View Full Version : Need Opinion - 1st Build

11-16-2010, 10:34 AM
Hello ,
I am going to be building my 1st CNC Router machine. I am not looking for speed , just accuracy. Where should I start? stepper motors , servo , etc...
Thanks for any help in advance.

11-16-2010, 11:12 AM
Steppers and servos are both accurate. Servos have feedback (encoders) to confirm the distances traveled. Steppers do what they are told and expect it to have been done. Steppers have no way to know if the last move was actually performed according to the g code or MDI. Steppers and their controllers and components are less expensive, seem to take less electrical understanding and work fine in most applications. If a stepper hits the end of the tables travel besides a noise that doesnt sound good nothing really happens besides losing your place and possibly ruining the part. No damage is done to the machine and if you have good limit and home switches set up right, you should be able to recover (if you know where the crash happened) otherwise you just rehome and rerun the whole file possibly saving the work. Servos I believe stop and or correct the toolpath to match the commanded coordinates. My understanding is that servos do not like to be stopped (due to incorrect commands most likely) and damage can occur to them when this occurs. Either way if this is your first time in the cnc world, there is a lot to learn. Steppers will be the cheapest and easiest way. I personally went with a Hobby Pro Cnc kit and ordered the steppers at the same time from them too. The support for the kit building was incredible and the results are fantastic. Not to say there were no problems along the way but it went well. I also purchased a Gecko G540 for another project, it too works very well and doesnt involve assembly besides a power supply. To tell you the truth I cant tell the difference in the performance between the 2. Again not to say there isnt a difference, I just dont know what it is. Well there is this 1 issue, the Hobby Pro Cnc kit has the ability to adjust the stepping between 10x microstepping to single stepping. The G540 is 10x with no adjustability. For 2 of my machines (which have a gear reduction) I believe this is a hinderance which theoretically provides an accuracy that is unacheivable or not even desirable. If 1 step only moves the table say .00001, then it would take 100 steps to move .001, in my mind it seems like alot of the computers resources are used or cant keep up if higher speeds are desired.

11-16-2010, 01:41 PM
Thanks for the info. Will steppers do intricate work?

11-16-2010, 01:58 PM
The resolution can be just as good. My machine are accurate to .001 pretty easily I would think. I dont need anything that close just yet.

11-16-2010, 03:28 PM
What happens if the stepper misses a step or something like that? Is the rest of the program going to be off without you knowing?

11-16-2010, 04:00 PM
Yes and that will happen in the beginning and possibly other times to. You do have to learn about the limits of whatever machine you decide on. If you can be reasonable in your expectations you will be fine. Watch any of Hoss' videos or Simpson36, those are mostly all stepper controlled machines. Stay away from the feed rate override button (the ability to make your machines table go faster during a program) and you probably wont miss any steps. The feed rate override can be like bringing in the torch to boil water! Realize that the machine you will probably run at home doesnt compete with the 6000lb machine the pros get to use and feeds will be reduced accordingly. Cnc is also not for 1 off items, it can and is done, but there is a lot of experience required to make it happen. The scrap pile is big around my house but I buy scrap to cut. I am not trying to discourage you in any way. Steppers are affordable for the masses and are plenty accurate if used within their specs. Btw if it only lost a step (a step could as little as .00001, it just depends upon lead or ballscrews, gear reductions, and how many steps per revolution the stepper is, most are 200) you would never see the mistake, however if it begins to lose many steps per cycle (which is usually what happens) then eventually everything gets skewed and the part or endmill breaks. Mistakes are going to happen, better to learn on an inexpensive machine first in my opinion.