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Author Topic: What's your fastest feed rate for your mill/parallel port.  (Read 10516 times)

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What's your fastest feed rate for your mill/parallel port.
« on: January 11, 2012, 10:26:00 PM »
This past week I 'upgraded' my pentium III 800mhz machine with a built in parallel port, to a core 2 duo 2.4ghz machine with a built in parallel port. The pentium could hit 135ipm with accel at 1 and have no pulses dropped. The new to me core 2 duo, and only hit 135ipm with accel at 1.5 and no dropped pulses.

Why did I not get a least a double in speed with the computer update.

All of this cutting air in a straight line.

Mike

Offline ger21

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Re: What's your fastest feed rate for your mill/parallel port.
« Reply #1 on: January 11, 2012, 10:55:21 PM »
What was limiting your speed to 135ipm with the old PC?

Generally, the only reason your PC will limit your speed is if it can't run at a high enough kernel speed. So if you were''t running at the maximum velocity for whatever kernel speed you were using, a new PC won't go any faster.

Say you were running as fast as you could at 25Khz kernel speed, but the PC wasn't capable of running at 35Khz kernel speed. IN that case, if the new PC could run at 35Khz kernel, then it might be able to go faster.

Generally, it's the motors torque that limits your speed. Not usually the PC.
Gerry

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Re: What's your fastest feed rate for your mill/parallel port.
« Reply #2 on: January 11, 2012, 11:29:27 PM »
Sorry I left those details out. The pentium III could only go to 45khz. The new pc can go to 100khz but it skips pulses until I lower it to 45khz. Anything higher than 45khz just misses too many pulses.

Mike
Re: What's your fastest feed rate for your mill/parallel port.
« Reply #3 on: January 11, 2012, 11:32:20 PM »
The motors are dc servo. I have run them at 75v for 12 years. The power supply is variable from 0-200vdc. I did raise them from 75v to 90v. That made them stiffer, but not faster.

Mike
Re: What's your fastest feed rate for your mill/parallel port.
« Reply #4 on: January 12, 2012, 12:16:01 AM »
Here is a video of the mill at 135ipm cutting a pocket in the air.

http://www.rotordesign.com/servolite/VID_cnc_135.3gp

I found this guys's cnc site. His ideas for debug of the parallel port are just what I needed. I will bring my scope downstairs and get started. http://cockrum.net/cnc.html

Mike

Offline RICH

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Re: What's your fastest feed rate for your mill/parallel port.
« Reply #5 on: January 12, 2012, 06:42:17 AM »
One needs to understand the complete system. By that i am meaning the pulse capability must be adequately supplied by each electronic  component.
PC ( sharing time with windows), PP, BOB, drive, and motor.
Then you have the other factors which relate, like the eletro mechinical of the motor and the mechanical.

The max stream of pulse delivered and used is only as good as the weakest link in the path.

In practical applications one defines an acceleration and velocity and finds what is required to achieve it …or … accepts the values based on
given parameters.

RICH
 




Re: What's your fastest feed rate for your mill/parallel port.
« Reply #6 on: January 12, 2012, 08:00:58 AM »
Thanks Rich. Understood. Has anyone ever hit 200ipm for example??

I'd just like to know what others have achieved as a max feed rate while cutting air. I don't care if their hardware is different from mine.

After finding Mr. Cockrum's site, I'll take my isolated scope to the shop and start finding the weakest link as I posted earlier. My BOB uses NEC 2501 optos.  The data sheet looks slow to me. My amplifier boards have a 6n137 opto. Much faster.

Mike

Offline ger21

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Re: What's your fastest feed rate for your mill/parallel port.
« Reply #7 on: January 12, 2012, 08:20:00 AM »
 Is your velocity slider maxed out in motor tuning? If not, then kernel speed isn't your problem. What is your steps/unit set at? That's the only setting that may require a higher kernel speed to go faster.

Also, many PC's are not capable of using kernel speeds faster than 45Khz, and it's usually not recommended to use higher kernel speeds, as the PC can become unstable.

It doesn't sound like the kernel speed is the issue, but if it is, A smoothsteper or Kflop would help/

I can run my router with a 250oz stepper and 24V at 200ipm using 25Khz.
Gerry

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Re: What's your fastest feed rate for your mill/parallel port.
« Reply #8 on: January 12, 2012, 09:15:35 AM »
No, the velocity slider is not even close to being maxed. I don't use it. I have always adjusted my max feed rates manually by changing the acceleration and feed rate individually. I could experiment with it. The acceleration has to stay under 2.0 to not miss pulses. I have gone as high as 10 for accel. Just looses pulses.

Do you think a 2.4ghz core 2 duo processor would really become unstable at higher than 45khz? My last pc was just a lowly PIII at 800mhz and it handled 45khz for years on end. These 2 comparisons alone show me it really isn't the pc.

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





Offline ger21

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Re: What's your fastest feed rate for your mill/parallel port.
« Reply #9 on: January 12, 2012, 09:17:47 AM »
If the velocity slider is not maxed, then you don't need a higher kernel speed.

Gerry

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

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