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Author Topic: What is Feedrate?  (Read 3859 times)

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What is Feedrate?
« on: June 27, 2012, 01:21:08 PM »
Hi,

Getting to know the machine better!

However, now i'm trying to mess with the speed of the machine (Kernel Speed). Could someone explain to me what exactly does increasing/decreasing the feedrate actually does? Because I've changed it to F200... but the actual speed of the machine doesn't increase of decrease unless I click the (+) and (-) on my program run..

V

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Re: What is Feedrate?
« Reply #1 on: June 27, 2012, 01:28:23 PM »
The F word is used when commanding a move, whether that be in your GCode file or from the MDI line. For example if you command G1X10F200 from the MDI  line your X axis would move to 10 at a speed of 200 units per minute. If you command a G0X10 it will move to 10 at the rapid speed of your axis which is the Velocity you have in Motor Tuning.
Hood
Re: What is Feedrate?
« Reply #2 on: June 27, 2012, 02:44:02 PM »
Thanks Hood! That makes more sense. I'm able to change the speed of it now to however I want.

 Is a feedrate of 200 is the fastest?

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Re: What is Feedrate?
« Reply #3 on: June 27, 2012, 03:41:30 PM »
depends if you are set in metric or imperial units. If imperial 200 is relatively fast but then it all depends on the type of machine and its setup.
For something like a Bridgeport mill with steppers then 200Inch per min is fast but for a router with course pitch ballscrews 200inch per min is likely slow.
If your machine is set in metric units then 200mm/min rapids are painfully slow, so as you can see it all depends what you are talking about and what type of machine.
Hood
Re: What is Feedrate?
« Reply #4 on: June 27, 2012, 04:29:48 PM »
I have a CNC mach3 mill machine running at 200mm/min.. It seems pretty slow? I'm wasn't sure because I haven't been able to program my machine any faster than what I have now.
V

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Re: What is Feedrate?
« Reply #5 on: June 27, 2012, 04:47:27 PM »
You have to set the velocity, acceleration and steps per unit, You should get faster than 200 for Velocity but again it will depend on the motors, screws, type of drives, reduction etc that you have.
Hood
Re: What is Feedrate?
« Reply #6 on: June 27, 2012, 05:06:44 PM »
It worked! Except its getting stuck when the feed rate is set too high now.. is there a problem with my motor?

Also.. my units in my x,y,z axis keep changing randomly to different numbers than what I originally have, is it because I'm changing the velocity of my motor? Is there any way to keep that number constant so my gcodes are still correct when I work my machine? Now I have to change all my units on my gcode..:(

sorry, I'm such a noob.

V
« Last Edit: June 27, 2012, 05:18:37 PM by vypham2 »

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Re: What is Feedrate?
« Reply #7 on: June 27, 2012, 05:27:03 PM »
You need to work out the correct steps per unit, they are set in stone by your hardware and you can not change them.
To know what steps per unit you will need you need to know a few things.
If steppers you need to know if they are 1.8 degree or 0.9 degree, the former is more likely.
You need to know what microstepping the drives are set to.
You need to know the gearing between the motors and the screw.
You need to know the pitch of the screw.
As an example say you have 1.8 degree stepper that will mean 200 steps per rev for the motor. If your drives are set to 10 microsteps then that will mean 200 x 10 = 2000 stepss to turn the motor 1 revolution. If you have 2:1 gearing then that is 2000 x 2 = 4000 steps to move the screw 1 rev. If the screw is 5mm pitch then the steps per mm would be 4000/8 = 500 steps per unit.
Hood
Re: What is Feedrate?
« Reply #8 on: June 27, 2012, 05:47:04 PM »
Okay I have mine set at 2000 steps per rev and it is 1.8 degree stepper.

I don't know if I make any sense because I am very new at this and do not have any prior knowledge to computer programming.. but I think something maybe wrong with my hardware then because the units of my x.y.z axis are fluctuating to different numbers..

ex:

I had my gcode set to
g1 x50 ... it would go to ZeroX: +50 correlated to my table 

then after I changed my velocity of each axis selection in my "Motor Tuning and Setup" ..the zeros changed in position to the table..
what used to be programmed as g1 x50 position on the table went to ZeroX: +30 instead of ZeroX: +50

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Re: What is Feedrate?
« Reply #9 on: June 27, 2012, 06:12:01 PM »
Ok so if 2000 steps makes it move the correct distance when you have a lower velocity then that is correct steps per unit.
If increasing the velocity makes it travel less then you are losing steps. You need to find the Max Velocity and Max Acceleration you can get away with  safely. This is all trial and error in a stepper system and it may be your setup is not very good and 200 will be near your limit due to underpowered motors etc.
Try setting your acceleration low and then see how high you can get the velocity before it stals and misses setps. Once you have found that drop the Velocity by 50% and start increasing the acceleration and see how high you get that before you lose steps. Then it is just a case of finding the happy medium of acceleration and Velocity that suits your machine and hardware.
What kind of drives do you have? What size of mill is it? What is the voltage of the power supply?
Hood