Stepper mottor amount and torque for brass/aluminium

[evensense]

Hi, this is my first post here!

I'm currently building a simple CNC plotter. At first, it's main duty will be writing with a fountain or a regular pen on a piece of paper of maximum A4 size. For the sake of safety margin and further development I would like my worksize to be 500mm x 400mm.
I plan to use linear shafts (fi 16mm) and a timing belts. Z axis would be no longer than 50mm, but for plotting purpose I think I would just use the servomotor.

Would it be later possible to modify that plotter for brass/aluminium machining? What stepper mottors should I use? My first choice was 3 V, 2 A, 2,5 mH, 0.88 Nm but I'm not sure if 3 V, 1.7 A, 2.88 mH and 0.48 N would be ok.
I believe that for pen plotting purpose weaker motor would be sufficient, but I'm not sure about brass/aluminium.

I also have a question about X axis drive. I will have only one motor driving X axis, on the one side of the machine. With my relatively small worksize, that asymmetry is negligible, and one motor would be sufficient, right?

I'm beginning to create model of my plotter now, I will upload it later, so you will have better overview of what do I have in mind.

PS As I said, this is my first post and first CNC machine, be forgiving!

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[awerby]

Hi, this is my first post here!

I'm currently building a simple CNC plotter. At first, it's main duty will be writing with a fountain or a regular pen on a piece of paper of maximum A4 size. For the sake of safety margin and further development I would like my worksize to be 500mm x 400mm.
I plan to use linear shafts (fi 16mm) and a timing belts. Z axis would be no longer than 50mm, but for plotting purpose I think I would just use the servomotor.

Would it be later possible to modify that plotter for brass/aluminium machining?

[If you build it rigid enough, and use the right sort of spindle.]

What stepper mottors should I use? My first choice was 3 V, 2 A, 2,5 mH, 0.88 Nm but I'm not sure if 3 V, 1.7 A, 2.88 mH and 0.48 N would be ok.
I believe that for pen plotting purpose weaker motor would be sufficient, but I'm not sure about brass/aluminium.

[I'd say go with the first motor, with the least inductance and highest torque. Give it a 48v power supply and run it with drivers that can handle that much voltage and current, like the Geckodrive G-540.]

I also have a question about X axis drive. I will have only one motor driving X axis, on the one side of the machine. With my relatively small worksize, that asymmetry is negligible, and one motor would be sufficient, right?

[It would be better to drive it from the middle.]

I'm beginning to create model of my plotter now, I will upload it later, so you will have better overview of what do I have in mind.

PS As I said, this is my first post and first CNC machine, be forgiving!

[It's usually best to construct your frame first, then worry about the steppers and drivers. Things often change as you're building, and you don't want to be boxed in by your earlier choices.]

[wizard]

Hi, this is my first post here!

Welcome aboard.

I'm currently building a simple CNC plotter. At first, it's main duty will be writing with a fountain or a regular pen on a piece of paper of maximum A4 size. For the sake of safety margin and further development I would like my worksize to be 500mm x 400mm.
I plan to use linear shafts (fi 16mm) and a timing belts. Z axis would be no longer than 50mm, but for plotting purpose I think I would just use the servomotor.

That isn't too bad for a pen plotter or maybe even a laser but even here 16mm unsupported linear shafts are a bit thin. This mainly due to the 500 mm span. It likely will work for a pen plotter or laser but that is about it.

Would it be later possible to modify that plotter for brass/aluminium machining?

No! At least not what I think about when discussing brass or aluminum machining. Especially brass which can come in some very hard alloys. The problem is that unsupported rials of that size will flex a lot over a 500mm span. Flex and especially vibrations would be a killer when it comes to machining quality.

What stepper mottors should I use? My first choice was 3 V, 2 A, 2,5 mH, 0.88 Nm but I'm not sure if 3 V, 1.7 A, 2.88 mH and 0.48 N would be ok.
I believe that for pen plotting purpose weaker motor would be sufficient, but I'm not sure about brass/aluminium.

I wouldn't worry about motor sizing for a machine you have yet to build. If you read up a bit you will likely find out that there are a lot of gotchas and engineering considerations when it comes to sizing stepper motors.

I also have a question about X axis drive. I will have only one motor driving X axis, on the one side of the machine. With my relatively small worksize, that asymmetry is negligible, and one motor would be sufficient, right?

Probably not. It depends a big upon how stiff you can get you gantry connection to the X-axis rails. It can certainly be done for a pen plotter but the cantilevered design is problematic for machining. It can be done but almost nobody puts in the proper amount of engineering.

I'm beginning to create model of my plotter now, I will upload it later, so you will have better overview of what do I have in mind.

PS As I said, this is my first post and first CNC machine, be forgiving!

We can only be honest here. A crap design will be called that but hopefully with an explanation of why.

In your case I don't see a huge problem if you keep the machines functionality as a pen plotter. However what you have describes so far would be less than ideal if I follow your image created in my mind. In fact if machining is in the machines future I wold suggest scrapping the design right away. a key to success when it comes to machining is stiffness of the machine. For the most part belt drives, unsupported linear bearings, and so forth, don't inspire confidence.

Personally I think your would be better off building your plotter no bigger than you need for plotting and consider a second machine build for a machine that can actually machine metals. The cost difference to you will be dramatic. A machine to route metal will be far more expensive than one designed to move a plotters pen around.