First ambitious cnc build
Hello people!!
Nice to be on here! First post.
We are building a quite ambitious cnc for wood,soft metals and sheet metal.
We are at the part where we should start ordering things. But to be sure that we dont have any...mishaps. we have some questions. I will start off with a few simple ones.
We are using nema34 1600oz motors. RP drive. Table bed is 2.1*3meters Planned on using shielded wire and stranded. But what awg should it be. Motors are 7.8amps and awg 22 is rated for 7 amps. But there are quite alot of variabales to consider so what do you recommend? I think awg 16-18?
Same goes with the spindle wire. We have a 4500w vfd air cooled spindle.
An actual example of the wire would be ofcourse perfect but any advice is greatly apprecciated
Cheers!
Re: First ambitious cnc build
There's not that much current going through the wires, so it's not the AWG rating that's most crucial, but the flexing that they have to withstand. Make sure you get finely stranded wire that can take a lot of it, and use cable carriers to limit the radius it has to bend to. The spindle should have a braided shield over the whole bundle, that's grounded only at the VFD end, to avoid creating a ground loop. Make sure the insulation on your wires can take a bit of heat as well; steppers often will run rather hot.
Check the inductance on those motors. Often steppers with a lot of holding torque like those also have a lot of inductance, and require a lot of voltage to overcome it and get up to top speed - which you'll need for cutting wood effectively. Drivers that can tolerate that much voltage tend to be more expensive than ones that can't. The formula is: Square root of the inductance (in mH) times 32 equals optimum voltage to run motor at top speed.
Re: First ambitious cnc build
I would look into 'continuous flex' cable. It's a bit pricey, but should last a lot longer. Normal flexible cable isn't meant to be flexed thousands or millions of times like will happen on a CNC machine. Something like this: https://www.igus.com/product/1084 You could use 18AWG without much trouble I wouldn't think.
If you can use much larger bend radii on your e-chains you can probably get away with standard cable.
Similar cable for the spindle, is it a 220V or 380V spindle? Probably 12Awg if 220V, 14AWG if 380.
Re: First ambitious cnc build
Hi Mike - Sounds like your acceleration is set too high. Its ramping up and then it can't accelerate anymore (as it can't overcome the inertia at that acceleration) so it stalls. So dial the Z acceleration way down and bring it up slowly. Peter
Re: First ambitious cnc build
The manufacturer of the spindle and the motor will spec their max service temps. In general speak, if its too hot to touch it's too hot. Peter