Hello Guest it is May 19, 2019, 05:11:36 PM

Author Topic: Mach3 always hesitates in arcs and circles  (Read 3173 times)

0 Members and 1 Guest are viewing this topic.

Re: Mach3 always hesitates in arcs and circles
« Reply #20 on: September 22, 2017, 05:47:03 AM »
Hi Stephane

OK. Sometimes hard to tell whether we are dealing with a 3 ton machine or a Chinese aluminium desktop...

Next bright suggestion: can you dive into the bowels of the config data and work out what the single step distance is? Some maths required. On my machine it is about 0.8 microns.

Then try commanding moves in steps of about half that in both directions. We are looking for a loose pulley on the motor shaft here: you probably would not see it with the previous test. See how many microns you have to move in one direction after going in the opposite direction before the DI flickers. Yeah, boring stuff, but the results can be illuminating.

I remember one poor guy who found that the grub screw going into the dimple on the motor shaft was really loose. He soon fixed that!

Cheers
Roger


Re: Mach3 always hesitates in arcs and circles
« Reply #21 on: September 22, 2017, 10:57:39 AM »
Hi,
I've done the same sort of thing on my mill.

The stepper/ planetary gearbox/ ballscrew resolution is 1um. The manufacturer of the planetary gearbox claims less than 2 arc min backlash equivalent
to 0.7um lash.

When I did the same measurement that Roger describes I got 4um lost motion? As it turns out I'm using some cheap aluminium shaft couplers with a spiral
slot cut into them. They wind and unwind a bit like a spring and there is my lost motion. I have retained those things because they are a bit weak, I've had
the occasional crash and the coupler twists itself up and shears rather than some other component breaking. While I didn't intend it they serve as a mechanical
fuse.

With the gearboxes and mechanical advantage of the screws the stall thrust of my axes is over 1500 N or 150kg thrust, enuf to crush things like hands and so
on. This machine is tiny, machining volume of 200mmx200mmx200mm, and yet its till got the grunt to injure badly. Was quite a surprise when I realised that.
As I've said before 'some surprises are surprisingly more surprising than others'.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach3 always hesitates in arcs and circles
« Reply #22 on: September 22, 2017, 04:49:35 PM »
Quote
some cheap aluminium shaft couplers with a spiral slot cut into them. They wind and unwind a bit like a spring and there is my lost motion. I have retained those things because they are a bit weak, I've had the occasional crash and the coupler twists itself up and shears rather than some other component breaking. While I didn't intend it they serve as a mechanical fuse.
Good analogy, good idea.
Yeah, belt reduction and ball screw drive - beats a Juicero easily.

Cheers
Roger
Re: Mach3 always hesitates in arcs and circles
« Reply #23 on: September 22, 2017, 05:12:03 PM »
These last suggestions I am a little lost on. What exactly do you wante to measure?

My machine is made of servo with planetary reducer (gearbox) in front . Only my z axis is directly placed on ballscrew. This one I remounted once, there are no loose screws there. On the motors also every screw is supertight.

So I am a little lost here guys.

Stephane

Re: Mach3 always hesitates in arcs and circles
« Reply #24 on: September 22, 2017, 05:27:03 PM »
Hi Stephane

We don't even know what your machine looks like, but we are trying to help anyhow. We can be reasonably sure that if we come up with 10 suggestions, 9 of them will be wrong.

What I was suggesting is a way of seeing how much backlash there is from the motor end. With a fine pitch ballscrew, well mounted, you might have zero backlash when measured from the mill table, but you could stll have backlash from the motor end.

Cheers
Roger
Re: Mach3 always hesitates in arcs and circles
« Reply #25 on: September 22, 2017, 05:59:59 PM »
Ok, I see.

Backlash is really small, this I can tell you, measuring it, I wouldn't know how to start
Re: Mach3 always hesitates in arcs and circles
« Reply #26 on: September 22, 2017, 07:36:25 PM »
Hi,
I don't hold Chinese made gear in high regard but I think in this case your concern is unfounded. Where Chinese made stuff falls down is that certain
features like backlash comp or probing don't work and the  companies don't seem to be bothered to upgrade their plugins. Also their
documentation is often execrable most probably due to language and they don't seem overly concerned that their customers are struggling.

They do work tho...and any well constructed pulse stream is just as good as any other well constructed pulse stream be it Chinese constructed or
otherwise.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach3 always hesitates in arcs and circles
« Reply #27 on: September 22, 2017, 08:07:08 PM »
Ok, so we can take out the card as the reason. So we are back to the settings
Re: Mach3 always hesitates in arcs and circles
« Reply #28 on: September 22, 2017, 09:32:32 PM »
Hi,
I hope I haven't put you wrong there...I use an ESS and so cannot say for sure that your board it not the cause of the complaint, just that I don't think
its likely.

Additionally with all those units in service do you not think that others would have commented if they had the same problem?

If you don't mind me asking but a 3000kg machine is pretty damn big and presumably must have steppers/servos and spindles to match and be worth
tens of thousands of dollars. If you are of the opinion that the controller is questionable why not buy an alternative like an ESS with a know reputation,
about $190 USD plus shipping sounds pretty minimal in comparison to you machine.

Can you post a pic or two?

Craig
My wife left with my best friend...
     and I miss him!