[moparx12]

Hi all,

I have been shopping around looking for the various components to build a CNC router. I plan to make the frame using t-slot extruded aluminum. X-axis will have 2 ball screws and the Y and Z axis will have one ball screw each and all will be directly driven.

My question is pertaining to the stepper motors/drivers combo I found from a Chinese supplier (see attached). I have read that its hit or miss, but I wanted to get the opinion of someone with experience in sourcing these things. table size is approximately 1000 x 600 x 300mm.

Thanks!

[awerby]

Your attachment didn't attach, but you'd be well-advised to build your frame first, and shop for the electronics after it's finished. That way, if your plans change and you end up building something different from what you'd originally intended, you won't be stuck with inappropriate motors and drives. If you abandon the project (which often happens) you'll be out less cash. And you'll have more time to research the motors and drives, and perhaps avoid purchasing kits that feature wildly mismatched motors and power supplies, with unreliable drives that lead to massive loss of hair, pulled out in frustration.

[moparx12]

haha! Thanks for the response! I guess I'm the only one who can see the attachment. I'm most concerned with the inductance and current draw specs and I'm also skeptical on how some suppliers say you can achieve 4Nm+ holding torque on a NEMA 24 framed motor and other suppliers say its not even possible. Here are the specs they claim:

Step Angle: 1.8 deg
Current per phase: 5.8 A
Resistance per phase: 0.75 ohm
Inductance per phase: 2.4 mH
Holding torque: 4.5 Nm
# of leads: 4
Detent torque: 1000 g-cm^2
Motor length: 102 mm
Mass: 1.65 Kg

I am currently getting the spec sheet on their controllers translated as its in Chinese only. It does have some numbers on it and the highest current I see is 4.2 A. That seems like too low of capacity to be paired with this motor, doesn't it? Which wiring scheme do most ball screw CNC routers use?

[awerby]

Those specs are a bit difficult to believe; all the motors I've ever seen with that much holding torque had a lot more inductance. But if true, that would be one heck of a motor. Yes, you'd need a drive for it that could handle 5.8 amps. So sure, get one of those motors and test it - get back to us if it actually meets those specs. But pass on the drives.

[James Newton]

Build the machine first, THEN figure out how much power you need to run it at the desired speed. Doing it the other way around makes no sense. This page may help
techref.massmind.org/techref/io/stepper/estimate.htm

[dharmic]

Why not incorporate power requirements into the designing, James? If there's a hard limit on cost for a general purpose machine it may impact the lead screw choice, the dimensions of the machine, the type of motors, the controller and the power supply plus a bunch of other stuff. I would have thought it would be worth sorting out nice and early.

[moparx12]

Thanks for the replies. I started a couple weeks ago when I found a design on youtube that i really liked. He doesnt give all of the info away, as it appears he's going to try to make a buck off it, but he does give enough in the description and comments for me to get most of the way there.

My goal is not to build CNC routers, but to get one so that I can make molds and patterns for composites construction. I am also interested of course in the aluminum cutting capability, hence a strong setup, but not to the point of having a fixed gantry which I have read makes for a more robust machine.

I have been browsing these forums for a few days and I see that there are A LOT of home brewed setups out there. I would like to take advantage of the information out there so that I don't have to buy things twice but I don't want to completely engineer a solution from the bottom up. I have been looking at screenshots from the youtube video and basically purchasing the same stuff he did, with minor tweaks here and there. I guess I should start a build thread in another section, and do some more digging for information.

Anyway, I chose those high torque motors because they are what the youtuber chose. Maybe you guys could take a look and tell me what you think of the design.https://www.youtube.com/watch?v=vjjTnn1KmRg Some changes I was thinking of were making the z axis guides square instead of round (15mm). I also want to be able to machine a part 6" deep and his looks more limited.

Thank you for the link. I will be sure to take a look after i get a little further along with the gantry. I have no idea on weight yet.

Whats this i read about the ball screws having backlash? The ones I am about to pull the trigger on supposedly are "anti-backlash" but they are from the heart of China so who knows. I am modeling it in solidworks and was able to find solid models for the ball screws, linear guides, and 80/20 which saved me a lot of time!

[James Newton]

It's difficult to know for sure what sort of friction etc... a design will have before you build it. If you can predict its characteristics accurately during the design, then yes, certainly, work it all up in advance. I should have said "Build or design the machine first..."