OT...Stepper vs Servo for a CNC Router

XtremeIN

Member
Join Date
Jun 2005
Location
Indiana
Posts
217
Hello all,
I know there is a huge amount of knowldege within the minds of the members on this forum so I thought I would ask for some input. The owner has decided that he wants to build/have built (the frame with us/me doing the controls) a CNC Router for cutting plastic. We have a small tool room with a mill and lathe but we have been sourcing out alot of cutting work. The CNC will be large enough to cut 4x8 sheets with a normal thickness of 1/2". There are a large number of sites for homebuilt CNC Routers online. But, I have been unable to find much on Stepper/Servo setups. I know servos tend to cost more and the decision on which to use depends on speed,accuracy and load. How do you calculate the load, how many in-lbs would be needed? I know with most things you get what you pay for, but there is a huge differenc in price from one brand to another....where is a good starting point.

Thanks,
Micheal
 
You may want to take a step back and see what your needs are from a programming standpoint. That might dictate which motors/drives you use.

Do you want CNC programming or something custom. With the CNC, you'll find more programmers but it might cost a little more up front.

With the custom approach, the initial cost could be less but you might be tied to the machine.

How will you bring information to the machine? Manual programming? Import from solid modeling software? Import of DXF profiles?

These questions shoudl probably be answered before you start selecting any hardware.

Then you have to define the physical aspects of the machine. Maximum speeds/feeds/depth of cuts/accuracies. The answers to those questions will dictate the type of support stucture, bearings, drive mechanisms and motors you will require.

Take the time up front to fully define what you want from the system and you will not be disappointed in the end. If you jump in an start piecing things together, chances are you won't get what you want or need.
 
Forget servos for now. You use those when you want speed plus accuracy. I don't see you cutting plastic fast. Start with steppers first. You can consider them later, after you've built your first machine and know EXACTLY what you need.

Parameters:
The 4x8 sheet is stationary. You move the router. Start with an integrated stepper motor/driver. This one will do for the 4 foot side - you might want to order custom to get past the 42 inch limit.
For the 8 foot side, I'd do a size 34 integrated motor on a rail with rollers. You could even do both sides with rollers.
The integrated stepper/motor driver with microstepping is the key first part if you want to start at the hardware side.

Talk to IMS , or choose from dozens of others. You're application is one of the most popular in the world (I want an XY drive). They'll be able to guide you.
 
Last edited:
You are right. There are lots of people building their own CNC routers, etc. Many are using Mach3 from http://www.artsoftcontrols.com/artsoft/index/index.htm as their control software. It is relatively cheap, runs on a PC, and generates step/direction signals on the parallel port or other 3rd party hardware. I think if you go to the CNCZone forums you will find lots of discussions on steppers vs. servos for this type of application. You can also search the archives of the following yahoogroups: [DIY-CNC], [geckodrive], [CAD_CAM_EDM_DRO]. Pay particular attention to any posts by Mariss of Geckodrive. Geckodrive builds both stepper and servo drives that are often used in these applications.
 
I've built a CNC plasma table using Automation Direct Steppers, Gecko G203V drives a CNC4PC breakout board and EMC2. I used timing belts to move the X gantry and the Y axis. I used 80/20 for the frame and slides but made my own corner connectors. Some things to consider are the force needed and the speed needed to select the proper stepper. Steppers are open loop (not a bad thing) so you can't overload them or you will loose steps. Servos get a lot more complicated. Just keep the stepper rpm in the best part of the torque range...

If you want to discuss this feel free to PM me...

John
 

Similar Topics

What are the pros and cons? I know the stepper hybrids are waaaayyyyy cheaper, but surely there's a draw back.. Any tips? Thanks!
Replies
5
Views
1,608
Hey guys this site is an awesome blessing for me. I am trying to get back up to speed with PLC program and I have finally decided on a home...
Replies
18
Views
7,893
Good day, Does anyone have a tutorial for Motion Controls basics? Also sample configuration and wiring would be helpful just to make me...
Replies
3
Views
2,113
I am thinking of changing pneumatic cylinder to electric motor type. which motor would be ideal force for equivalent to 5.5bar cylinder pressure...
Replies
3
Views
1,716
Greetings all, I'm working on a project where, for cost reasons, we've decided to use a stepper instead of a servo on the second system. The...
Replies
5
Views
2,726
Back
Top Bottom