Messages

31

General Mach Discussion / Re: deviations of 0.3 mm, in small parts: MACH3

« on: January 07, 2010, 05:27:11 PM »

 

maybe "under all circumstances" was a little keen  

In fact, I don't know any manufacturer that sells his toothbelts as "zero backlash"...
They all advertise how much the reduced the remaining problems in application.

But on the other hand, depending what is surrounding the toothbelt drive, the backlash and resilience of the belt driven stage becomes just irrelevant.
For example, using a belt as a reduction stage between drive motor and screw, is very common and does not affect the machine's precision in critical means.
Another example is using a belt-drive as "torque distribution" in machines that use two or more screws in parallel.


I like Overloaded's words "Wood router....maybe. Pick and place, torch/plasma, plotter.....fine."
Everything depends on the force applied by/to the system and the desired precision.

Konrad

PS:
* now putting the pair of gold scales back into the locker...*

32

General Mach Discussion / Re: deviations of 0.3 mm, in small parts: MACH3

« on: January 07, 2010, 12:30:07 PM »

Hi all,

I just had a look on the website www.zenbotcnc.com....

The Zenbot mill is made from plastic material and furthermore is belt-driven. So, there is no threaded rod (screw) at all at the axis' drives.

Under all circumstances, most tooth-belts have remarkable backlash, depending on material and pulley geometry used.
(of course, there are "low-backlash" belts, but even the pictures on the zenbot website show a very small belt, which cannot be low-backlash.)

In other words: For this type of machine (and price...) the reported tolerance seems to be normal 


  On the other hand, it seems to be a very good deal for beginners to get familiar with CNC-technology as the price is very low.


best regards
Konrad

33

General Mach Discussion / Re: deviations of 0.3 mm, in small parts: MACH3

« on: January 06, 2010, 02:45:17 PM »

Hi all,

just a few questions:

- How is the drive setup of the table?  Conventional screws or ballscrews? Steppers or servos?
- Is the machine new, or a used one with CNC retrofit? Possibly there is some wear of the screws causing your trouble.
- Of course, flex could be a possible cause.

Maybe, try to check wether the drive motors do the exact steps needed to move the table precisely, by marking "0°" on a flywheel or similar and make a part which needs exactly x revolutions to make the necessary travel.



Have fun
Konrad

34

General Mach Discussion / Re: HOLD machine via LPT pin?

« on: October 25, 2009, 06:12:31 PM »

Hi Hood,

I checked... No surprise for you: of course NO acceleration and decelaration when opening the window.   

Frankly speaking: After Art said this, I didn't even believe that there woud be proper start or stop...


Konrad

35

General Mach Discussion / Re: HOLD machine via LPT pin?

« on: October 22, 2009, 04:19:11 PM »

If this is molded hot wire and from some case it isn't enough "hot" the shape will be deformed and all next process will be for nothing.

... sounds like you need to modulate the feedrate by tool condition.

High temperature -> High feedrate
Low temperature -> low feedrate.

Wasn't there a possibility to do a "feed per revolution" mode? (Hood?    )
If so, you just needed to transform the hot wire temperature to spindle index pulses some way.   

Konrad

36

General Mach Discussion / Re: HOLD machine via LPT pin?

« on: October 22, 2009, 04:12:04 PM »

Do your motors decelerate to a stop and the DROs show that deceleration?

Hood

This would have to be checked on the machine... Can report on Saturday, or Sunday. But I can state that I use a stepper motor drive and it doesn't lose steps at all when opening the protective window and the machine is forced to stop that way. - In E-Stop it definitely does.

But now, I am courious. Let's wait the weekend. :-)

Konrad

37

General Mach Discussion / Re: HOLD machine via LPT pin?

« on: October 22, 2009, 03:40:02 PM »

Thanks Hood.
It's useful to learn that it works in my case, but not in all cases...


(I was writing about experience... In some cases, knowledge is actually better than experience ;-) )

Konrad

38

General Mach Discussion / Re: HOLD machine via LPT pin?

« on: October 22, 2009, 03:22:58 PM »

Good afternoon,

in my experience, using the safety lockout should work fine. This input is normally used to stop the machine immediately if an external guard is triggered, and also inhibits re-start. (Of course, it is done by software, and thus not as reliable as an E-Stop, but works very well)


To enable the safety lockout, tick "program safety lockout " in "General Config".  (bottem left corner of the menu)
Also assign your input pin to "Input #1".


Have fun ;-)
Konrad

39

General Mach Discussion / Re: homing order

« on: October 20, 2009, 06:30:40 PM »

   Should have read the docs more carefully...

   Question appeared too spontaneous for reading the docs first.



Thanks a lot.
Konrad

40

General Mach Discussion / Re: homing order / 2 axis simultaneous

« on: October 20, 2009, 02:15:24 PM »

   Extra question:

Would it be possible to do homing for 2axis at the same time?

For example:

1. Z
2. X & Y

This would save hours of precious time.  ;-)


Best regards
Konrad