Hello Guest it is March 28, 2024, 06:54:20 PM

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - Pmw

Pages: 1
1
Hi guys,

Thanks for your replys and input. After spending alot of time trouble shooting and testing different things which both of you guys touched on, I believe that the errors have been caused by an eccentric pinion. The circumference of my pinion is 137.4 mm, and when I MDI multiples of this distance form zero, the marks are hit spot on (as they should as they are full revolutions). However distances anywhere under this value can run long or short depending on where abouts they land on the rotation of the eccentric pinion. The  pinions are probably the cheapest thing on my machine and I must have fallen lucky with the y/slave axis. I removed the pinion and measured the hole to be off centre by 0.15mm at worst. Anyway lesson learned, I'll do the machining myself with the new one. Thanks again for you time and sharing your knowledge.

Cheers
Chris

2
Hi all,

I'm new to the forum but have spent quite a bit of time looking through past topics finding a lot of helpful information along the way. However I am at a total loss for a solution to the following problem I am encountering. Some previous posts have eluded to what sounds like the same or similar problem but no definite solutions seem to have been found.

I have a self built 4x8 rack and pinion gantry router, running a closed loop system with 2hss86h drivers and nema 34 steppers with encoders to suit on both the x axis and the y/slave axis (one stepper either side of the machine). Each stepper then runs through a 6:1 planetary gear box.

I have set the steps per unit for both axis using an accurate 1000mm steel rule and microscope over the full length of the rule.

The y axis works exactly as it should, I can move from 0 to 1000mm and it hits the mark perfectly. I can move along the axis incrementaly using MDI Y100,Y200,Y300 etc and it hits each mark. It works in 10s or single units.

With the x axis I again set steps per unit over the full length of the rule. As with the y axis I can move from 0 to 1000mm and it with hit the mark perfectly. However if I move along the axis incrementaly X100, X200, X300 the movements are inconsistent, with some running too long and some coming up short, there seems to be no pattern.

X0 = 0
X100 = 100.05
X200 = 200.10
X300 = 300.20
X400 = 400
X500 = 499.95
X600 = 599.95
X700 = 699.9
X800 = 800
X900 = 900.05
X1000 = 1000

I have checked the machine over mechanically and everything is sound, no loose grub screw holding the pinion to the planetary shaft, no lose grub screw holding the planetary shaft to the stepper motor. Steppers are bolted down tightly. Large springs engage the pinion with rack at all times. The rack is fix tight, the spindle is trammed and fixed tight and there is no binding along the axis. I can even perform the above incremental movements using my fully body weight to resis the x axis movement and it just moves me out of the way and still hits the inconsistent measurements shown above time and time again.

I have also carried out the test further along the X axis, zeroing at what would have been my previous X500 position, and again it gives the same inconsistent results as shown above (I was only able to  test to X500 that time as I was only using the second half of the axis). Yet this showed me that the errors weren't localised to a section of the axis as it behaved the same when moved to another part of the axis, so ruling out possible damaged or deformed rack or pinion.

I have also swapped the x and y stepper motor with the thought that the encoder on the x axis stepper might be faulty, but the y axis stepper performed exactly the same when in its place

With regard to Mach3 both the x and y axis are set up exactly the same. I have set the step and direction pulse within the motor tuning page to 3 and 3 after reading some previous treads on this forum but with no luck.

Sorry for waffling on but does anyone have any ideas to a cause or a solution or this problem?
Has anyone encountered anything like this previously?
I have pretty much run out of ideas now

Thank you for reading this far and thank you for any help in advance
Cheers
Chris


Pages: 1