Saturday, December 3, 2011

My Shop-Made Tool Sharpener

I mentioned that I made my own sharpening system a few weeks ago on the Woodcarving Illustrated forum and was inundated with questions about it.  I thought that I might take some time and share it with you.  Here’s a photo of the overall sharpening unit.

First of all, let me say, I made this as a prototype with the materials that I had lying around my workshop, so it's not as pretty and polished as it could be.  I built the box out of scrap 3/4" MDF and the front from a piece of 1/4" underlayment, all held together with wood screws and no glue so that I can open it up for maintenance.  I really made it as an experiment to see if it could be done and it worked so well that I never got around to making the finished product.  Let's take a look at the parts.

Here's the meat and potatoes of the sharpener.  I went to my local thrift shop looking for a motor that I could use for this project.  I found a foot massager that had a DC motor in it that looked like it would have enough power to get the job done for about $8.00.  After stealing the motor, AC to DC transforming circuit, belt, bearings, and pulley with spindle, I mounted them in the configuration that you see here.  The spindle protrudes through the top table of the unit to give me a place to mount my sharpening disks.  It's not very technical, I just adapted the equipment that I found.  I also used the power chord and wiring from the foot massager too.  Now that I have the mechanical system in place, I needed to add some controls.

Here's the front face showing the sharpener's controls.  As the prototype developed, I kept asking myself questions like, "what if I did this?" and, "I wonder if this would work."  I started with a simple on/off switch, the toggle switch in the upper right corner for about $3.00.  I wired in the switch and gave the unit a test run.  It spun around in a circle just like I though it would, which was very encouraging.  In retrospect, the original on/off switch is redundant after adding the additional controls. So, if you decide to try your own version, you can skip this switch.
Now the questions started coming into my head.  I wondered if I could switch the direction of spin.  With a DC motor, if you switch the polarity to the motor, you change the direction in which it rotates. 
Tip from the Stump:  You have to use a DC motor for this to work.  Switching the polarity on an AC motor will not change the direction of spin.  It's just the nature of Alternating Current power.
After a trip the local hardware store, I returned with a switch called an on/off/on, the toggle switch in the lower right corner, which I purchased for about $5.00.  After a little head scratching and testing with my multimeter, I wired the switch in place and fired the unit up again.  SUCCESS!!!  Flip the switch to the right, the motor spins counterclockwise.  Flip the switch to the left, the motor spins clockwise.  Now I can sharpen both sides of a knife without any trouble.
Next, I really wanted to be able to control the speed at which the motor turned.  After another trip to the store, and another $5.00, I returned with a dimmer switch used for lighting.  The dimmer switch changes the resistance and effectively the current and voltage to the motor.  I squeezed the dimmer into the the box and wired it in place.  SUCCESS AGAIN!!!  I was on a roll.  It worked perfectly.  Here are a couple of photos of the "guts" of the sharpener.  The first picture shows the switches wired in place.  The second shows the AC to DC circuit board that I used from the foot massager.  It looks kind of complicated, but it really wasn't too bad.

With the unit working, it was time to mount the sharpening disks.

Here's a picture of the mounting disk.  I cut this mounting disks and all of my abrasive disks out of a piece of melamine shelving that I picked up from the hardware store for about $10.00.  Melamine is nice and flat, smooth, and very stable, all the characteristic that I was looking for in my sanding disks.  Using my circle cutting jig that I built for my band saw, I cut out 5 inch disks and, using my disk sander and another jig, I trued them up so that they would spin without vibrating.  They aren't perfect, but the vibration is minimal.  The two pins sticking up from the disk are finishing nails and are for mounting the abrasive disks which I'll show you in the next photo.  A little 5 minute epoxy, and the mounting disk is fastened to the spindle below.

This is the bottom of one of my abrasive disks.  The Left and Right holes are drilled to accept the mounting pins from the mounting disk below.  It's a primitive, yet extremely effective method for mounting and interchanging disks as I progress through the sharpening process.

Here are my abrasive disks all lined out.  I cut circles out of progressively finer grit sand paper ranging from 150 to 1500.  The sandpaper costs around $1.25 per sheet for the good-grade wet/dry paper.  To attach the paper to the disks, I simply use rubber cement, the kind you used back in grade school.  It holds the paper in place, and is easy to remove when it's time to change out the paper for a new piece.  The last disk is my strop.  Using an old piece of leather that I had lying around from recent craft projects, I used rubber cement to attach it to a disk, smooth side of the leather down.  After charging it with stropping compound, it's ready to go.

This last photographs shows the stropping disk mounted in place.  The finishing touch was to attach a dowel to the unit to give me a place to wind up the chord when it's not in use.

There you have it.  The shop-made tool sharpener that I build for about $30.00.  It works great!!!  I've sharpened a bunch of my custom knives with it and it just keeps on going.  I think it works just as well as the commercial sharpeners that you might spend $200 to $300 and offers extra controls that they may not.  Not too bad for $30.00 and a lazy afternoon in the workshop.

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