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Author Topic: Why is this happening at higher feed rates?  (Read 3346 times)

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Why is this happening at higher feed rates?
« on: June 07, 2015, 06:35:10 PM »
The effect in the photo occurs at 300 ipm and lessens as I slow the feed rate.  I have to slow the feed rate down to 50 ipm before I can get acceptable, clean corners, but that's just way too slow.

Sorry if this has already been discussed at length.  I just wasn't sure what keywords to search for.
« Last Edit: June 07, 2015, 08:08:32 PM by Overloaded »

Offline ger21

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Re: Why is this happening at higher feed rates?
« Reply #1 on: June 07, 2015, 07:24:42 PM »
Looks like a mechanical issue maybe? Not sure if I've ever seen anything like that?
Gerry

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Re: Why is this happening at higher feed rates?
« Reply #2 on: June 07, 2015, 07:31:26 PM »
I don't know about your machine but could it be tool deflection and just before the corner, the machine slow down and the tool have less of it.

Jeff
Re: Why is this happening at higher feed rates?
« Reply #3 on: June 07, 2015, 08:13:31 PM »
Backlash in the axis'.
Running slower, there isn't enough influence from the rotation of the tool to move the table.
The heavier cuts will displace the amount of backlash.
Possible ?

Russ
Re: Why is this happening at higher feed rates?
« Reply #4 on: June 07, 2015, 08:19:55 PM »
Hmmm looking again, that notion would require a left hand CCW cutter in the direction shown.

Might be more like the servo tuning issues we've seen earlier.

Are you using servos ?

Russ

Offline BR549

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Re: Why is this happening at higher feed rates?
« Reply #5 on: June 07, 2015, 09:40:01 PM »
Can you tell WHICH is the correct cut as just after the turn or after it moves over a step.

SO the FASTER it runs the worse it gets ?

Stepper or servo system ?

Are your velocity and accelleration settings the SAME for both axis's ?

Have you set ANY CV settings ?

Try running the program in exact stop mode.

(;-) TP
Re: Why is this happening at higher feed rates?
« Reply #6 on: June 07, 2015, 09:52:30 PM »
I'm using steppers.

The cut was CW.

The faster the cut, the worse it gets.

The velocity and acceleration are the sane for both axes.

I have not set any CV settings.

Offline TimGS

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Re: Why is this happening at higher feed rates?
« Reply #7 on: June 08, 2015, 08:03:27 AM »
Looks like tool deflection; what is the diameter of the bit and how much sticks out of the chuck?  To confirm, Stick a marker in the chuck and use your mill like a printer and see if you see the same problem.  The small Sharpies work well.
« Last Edit: June 08, 2015, 08:05:16 AM by TimGS »

Offline BR549

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Re: Why is this happening at higher feed rates?
« Reply #8 on: June 08, 2015, 01:50:47 PM »
It is odd that it happens AFTER each corner and at teh same point in the  next LINE,  and it is happening in both axis.  That looks mechanic and looks like  flex OR axis shift(slipping coupler, belt stretch) in both axis.  The main indicator is it gets worse with higher speeds . That is when cutting forces grow higher.

Try the sequence in Exact stop mode (G61)  OR reverse the direction of the cutting and see IF the shape of the problem changes.

Does the toolpath LOOK correct in Mach3 ?

(;-) TP

(;-) TP
« Last Edit: June 08, 2015, 01:53:36 PM by BR549 »

Offline TimGS

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Re: Why is this happening at higher feed rates?
« Reply #9 on: June 08, 2015, 02:16:20 PM »
Look at the GCode too you should only see one axis vector changes; not multiple axis vector course corrections like you would in a circle.

If the GCode looks ok, look for play (backlash in the screws/couplings/pulleys/motor mounts) as well.