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feed speed not matching
« on: April 18, 2012, 11:26:39 AM »
hi, I'm new to mach3 so maybe this has been covered tho I was unable to come up with keywords to find answers.

when I set feedrate to 30ipm it only gets up to 27.87 max, even on straightaways, is this a known issue? could it have something to do with the big-tex screen I'm using?

John

Offline BR549

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Re: feed speed not matching
« Reply #1 on: April 18, 2012, 01:26:53 PM »
It is HOW mach3 works now.The actual feedrate is based on the kernal freq AND most computers do not lock in at exactly what the set kernal freq is set to. The the difference between the set frq and the actual freq is th edifference you will see in the actual feedrate.

YEP I agree it aint right BUT that is how it works .

(;-) TP
Re: feed speed not matching
« Reply #2 on: April 18, 2012, 01:33:47 PM »
thank you, so I guess I need to figure out what to set it to in order to attain the speed I actually want, would this difference be less if I ran a higher frequency?

Offline Hood

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Re: feed speed not matching
« Reply #3 on: April 18, 2012, 01:58:37 PM »
27.87 for a called feed of 30 seems low, could it be you have feed override set?
When I used the parallel port I used to see a small amount below the commanded feedrate showing in the DRO but it was only 1 or so at the most and I use metric so that is why I am surprised that you are seeing over 2 IPM.
As said however I do not used the parallel port now so it may well just be the way things have changed in the last 4 or so years.
Hood
« Last Edit: April 18, 2012, 02:02:57 PM by Hood »

Offline BR549

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Re: feed speed not matching
« Reply #4 on: April 18, 2012, 02:32:53 PM »
Look at the set kernal frq in diagnostics the % of difference of the set frq and actual frq will be the amount of difference of the commanded feedrate.

I questioned this when ART changed it to help TURN worked out the threading problems. Mach3 now LOCKS in a freq to base everything on. and IF it is lower than set freq it effects everything time based.

(;-) TP

Re: feed speed not matching
« Reply #5 on: April 18, 2012, 10:47:48 PM »
Thank you

Look at the set kernal frq in diagnostics the % of difference of the set frq and actual frq will be the amount of difference of the commanded feedrate.

I questioned this when ART changed it to help TURN worked out the threading problems. Mach3 now LOCKS in a freq to base everything on. and IF it is lower than set freq it effects everything time based.

(;-) TP


Offline Hood

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Re: feed speed not matching
« Reply #6 on: April 19, 2012, 02:51:23 AM »
So what is the difference in your kernel and reported frequency?
Hood

Offline RICH

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Re: feed speed not matching
« Reply #7 on: April 19, 2012, 07:11:30 AM »
Quote
would this difference be less if I ran a higher frequency?

The selected Kernel Speed defines how many pulses you want the computer to output when using Mach3.
 The Driver Test, when run, will confirm that the selected Kernel Speed can be used in harmony with Windows since Mach is sharing time with the operating system. Changing the Kernel Speed will change the graph in tuning increasing or decreasing the max allowable velocity the software will use. There is no advantage to using a higher Kernel speed than necessary.

 The computer output ( number of available pulse instructions to the drive ) can restrict
the velocity, the steps per unit input is calculated and is composed of the axis components, the drive may be limited to how many pulses it can send to the motors,how fast something can accelerate to a velocity is dependant on the axis systems ability to provide adequate torque at some rate to address the systems inertia. All this is inter-related.

Using a higher Kernel speed does not mean your machine has the capability to achieve the higher velocity that the software is using.

I would be interested in your reply to Hood's question. Are you near the max velocity that your machine can run at for 30ipm?

RICH

Re: feed speed not matching
« Reply #8 on: April 19, 2012, 02:46:12 PM »
So what is the difference in your kernel and reported frequency?
Hood

I finally made it out to the shop and checked, while set to 25000hz it reports 23224 and at 35000hz it reports 35557, I put it back to 25k since my system is so slow(5/16 18tpi screws) max jog speed is about 60ipm on my machine.

Offline Hood

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Re: feed speed not matching
« Reply #9 on: April 19, 2012, 03:07:15 PM »
That ties in with what Terry said then, you would be better off at the 35KHz if it being as close as possible to commanded speed is important as the 30IPM would be slightly faster at around 30.47.

Hood