oh god help me pick a motor size

[joe kilo]

hello brothers and maybe sisters. We my bro and I are starting a gantry build. The cutting travel is 2'x4'. a mad skate bearing X axis and linear ball on YandZ because they where in the surplus house. will use 1/2 inch acme leadscrews. Its going to be beefy so I like for it to be able to do some moderate duty work. been looking at steppers my brain is gone, I can't for the life of me figure out a decent size motor a 400 600 800 900 1200 oz. I want something right not worried about $$$. Hoping to try one kruetz's new axis controllers. I'm a on the fly engineer type and this is being a fly in the engineer. Is the biggest the best? thanks and let the madness begin. thats a happy madness haha.

[wcarrothers1]

for 2' by 4' you should not need anything close to 1200 oz if you ask me.

I'd say 400 or less.

Sure others would have more to say. I'm a servo guy anyway..

b./

[harryn]

I am still very new at this, but many people end up building a second machine with even more power and more range. In many cases, the stepper motors and drivers represent a significant part of the build cost.

Given that, if you target 1200 oz in or so, you will have plenty of room to grow. If you are much under 400, you could potentially get stalling / missed steps - at least based on machines I have read about here on the forum.

It is a lot easier to turn down the power to the motor than to make a motor have bigger magnets.

[ger21]

There are a lot more factors involved than just 2x4 size. And 1/2" acme screws come in many different types, from 1 turn per inch to 10 turns per inch. You want to design for a target speed and acceleration. Ideally, you want to get your top speed at the rpm right before your steppers torque begins to fall off. This will vary with the drives your using and the voltage your running them at. Also, you can get three different motors with the same torque rating, that will give very different performance. Ideally, you want very low voltage motors, under 2V. But these will typically have much higher current ratings, and need more expensive drives.

[joe kilo]

I,m studying all the info i can get the nook industries site is very helpful it looking like 30 ipm with 600 oz motors is going to do the job. been doing mock ups and taking pics hope to post some soon. hers something funny for everyone, I have a 1600 sq ft garage with 16 ft ceilings and I'm doing mock ups in my kitchen. good thing I,m single. thank god for calculators to do the algebra. thanks ger21 your post here and on other needs and question are very techy yet freindly.

[fatal-exception]

I'm with Harry, buy the biggest you can (within reason). I have 2 mini mills using 400ozin steppers, and wish I would have gone bigger. The max speed I can get is 100in/min without stalling, bigger motors would allow the machine to go faster without stalling.