Introduction: Fulcrum

If you ever want to pull a fence post out you'll want a fulcrum to help. The idea is simple, apply leverage to pull the post out like a crowbar does a nail. This instructable will tell you how to build the fulcrum. How you use it is up to you. Like any tool, fulcrums pose a risk of danger when used. Use these plans and the fulcrum you build at your own risk. I accept no liability for any impact incurred from their use.

Tools:

  • Miter Saw
  • 1/2" socket wrench and handle extender
  • Drill
  • 10" x 3/8" auger drill bit
  • 1/8" drill bit
  • Square

Materials:

  • One 4"x6"x10' wood beam
  • One 1"x4"x4' piece of scrap wood
  • Four 10"x3/8" lag screws with 1/2" socket cap head
  • Two 6"x3/8" lag screws with 1/2" socket cap head
  • Two 4 inch wood screws

Step 1: Cut the Lumber

  1. Cut the 10 foot 4x6x10 in half (at 5 feet).
  2. Cut one of the 5 foot sections in half again with a 45 degree cut. The cut should start at 27.5 and end at 32.5 inches.

Step 2: Dry Fit Assembly

  1. Using the drill and a 1/8 inch bit, pre-drill one 4" hole in each of the short pieces as shown in the first picture. This will be for a set screw, after you finish dry-fitting the fulcrum together.
  2. Place a square at the end of the 5 foot beam. Dry-fit the pieces together. The shorter pieces should be flush with the center 5 foot beam.
  3. Screw a scrap piece of wood to all three pieces of the beam to help hold the legs in place.
  4. Screw the 4 inch set screws into the holes you pre-drilled.

Step 3: Final Assembly

  1. Using the auger bit, pre-drill three holes for the lag screws in each leg in a triangle pattern. Note, try to aim the bit so that your screws from each side of the fulcrum don’t run into each other. The holes should go at minimum 2 to 3 inches through the center 5 foot beam.
  2. If your drill can muster it, save some time and drill the lag screws in as far as you can then finish the job with the socket wrench and the handle extender. The shorter lag screws go in at the short end of the junction. The log lag screws go in lower, where there is more material to go through.
  3. Finally move the 1"x4"x4' to the bottom of the fulcrum, maybe three inches from the bottom. Then cut the excess off.
  4. Remove the temporary scrap piece of wood you used during the dry fit process.

Comments

author
asred made it!(author)2016-04-24

I'm no mechanical engineer, but this was the only thing that worked after several other methods. Tuns out that the post footings were mushroomed at the bottom. A bit over kill, but apparently that's code around these parts. I digress. . . My point is that even if it doesn't multiply the force it applied it in the right way. Plus it allowed me to use a truck to pull the posts out. :)

Cheers.

author
TomV4 made it!(author)2016-04-24

Good work, asred!

author
TomV4 made it!(author)2016-04-23

This certainly is a useful tool, but it is not providing the mechanical advantage of a lever as much as changing the direction of the force like a pulley. And I don't see that it is multiplying the force either. A fulcrum is more of a stationary pivot point for a rigid lever. Don't misunderstand, this is great and clever work. And your generosity in sharing is very much appreciated.

author
jccruzh made it!(author)2016-04-23

Sorry but I don't agree with you it can be force multiplier or a force divider depending on how you use it. the force is a function of cos of the slope so at 45 deg you're ritgh but at 60 deg you are having a factor multipier of 2. I have lifted very heavy load using 70 or 80 deg.

author
TomV4 made it!(author)2016-04-24

Oh, I see how that works now. I was thinking the intent was for the chain to somehow pass over the fulcrum arm, but the chain is fixed there. And I see how the force multiplier could be equal to the tangent of the angle formed by the fulcrum arm with the ground. Thanks for setting me back on track.

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