that is doing something wrong but I'm not seeing it.

Hmm, now I'm wondering about my Jog. I'm wondering if the speed I see when jogging in MOTOR TUNE is actually a lower velocity than selected (lower than 120, which of course would be wrong) and that the velocity I see when RAPIDS occur in the cut program is actually the correct speed for what I have selected (120)......

Now that I'm calculating what 120 would be in terms of velocity, it would be 2 inches/second. Pretty damn fast......So, now I have something to look at and that would be the jog speed I see in tuning.....

Just went to have a look at my jog speed....Sure enough, it was set to 25% and the velocity I was seeing when tuning was 1/4 the velocity set....What a dope! That explains it all. Like most people I was tuning by eye/ear and selecting a "comfortable velocity" by eye instead of actually working the numbers like I just did above.
I'll have to lower the velocity to around 60 and the accel to 12 and of course change my jog speed to 100%!!....That should do it!

Thanks for the help,

Bob T.