Thread: Jobs ruined after long run
ive had a brand new bearing give me nightmares on my Y axis ballscrew, it was on the floating end of the screw
randomly it would start to shudder for a few seconds and then go away, it took me many hours to pin point it, but when i found it ... oh boy it flew out the shop like a rocket on 'roids
The Following User Says Thank You to Blackrat For This Useful Post:
I thought i would post my results in the off chance it may help another new person if they have a similar issue as me with the high-z s model.
It turns out it was me, i was driving it too hard at 45mm/sec and as Jazzcnc thought the bushes were getting too hot and were binding, i have now run at both 20 and 30mm with total success, just it ran longer obviously, the model above mine the t series does not have the same bushes so i imagine the problem may not occur so easily.
Thanks to Jazzcnc and Philip at Protools who walked me through the reasoning.
One happy camper again
Don't know what reasoning phillip at Proto may have tried to parm off on you but any machine at the price they charge for those things should easily be capable of cutting at 2700mm/min. If not then send it back because it's unfit for purpose.? By that I mean they sell it for cutting woods and plastics which both need cutting at those kinds of speeds and higher.!
Now provided the machine is mechanicly sound, which it should be with such low millage and that Mid band resonance isn't the cause(Which it very well could be!) Then there are only a few reasons that you would struggle to get speeds you need and none of them very good or what Philip would be keen to admit.!!
Low ballscrew pitch less than 5mm or very poor quality low effieciency lead screws.
Under sized motors or poor spec motors.
Drives running motors with Low voltage. ie 24Vdc
Drives running motors with wrong current settings.
Very poor or low frequency pulse engine.
Now I'd guess the screw pitch is at least 5mm so I'll count that out and even Low spec 5mm pitch lead screw should give 2700mm.
Next and prime suspect is Low voltage driving the motors. Steppers get there speed and to some degree torque from Voltage. So if the drives are being run on low voltage of less than 36vdc then they struggle with torque when the rpm rise. Also if the motors are wound or wired series type then torque drops away very quickly when rpm rise.
Too low voltage and motors using series wired or low spec motors with very high inductance are common cause of low performance.
So why would manufacturer use Low voltage.? Because it means they can use cheaper drives and less chance of problems because they don't run the voltage near the drives Max capabiltys.
Correct Motors using decent drives driven with good supply of Voltage 44vdc or more and connected to 5mm pitch ballscrew should easily achive 2700mm/min cutting speeds on machine this size. Even if using less efficient Acme lead screws should still be no problem.
So what I'm saying is you either have another issue like Mid band resonance, which is what I would like to hope it is. Or the Spec of the machine is very poor and IMO unfit for purpose considering they advertise it for cutting woods plastics etc which it should do at correct feeds n speeds.
The Following User Says Thank You to JAZZCNC For This Useful Post:
Thank you for that very informative post, one that I shall follow up.
In a like for like world what would be its competitor so I can glean a bit more info about specs etc, if that's possible :-)
But what I can tell you for sure is what minimum feeds I would expect from any machine built using decent electronics and components.
If 5mm pitch ballscrews with 50Vdc drives running on approx 44Vdc and using parallel port then I'd expect at least 3500-4000mm/min cutting speeds and 5000mm/min rapid speeds. If same setup but with 10mm pitch then nearly double those speeds.
With Decent external motion control card then even higher speeds could be run like below will show. The only difference between these figures above and those achieved below was I used Cslabs IP-M motion controller.
To give some Idea of type of feeds that setup should give. Not so long ago I converted well used Denford router which used 5mm pitch and fitted with 50v digital drives running 44Vdc and it could reach well above 10,000mm/min. It wasn't run or tuned to work at those feeds to give very healthy safety margin but hopefully it shows what can be achieved with that kind of setup.
Last edited by JAZZCNC; 23-03-2016 at 09:09 AM.
TBH I don't have anything specific to achieve except light work on wood, mostly 2.5d or some 3d plaques, so I was not looking for high speeds or big cuts. That said now I have got into the hobby a bit more I find that I do want to go faster certainly would like to be at 45mm/sec as I am conscious of the electric bill as well (yes laugh :-) ) but as all my work is for charity fundraising it eats into the money I can give out if I have to start covering the bills, so the High-z out of the box really fits the bill.
Changes I would like......well back to my original speed if possible, a quieter router (currently a trend t4), it works lovely but dam its noisy and it goes through the house, and I need to make a better extraction at the cutting point as the one I brought with the machine does not do the job it really needs a proper skirt.
So all in all I don't need a lot, I will get some more details on current setup and post to see if that offers up any more info.
The feeds are really dictated by the material and cutter your using not your preference or desire to be in rush or not. Also 3D work (dispite what you see there's really only 2D or 3D) often means high feeds rates or/and fast acceleration because of the small moves with light DOC or tiny step over amounts.
Cutting slower just costs you more money because of excess tool wear and leaves poorer finish. It also as you say cost's more in electricty and time.
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