Hello Guest it is July 17, 2019, 07:24:37 PM

Author Topic: What's your fastest feed rate for your mill/parallel port.  (Read 10514 times)

0 Members and 1 Guest are viewing this topic.

Re: What's your fastest feed rate for your mill/parallel port.
« Reply #10 on: January 12, 2012, 11:22:45 AM »
And if you can't set accel over 2 without losing steps, you have some pretty seriously under-powered motors.  I run accel of 25, which is not particularly high, but going higher just makes for more shaking when the big machine changes direction.  Steppers lose torque rapidly as speed goes up.  If you can't handle high accel, even at low speeds, then you simply don't have a lot of torque to work with, and you won't be able to reach high rapid speeds.  LOTs of people have hit 200IPM, and well beyond, with Mach3.  Your problem is your hardware.

Regards,
Ray L.
Regards,
Ray L.

Offline ger21

*
  • *
  •  6,288 6,288
    • View Profile
    • The CNC Woodworker
Re: What's your fastest feed rate for your mill/parallel port.
« Reply #11 on: January 12, 2012, 11:28:02 AM »
Ray, he's using servos
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline stirling

*
  • *
  •  2,188 2,188
  • UK
    • View Profile
    • www.razordance.co.uk
Re: What's your fastest feed rate for your mill/parallel port.
« Reply #12 on: January 12, 2012, 11:38:46 AM »
As I think has been more or less said, your kernel frequency only needs to be fast enough for your machine. You can't make a machine that doesn't need a faster kernel go any faster by upping the kernel speed.

200ipm on 25khz is great. I have zero experience with steppers. Mine is a servo.

How does a 15m/min @ 2500mm/sec/sec grab you? (that's 590 ipm @ 98 in/s/s) ;D and that's steppers on a 25KHz kernel. It'll actually do quite a lot more both in vel and accel but it gets a bit scary. It's a router but it'll snap cast iron G clamps if they get in its way.

Ian
Re: What's your fastest feed rate for your mill/parallel port.
« Reply #13 on: January 12, 2012, 11:48:20 AM »
If you are losing steps with servoes just by changing acceleration you have a problem. Servoes should either fault or catch up.

Something like Wrong active setting of step line????
Re: What's your fastest feed rate for your mill/parallel port.
« Reply #14 on: January 12, 2012, 11:57:58 AM »
Ray, he's using servos

Gerry,

Well, then, what I said goes double.  He should be able to set accel MUCH higher with servos.  Either they're not tuned right, or they're gorssly under-
sized for the machine.

Regards,
Ray L.
Regards,
Ray L.
Re: What's your fastest feed rate for your mill/parallel port.
« Reply #15 on: January 12, 2012, 01:37:24 PM »

How does a 15m/min @ 2500mm/sec/sec grab you? (that's 590 ipm @ 98 in/s/s) ;D and that's steppers on a 25KHz kernel. It'll actually do quite a lot more both in vel and accel but it gets a bit scary. It's a router but it'll snap cast iron G clamps if they get in its way.

Ian

Ian, you set the bar very high!! I'm thrilled! What size is your table/gantry? My table is a 42" wide cast iron Bridgeport mill table. So it's heavy.

Have any of you looked at the video of mine in action? Does it look sluggish? It's cutting air using code for a spiral cut pocket. It's set to 135ipm. I don't remember what the acceleration is set to.

 http://www.rotordesign.com/servolite/VID_cnc_135.3gp
Re: What's your fastest feed rate for your mill/parallel port.
« Reply #16 on: January 12, 2012, 02:08:13 PM »
My x and y axis are set to 20,000 pulses per inch. This is why I needed a faster computer that can handle a faster kernel.

1. Kernel=25khz, vel=135ipm, accel=1 the velocity slider is at 100%.

2. Kernel=45khz, vel=135ipm, accel=1 the velocity slider is at 100%.

3. Kernel=60khz, vel=135ipm, accel=1 the velocity slider is at 75%.

4. Kernel=65khz, vel=135ipm, accel=1 the velocity slider is at 66%

5. Kernel=75khz, vel=135ipm, accel=1 the velocity slider is at 55%.

6. Kernel=100khz, vel=135ipm, accel=1 the velocity slider is at 45%.

So I have to apologize for being wrong about my slider position earlier in this thread!!

Right now my accel is set around 1-2 as i recall. It's 3 stories down stairs. So I'm replicating my system settings on it's twin computer upstairs.

20,000 pulses per inch uses up a lot of cycles. So I was pretty lucky to get 135ipm out of the old pentium III 800mhz machine. But the machine won't go any faster at 2.4ghz. In fact, it actually skips slightly more steps if the kernel is set higher than 45khz, if I leave all of the motor settings the same. This is why I think the scope needs to be applied to the hardware to see if there is a mismatch in timing between the step and direction pulses. Or maybe my PS2501 opto board on the parallel port is the bottle neck.

Mike



« Last Edit: January 12, 2012, 02:10:04 PM by mikep_95133 »
Re: What's your fastest feed rate for your mill/parallel port.
« Reply #17 on: January 12, 2012, 02:13:53 PM »
I think the reason having a kernel over 45khz causes more missed pulses, is that the velocity slider is already at 100%. So going to a faster kernel actually increases the pulse rate and makes a bad situation worse. All because the slider is already at 100%.

Then on the other hand, once the slider comes down off of 100%, I still get missing pulses. Dang. Sorry, just thinking out loud.

Mike

Offline RICH

*
  • *
  •  7,341 7,341
    • View Profile
Re: What's your fastest feed rate for your mill/parallel port.
« Reply #18 on: January 12, 2012, 06:05:40 PM »
Mike,
You are missing basic concepts of motion (the motion profile in tuning) which is used by the controlling software to provide pulses to dowstream devices. Changing the Kernel Speed allows Mach to assume some pulsing is possible in Motor Tuning. The driver test confrims if the selected Kernel speed is usable.
Thus, higher is of no value if the axis "system" is not capable of using the pulses. Note that an axis is made up of both electronic and mechanical items and all of them are relative to each other.

Velocity is calculated or tested by trial to find the max velocity. It is a user defined input value in motor tuning. If calculated then one assumes a safety factor. If tested one again provides a safety factor. The value can be restricted if the steps per unit are high, but if the axis can provide for a great velocity
and the computer train output is proper, then usable velocity can be varied over some range. Since velocity is constant speed in time, the tuning will show you the IPM avialable based on input velocity and steps per unit. Just because the controller indicates a high IPM dosen't mean you can use it.
So velocity is related to other inputs. What velocity can be acquired by a axis system is based on the motor characteristics to provide power / rpm / speed to overcome the forces acting on the motion of the axis. The mechanical aspects can be used to change the rotational to linear motion to provide for a different end use velocity. So how fast you can constantly go is dependant on a number of  related items.

Acceleration is different than velocity since it is defined as a time rate of change of velocity. It also can be calculated, tested to find, and is a user defined input value. What determines the acceleration is again defined by available power to overcome the forces acting on the axis. The forces are different in that greater power / force is required to accelerate to some velocity. You need to overcome the inertia ....resistance to a change in motion.
Same goes for decelerating.

What motion is available by others is totally irrelevant to YOUR machine unless you are comparing "apples to apples".

Just because you have changed the computer and increased only one part of a number of interelated factors may not necessarily give you a great
feed rate. It's all related and usually will require a compromise.

RICH

Offline RICH

*
  • *
  •  7,341 7,341
    • View Profile
Re: What's your fastest feed rate for your mill/parallel port.
« Reply #19 on: January 12, 2012, 06:11:50 PM »
I forgot to ask a very important question.

What are you trying to use / accomplish with your cnc machine?

RICH