stepper power question

[endgrainguy]

I'm building a fixed gantry, moving table CNC router for joinery and inlay. I'm looking for advice on stepper sizing. The heaviest cuts I plan on making would be with the router in horizontal position, cutting pins for through dovetails with a 1/2" spiral bit in 5/8" hardwood, with the cut 5/8" deep. X axis (on fixed gantry) is ball screw drive, 4 start 20 MM dia, 20 mil/ revolution travel. I"ll use 1/2 acme with Dumstercnc nuts for z and moving table-whichever start/thread combo you all recommend. Which of the many available 3 axis stepper kits would people with experience or knowledge about this recommend? I'll be working in multiples on the joinery work, 200 or so pieces at a batch, but only running the machine a few (10 maybe?)hours a week. Would like to cut at speeds of maybe 100 inches/minute or so. Thanks! Al Ladd . See my work at www.alladd.com

[BobF]

The hobbyCNC 3 axis kit with 305 motors works well on many systems of similar size. I built Joes 2006 and these motors drive it quite well.
I regularly cut 100 ipm on my machine.
There are other kits in the same range that would probably also work well.
Here are a couple of formulas:
If you know the load and want to calculate motor torque needed.
Screw Torque: in-oz = (8 * Lbs) / (pi * TPI)
If you know what motors you have and want force they can create on screws.
Lbs = (pi * TPI * in-oz) / 8

The efficiency of the system will take a little away from these numbers so don't cut it too close. Also motor output is not the same at all rpm, published numbers are usually max. You need the torque curve to get all speeds.

Go to the Geckodrive site and download the steppers 101 pdf under support.
www.geckodrive.com

[tag1987]

I would second what BobF said about looking at the Gecko drive site. Merris F. is a wealth of information and last time I talked to him seemed open to educating people on steppers that work well with his drives. http://www.geckodrive.com/

Another good source of info and parts is Dan Mauch at http://www.camtronics-cnc.com/
He often has a good selection of stepper and servo motors at a good price. He also sells a package that includes the control enclosure, power supply, with Gecko drives optional. A good bang for the buck.

Another good source is Bob Campbell at Campbell Designs. http://campbelldesigns.net/

I've looked at your work (real nice by the way) and if you plan to put this machine into a production environment I would skip the acme screw and find a more precision drive mechanism. There are lots of precision lead screw mfg out there, from Nook, Kirk to Thomson and some of the Asian mfg have greatly improved, like Hiwin. http://www.hiwin.com/home3.html.

I'm in a business similar to yours and rely heavily on my 2 desktop CNC machines (Emco F1 and Dynamite) to produce small parts, precision joints and small mortises. All of my machines were retrofitted with Gecko drives, one running Mach3 and one of Flashcut. It's nice to have a supplier that understands you make money with the machine and treats you accordingly.
PM me if you need further info.