[NewDay]

I'm new to the group. Also new to the world of CNC. I would like to build a CNC router strong enough to cut out guitar bodies and also engrave signs. What size x,y & z motors would you recommend?

[BobF]

Build Joes2006.

[CarveOne]

A machine with 24" x 48" working area is about right for guitars. The Joes 2006 and the Solsylva 25x37 (and their belt drive machine) are popular for this. They typically use Nema23 frame steppers of 207 to 305 oz/in torque but a 425 oz/in will work well also (but they will have lower jog speeds unless multi-start lead screws are used).

General recommendations are to use ACME lead screws not all-thread rods, use a Gecko G540 driver, use supported rails not unsupported rails.

CarveOne

[BobF]

Many of the Joes 2006 machines have been built with hobbyCNC kit. This is a driver board you have to solder together and includes a BOB and power supply parts except a transformer. if you go this route get the 305 motors.
One thing you may not realize until you have read about 1/2 of the Zone is that the hobbyCNC kit is unipolar drive and the motors are rated unipolar. This is an easy kit to build and one of the more inexpensive ways to start. Later, you can upgrade to a Gecko G540 drive, which is bipolar. The same 305 motors are 425 oz in in bipolar drive, and work well with the Gecko.
Get the Acme screws from Mcmaster, either 1/2-8 2 start or 1/2-10 5 start. These will give you good speed, reasonable accuracy, and take advantage of stepper motors high torque at low speed.
Good luck and let us know what you decide to build.

[NewDay]

Thanks for all the help!!! I have a few more questions....
Would a 700 oz/in. be a problem? I am also thinking of a End Mill conversion. If this motor size is suitable, then I could enter-change motors and electronics between the two. Will this work?

[BobF]

700 oz/in is much larger than needed for router table usually.
Probably a nema 34 size.
you can probably make it work if you design for it.
you would want the new 1/2-8 8 start screws to keep the motor rpm low.
If you have a motor in mind, you need its torque curve and driver requirements so you can design to that.

Are you sure you need that motor. Many mill conversions have been done with smaller motors. It all depends on the mill and the motors

[BobF]

Look at Gecko's site and read there information on how to choose a motor.

[rlrhett]

One problem to watch out for is that some of the popular drivers max out at 3 or 3.5 amps per phase. That will cover most of the Nema 23 sized motors, but could be a problem with some of the larger Nema 34 size motors. Your 700oz motor MAY exceed the capacity of the G540, HobbyCNC and probotix drivers.

[BobF]

rlrhett is correct. You would like need Gecko 200 series drivers and an appropriate BOB to build the system. This would also call for a fairly large power supply.

1) Power: Watts = Lbs * IPM / 531
How heavy is your gantry?
How fast?
Plugging your numbers in: Watts = 500 Lbs * 100 IPM / 531 and you get 94 Watts
of power required, which you can easily get from a NEMA-34 step motor. This
assumes you want to accelerate at 1G.

2) Screw Torque: in-oz = (8 * Lbs) / (pi * TPI)
Plugging your numbers in: in-oz = (8 * 500 Lbs) / (3.14 * 4 TPI) which gives
637 in-oz needed on the screw.

These formulas are from a post by Maris Fremanis of Gecko. The numbers given were in reply to another poster with a 500lb gantry. If your gantry weighs less, plug in your own numbers and see if you need a motor that large.