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Good Evening,
I am totaly a newbie to CNC world.
I bought a CNC without its electronics. It is 5' x 3' (150cm x 100cm) and has steel gantry of 60lbs (27 kilo) which moves on ball bearings.
The size has to be Nema 23.
I was wondering if 439 oz-in.(3.1nm) will be enough or should I go for 566 oz-in.(4.0nm) versions?
Thanks a lot in advance.
You're focusing on the wrong numbers. Those figures are about holding torque - how hard the motor holds still. This is not as important as how well it moves. That's determined by other things, like inductance (lower inductance means higher speeds without faulting) and voltage (more voltage makes a motor go faster, up to a certain point). The formula is: square root of the inductance times 32 equals optimum voltage to be supplied. So if you want the motor to go fast, you need to use a driver that will handle enough voltage, and give it an appropriate power supply. In practice, the sweet spot is around 50 volts for most NEMA 23 steppers, which works out to about 2.3 milliHenries of inductance. The running torque of a stepper depends on how much current it can handle. In a 23-frame motor, that will vary between about 2.5 to 4 amps per phase. But the inductance goes up along with amperage, so you have to balance all these factors. Look at the torque curves that should be listed with the motors to find one that maintains good torque at the speed you think you'll be running them, since torque falls off with speed, sometimes drastically.
Thanks a lot for the reply.Quote:
Originally Posted by awerby
I was just wondering what inductance means as I was reading the threads... :)
I have no idea in reality about what speed that I need, but as I was going through some sites etc. lets say, it could be around average of 16 inches/min as suggested on one of the sites. Or should I be looking something with more speed?
I will be working mostly on wood and perhaps some aluminium.
The kits that I found are 4.2 ampers for motor with either CW5045/DM542
or
tb6560 for 3.0A motor with 3.5A drivers and 36V power supplies.
The DM542's are a great driver and pretty bullet proof, I would suggest don't even bother wasting your time on anything TB6560 based, you'll be bitterly disappointed and after spending weeks of time trying to turn that pigs ear into a silk purse, will go and buy better drivers.Quote:
Originally Posted by Crimson11
A 48VDC PSU would be much better than a 36VDC PSU in this case.
cheers, Ian
You want at least 200-300ipm, if possible.Quote:
I have no idea in reality about what speed that I need, but as I was going through some sites etc. lets say, it could be around average of 16 inches/min as suggested on one of the sites.
How is the machine driven? Screws, or rack and pinion? What are the specs of the drive components?
Thanks a lot for the reply.Quote:
Originally Posted by aarggh
Here are more likely options that I have:
(they have single shaft version for the same price)
IT FREE,3 AXIS Nema 23 Stepper motor 4.2A 425oz-in 8mmshaft 4-Lead 115MM CNC HOT | eBay
or
Nema23 Stepper Motor Kit 4Nm x 3 Axis + Mounts CNC Parts Mill Router DIY Hobby | eBay
Thank you for the reply.Quote:
Originally Posted by ger21
Leadscrew of 25mm diameter / 3mm.
Don't know what other specs you need?
The leg of the gantry slides on 2 triangular profiles.
I wouldn't consider either of those two to be very great kits, one has steppers with 9mH inductance and is supplied with a 36VDC PSU, the other has 12mH inductance if you wire is series, and 3mH in parallel, but at double the current load. And again supplied with a 36VDC PSU.Quote:
Originally Posted by Crimson11
The DM542's or equivalent, a 48VDC PSU, and steppers as close to 2.3mH or so inductance for any small to mid (or even large) machine will usually be the sweet spot and most optimal config.
The rough but tested way to size a stepper's PSU is 32 x square root of the inductance, so as an example a 2.3mH stepper works out to around 50VDC, so a standard 48VDC PSU is just perfect.
cheers, Ian
so dm542 is OK.Quote:
Originally Posted by aarggh
psu of 48VDC is OK.
*
The thing that I can not understand is they wrote 9mH but under where there is the specs "image" it says 3.8.
or am I missing something?
here is 2.4 mh:
ACT Motor GmbH 3PCs Nema23 Schrittmotor 23HS6430 Stepper Motor 3.0A 56mm 110Ncm | eBay
So you say that the torque / amper etc. does not matter in my case? These steppers with dm542 + 48vdc psu will be way better then the others?
The torque/ratings do matter, but you can actually size a stepper too large for the purpose. A PSU that is matched to a good stepper can be far more efficient than a larger stepper incorrectly matched to the load and PSU.Quote:
Originally Posted by Crimson11
The specs in the listing don't all add up to the details in the image, so I don't know what's going on there or if I'd trust it.
But the latest listing are good steppers. They'd be a great match for most machines. In fact they are pretty much identical to the ones on my large 6090 machine and perform flawlessly.
cheers, Ian
Thanks a lot again,Quote:
Originally Posted by aarggh
I am just a little bit worried because perhaps your 6090 machine has a lighter gantry, smaller leadscrew (mine is 25mm), 100 x 150 cm and I am pretty sure mine is less efficient.
Considering these I wanted a little bit more power. So in your opinion, what could be a little bit more powerful setup? or am i worried too much? :)
How about these? with dm542 and 48v psu?
ACT Motor GmbH 3PCS Nema23 Stepper Motor 23HS2442 Schrittmotor 4.2A 112mm 3.0N. | eBay
http://cnc4you.co.uk/resources/Stepp...1B%203.1Nm.pdf
http://cnc4you.co.uk/resources/Stepp...8B%202.2Nm.pdf
there is23HS1442 model with a inductance of 3.0 value but has a smaller shaft of 6.35mm. I prefer 8mm.
My X leadscrew is 20mm from memory, but my Y leadscrew is 25mm, although my machine is a smaller footprint and working area than yours, my gantry is very sizable and quite heavy. I have around 300 oz/in NEMA23's on the Z and X axis, and the Y axis is a NEMA34 about 330or so oz/in. These perform well more than adequately, mainly because the PSU and drivers are well matched in specs and requirements.Quote:
Originally Posted by Crimson11
cheers, Ian
You can get more optimal, bringing you closer to the max possible match, but those steppers are really good and will be more than capable of pushing a few hundred kilo's around!Quote:
Originally Posted by Crimson11
cheers, Ian
oh now here we go! :)Quote:
Originally Posted by aarggh
I decided that I need to design a Nema 32 adapter to Nema 23 for X and Y axis so that this thing of being insufficient goes away...
So another newbie question is: Can I have 2 Nema 32 with adapted driver and psu (which I have no idea what to look for) and for Z axis one nema 23 would be ok? and a breakout board will support it as the voltage etc. stuff is handled by the driver?
exatly which steppers you are talking about?Quote:
Originally Posted by aarggh
This is a much closer match:Quote:
Originally Posted by Crimson11
Nema 23 Stepper Motor, 3.5A 300oz in. 2.4mh Inductance (1/4in Double Shaft)
Although around 2.3mH is going to be about the best achievable. As I stated before, multiply the square root of the inductance x 32 to work out the PSU value needed. The higher the inductance, the higher the PSU required, so if a low value PSU is used to match the drivers, but high inductance steppers are used, obviously they won't run optimally. This can mean stalling at higher speeds, lost steps, drop in torque, etc.
Go for the highest rated available driver in the price range, in this case 542's are just great, a 48VDC PSU of at least 5-9A, and steppers as close to 2.3mH inductance as possible, and you have a well matched system capable or really grunty work.
cheers, Ian
cheers, Ian
.Thanks a lot again. I decided to go for nema 23 to nema 34 mount adapter so that this problem will go away.Quote:
Originally Posted by aarggh
By your formula it seems that this kit is OK for me:
ACT Motor GmbH 3Axis Nema34 34HS9456 5,6A 98mm 7,7N.m + 3PCS DM860+PowerSupply | eBay