2 TPI Ground ballscrew/ 203V/SmoothStepper...

[nate]

Hey all!

Can anyone tell me if this all sounds right?

A 2 TPI ground ballscrew would require 400 steps (on a 1.8Deg stepper motor) to move 1 inch.

Assuming this is correct, what is the best way to drive this screw with my G203V's, pac/sci 850 Oz motors, and smooth stepper board. I also am planning on running 1.8:1 belt reduction with some large timing pullys I have.

Is there a way to make the motors have more steps per rev, thus increasing smoothness of travel and decreasing minimum travel distance?

If my math is correct, with a 1.8:1 reduction, I will require 720 steps to achieve a one inch movement?

Are there smooth stepper settings that can be changed to micro step? Gecko settings?

I would love to hear your thoughts...

Nate,

[ger21]

The Gecko's are 10 microsteps. So you'll be at 4000 steps / inch.

Is this a plasma machine? I'd run it direct drive and see how it works. The router guys are running 2 tpi acme with no problems.

[nate]

Hey Gerry!

Long time no talk. I still owe you a beer for all the help youve given me over the past few years...

Anyway, its not for plasma. its for a large lathe/mill that im scratch building on a Vinco optical inspecion machine table. 72"x20" hand scraped surface plate essentially. 3000 frigging lbs!!

I picked up a few 1.5inch dia, 2tpi ground ballscrews for pennies. The're monsters, but with reduction, Im guessing I will be able to drive them just fine.

your thoughts?

[Jeff-Birt]

Lets see: 2 TPI * 1.8 = 3.6 TPI

850 oz-in motors * 3.6 ratio = 3060 oz-in holding torque or about 2500 oz-in dynamic torque (max)

3.6 TPI * 200 steps (motor) * 10 uS = 7200 steps/inch

Ignoring backlash that would give you about +-0.00014 step resolution based on the resolution of the stepper itself. Somewhere I remember reading where one of the Gecko guys were talking about the phase lag of the stepper while moving could be as much as 1/2 step. So given that number you would have a step resolution of +-0.00069, about a 1.4 thou window (ignoring backlash).

The big question is will you have enough torque to accelerate the mass of the machine?

[nate]

Wow. very interesting calculations. I can only vaguely comprehend them. Any chance I can get you to explain in laymans terms how you did that calculation.

The machine is being built on a large surface plate with linear rails (angled flat roller INA) 55" long for the Z axis. The Y will be on 30" ball rails of similar weight and size.

The above applies to when its being used as a lathe. When in mill mode, it will have around a 20" X and a 15" Y and a 4" Z.

Im ballparking my weight of the "carriage" of the Lathe will be around 200 Lbs (MAX, this is my high side estimate)This will include Y axis rails and trucks, ballscrew and mounts, aluminum plates(construction of the carriage), tools etc...

I am unclear on how to calculate if this is feasable or not...

[ger21]

2 turns per inch of the screw x the gear reduction of 1.8 = 3.6 turns of the stepper per inch of movement.
At 2000 steps per revolution, that gives you 7200 steps/inch. 1/7200 = .00014" per step.

[nate]

Huh, ok, its starting to make sense!

Belt reduction is almost done, ballscrew mount is in the works. I have a few more days worth of evenings working on this thing before I can run the Z (in lathe mode) and see if this motor can turn the ballscrew and push some weight around.

Nothing is really built yet, but my first test is just turning the Z ballscrew and seeing if it will push some weight across the table.