operation cnc

[Jonathan]

2.)keep the dual motors (as I have all the gear to hand) where there is one stepper for each of the two screws (the gantry is quite heavy!) but I guess this may entail buying the motor controllers to replace the above?

I would keep the two steppers with the drivers you already have. I don't consider one stepper stalling and twisting the gantry to be an issue, since once you've set up the motors properly they will not stall. If they do stall then clearly having the stall detection feature is excellent, since it can prevent any damage, but the motors have no reason to stall so to me it's protecting against something that wont happen anyway. You also have more input power, since there are two motors, unless you use a reasonable size Nema 34 motor if just using one. With either system you always set the motors up such that they will never stall in normal operation, so you don't have to run it slower with two motors to play safe since if either configuration stalls it's set up wrong. Since you already have the drivers and motors(?) it doesn't really cost much to try it and plenty of people use either system. I don't have problems caused by having two motors.

Jazz will now vote for option 1.

[Kerryfisher]

Coming along nicely KC, I'm researching building a plasma table, thanks for some good info along the way, good luck with the rest of the build.

[JAZZCNC]

Jazz will now vote for option 1.

Won't go there regards stalling/racking has it's all been said.!! But there is more to this than just Stalling motors racking gantry's.?

The Main reason why I like it is Synchronization.?
My machine never loses position and the two ball-screws are synchronized exactly the same today has they were when first installed.
I don't have to worry that on long Jobs the machine will lose sync has the slaved steppers drop the odd step here or there running out of sync with each other slowly racking the gantry.

Don't have to worry that after 10-12 hours cutting I'm going to find that holes aren't where there supposed to be.!! Or the part isn't actually square after cutting profile out because the gantry slowly racked fraction of degree.!

The only way to ensure slaved steppers stay in sync is to either have very accurate Home switches or Home to hard stop and do it often. Certainly after every Job to be safe.
Even then if motors are tuned anywhere near close to the edge, esp regards Acceleration, they can easily lose steps without realising on jobs just a few hours long.
On Jobs that run non stop for 10-12 plus hours like litho-pains this could and has been for some slaved stepper users disastrous often resulting in not just in in-accurate work but stalls thru accumulative error over hours.!

Both work and won't argue that fact but I know which works best.!!

[Jonathan]

has the slaved steppers drop the odd step here or there
[...]
On Jobs that run non stop for 10-12 plus hours like litho-pains this could and has been for some slaved stepper users disastrous often resulting in not just in in-accurate work but stalls thru accumulative error over hours.!

I have never seen any evidence of stepper motors on any of my machines loosing 'the odd step'. If it did they would be practically useless - it's either stall and loose lots of step or run perfectly.

If a motor does stall (which it wont if set properly) then it will only start moving when the step frequency has dropped to a low frequency, so it is possible to loose maybe a few steps (or tens of microsteps) if the motion is very small movements which constantly accelerate each motor, but that's still likely to damage the part whether it's one motor or two. Again, if the motors are tuned properly then, just like on Jazz's machine, you wont loose position so it doesn't matter if it's one motor or two. The only difference worth discussing is the input power considered with the whole system - if the basic calculations show that the motor and driver you can afford to use if just using one will perform better than the same calculation with two motors then go for it. If not it's illogical to use one.

[JAZZCNC]

I have never seen any evidence of stepper motors on any of my machines loosing 'the odd step'. If it did they would be practically useless - it's either stall and loose lots of step or run perfectly.

Jonathan I've had to correct stuff you made because the fucking things weren't square or correct so don't give me that bollocks.!!

Also if your going to quote me then make sure you quote the whole fucking picture not just what you want to make fit.!!

Even then if motors are tuned anywhere near close to the edge, esp regards Acceleration, they can easily lose steps without realising on jobs just a few hours long.
On Jobs that run non stop for 10-12 plus hours like litho-pains this could and has been for some slaved stepper users disastrous often resulting in not just in in-accurate work but stalls thru accumulative error over hours.!

Both work and won't argue that fact but I know which works best.!!

[kingcreaky]

Guys, I welcome all your comments, but really didnt mean to cause an argument. Lets just put the subject to bed.

Im in one of these junctions in the road now. Whatever I decide I dont want to alienate myself from advice from either of you.

I must say however, I think wilfy's comment summerises my present thought chain. and as I have genuinely lost, Yes Lost. one of my 3 steppers it was a case of buying two more for the X axis anyway. So simplifying the bits you cant bite (ie the electronics) and only having to buy one (bigger) stepper & a longer belt & some pulleys seems to me a favourable way forward.

Don't have to worry that after 10-12 hours cutting I'm going to find that holes aren't where there supposed to be.!! Or the part isn't actually square after cutting profile out because the gantry slowly racked fraction of degree.!

This machine has cost me an arm and a leg. Im worrying about lots of aspects of it all the time, so Simplifying this area I guess is one less thing to worry about.

On a seperate note; Im also worrying about how accurately I have mounted the gantry to the slide plates. I mean with my Set Square its bang on; when i slide it along the rails; the rails dont move out or in (however I havent yet bolted them down I think im looking to see if it gets tighter at one end) but if the gantry is not square like Jazz has mentioned above the work wont be square... I guess Il find out in time... Its this kind of think that is doing loops in my head everytime im down the workshop. I find myself standing there drinking coffee and smoking staring at it just thinking about (and questioning) the accuracy of my work.