Wobblycogs CNC Mk2

[Robin Hewitt]

Is there any other signalling taking place along these lines?

What pattern does the driver put on it's outputs when you switch on?

It may go to a set start position, it may go to the position it was at when you switched off.

You have to figure out if this can blow your start location.

[Wobblycogs]

What pattern does the driver put on it's outputs when you switch on?

It may go to a set start position, it may go to the position it was at when you switched off.

You have to figure out if this can blow your start location.

This is all hypothetical at the moment. I've been reading the manual for the CSMIO/IP-M which doesn't support slaving and I was wondering why I've not seen people just wiring drivers in parallel. I came to the conclusion there must be a good reason for it or BOB makers wouldn't advertise support for slaved drives as a selling point.

[JAZZCNC]

Think it's mostly to do with timing issues and resonance handling. The BOB's that handle slaving do some internal trickery and split/buffer and boost the signals so they arrive at the same time with enough juice.!

Slaved motors can remain sync'd but they need to be tuned correctly and run well below there limit. If you run near the limit and have half decent weight gantry and cutting hard or fast then it's easy to start dropping steps over the job period.

Most troubles with missed steps come from over tuning and running too fast losing the steps from gantry pushing on de-acceleration or sharp directional changes.
This happens more than you realise when cutting materials that need higher feeds like woods and plastics and jobs which take several hours.
Now over the course of a job these lost steps don't often add up enough to cause trouble with woods etc because of the lower resolution and tolerances required but if not homed regularly then they would accumulate and cause troubles so home switches are needed and because you can't instantly see which motor lost what with out using dial gauge etc so then easiest solution is use Home switches and square back up.

Like Jonathan I'm not a fan of twisting gantry back into square but my solution is to not bother with slaved motors and connect screws with belts so Eliminating these hassles.!!

Run the motors within there comfort zone when at high feeds and slaved screws work fine.. . .Push it and you'll encounter troubles guaranteed.!!

[Jonathan]

Occaisionally, I check the squareness of my machine by drilling 3 holes to prescribe a right angled triangle and accurately measure their center distance to determine skewness, and proceed to compensate back to square. I've taken to putting marks on the rotating ballnuts to aid the correction process.

I've never seen the machine loose or gain even just one microstep on either motor, except when I've crashed it. That's including on a job where the machine was left running for the best part of 47 hours.

[Wobblycogs]

Thanks both.

So, I really like the look of the CSMIO/IP-M but the lack of built in support for slaving makes me nervous. From the manual it looks like it could be done via Mach3 but it's not at all clear what the consequences of doing this would be e.g. would homing / squaring work correctly.

I would happily just ditch one of the x-axis steppers (less hassle, cheaper, etc) but I can't see a way to combine an open back to the machine and a belt drive system without ending up with belts all over the place or the set up being impossible to tension. Any ideas would be greatly appreciated.



I should say I'm not totally fixated on having an open back to the machine, it's nice to have and may make it more versatile but it's not the end of the world if it goes.

[Jonathan]

If the output from the breakout board can't source enough current for two driver inputs, then you can buffer it with just one transistor and two resistors and that's guaranteed to work.

[JAZZCNC]

Occaisionally, I check the squareness of my machine by drilling 3 holes to prescribe a right angled triangle and accurately measure their center distance to determine skewness, and proceed to compensate back to square. I've taken to putting marks on the rotating ballnuts to aid the correction process.

Ok but why would you need marks on rotating nuts to aid correction if it never loses a step or position.?? Should be nothing to correct.!!

I've never seen the machine loose or gain even just one microstep on either motor, except when I've crashed it. That's including on a job where the machine was left running for the best part of 47 hours.

But what was you cutting and at what feeds.? . . Aluminium I presume.! . . . Try cutting wood with inertia of rotating screws not rotating nuts around 7-8mtr/min for 47hrs and check it.!!
Also your machine is setup correctly and presumably with plenty of torque left, I'm talking higher feeds and motors tuned close to edge which often happens causing lost steps and much sooner than 47hrs.!!

Again I'll say it " Tune the motors properly with plenty of safety margin and there's no problem with slaved motors" but still it can happen and that's not good and healthy for screws or machine if one motor stalls racking gantry at rapid speeds.!!!!. . . . With belts running out of sync is not even in the frame and stays set just like the day it was set regardless of crashing or motor tuning.!! . . . .And trust me I've crashed hard and plenty so it's well tested. . .Lol

[Jonathan]

Ok but why would you need marks on rotating nuts to aid correction if it never loses a step or position.?? Should be nothing to correct.!!

The marks are there so I can check that it's square when I switch the motors on, as clearly they can move when turned off. I could do the same with switches, but a permanent marker is cheaper!

But what was you cutting and at what feeds.? . . Aluminium I presume.! . . . Try cutting wood with inertia of rotating screws not rotating nuts around 7-8mtr/min for 47hrs and check it.!!

Not aluminium. The feedrates were low and the acceleration set quite high. The result would be the same if I ran my machine for that amount of time with the maximum feedrates, because the motors are tuned properly. Yes, I could set the rapid feedrate slightly higher and loose the odd step here and there, but there's no reason to as I chose the correct size motors for the machine, so the safe feedrates are adequate.

Also your machine is setup correctly and presumably with plenty of torque left,I'm talking higher feeds and motors tuned close to edge

If that's the case then they should buy the right motors and set up the machine correctly in the first place, instead of linking the screws with a belt so it doesn't matter if there's a missed step.

How do you accurately set the machine square when a belt is linking the screws?

[JAZZCNC]

If that's the case then they should buy the right motors and set up the machine correctly in the first place, instead of linking the screws with a belt so it doesn't matter if there's a missed step.

Yep agreed but that's not always the case and some don't have knowledge to setup correctly from beginning and damage can be done before they learn.!! Plus there's the other added benefits using belts give like piece of mind a stall isn't going to turn gantry into a Twizzler.!! . . . Anyway it's bit Linux vs Mach thing we are obviously going to have to agrees to disagree.!

How do you accurately set the machine square when a belt is linking the screws?

Loosen bolts on gantry etc and pulleys then turn ball screws . . . . Simplizz.!! . . . Bit fiddly and time consuming at first but one time deal so no problem.