1.85nm steppers and vertical router cnc

[freddean2006]

What would be the lifting maximum of a stepper motor of 1.85nm?

I ask because Im thinking of trying to reduce the footprint of a cnc im designing which will be similar to the roland mdx 3 so I can maximise cutting.

Im thinking of having the table at a 60 degree angle using skate bearings but wondered if a moving gantry would be too difficult to implement, given the weight.

To follow on what would be the pitfalls of mounting the table at 90 degress with the router on the horizontal? Would I be able to make a 4ft x 4ft moving gantry cnc this way?

thanks for any replies

[jsheerin]

Force depends on your lead screw setup. Different pitch screws will give different forces for a given input torque. There is a CNCMechanics v1.2.pdf file available on this site, possibly in the linear motion group, that you should be able to search for and see the appropriate equations. You'd have to modify them to take into acount the vertical motion. However, you should also consider that a stepper's torque will fall off with speed. So even if 1.85Nm is enough to lift the weight you have with your screw setup, and even is enough to accelerate it at a reasonable rate (above the acceleration of gravity required to lift it), that torque will drop off at higher speeds and would possibly limit you to a lower max speed than you would otherwise have. It is definitely possible (and possible to calculate the required components), but I would definitely recommend doing the calculations before building. I would also recommend thinking about moving the gantry horizontally so you would only have to lift your Z axis assembly. However, to give you an idea, I have dual 3Nm holding torque steppers on my X axis for a similar sized machine (although mine is pretty sturdy), and I would not imagine it could lift the gantry vertically at any reasonable rate.

[freddean2006]

Originally Posted by jsheerin I would also recommend thinking about moving the gantry horizontally so you would only have to lift your Z axis assembly. However, to give you an idea, I have dual 3Nm holding torque steppers on my X axis for a similar sized machine (although mine is pretty sturdy), and I would not imagine it could lift the gantry vertically at any reasonable rate.

Thanks for your insight.

Maybe I should make it a moving table with a fixed gantry, like the mdx-3. So the forces would be the cutting head and the weight of the table and material.

[Rene Nuñez Paz]

Hello

Look at that link, here are a machine like you want to build
the solution for the aditional weight for move the gantry
is add a counterweight (contrapeso) I put the word also
in spanish I don't know if counterweight is the appropiate word.


http://www.vectric.com/forum/viewtop...&sd=a&start=75

In this way, your only problem is the real weight of the gantry.


Bye

Rene

Excuseme my bad english I hope you understand.

[freddean2006]

Originally Posted by Rene Nuñez Paz In this way, your only problem is the real weight of the gantry.

So that would mean you compensate by using more powerful stepper?

Great link though. Exactly what Id planned, except smaller.

What I dont understand is dont the weights add to the weight of the gantry? Shouldnt there be two weights to balance it out on both directions, up and down?

[Rene Nuñez Paz]

Excuseme , maybe I didn't explain well, If your 185oz/in are able to move your gantry and do cuts in horizontal position, and if you want to build another similar router in inclined position and get more space in your workshop, the only thing that you need is add a counterweght to compensate the additional weight in this axis. In this way you get the gantry in equilibrium like if are in hztal position, no matter add the stepper force or the screwed bar diameter, Iam attaching a simple drawing of this. I supposed 100 lbs in gantry.

Best regards

Rene

Excuseme my bad english I hope you understand

[freddean2006]

Originally Posted by Rene Nuñez Paz Excuseme , maybe I didn't explain well, If your 185oz/in are able to move your gantry and do cuts in horizontal position, and if you want to build another similar router in inclined position and get more space in your workshop, the only thing that you need is add a counterweght to compensate the additional weight in this axis. In this way you get the gantry in equilibrium like if are in hztal position, no matter add the stepper force or the screwed bar diameter, Iam attaching a simple drawing of this. I supposed 100 lbs in gantry. Best regards Rene Excuseme my bad english I hope you understand

If the gantry is going down, is it gravity that cancels out the extra weight on the drive screw?

[Rene Nuñez Paz]

Exactly, if you disconect the drive screw you'll see that the gantry don't move down if
is exctly compensated. You can move by hand, but stop it when you leave alone in any position. Be careful to select the position to attach the cable weight in the gantry , to get similar forces in the superior and inferior linear bearings.

In this moment, for the steppers are the same thing if the gantry are horizontal or vertical.

Bye

Rene

[jsheerin]

If you do the counter weight, the gantry would only be stopped by drag once set in motion. In other words, the lead screw would have to supply the force necessary to stop motion as well as start it. But the screw would not have to lift it (overcome acceleration of gravity).

However, now you will have to accelerate the mass of the counterweight in addition to the gantry, so you will effectively double the force required for a given acceleration: f=m*a. Once again, you'd have to look at motor torque curves to figure out if this would work for how fast you want to go.

John

[Rene Nuñez Paz]

Not sure for me,,, if the gantry and counterweigt are in equilibrium you can move it with without aditional forces, I'll do some practices about it , and leter I'll tell you.

Bye

Rene

[jsheerin]

It always takes force to accelerate (start moving - increase velocity) a mass. If you have a counterweight, you have balanced your moving assembly for the case of no movement. To start it moving, you must apply a force. To stop it, you must apply the same force in the opposite direction (although in real life drag forces in the bearings, etc. will contribute to the stopping force). With the counterweight, the weight now moves with the gantry - it is connected to it through a cable (or some mechanism). So you must accelerate both now. So the mass to accelerate is increased. Maybe it is not doubled if the mass hangs straight down and the gantry is on an incline, for example, but the mass will still increase, and F=m*a. If mass increases and acceleration stays the same, the force applied must increase. However I think this is still much less than overcoming gravity, so you are still likely better off.