"Holding Torque" is the torque when the motors are not spinning.
What you really need is the torque at max speed.
The simple answer is that's a general assumption. A properly machine will have a motor that provides the required torque to meet the performance goals of the machine, plus a certain amount of headroom so the motor won't stall or lose position. This may be 50% more than the minimum required torque.I keep meaning to read up more on why metal cutting machines use much larger stepper (or servo) motors
A big router will have bigger motors than a small milling machine. It all depends on the specific machine.
Gerry
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CNC, Mechatronics Integration and Custom Machine Design
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But an increase in diameter increases inertia, which can require more effort to get it turning.So an increase in dia, and/or a decrease in pitch will result in less effort required.
Gerry
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[URL]http://www.thecncwoodworker.com/2017.html[/URL]
Mach3 2010 Screenset
[URL]http://www.thecncwoodworker.com/2010.html[/URL]
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[URL]http://www.g-forcecnc.com/jointcam.html[/URL]
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
Do you think I should buy a larger motor for my long axis then (the one that has the larger diameter screw)? I currently have the 381oz "low inductance" motors that many here start with.
looking at the specs for these motors, they seem to have a decent amount of torque and peak torque for the job but i'm not really sure how much torque is optimal for this purpose. My inclination is to wait and see how well these motors cope before deciding to upgrade or not but.... if I am going to need to invest in new motor mounts and motor couplings plus redesigning the axis to make them fit, it would be easier to do that now if you think I'm likely to need more juice?
If I can do what I need with the 381oz motors then I would prefer to wait until I am ready to upgrade to a decent servo set-up.
I would get the machine running, and then see if what you have works.
Gerry
UCCNC 2017 Screenset
[URL]http://www.thecncwoodworker.com/2017.html[/URL]
Mach3 2010 Screenset
[URL]http://www.thecncwoodworker.com/2010.html[/URL]
JointCAM - CNC Dovetails & Box Joints
[URL]http://www.g-forcecnc.com/jointcam.html[/URL]
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
Good deals are only so if you can use them. You're beginning to amass a collection of parts that could have went to funding the right parts the first time. As Gerry says, at some point you just have to get the thing running; it's the only way you'll learn what works and doesn't for you. And we scold you for it, but we've all made crazy purchases in the past. Realizing it and moving on from it is the key.
I don't think your mechanicals are going to screw up your molds. Most all screw up are from some form of human error. Your machine can only do what you tell it to do, within its capabilities. And you won't know until the most inopportune of time. You WILL screw up, everyone does at one time or another. And it's not the cost of the aluminum that will kill you, it's the 22 hours of machining time into a job, and something goes wrong at 21:30. Or it's the endmill that galls up, going through the aluminum by friction alone, before stalling your spindle and moving your whole setup out of alignment. Then you hit the e-stop. It's not a question of if it'll happen; it WILL, in one way or another.
Metalworking machines are usually massive. And in an industrial setting, time is money, so moving heavy things at high speeds, as accurately as possible, is key. Then there is the force needed to plow through material, as well as absorb any shock forces, which can be multiple times the cutting force, and not lose position.
It is not the torque that pushes the machine through metal. (Although on a router-type machine, you're using the speed of the spindle to get through the part) It is the power that is generated from that torque. Think of the scissor jack for your car. Look at that screw. You (small motor) have a finite amount of torque (your weight times the length of the crank) you can apply to that screw. Easy to crank, but takes a bit of time. Now replace that screw with one of those 20mm ballscrews. You'd have a LOT harder time raising the car, and when it gets up there it would be all but impossible to keep it there. A heavier guy (larger motor) could possibly do it, but he's got to eat more (more electricity). Somewhere in between is a screw that gets the car up in a reasonable amount of time, with about the same effort as the standard screw. We don't always have the luxury of picking the ideal parts when we are up at 3am going through eBay listing after listing. You could however achieve the same mechanical resolution in each axis by means of timing pulleys and belts. Which is probably what I'd recommend in your situation.
I think that's fair. If the goal is "to make it the best it could possibly be" then I have no doubt that I could spend forever upgrading components - something I have no desire to do. It's time to finish this...
I'm not far off now (I think). My Z and X ball screw assemblies arrived today and, for the most part, I am happy with what I bought. The parts all move well and, by chance, they fit my existing motor shaft couplers but there is something I don't understand on the NSK parts for the X axis.
My (THK) Z axis ball screw comes with two pillow blocks with bearings that fit neatly inside but the (NSK) X axis ball screw seems to have bearings at one end that don't fit inside the pillow block:
The pillow block is loose and I can't push either of the two bearings into the block or remove the black collar at the end (I removed the set-screws but it seems to be stuck).
Before I get my heat gun and wd40 out to try and force the bearings into the pillow block, Is this a problem you guys have seen before? Am I right in assuming that those two bearings are meant to be be inside the block?
I looked all over the pillow block for set screws or equivalent but there were only two screws and a broken plate of some kind which did nothing to make it easier to insert the bearings. This is the broken plate I removed from the sides:
It is going to be a huge issue if I can't push the block and bearings further up because as it stands, I don't have the 30" of travel I need. I didn't realize that the double nut was over 5" long. If the two bearings go inside the block then I have just about enough travel.