Reply with QuoteThe same person who spec'd that stepper has many video of him hogging. Not enough?
Stepper Sizing: G0704 Question:
I'm working on converting my G0704 over to CNC like many others and have a question on the stepper sizing.
I purchased Hoss's plans and have a few questions.
The 570 oz/in steppers recommended for x and y fall off to only .5Nm at 600 rpm or so and with a 5mm lead that is at around 120 inches per minute travel.
I see people showing travel speeds of near 200 ipm where this motor has a torque of around .4Nm.
It seems that the 425 oz/in steppers would be better sized for the unit with a torque at 120 ipm of 1.2Nm and .5Nm at 200 ipm.
The sacrifice would be start up torque going from 3.1Nm to 2.2Nm.
The force developed on the lead screw is about 750 lbf at 100 rpm rating for the 425oz/in motor.
I've read lots of threads on stepper sizing.... bigger is better, bigger isn't always better etc.
Has anyone tried both steppers and have some real world info?
I'm looking at using the 16mm ball screws for X, Y, and Z with a custom double nut setup.
Thanks for the help.
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Re: Stepper Sizing: G0704 Question:
The same person who spec'd that stepper has many video of him hogging. Not enough?
A lazy man does it twice.
Re: Stepper Sizing: G0704 Question:
You are looking at torque curves that were obviously derived by different people. When comparing the two that look the same and that would therefore probably have been made and torque measured by the same methods. When you do that you see the attached plots that show at 600 rpm the 570 puts out about 1.5 Nm and doesn't drop to below 0.5 Nm until 1100 rpm.
Re: Stepper Sizing: G0704 Question:
No I think the 570's will work... There is a ton of information and opinions out there.
My question is the theory behind the 570's is it to give more torque when hogging at slower feed rates and live with the fall off in torque while you are doing rapid movements because the torque isn't needed?
Re: Stepper Sizing: G0704 Question:
Originally Posted by 109jb
You are looking at torque curves that were obviously derived by different people. When comparing the two that look the same and that would therefore probably have been made and torque measured by the same methods. When you do that you see the attached plots that show at 600 rpm the 570 puts out about 1.5 Nm and doesn't drop to below 0.5 Nm until 1100 rpm.
Here is the torque curve I was looking at from Automation Technologies
Re: Stepper Sizing: G0704 Question:
Though you do see some videos of many of us doing speed trials (I have one at 331 IPM). Those speeds are never really used. In my case if I approached 60 IPM in cutting I would be surprised. I would like to but it isnt feasible. The big machines that do cut at 200-300 IPM or more, rapid at 600-1000 IPM ;-) I think you are correct on the reason as to why the stepper is sufficient.
A lazy man does it twice.
Re: Stepper Sizing: G0704 Question:
Like I said, just the fact that the plot you used looks different raises the question of whether the torque measurements were done the same. The plots I posted were also from automation tech, but the 570 plot was for the 1/4 shaft motor. This should not make a difference in the torque curves so one of them is wrong. Basically what I am saying is that the plot you looked at may not be right. The plot I used may not be either, but it looks the same format as the 425 plot, so at least they should be an apples to apples comparison. The plot I posted shows the 570 will have more torque than the 425 at ALL rpms.Here is the torque curve I was looking at from Automation Technologies
Re: Stepper Sizing: G0704 Question:
Today NEMA 34 1600 oz in or NEMA 23 650 oz in are cheap and affordable, why not use big torque motor plus ethernet...ESS or UCCNC...I've read lots of threads on stepper sizing.... bigger is better, bigger isn't always better etc.
Re: Stepper Sizing: G0704 Question:
Like the others have said, you aren't going to be cutting at 150ipm with this machine. The fastest I cut is maybe 90 ipm but that's rare. 25 to 70 ipm is the common range. Sure my rapids are 180 ipm, and I could probably get 200 or 225 from it, but there's no reason to. The bed is only 20 inches long so it's not like the machine is wasting a bunch of time running end to end, there just isn't enough travel to worry about it. The high torque larger steppers are better at direction changes (i.e. Near zero RPM), and when handling the inertia of the the table, part, fixturing, that's likely the highest loads the stepper sees, barring tool crashes.
Re: Stepper Sizing: G0704 Question:
Those motors would work, but would be overkill. With 570 oz-in motors I can rapid at 200 IPM and I can take a heavy enough cut at normal cutting feed rates to stall the spindle and snap off a 1/2" end mill before losing steps.
Re: Stepper Sizing: G0704 Question:
That makes sense thanks for the reality check on feed rates.
Re: Stepper Sizing: G0704 Question:
Are you using a 570oz-in motor on the Z or something else?
Re: Stepper Sizing: G0704 Question:
The Z wont be moving very far at a time except during homing or a tool change. Even in 3D the travel will be minimal. Though I run a 34/960 IIRC on the Z, a 570 would likely be fine.
A lazy man does it twice.
Re: Stepper Sizing: G0704 Question:
yes. 570 on z and no problems with the stock spindle. I can stall the stock spindle with the 570. With more spindle power you may need a bit bigger on the Z, but the Hoss recommended, which if I remember right is a 960 oz-in is as big as would ever be needed.
Re: Stepper Sizing: G0704 Question:
Forgot to mention. Since it doesn;t drill larger sizes that well, I just drill about a 1/4" hole and open it up with an end mill and circular interpolation.
Re: Stepper Sizing: G0704 Question:
Okay now for the stupid question...
Automation tech offers two 570oz-in motors a 4 wire and a 8 wire, the 8 wire has the torque curve that "looks" better with a more normal fall off with rpm and the 4 wire has a pretty flat torque curve for the first 400 rpm or so.
400 rpm is about 80ipm
The motor with the better torque curve (8 wire) has 1/4" shafts out both ends while the one that falls off at 400 rpm has 3/8" shaft any issues with the 1/4" shaft and the coupling? 1/4" shaft seems kind of small / hard to keep from turning in the coupling over time.
Thoughts? or is there a better motor out there?
Re: Stepper Sizing: G0704 Question:
As I said twice before. You are looking at plots that don't even look reasonably close to each other. Not the plot styles, the text, the background color or anything. As such you can assume that the torque curve measurements were not made by the same people and you don't know what methods were used for the different tests. The 4 wire motor should perform exactly the same as the 8 wire motor if the 8 wire is connected in bi-polar parallel. Therefore it makes no difference which one you buy. You will get the exact same performance from each.
Re: Stepper Sizing: G0704 Question:
I dont have any issues with couplers turning on either shaft size. Get good couplers! Not the spiral cut aluminum ones.
A lazy man does it twice.
Re: Stepper Sizing: G0704 Question:
Get the four wire, it's easier to solder up by a handful of connections.
Re: Stepper Sizing: G0704 Question:
Seriously? Cutting and twisting two wires into one isn't rocket science. If you've got to solder wires into a connector it makes no difference IMO
