# ElectroMagnet Force Calculations?

1. Aug 15, 2012

### SkiWebb

I was toying with the idea of making an iron core electromagnet to retrieve a broken portion of my driveshaft from a recess in the end of the crankshaft on my boat motor. The mechanic at my work said I wouldn’t be able to do it, so I figured I would entertain the idea.

The driveshaft is somewhere between 5/8 and 3/4 of an inch in diameter. The crankshaft has a female splined hole that is about 1-1/4 inches deep and accepts the male splines or the driveshaft. About 3/4 of an inch of the the driveshaft is broken off in the crankshaft, leaving a 1/2 inch recess.

I have a basic understanding of electricity, the relationship between volts, amps, watts and resistance and the ability to use a multimeter.

Here are some things I know about iron core electromagnets.
*The more windings, the greater the magnetic force.

*The more amps flowing through the windings, the greater the magnetic force.

*Once I figure out my power supply, I can obtain a suitable amp rate for my
windings through the use resistors and/or a load such as a light.

Here are some things I don’t know.
*What direction is the force the strongest? Toward the end of the iron core?

*How does the size and composition of the core effect the strength of the magnetic force?

*Is it a reasonable task to build an electromagnet that can create 10-25lbs of pull, if so would that force be able to act on a slug of metal that’s not much more than a few cubic centimeters?

*Would I be better off to build a big magnet that will not fit in the recess but may have more overall force, or make a small one that can fit into the recess and directly contact the piece to be removed. How much will the force diminish over that 1/2 inch gap?

*Is the metal of the crank around the slug I’m trying to remove going to deflect or redirect the magnetic force in any way?

*Do these examples have an iron core? http://www.solenoidcity.com/electromagnet/E-28-150p1.htm

Any input would be great, thanks.

2. Sep 1, 2012