Help calculating load on a nut

[Brenck]

Hi everyone,

I need help on how calculate a load on a nut. Basically what I have is a trapezoidal rod with 18mm with 4mm and a 14mm with 3mm thread both of them just regular trap. rods, single start... And both of them with a 1.5 NM ( 15kgf ) motor. Well what I want to know is what is gonna be the load in the nut if lets say the 1.5NM of the motor rotates and press the nut against a wall or something. Like if you would be tightening it up with a 1.5NM wrench.

If someone can help I aprecciate.

Thank You

[H.O]

Hi,
Think of it this way: When the screw turns one revolution it moves your object 4mm, that is the same as hoisting the object 4mm by attaching a string to a shaft or drum with a circumference of 4mm - one revolution will move the object 4mm in both cases.

The shaft or drum will have a radius of 4 / PI / 2 = 0.637mm. So 1.5Nm / 0.000637 = 2355N. Now, this is if the screw would have 100% effeciency, which it hasn't, so you need to derate for the type of screw you have.

/H.O

[Brenck]

Thanks for the help

Its gonna be a trapezoidal steel shaft, 1045 steel with teflon nut...

Do you know how to calculate the efficiency? Teflon with steel friction coeficient is about 0,05 - 0,08.

Do you know how to calculate how long the nut needs to be so it have a good resistance or it wont ripp or something...

Thank you

[H.O]

Hi,
I'm afraid I'll have to answer no to both questions. I belive that a trapetzoidal screw is in the efficiency range of 30-60% while a ballscrew is somewhere around 90-95% or even more in some cases. A nut made from acetal or similar is probably more efficient than a steel- or bronze nut but it lacks the rigidty, obviously.

Here's a plugin in the numbers website that you might find useful and here's another site with alot more "background info".

Good luck!