Gas Powered Pencil Sharpener- for Students That Spend the Entire Class Sharpening a Pencil.

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Every now and then, a student will spend a big chunk of class making sure his/her pencil is SHARP. For some reason, after a particularly long day, I was vegging at my desk staring blank-eyed at my pencil sharpener. It was one of those *LIGHT-BULB!!!!* moments.

You, too, can have a gas powered pencil sharpener. All you need is a weedeater, a pencil sharpener, and a few scraps of wood and metal.

This weedeater was left in pieces after one of my students decided they didn't want to fix it. I managed to mix and match enough parts to get it running and piece this together.

Still isn't running quite right yet because the carburetor isn't correct, but it runs enough to sharpen a pencil and get real hot!

Step 1: Gather Materials

Supplies:

A running weedeater.  If you can find one that has a clutch, it would work MUCH better than the one I used!
A useable pencil sharpener
Scrap of wood to mount to
Scraps of metal for motor mounts
Screws
Misc. nuts and bolts
Duct tape.  VERY important...

Tools:

Screwdrivers for screws
Saw for wood
Metal cutting tools- snips, shears, saw, whatever
Metal punching tools- pin punch, turrent punch, knockout punch, whatever
Bolt cutters
Hacksaw
Welder
Tap and Die set

Step 2: Destroy a Perfectly Good Weed Whacker

Weedeaters are pretty simple machines.  Remove the engine and throttle from the shaft of the weedeater.  Usually there are a few pinch bolts that clamp it to the shaft.  Loosen them and slide the engine off the back. 

Inside of the shaft will be a long thin flexible rod.  Pull it straight out of the shaft and set it aside.  Careful, its greasy.

Set the shaft back in the handle, mark the shaft roughly where it sticks out of the handle, and then take it back out.  Using the hacksaw, cut the piece of shaft off.  There is a plastic bushing inside the shaft, cut through that as well!

The rest of the shaft will not be used, you can toss it in the trash or save it for the next hair-brained idea you come up with.

Set the cut piece of shaft back in the motor housing.  Take the long thin rod and slide it through the plastic busing until it seats inside the engine- make sure it is seated!  The end of this rod is squared, twist the rod a little to make sure it goes into the square hole inside the engine.

Mark the rod roughly 1/2" past the end of the shaft, then remove the rod and cut it with the bolt cutters.  The rod is made of tightly wound wires, so it may take some clean up cutting with a pair of wire cutters. 

Set the cut rod and shaft aside.

Step 3: Mount the Motor

This step can be a little more tricky. Theoretically, you don't really need to mount the motor to anything, but you need a way to hold the pencil sharpener still while the engine is running.  Find a scrap of wood that is long enough to hold the engine, handle, and sharpener.

Decide how best to mount your engine.  I built to mounts out of sheet metal, screwed them to the wood, and bolted them to existing bolts on the engine.  Every engine is going to be different, so its really up to you how to get it mounted.

Step 4: Attach the Drive Rod to the Sharpener

Here's where the welder, tap and die, and misc nuts and bolts come in.  First thing to do is to take apart a pencil sharpener.  The cap on the back by the handle needs to be pried off, then the handle comes off and the blades will pull out from the other side.

Find a die that will fit over the piece of the shaft on the back of the blades where the handle goes and thread it.  I believe I used a 5/16-20 die. 

Now the tricky part- weld the drive rod to the nut that will thread on to the blades.  My first attempt was off-center so the pencil sharpener shook pretty bad.  The second attempt went much better- I found a nut that just barely fit over the drive rod and welded it together with about 1/8" of the rod sticking out.  Then I welded the correct nut to the nut and rod.  MUCH better!

Step 5: Put It All Together.

Start with the pencil sharpener.  Grease the shaft where it goes into the housing.  Insert the blades, and screw on the drive rod.

If you havent already, mount the engine to the base.

Insert the shaft into the handle and tighten the pinch bolts.

Slide the drive rod into the shaft, again making sure the rod seats into the square hole inside.

Screw the pencil sharpener down.

PUT THE BLADE COVER BACK ON!!!  ****VERY IMPORTANT**** - put a piece of duct tape on the blade cover.  If you don't, it WILL vibrate loose, hit the blades as they are spinning, and get FLUNG clear across the shop.  Speakin' from experience here...  :)

Step 6: Fill'er Up and Let'er Rip! (and Some Safety Advice)

Gas it up and try it out! 

***PLEASE KEEP IN MIND!***  A pencil sharpener is designed to run at maybe 100 rpm's for very short periods of time... At idle the sharpener will be spinning at roughly SEVEN HUNDRED rpm on the low side, and at full throttle could be more like SEVEN THOUSAND. 

What I'm trying to say here, is safety glasses are a VERY good idea, and y'all should stay well away from the moving bits.  I've only run mine for about 30 seconds at a time, at just a little higher rpm than idle, and the base of the sharpener gets pretty warm.  Planning on adding a grease zerk to hopefully help that, but it still is a shaft spinning at a high rate of speed inside a metal sleeve- no bushing, no bearing, no nothing.