Manual Operation After Cnc Conversion

[JimDawson]

PS. - Do you realize that that 439 oz-in motor produces about a 1000 lbs of thrust when it stalls out driving a .2" pitch ball screw???

That is true. That would be the virtually instant torque just before the stepper motor decouples and the torque drops to about zero. Stepper motor are friendly to machines in that regard. AC and DC servos are not so friendly and you have to plan for max torque at 0 RPM by torque limiting or throwing an excess lag error that shuts the system down. With servos on a CNC mill, it normally just breaks the tool bit and continues on. Yeah, I've done that a time or two

 

[JimDawson]

Last question before I finalize my order.

Because I want to add handles for manual operation, (and be able to quickly remove them), I was thinking of ordering the motor shafts D cut to facilitate a set screw in the handle.

Any problems with that as far as ball screw mounting? I'm guessing not, but I thought I'd ask.

That should work fine. That's pretty common.

 

[Jim_Hbar]

What are you trying to tell me?

You are in "analysis paralysis", picking a motor based on a number that you are never going to use.
I'm being a bit of a "devils advocate", getting you to think about things that you haven't, but maybe should.
It's a habit I picked up mentoring young engineers.

You should make sure to limit the current to the motor(s) so that they can't break your machine if/when it jams, particularly when doing the initial start-up.
First you crawl, then you walk, then you run!

I was thinking of ordering the motor shafts D cut to facilitate a set screw in the handle.

It's easy enough to file a bit of a flat, or dimple the shaft for the set screw. It would be PITA for the vendor to do it, if they even would.

 

[Jim_Hbar]

Jim D posted while I was typing...

Mark's mill is 125lbs total - there can't be a lot of meat where the steppers mount.

 

[grepper]

You are in "analysis paralysis", picking a motor based on a number that you are never going to use.

"analysis paralysis" No kidding. I've been at this research 8 hours/day for days now. Brain = toast. But... Five days ago I knew nothing, and now thanks to yourself, Jim W. and a couple others, I think I am up to speed enough to make at least somewhat educated selections.

While grueling, I can't help but do the research. I just can't make equipment decisions without at least some understanding of what I'm doing!

I'm being a bit of a "devils advocate", getting you to think about things that you haven't, but maybe should.
It's a habit I picked up mentoring young engineers.

Please don't stop! I love a devil's advocate! It's exactly how I think and why I keep asking all these pesky questions!

You should make sure to limit the current to the motor(s) so that they can't break your machine if/when it jams, particularly when doing the initial start-up.

I don't know enough about this yet to know how to limit the motor current. I thought the drive took care of that.

 

[Jim_Hbar]

I don't know enough about this yet to know how to limit the motor current. I thought the drive took care of that.

Read up on the drives - it's one of the things you set when you are configuring the drives.

and you have to plan for max torque at 0 RPM

Actually, 3 or 4 times full load torque, plus the impulse from the load back driving the screw
Then have a good "safety factor" so the controls guy doesn't break anything when he does it all over again..

 

[grepper]

It's easy enough to file a bit of a flat, or dimple the shaft for the set screw. It would be PITA for the vendor to do it, if they even would.

Correct. Filing a flat spot, etc., would be easy enough. FWIW, it says:

http://us.stepperonline.com/3pcs-of...motor-35a-31nm439-ozin-24hs343504d-p-398.html

Custom Options
[/QUOTE]
Connectors: Molex, Harwin, Tyco/AMP, JST etc.
Lead wires & cables: Special lengths, Protective hose
Shaft: Round, D-Cut, Cross drilled, Key-Way, Thread or Hollow

I don't know if they are already manufactured that way and ready to ship or is truly a PITA custom thing. I want simple, no hassle, no additional cost ordering. I'll probably end up just filing a flat spot.

 

[grepper]

That is true. That would be the virtually instant torque just before the stepper motor decouples and the torque drops to about zero. Stepper motor are friendly to machines in that regard. AC and DC servos are not so friendly and you have to plan for max torque at 0 RPM by torque limiting or throwing an excess lag error that shuts the system down. With servos on a CNC mill, it normally just breaks the tool bit and continues on. Yeah, I've done that a time or two

With steppers, are the drives/motors intelligent enough to bail if a full torque stall occurs? You said, "before the stepper motor decouples and the torque drops to about zero." I take it that [decouple] is electrical rather than mechanical?

 

[Jim_Hbar]

With steppers, are the drives/motors intelligent enough to bail if a full torque stall occurs?

Nope. You need to "close the loop" to get that functionality. And that's a huge jump in cost and complexity.

The shaft option question can only be answered by the supplier - my previous comment was based on the assumption that the rear shaft would be stocked unkeyed and round - I could very well be wrong.

 

[grepper]

Thanks to all of the amazing assistance I've received here, this is what I've come up with. I believe all components are well matched. If any of you gurus see anything you think won't pan out, please let me know!

LMS HiTorque 3990 Mini Mill
http://littlemachineshop.com/products/product_view.php?ProductID=3990&category=1387807683

CNCFusion Kit #5
http://www.cncfusion.com/minimill1.html

Gecko G540
http://www.geckodrive.com/geckodrive-step-motor-drives/g540.html

Ethernet SmoothStepper:
http://warp9td.com/index.php/products/#details

3Pcs of Nema 24 Dual Shaft CNC Stepper Motor 3.5A 3.1Nm(439 oz.in) 24HS34-3504D:
http://us.stepperonline.com/3pcs-of...motor-35a-31nm439-ozin-24hs343504d-p-398.html

Switching Power Supply 500W 48V 10.4A for CNC Router 115V/230V S-500-48:
http://us.stepperonline.com/switchi...04a-for-cnc-router-115v230v-s50048-p-168.html

Motor cables:
http://www.cncrouterparts.com/cnc-motor-cable-p-45.html

Mach4 software:
http://www.machsupport.com/software/mach4/