ZAY7045 + Gecko G540?

[clocker]

Hi folks!
I'm very new here, but have spent the last few months reading the forums and doing some research on a CNC mill. The general advice on machines was bigger is better, so I jumped on a deal for a ZAY7045. The machine is set up in the shop and has made some manual chips, but now it is time to make the machine sing. The G540 driver seems like a fantastic bargain, but I am wondering if it is too small for this mill? I don't need super fast rapids, so 1200 oz-in steppers seem overkill. I am mainly making small aluminum parts right now that have less than a 4" x 4" x 2" envelope.

In your experience, what size stepper motors do I really need?
It seems that any motor over 480 oz-in would be fine with reasonable travel speed.

homeshopcnc.com sells a RS23-570 @ 570oz-in that seems like it would work with the G540 (inductance is right, but it can take more current than a G540 can provide) = lower torque if only driven with 3.5A?

kelinginc.net has a KL23H2100-30-4BM @ 495oz-in, but the inductance is ~7mH which is more than the specs for G540

Are there any other steppers out there that would match up better?

Budget for the electronics (3 motors, drivers, BOB) is <$800 and simple is better. Am I asking too much out of the G540? Should I step up to G203s and NEMA 34 motors?

Thanks for your help!
-Chris

[jalessi]

Chris,

Go with the Gecko G203.

The Zay 7045 Z axis weighs about 200 lbs, it really requires a nema 34.

Where did you pick the Zay 7045 up at?

Jeff...

[clocker]

Thanks for the advice Jeff!

With a counterweight or strut system, it seems that the Z weight problem could be minimized. It won't kill me to spend the extra on a G203V / NEMA 34 system, but at ~ double the price of a G540 system... it is a hard sell.

+ at the ~$1000 for the 3 axis set of NEMA34, why not just go servo? Price diff is close to 0.

The Mill came from LatheMaster. I looked at craigslist and ebay for a month. Considered the X3s. But after seeing the ZAY still on sale at Bob's website it just looked right. Bob has been great to deal with and the mill arrived in the same week that I ordered it. IH would have been a no brainer, if not for the over $1000 premium. (my wife already balks at this hobby. no need to send her on the warpath)

So here is the confusing part... 500 oz-in is plenty to turn the ballscrews at 1:1 ratio (overcome gib friction + force to push cutter into material). What does a larger motor buy me? More acceleration?

[jalessi]

Chris,

Overcoming the heavy moving weight coupled with rapid inertia is a concern.

The NEMA 34 motors and G203 drives would produce double or even triple the torque and holding power.

On the other hand it would be interesting to see the performance of the G540 and NEMA 23 motors on a RF45 style mill, it may work just fine.

If it works well you would not only save yourself some cash, a lot of Zone members would benefit with the knowledge.

Worst case scenario you could always sell the Nema 23 motors and G540.
There is a big demand for them here on the Zone.

Please keep us posted.

Jeff...

[BobWarfield]

Sometimes really big steppers can be a disadvantage, as they can't produce much torque at higher rpms.

One way to look at your sizing problem is to try comparing to other commercial machines.

Tormach is in the same category size-wise as your ZAY and is well regarded, what size steppers do they run on their direct drive? I have a vague recollection it was on the order of 650 oz in, but someone will know for sure.

Industrial Hobbies runs 410 oz in servos, but they are not direct drive, they have a 4:1 ratio, so you'd need 1600 oz in on a direct drive to match. That's almost certainly radical overkill, so somewhere between 410 and 1000 may be about right.

I have 850 oz in HomeShopCNC servos on my IH mill with a 2.8:1 reduction on X and Y, so that's still a whole lot of oz inches! Is it needed? Hard to say it was really necessary. I was playing with tuning the servos the other day and had the table flying around at 180 IPM. Mind you, I was just playing and made no cuts, that is likely not a workable speed for production!

I do think I'd opt for NEMA 34 frame steppers as these are heavy machines. At the least, if you really want smaller motors, you could consider NEMA 34 for the Z-axis only. It's very heavy as was mentioned.

Lastly, don't scrimp on the voltage to the motors. Read the articles available on running pretty high voltages relative to the motor's continuous rated voltage with the Gecko current limiting to keep things from melting down. That voltage really helps your acceleration.

Should be a fascinating project that'll leave you with a very capable machine.

Cheers,

BW

[clocker]

Thanks to both of you for the insight and encouragement. I dusted off some of the old physics books last night and started to do the calculations to really find out where the limitations were. The conversion factors were a bear, so I did a little more searching online and found http://www.linearmotioneering.com/
W00t! all the hard stuff is computed.

From what I understand now, a 100lb x axis with a 5tpi screw, 120ipm rapid, .1m/s2 acceleration and direct drive will require 80Ncm @ 600rpm

The stepper motor torque curves from Keling show that there are NEMA23s that will do this. The big problem is the mill head because not only do you have inertia, you have to overcome gravity. Here you would need roughly 1Nm @ 600rpm. That is NEMA 34 territory, but adding gas struts or counterbalance could reduce the torque needs.

So, the main reason to go to a larger motor is acceleration and faster rapids. The faster you want to get the axis moving, the more oomph you need from the motor. And since the steppers drop off in torque very quickly, you run out of oomph to keep accelerating.

Can these limitations be overcome? I think so... I'm looking at using Mach 3 and I think that it has acceleration settings. If I limited the acceleration or maybe used some of the anti-jerk settings in Quantum, the motor system may not have to be as over engineered as it was in the past.

Hmm, cost of tinkering time + risk of being wrong + cost of head strut parts is > the ~$500 premium to go to NEMA34 setup

[HimyKabibble]

Thanks to both of you for the insight and encouragement. I dusted off some of the old physics books last night and started to do the calculations to really find out where the limitations were. The conversion factors were a bear, so I did a little more searching online and found http://www.linearmotioneering.com/
W00t! all the hard stuff is computed.

From what I understand now, a 100lb x axis with a 5tpi screw, 120ipm rapid, .1m/s2 acceleration and direct drive will require 80Ncm @ 600rpm

The stepper motor torque curves from Keling show that there are NEMA23s that will do this. The big problem is the mill head because not only do you have inertia, you have to overcome gravity. Here you would need roughly 1Nm @ 600rpm. That is NEMA 34 territory, but adding gas struts or counterbalance could reduce the torque needs.

So, the main reason to go to a larger motor is acceleration and faster rapids. The faster you want to get the axis moving, the more oomph you need from the motor. And since the steppers drop off in torque very quickly, you run out of oomph to keep accelerating.

Can these limitations be overcome? I think so... I'm looking at using Mach 3 and I think that it has acceleration settings. If I limited the acceleration or maybe used some of the anti-jerk settings in Quantum, the motor system may not have to be as over engineered as it was in the past.

Hmm, cost of tinkering time + risk of being wrong + cost of head strut parts is > the ~$500 premium to go to NEMA34 setup

Keep in mind those calculations are probably neglecting friction, which you can't do. So don't forget to "pad" them, especially if you operate in the winter in a cold shop. You'd be amazed what a difference temperature makes.

Regards,
Ray L.

[cjdavis618]

I'm not a physics guy and can barely do math. But I can tell you that I had the smaller Super X3 mill and I tried to do the Nema23 motors all around on it.

The X and Y worked fine with the Nema23s on Gecko 203v. The Z axis eventually snapped the shaft on the motor after about 3 months from fatigue. Luckily, I wasn't cutting anything at the time and the head didn't fall due to the way the belt works on my Super X3.

Don't skimp, you will pay for it one way or the other.

[BobWarfield]

The Z axis eventually snapped the shaft on the motor after about 3 months from fatigue. Luckily, I wasn't cutting anything at the time and the head didn't fall due to the way the belt works on my Super X3.

[cjdavis618]

Exactly. I started off using the Xylotex controller and a counterweight setup. I would get around 10ipm for Z speed and no more than 30 with X and Y.

I then upgraded to the 203Vs, C11G Breakout board and a 12amp 72 volt PS. I was then able to get about 60ipm all around and even rapid at 120 on X and y. Using the 425oz nema 23 motors that came from my xylotex kit. The motor wasn't able to run the 100lb load without loosing steps. I put the Counterweight back on which was a 1:1 weight ratio and was able to keep up with the X and Y in speed. After a while though, the shaft snapped right at the motor shaft base. It was a clean twisted snap. I was in the process of setting up a new part and it snapped on the Z axis offset measuring. There was no force on the head at the time.

There is a good reason for the Nema 34 motors having a 1/2" shaft.
The 1/4" shaft of the Nema23s just isn't a good fit for a large mill. I would rather put larger motors in with direct connections. Even with gear reduction or pulleys to increase the ratio, I don't know that you will gain anything by reducing speed to get torque. Especially on an RF45

[skippy]

I am also the proud owner of a ZAY 7045 although I don't have the money at this point in time to get it going with tooling, etc. and much less so with a cnc conversion. Speaking of being low on money, I still owe €200 more to my friend that I bought it off. I did do some searches a couple of months ago to look for ZAY 7045 cnc conversions but don't remember finding anything. This thread is in fact the first log I've seen of such a conversion. With that in mind I'll be looking in from time to time to see how it's going for you so "good luck with it".

[clocker]

Thanks for sharing your experience. I sure don't want that to happen with this beast
I totally agree with the penny wise pound foolish thought especially with these heavy machines. The one thought that keeps coming back though is that 100W is a huge amount of energy. It seems that the vendors are finally supplying motors that work within the recommended specs for the G250 drivers, so maybe it will work. Worst case I can transfer the setup over to the 11x26 lathe and get that running