Using A Magnetic Puller To Guide Cables And Wires Through Walls And Conduits

**machining 4 all** · Mar 6, 2021, 01:59 PM

https://thumbs.gfycat.com/UltimateBowedBasil-mobile.mp4

**Jon** · Mar 8, 2021, 03:09 PM

Good find. Here's the video inline:

**Toolmaker51** · Mar 8, 2021, 06:22 PM

The real trick is obround shape of the fishing tool, able to climb obstructions and have little contact on rough surfaces.

**nova_robotics** · Mar 8, 2021, 08:15 PM

How strong is that magnet that it can pull a fish through a half inch of plywood?

**Toolmaker51** · Mar 8, 2021, 10:45 PM

A single .75 x .125 neodymium is 8 lbs of pull....2 or 3 oriented poles must have 12 minimum pounds at that distance. maybe a thick soft iron puck in slick plastic sled, is enough. It doesn't have to pull wire, just the nylon leader.
Another way they send leader through conduit is compressed air, connected to a feathered dart like a blow gun.

**nova_robotics** · Mar 8, 2021, 11:08 PM

Originally Posted by Toolmaker51

A single .75 x .125 neodymium is 8 lbs of pull....2 or 3 oriented poles must have 12 minimum pounds at that distance.

No way. Magnetic attraction falls off rapidly with distance. 1/distance^2 in fact. I don't believe that tool will have 12 lbs of force at that distance. If it did, it would be a legitimate health hazard when they snap together.

If they're overmolded with 1mm of x plastic, and they have 12 lbs of force through 1/2" of plywood, then they'll be held together with over 2200 lbs of force when they snap together. 1. You're not getting that tool apart with your hands. 2. That's a trip to the hospital the first time you use it. Completely impossible.

Also they just slide them apart with almost no effort at the 27 second mark. Zero chance there's 12 lbs at 1/2".

**mklotz** · Mar 9, 2021, 09:15 AM

Originally Posted by nova_robotics

No way. Magnetic attraction falls off rapidly with distance. 1/distance^2 in fact. ...

Magnetic field strength falls off as distance cubed (R^-3), not distance squared. But things aren't that simplistic...

https://van.physics.illinois.edu/QA/...-at-a-distance

**Rikk** · Mar 11, 2021, 07:36 AM

Originally Posted by Toolmaker51

Another way they send leader through conduit is compressed air, connected to a feathered dart like a blow gun.

When building my shop, I ran three 2" conduit runs from my house basement, ~40 out to my shop. To run my mason's line for pulling wire, cable, etc. I attached a shop vac to one end of a run in the basement, took a plastic shopping bag and tied the line around the center, turned on the vac, stuffed the bag into the shop side and it sucked it right through to the basement. It worked pretty well.

**Toolmaker51** · Mar 9, 2021, 02:40 PM

1] I guess-t-rated three 8 pounders conservatively at 12 pounds, wouldn't be surprised if higher.
2] Only the tool [puller] portion is a magnet - acting on whatever suitable material they chose for the chaser.

As well, packaging on neodymium magnets any bigger than 4-5mm diameter affirm definite risk around mishandling them.
Compared with two flat surfaces adhering [and pinching] so well, a chord-like form of minimal contact is less challenging.
Don't all of us picture a common magnet holding an inverted straight pin, even a nail, with hardly any surface area at all?

The page offered by our friend Mr. K points out mere strength isn't only consideration in attraction of magnetic materials.

Just conducted highly scientific test with a common refrigerator magnet and a washer; there was noticeable magnetic activity through what I surmise a 3/8" plywood cabinet door.....holding the washer in place.

**nova_robotics** · Mar 9, 2021, 03:25 PM

Originally Posted by Toolmaker51

1] I guess-t-rated three 8 pounders conservatively at 12 pounds, wouldn't be surprised if higher.
2] Only the tool [puller] portion is a magnet - acting on whatever suitable material they chose for the chaser.

As well, packaging on neodymium magnets any bigger than 4-5mm diameter affirm definite risk around mishandling them.
Compared with two flat surfaces adhering [and pinching] so well, a chord-like form of minimal contact is less challenging.
Don't all of us picture a common magnet holding an inverted straight pin, even a nail, with hardly any surface area at all?

The page offered by our friend Mr. K points out mere strength isn't only consideration in attraction of magnetic materials.

Just conducted highly scientific test with a common refrigerator magnet and a washer; there was noticeable magnetic activity through what I surmise a 3/8" plywood cabinet door.....holding the washer in place.

Inverse cubed causes force to fall off faster than squared. Inverse cubed makes it even less feasible to have to 12 lbs at 1/2". That wire fish does not have 12 lbs of pull through that plywood.