Need Help!- First time poster/builder needs help with Electronics. (Motors etc)

[Lapin]

Hi zone ppl!

i have been lurking around on this forum for a while now and iv'e decided to build my own cnc router.

The steeltable which everything will be built on is already made and painted and this past weeks i have worked on a couple designs which involves linear guides and nexen rps system.

The machine is going to have the size of 3 meters x 1.7 meters and im therefore a little bit confused over this common "steppers vs servo" issue.
AND this is where u guys need to guide me.

The machine will mostly cut wood such as MDF, teak, maple etc. And also some aluminium from time to time (panels and such).

so to the problem:
The grantys weight is calculated to aprox. 77 kg but i go with 100 kg even so i dont build to weak in a future approach.
at jogging it would be nice with about 1000 ipm, because of the size and hopefully much cutting, and cutting speed maby 3-400 ipm?

The z axis assembly is calculated to 33 Kg and here i go with 50 Kg just to be sure.

From what i read in the stepper/servo threads its obvious that i would go servo but what makes me insure is that some machines like mechmate uses steppers with which i can see good results. BUT servos speaks more to me than steppers actually (thus i have no experience from either). the noise, vibration and lost steps scares me too. On the other hand the installation seems good to start with, but a am a fast learner so its not that big of a problem.

so if any kind soul out there could recommend some servo/stepper, to compare, system which can power my machine i would be happy

the questions are maby a little dull but feel free ask if anything comes up in ur minds.

Oh... and the current design, not fully finished due to above problem.

http://img265.imageshack.us/gal.php?g=cncfrsver3.png

cheers from Sweden

[Al_The_Man]

I do not use steppers, but I suspect that 1000"/min will require servo's especially if you need high accel/decel rates.
I find it helps to plug the numbers into a sizing program such as
http://www.electromate.com/technical...morgansoftware
To get an idea of sizing and gear reduction etc.
Servo's tend to allow economical spec in of motors size due to their relatively flat torque curve from 0 up to their maximum rpm range, which allows for gear reduction capability.
Al.

[Lapin]

hmm, me and that program are not friends

i calculated the motors as Nexen describes in their manual for rps and the results i get from there is 1.2 kw for the x axis and 0.55 kw on y axis.

which motors is recomended and with which gearing?

http://www.nexengroup.com/nexen/docs/21238.pdf

the calculations starts at page 6.

[analogman]

Check out the FAQ on the Gecko site for servos vs steppers. Good document.

I think for a machine that size you will want servos

[Lapin]

yea its pointing towards servos. but which ones and which drivers? gecko only support brushed servos, and their are shorter lifespan on right?

[Al_The_Man]

There is an industry recommended standard that the motor to load inertia not exceed 10:1.
One of the most flexible factors that affect this is acceleration rate.
Fortunately inertia is reduced by the Square of any reduction in place.
Al.