G3616 Conversion.

[jcdammeyer]

If I understand what @jcdammeyer is looking for, it is the dynamic torque at startup, not the static torque it takes to turn it. The dynamic torque required to spin the gear train up could be quite a bit higher than the static torque required to just get it turning.

Such a measurement might require a torque transducer and a plot of the torque value as it changes with acceleration.

Another way to do it might use a torque limiter and just keep reducing the torque till it works as desired.

Actually I wasn't looking for anything. As I recall from Physics Static Friction is higher than Kinetic Friction. So it takes more torque to start something up than it does to keep it moving. What I did was empirically test what torque it took to get the shaft moving. Then doubled that and selected a motor that could produce that within the 3A limit of my ELS driver.
Direct mount wasn't an option so instead I went belt drive and doubled the torque I calculated with pulleys. I can't run the motor full speed but I can cut any thread at a variety of spindle speeds.

For the Mill I did the same thing since I was tired of hand cranking. However there I found the 600 oz-in motor even with 3:1 couldn't move as fast as I could hand crank. It moved it but I would get bored waiting. Going to 1200 oz-in had it go to 25 IPM and that was as fast or faster than I could crank so I was happy until the Gecko failed. Now with the AC servo which is smaller physically than the 1200 oz-in stepper I'm very very happy.

 

[slow-poke]

If I understand what @jcdammeyer is looking for, it is the dynamic torque at startup, not the static torque it takes to turn it. The dynamic torque required to spin the gear train up could be quite a bit higher than the static torque required to just get it turning.

Such a measurement might require a torque transducer and a plot of the torque value as it changes with acceleration.

Another way to do it might use a torque limiter and just keep reducing the torque till it works as desired.

I think it's the other way around. Steppers have maximum torque when stopped so moving from stopped is their strong point, their weak point is that they loose torque as they speed up so they have a tendency to stall when you try and go too fast. DC servos are better than steppers in this regard as they have a flatter torque curve, but they too loose torque with RPM, just less than steppers, ac servos have the flattest torque curve of the three (significantly flatter) with torque typically extending to about 10x that of a dc servo.

In addition to the flatter torque curve, servos have a short term peak torque rating typically about 4x their continuous rating. AC servos make steppers look pretty lame when you want to go fast with a heavy load.

 

[Susquatch]

Actually I wasn't looking for anything.

Then what in the world are we all talking about! That figures. Leave it to you to get us all going in different directions in a giant rabbit hole.

As I recall from Physics Static Friction is higher than Kinetic Friction. So it takes more torque to start something up than it does to keep it moving.

I didn't say kinetic and I didn't say friction. I said dynamic torque. Dynamic torque is more like HP in that Dynamic Torque is a force that does work.

Its the additional torque it takes to achieve a given level of acceleration of all the components. It is one thing to move it, and another to accelerate it. Dynamic torque is much more important in multi geared assemblies like lathes vs simple drives like mills because the torque required to bring a lathe up to speed is so much greater than it is in a mill.

But all this is a moot point if you aren't asking a question about it. LOL!

 

[Susquatch]

I think it's the other way around. Steppers have maximum torque when stopped so moving from stopped is their strong point, their weak point is that they loose torque as they speed up so they have a tendency to stall when you try and go too fast.

I wasn't talking about the kind of motor. Only about the torque needed by the lathe.

You points about the differences in the different kinds of drives are all valid.

 

[Susquatch]

As I recall from Physics Static Friction is higher than Kinetic Friction.

After my previous post on this, I got to thinking about some of your earlier related issues.

Is it possible that you have been confusing the torque it takes to overcome static friction with the dynamic torque it takes to accelerate a mechanism up to its design speed? Static torque is very much related to static friction. But dynamic torque is related to both the kinetic friction that changes with speed, AND the desired rate of acceleration for masses with differing inertia.

If so, I'd be happy to explore it more with you. If not, just chalk it up to a hairy guy making a racket in the forest.

 

[jcdammeyer]

After my previous post on this, I got to thinking about some of your earlier related issues.
If so, I'd be happy to explore it more with you. If not, just chalk it up to a hairy guy making a racket in the forest.

If there isn't anyone else in the forest is there any racket to be heard????

 

[jcdammeyer]

Then what in the world are we all talking about! That figures. Leave it to you to get us all going in different directions in a giant rabbit hole.
But all this is a moot point if you aren't asking a question about it. LOL!

I was responding to another post and just added my two cents as to how I did it. Also that my approach worked perfectly for both mill and lathe. The problem with the mill was impatience on my part knowing full well that torque on steppers drops with speed.

 

[Former Member]

For me the plan is some maintenance to see what wear hard CNC is causing and plan mitigation. Measure up and design mounts for the ballscrews. Assemble and continue work will setting up for next retrofit (without glitches one hopes).

Well the first ballscrew has been installed and it needs more support. I'm surprised at how much I can flex a short piece of 1/2" thick 6061 with a ballscrew. Currently this is causing the most inaccuracy.