[David_Nolan]

Hi,

So I've recently purchased a Sherline Ballscrew Mill. I've already spent quite a lot on the machine and don't want to buy expensive drive components. The machines part tolerance will be 0.001" or 1 thou thanks to the pre-installed ballscrews. I'm going to be using a 2 phase, 4 amp NEMA 23 steppers and since I'm going to be micro-stepping that means each motor could possibly draw 8 amps. I think that's how it works anyway. I'm looking for advice on what drivers to buy that won't screw with the 1 thou part tolerance or break after 3 days. I hear the Gekko drives are good but they are expensive and the one's I can find are only rated for 7 Amps. Please advise on what to buy/where to buy. Also how much I should spend per Drive.

Second question, I'm controlling the stepper motors with an Arduino UNO and a shield , will that cause problems with the tolerances/ reliability of the CNC components


Thanks,

- David.

[Dean448]

I think you’ll get a lot of responses.
3 to 4 amp stepper drive will work fine. There a ton of them out there to choose from.
Arduino Uno isn’t a suitable controller for a three axis mill. Especially if you are looking for accuracy. Keep investigating possible alternatives. It would help if you say what your budget is.


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[David_Nolan]

Can I ask, how precisely does the Arduino Uno fail? It sends the incorrect number of signals? Also how will a 3 to 4 amp driver work fine when the motor could draw up to 8 Amps? Thank you.

[awerby]

What makes you think it'll draw 8 amps? That would be a huge load for a little motor like that. The phases in a stepper motor alternate; they don't draw current at the same time.

[David_Nolan]

Hi Andrew, The rated amps is 4 Amps, and if you are Microstepping I was instructed in this video around 3:15 ...

https://www.youtube.com/watch?v=iY_4...st=WL&index=57


To multiply the amperage rating per phase by the number of phases in which my case is two, because there are two coils. I'm guessing I misunderstood something?

[joeavaerage]

Hi,
all steppers lose torque the faster they go, it's physics and you can't get around it.

Inductance is a fair measure of how bad that degradation will be, the lower the inductance the better.

I would suggest that you look for 23 size steppers with 1mH preferred and reject anything over 2mH.

The second way to combat degrading torque is to use the highest voltage drivers and power supply you can find. At the current time 80VDC is about the highest readily
available and cheap(ish) drivers out there....get some, and an 80V supply to match. Remember if you buy well in the first place you'll have these things for many
years and get untold use out of them, buy substandard and you'll want to throw them out in a months time.

Arduinos will severely limit what you can do. If you want a Windows CNC solution then Mach4 or UCCNC, or LinuxCNC with a Linux platform.

Craig

[Dean448]

I would first get a recommendation on the ideal motor for that machine. ‘Big’ in the title of the video means it’s for a big machine not a Sherline mill. Then choose an appropriate driver. Amazon has many around of $30. Then consider how you want to control it. You can use low cost Arduino using something called GRBL. But they often use small drives that plug into the shield. Great for nema 17. Most folks use the better methods as mentioned above. More involved and more cost.
Keep in mind that the lighter and smaller the machine the less power you can put into it. Don’t invest in all this hardware only to find that the machine can’t handle the cut.
Btw accuracy is a partly stepper position and also machine deflection. Something like a 3D printer has no loads so stepper accuracy is everything. Cutting machines are far different.


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[joeavaerage]

Hi David-Nolan,
you prefaced this thread with:

I've already spent quite a lot on the machine and don't want to buy expensive drive components. The machines part tolerance will be 0.001" or 1 thou thanks to the pre-installed ballscrews.

I understand the sentiment, I've been there also but I disagree strongly. You have obviously paid a premium to get the machine with ballscrews, you want the accuracy....so you
can't afford not to match that with appropriate control hardware.

As Dean448 has correctly posted you can get cheap drives for $30....but you can get good 80V drives for $60 and your talking three drives, so the difference is $90, and
the 80V drives will eat any cheap low voltage drive. Do you really want to compromise the investment you have already made just to save a few olloars?

Craig

[joeavaerage]

Hi,
have a look at this one for instance:

https://www.ebay.com/itm/11485440154...Cclp%3A2334524

Note that it is 18-80VAC OR 24-110VDC.....now your talking. A single transformer of say 70-80VAC @ 10A output would be enough to power three of these.

Craig

[Dean448]

Now that we are into randomly recommending stuff off eBay, my recommendation is G540. High quality compact drive that can expand into a fourth axis. Perfect for this size machine.


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[joeavaerage]

Hi,
a G540 is a good recommendation, although it only capable of 50V and costs $300.

Craig

[David_Nolan]

Hey Guys, Thanks for all the advice, I'm taking it onboard. Hypothetically, If I bought three of these.

https://www.robotshop.com/eu/en/geck...r.html?gclid=C

I'd still like to at least try running it with the Arduino, I've ran 3 Axis mills from it before. Cause I don't want to have to buy Mach 3 or an expensive controller...

I'd really prefer just to use that. I just want that 1 thou tolerance, what tolerance can I expect, is a one thou tolerance out of the question?

So If I used...

The Gecko drives, the Arduino and CNC JS and your regular $40 dollar Nema 23 Stepper motor

Am I being completely foolish expecting good results... (By good results I mean a 1 thou part tolerance.)

Extra questions...

Can the Gecko drives I linked even power the 4amp Nema 23 Steppers sufficiently if I'm Micro stepping

I'm not intentionally being ignorant and selective with your advice here even though it may seem that way from my line of questioning. Though I don't understand why some of you brought up torque... I'm pretty sure the motors I'm using will easily provide enough torque, does it have something to do with accuracy? I thought I could save money doing it myself but honestly now I'm considering buying this https://www.sherline.com/product/877...specifications

Cheers,

- David

[Dean448]

So a typical steppers moves 1.8 deg per step. Using a 1/2 -20 nut (for example) you would turn it 7.2 degrees per 0.001” traveled. That drive micro G210 would hit that easily and has plenty of power. Be prepared to add current limiting resistors.
Can you get to a 0.001” tolerance? That depends on machine stiffness, material and how aggressive you are when cutting the part.
Still not sure how an Uno would work. I could see it working if the part were simple straight cuts and no two axis moved simultaneously. I once bought a Uno clone for $6 so you don’t have much to drive your high quality Gecko drives
That sherline cnc add on is crazy expensive. And you need a Linux computer or your on your own.


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[joeavaerage]

Hi,
I agree with Dean448, that Sherline stepper kit is a rip-off, and only 24V.......the planet is going to warm and drown before this machine completes its first job!!!

Those Gecko drivers you linked to are superb, expensive but superb. Gecko has the industry leading reputation for reliability. You could get Chinese made
drivers, still 80VDC capable for about 1/2 what the Geckos cost....but if you can afford Geckos then get them.

The problem with Arduino is that it has a restrictive subset of ANSI standard Gcode called GRBL. Its not that you would lose accuracy but lose functionality that you'd get with
Mach, UCCNC or Linuxcnc.

LinuxCNC is free and open source, and will run with just an el-cheapo $20 breakout board connected to a PC parallel port. A single parallel port has strictly
limited number of inputs and outputs but for a simple machine is still very adequate. Despite my aversion/unfamiliarity with Linux I would much prefer LinuxCNC
over GRBL.

I personally have been using Mach4 for seven years, and wouldn't be bothered with Mach3, all development ceased on it seven years ago and Mach4 supersedes
it in every respect. Mach4 does, or, all but does, require an external motion controller. In my case I use an Ethernet SmoothStepper. Given your aversion to spending
money I couldn't recommend Mach4 to you, being that Mach4 costs $200 and a SmoothStepper another $180. Notwithstanding I've got the functionality I wanted.

Craig