Converting a screw's linear speed to rotational

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Discussion Overview

The discussion revolves around converting the linear speed of a screw's nut to its rotational speed in RPM. Participants explore the relationship between the screw's pitch, axial speed, and the resulting rotational speed, while addressing the necessary calculations involved.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant proposes a formula involving the mean diameter of the screw to calculate RPM based on linear speed.
  • Another participant emphasizes the importance of knowing the screw thread's pitch, noting that a coarse pitch results in greater linear movement per revolution compared to a fine pitch.
  • A participant clarifies that their reference to "linear speed" pertains to axial speed along the screw's axis.
  • One participant states the pitch of the screw is 4mm and seeks the formula that connects axial speed to rotational speed.
  • Another participant explains that the pitch indicates how far the nut moves with one complete screw rotation, suggesting a method to calculate revolutions needed for a specific distance.
  • Calculations are presented, showing that with a pitch of 4mm, the rotational speed can be derived to yield 4500 RPM for a linear movement of 300mm.

Areas of Agreement / Disagreement

Participants generally agree on the method of calculating RPM from linear speed and pitch, but there is no explicit consensus on the correctness of the final calculation presented.

Contextual Notes

The discussion does not resolve potential assumptions regarding the definitions of terms like "linear speed" and "mean diameter," nor does it clarify the context of the initial formula proposed.

Femme_physics
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Suppose I have a screw that makes some sort of frictionless ball bearing move at 0.3 m/sec

That means that to find the RPM of the screw I do

pi x mean diameter of the screw x rotation per minutes / 60000

and I get the answer?
 
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You need to know the pitch of the screw thread. eg how many turns per meter.

If the thread has a very coarse pitch the ball will move a long way for each revolution. If the thread has a very fine pitch it will move only a short distance for each revolution.

EDIT: I assume by "linear speed" you mean the speed along the threaded rod parallel to it's axis not the velocity around the rod? Perhaps I misunderstand what you mean?
 
By linear speed I do mean axial speed, yes.

I know the pitch (it's 4mm)

I just can't find the formula that relates it to rotational speed, taking the axial speed of the nut into consideration
 
The pitch is the distance the nut will move if the screw rotates once.

So you can work out how many times it rotates for the nut to travel 300 mm.

This gives revs per second, so you can work out how many revs per minute that is.
 
4mm x RPS = 300mm
RPS = 75
RPM = 75 x 60 = 4500 [RPM]

Is that right?
 
Femme_physics said:
4mm x RPS = 300mm
RPS = 75
RPM = 75 x 60 = 4500 [RPM]

Is that right?

4500 RPM looks good.
 
Thank you all :-)
 

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