[papp101]

Hi all,

Designing a 24" x 60" gantry CNC for a specific production purpose. I'd like some ideas based upon the givens below if you have a few moments to respond:

1. The gantry will be 24" wide and run on rails the width of the table.
2. On the gantry will be a 45 LB motor/spindle.
3. The motor/spindle will be on a vertical z axis with linear guides, etc.
4. the "Y" travel will be back and forth on the 24" gantry.
5. The base will hold a constant jig that will be loaded and unloaded with the part to be cut.
6. There are minimal lateral forces during cutting.

I'm thinking of doing the gantry from steel - unless you think I could use extruded aluminum with that weight?

I'm feeling 320 ozin motors for x and y, and a larger stepper up top for the z, like 400+ oz in.

What linear guides would you use for the weight?

Movement speed - probably no faster rapid move than 20 ipm, with slow acceleration.

Please weigh in! I've been out of the CNC building for 2 years since I converted my mini-mill.

Accuracy to about 0.002 would be nice running ball screws.

Thank you!

[hanermo]

Your building a commercial product.
Use 25 mm rails or bigger.

Forget steppers - use small ac servos.
Total cost difference to other options < 400$.

[FMTcncs]

Forget steppers - use small ac servos.
Total cost difference to other options < 400$.[/QUOTE]

THIS!!! With the tolerance you are trying to hit and overall reliability use ac servos. You'll be happy you did.

[awerby]

Either that, or go with a fixed bridge/moving table design. Then you can make the overhead bridge as heavy as you want, since you don't have to move it.

[LeeWay]

He didn't specify the kind of precision needed nor the amount of parts that will be cut. My gantry is about 32" wide and weighs about 150 pounds. It uses roller skate bearings on flat steel bar. I have replaced one bearing on it in 10 years and that just recently. I can rapid easily at 250 IPM. I use a single direct drive 400 oz stepper to drive the gantry with Thompson double nut ball screws. It uses a Gecko 203V and a 72 VDC PS.

That is about as cheap as you can get away with and still be pretty reliable.
You can always go better with servo's and profile raills and with you knowing the tolerances needed and the amount of parts wit will produce will help you decide which direction to go in.