[matth]

In need of some help from all you guys.

I have got to the point with my 4' x 2' gantry router of cutting in anger and of course the tune up requirements and problems are starting to show!

So, I'm at the stage where I want to router my cutting top flat (this is the biggest, longest job I've run).
Every time I try to complete this job my router losses half an entire x move then starts again after the next y move, this drives the gantry into the x limits and the job fails.

I can't replicate this problem with smaller jobs or long jogging moves.
Now, the y axis is running a 400Oz/inch with a 20mm lead ballscrew, but the x is running an identical stepper on a 2mm lead screw.
Obviously the x stepper is having to run a hell of a lot faster to drive the x axis plus it's having to move the weight of the gantry.
When I encounter this problem the x stepper is very VERY hot, is it possible that this motor is stalling due to the heat (motor is running at 70V and maximum bipolar current)?

My drivers can run upto 8Amps and I have my eye on a 1600Oz/inch stepper to replace the x motor, would this help.

Input anybody???

[ger21]

What is the current rating of the motor, and what is it set at? What's the voltage rating? How fast are you trying to cut?

When you say very, very hot. Can you hold it? Heat is usually from either too much voltage, or too high of current.

A bigger motor may not help, because larger motors usually have a lower top speed.

A higher lead ballscrew may be a better answer.

[matth]

I can't remember the motor spec at the mo but I know its running within its ratings.
The Y axis is running exactly the same motor, voltage, current settings with no problems.

The axis is setup to run at 2300mm/min. The motor is to hot to touch for more than a couple of seconds.

I don't really want to entertain the idea of replacing the ballscrew as this was a second hand purchase and the entire router has been built around this.

Maybe gearing the stepper and the ballscrew 1:2 or last option swap to a servo (I asume these are better at higher RPM's).

WOW, just revisited my MACH motor tuning settings. The X ballscrew is only 0.5mm lead which means that the x stepper to do rapids of 2300mm.min is running at 4600 RPM! I didn't even know a stepper could run that fast.

[ger21]

If you are actualy seeeing 4600 rpm, you probably have virtually zero torque at that high of an rpm.

So your X screw needs to turn 40 times faster than Y to go the same speed? You definately need to change something. Gearing 1:2 might help a little. 1:5 would be better.

If you can touch the motor for a few seconds, it's probably not too hot. Most are rated at ~100°C

[matth]

Thanks for the replies Ger.

Now I am confused, I have had the machine running with 2300mm/min rapids and pushing against the gantry I have not been able to stall the axis.
The cutting that stalled today was with a 1/4" router bit in a 1 3/4HP router cutting 2mm per pass.
I persume that the very small lead of the screw is reintroducing the torque lost at the stepper.
So if I add a 1600Qz/inch stepper geared at 5:1 that will mean that my stpper only has to run at ~900RPM but I will only see ~320Oz/inch torque at the screw. Would this amount be ok??

If the motor is not running to hot, where should I look for the cause of the x axis stalling during a long job?

[ger21]

I presume that the very small lead of the screw is reintroducing the torque lost at the stepper.
So if I add a 1600Qz/inch stepper geared at 5:1 that will mean that my stpper only has to run at ~900RPM but I will only see ~320Oz/inch torque at the screw. Would this amount be ok??

It's more complicated than that. There is a formula to figure out how much force a screw will deliver when turned with a given torque. I don't have it handy, though.

The higher the lead, the lower the force. A .5mm lead screw will provide 40 times more force than a 20mm lead screw. The problem, is that steppers lose torque as rpm's increase. Full torque is only available when the stepper is NOT turning. As soon as it starts to spin, it's torque starts to drop. At some rpm, you won't have enough torque to move the machine. Usually that would be under 1500 rpm, but it varies with different motors, and with the voltage applied. Higher voltages will give you more top speed. With larger motors, torque usually drops off faster with rpm than with smaller motors. So, a larger motor may actually have less torque at higher rpm's than smaller ones

You need to see a torque curve chart for your motor to see where the torque drops off. You should gear the motor to stay in the higher torque range of the motor.

One other thing, is that you could be getting binding somewhere as the machine warms up. But I think your trying to spin the stepper too fast.

[dertsap]

if you add a fan to the motor the motor should run much cooler , i have 400oz motors and they get extremely hot due to the voltage i'm pumping to them ,enough that i forgot to turn off the system and when i went into my 10x12 work shop i could feel the heat in the air , which could save me from having to heat the shop in the winter (flame2) , a couple days ago i got some pc type 12v fans from the local surplus store at 3 bucks a piece , what a difference that made , much better now ,the motors would have crapped out sooner or later from the heat

[matth]

It's more complicated than that. There is a formula to figure out how much force a screw will deliver when turned with a given torque. I don't have it handy, though.

The higher the lead, the lower the force. A .5mm lead screw will provide 40 times more force than a 20mm lead screw. The problem, is that steppers lose torque as rpm's increase. Full torque is only available when the stepper is NOT turning. As soon as it starts to spin, it's torque starts to drop. At some rpm, you won't have enough torque to move the machine. Usually that would be under 1500 rpm, but it varies with different motors, and with the voltage applied. Higher voltages will give you more top speed. With larger motors, torque usually drops off faster with rpm than with smaller motors. So, a larger motor may actually have less torque at higher rpm's than smaller ones

You need to see a torque curve chart for your motor to see where the torque drops off. You should gear the motor to stay in the higher torque range of the motor.

One other thing, is that you could be getting binding somewhere as the machine warms up. But I think your trying to spin the stepper too fast.

I think I agree with your last statement here.
So my plan is to gear my current 400Qz stepper 5:1 and then see what I can do and then if necessary upgrade to the 1600Qz.
I'll rerun the last program at half the feed rate to see if the axis stalls again.

[matth]

LOL, I need a coffee or some other simulation for my brain!
I'm sorry for making you guys waste typing time but...

5mm lead not 0.5mm meaning that the stepper is running at 460RPM at max feed.

So, the question still stands. What could be making the x axis stall during a long job?

[dertsap]

acceleration setting ?

[matth]

Acceleration is set in Mach to 250. I have however completed some very long small jobs (milling very complex pcb) which obviously involves a lot of x acceleration and decceleration with no problems!

[pminmo]

Maybe your drive (or other electronics) is overheating and as a consequence falting.

[matth]

That's what I'm thinking but my controller box has a whopping 120mm fan that blows like a hurricane over the heatsinks of my drivers.
I'll post a piccy of the box tomorrow and I'll try to moniter the temps of the three drivers whilst performing a long job.

[matth]

Well I've found the problem.

The laptop that is running Mach3 was turning the moniter off after 25mins. This simple action was interupting the parallel port/Mach just long enough for the stepper to lose syncronisation and stall the axis. Once the axis was commanded to run again off it went.

A simple and free fix!:banana:

[project5k]

darn that power saver setting!

[pminmo]

Why would the power saver cause a problem? I would think the mach3 engine would handle system interrupts with no issue.

[project5k]

well to be honest, im not sure why, but i know that if i leave a program running that is processor cycle dependant, when the time comes to "power off monitors" it causes some glitching.... i would have to guess that its a combination of windows ediocyncries and processor usage... i'll try it sometime while watching my processor usage % and see if i can find anything... when i know that im going to be using something that is very time based and processor dependant i reset my screen savers and powersaver settings so that they dont activate... it might be a little hard on the old crt's to leave the images up for that long, but i would rather have to replace a monitor a little sooner (which i seem to do regularly anyway) rather than have something that i have left grinding away for hours get messed up...

[ger21]

Why would the power saver cause a problem? I would think the mach3 engine would handle system interrupts with no issue.

While Mach pretty much takes control of Windows to do it's thing, it doesn't have the ability to block other processes from interfering with what it's doing. On a very fast PC, it may not be a problem, but on slower PC's, it may not take much at all to interfere. Mach can be pretty CPU intensive, may and not have much headroom available for any other tasks.

[fyffe555]

I don't know how much control mach3 takes, or what the priority is as installed on your systems but I do know the XP 'background' processes run at a higher base priority than the applications. I've had a message queuing problem that was caused by a high priority system process jumping in over the top of the application and loosing sync. I'd suspect the power funtion is a system priority - i.e. base priority 'high' ? might account for the apparent problem.

having said that Art is a smart guy and I'm sure he's covered this.

To test it, in 2k and XP you can set the base priority from the task manager, taskmanager/processes right click the process (mach3?) and take the bottom option 'set priority' and set it to 'high' or 'realtime'

I'm not a knowlegable user of Mach3 so this might be irrelevant but my install shows the priority as normal..

[ger21]

I know if your network card speed is set to "auto", it'll mess up Mach3. So will Quicktime if it's installed on your system.