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Feed rate not steady
« on: February 10, 2018, 06:46:44 AM »
I'm setting up a control box and configuring the motors for a small mill, and I noticed that when I give a command for movement the feed rate readout is not a steady value. The rate changes with FRO slider and feed rate command, but it fluctuates about the desired value when driving. The sound of the motor is not steady, and the feed rate readout is jumping around for some reason.
From a knube pov I thought the feed rate would be a fixed value.  What would modify a simple feed rate output?
The motors are set for 60 in/ min with an acceleration of 4.0 and 2032 steps per unit.
Re: Feed rate not steady
« Reply #1 on: February 10, 2018, 09:22:51 AM »
What are you using for a motion control board?
Steppers or servos?
How much variation in the feed rate are you getting?

We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.
Re: Feed rate not steady
« Reply #2 on: February 10, 2018, 10:39:48 AM »
It's an XHC usb motion controller.  The variation I'm seeing is in the Mach4 DRO for feed rate, and it fluctuates from approx 9.5 to 10 when set to f10.  It's hard to read bcause it never settles down.
The motors are loose on the bench at the moment, just hooked up for testing, and the sound is all I have to go by at the moment.
I thought feed rate from Mach4 would be a fixed value based on velocity selected and feedrate %
Re: Feed rate not steady
« Reply #3 on: February 10, 2018, 03:53:53 PM »
I notice from your other thread you are planning to replace your external controller.

It is not clear to me that the feedrate variation you are seeing is in either Mach or the controller. Most certainly the motors are driven by the controller
and from your description they sound like they a varying.

I think you should replace your controller with a 'known good' one and try the same experiment again.

I use an ESS. When I command a move say:
g1 x100 f900
the feedrate DRO shows 810mm/min. Note that I just did this experiment so these are actual numbers. I don't know why Mach/ESS don't produce exactly the
commanded feedrate . I'm guessing that the internal arrangement is such that Mach can cause a number of distinct feedrates and it selects the closest one.

My wife left with my best friend...
     and I miss him!
Re: Feed rate not steady
« Reply #4 on: February 10, 2018, 05:39:02 PM »
Hi Craig
I'm definitely ditching the xhc. Too many quirks. I don't understand the give and take between the motion controller and Mach4 output, but there seems to be something going on. The sound of the stepper motor varies in a pulsing fashion in exact time with the blinking communication light on the mc. I thought it was passive and just took orders, but it's becoming moot.
Right now I only have an arduino mega with grbl on it to play with as an alternative, and it is crisp and precise by comparison. Partly because Universal G code Sender does just that. It doesn't interpret the commands so what you ask for is what happens. It also prints the dialog on the command screen for every transaction, and the card reports back what it's doing. It's really very friendly by comparison, and I don't see right off what Mach4 can do that this thing can't. Except maybe edit the screens. It's freeware too. $40 for a Mega and you're rockin.
Are there any real advantages to running mach4 for a casual hobby mill?
Re: Feed rate not steady
« Reply #5 on: February 10, 2018, 06:38:39 PM »
yes you can run industry standard Gcode which means all your CAD/CAM programs come into scope.

Mach4Hobby is trying to be an industrial player on a hobbyists budget. A genuine Fanuc or Seimns control would cost $20,000 and annual fees.

My wife left with my best friend...
     and I miss him!