Introduction: CNC Wooden Magnifier With Extreme Battery Life

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I have a commercially-made magnifying glass with LED illumination, but it's not bright enough and it eats batteries.  So I made a new magnifying glass that fixes those problems.

This is sort of a sequel to my Instructable: https://www.instructables.com/id/Ultra-Bright-24-LED-Lighted-Magnifier/  That Instructable described a lighted magnifier that runs on AC power, to get maximum brightness without worrying about charging or changing batteries.  I use that magnifier all the time.  In fact, I've made three of them, and keep one in each of my work areas.  But sometimes I really need the portability of a battery-powered magnifier.

This new magnifying glass has a bright array of 15 LEDs producing 37500 mcd.  It has an optical glass lens with about 3.5x magnification.   The handle was made on a CNC machine from European beech hardwood.

And it has a power supply using four lithium cells to provide years and years of regular use without having to think about the batteries!  (If I use it every other day, keeping the light on for a full minute every time I use it, the batteries will last more than six years.)

I made it at TechShop.  http://techshop.ws/

Step 1: Tools and Materials

This project uses a ring-shaped LED array which is marketed for use as an accent light on automobiles.  It's a circuit board 60mm in diameter  with 15 surface mount LEDs on one side and current limiting resistors on the other side.  I used Natural White, but they're available in Cool White and Warm White if you prefer.

The lens was an "experimental grade" lens to keep the cost moderate.  I chose a focal length of 141mm, which yields about 3.5x magnification.  You can select a lens to give you more or less magnification, but if you get much higher than 5x, the spherical distortion will start to be a problem.

The battery pack consists of a PCB (which you'll make yourself) and four individual battery holders.  No one seems to make an off-the-shelf 4-cell CR123 holder.  The PCB also keeps the wiring simple.


This project requires the following parts and materials:
You'll need the following tools:
  •  ShopBot (or other) CNC router
  •  appropriate CAM software
  •  router bits or end mills  (I used 1/8" and 1/4")
  •  drill press
  •  drill bits: #60, 1/16", 5/64", 5/32" and 1/4"
  •  medium Phillips head screwdriver
  •  soldering iron and solder
  •  sandpaper (150, 220 and 320 grits)

Step 2: Make the Wooden Handle

I made the housing / handle for the magnifier with a ShopBot CNC router.   The attached zip file includes the vectors in Corel Draw and .eps formats.  The drawing on this page (also in the zip file) gives the depths of the cuts.  These depths are for wood that is 3/4" (0.745 actual) in thickness.  I was initially going to make this project out of pine, but since it was small and wouldn't consume much wood, I decided to splurge a little and use nicer wood.  I found a piece of European beech about 5" x 19" that worked nicely.  All cutting can be done from one side; there is no need to flip the material.

After cutting, sand off any tabs you added during the CAM process.  Try the fit of your lens and of your LED ring.  If either is too tight, sand the interior a bit.   Then sand the top edge of the case and the bottom edge of the battery cover to round them into a comfortable shape.  You could also use a router with a 1/8" round over bit, but I didn't find it necessary.  I did most of the shaping with 150 grit sandpaper and a sanding block, switching to 220 grit as I got close to the shape I wanted.  Also slightly round the inside top edge of the hole where you'll be looking through the lens.

Drill a hole for the switch in the side of the handle.  My switch took a 1/4 inch hole, but yours may be different.  You also need to drill holes for the screws which will hold the battery cover in place.  Start by measuring, marking and drilling the holes in the cover, using a 1/16" drill bit.  You can drill from the inside of the cover to make measurements easier.  Now align the cover exactly with the upper portion of the handle, and fasten them firmly together with clamps or a few laps of masking tape.  Using the holes in the cover as a guide, drill pilot holes about 1/2" deep into the handle.  Separate the parts again, and enlarge the holes in the cover to 5/64".  Finally, use a 5/32" bit to countersink the holes so the screw heads will be below the surface.

Now sand the whole exterior as appropriate for your wood finishing technique.  I was using polyurethane, so I just sanded it with 220 grit.  I applied three coats of polyurethane, sanding lightly between coats with 320 grit sandpaper. Do not finish the the interior of the rings where the LED and lens will be attached.  It's also not necessary to finish the interior of the battery compartment.

Attachments

Step 3: Make the Battery Holder

The battery holder requires a printed circuit board.  If you are not familiar with making a PCB, many good Instructables are available on the subject.

I sketched this using an old DOS-era PCB tool.  I have not included the file because the software is no longer available and the file format is proprietary.  However, the design is extremely simple.  This board could be made by drawing the traces with a Sharpie; rendering it with a CAD tool is not really necessary.  Here's an image of the PCB traces as seen from the top OR from the bottom of the board... it doesn't make any difference! 

Using your favorite tools and process, lay out and etch the board.  The PCB exterior dimensions are 1.5" x 3.75". 

Drill all holes with a #60 drill bit.  Insert and solder the four battery connectors, making sure to observe polarity.   The pictures in the next step show the correct battery arrangement.

Step 4: Final Assembly

The handle is designed so that you can assemble everything separately, then install the whole "guts" into the housing.

Mount the lens into the handle.  To do this, apply a thin film of catalyzed epoxy glue to the interior walls of the handle where the lens fits.  Then press the lens into place, being careful not to get any epoxy on the top or bottom surfaces of the lens.  (If a little epoxy does get on the lens, remove it promptly with 99% isopropyl alcohol.) Leave the handle & lens assembly undisturbed while the epoxy hardens.

The LED array comes with wires attached.  However, the LEDs will be installed with adhesive foam tape, so getting this thing apart for repairs would be difficult.  Therefore, I de-soldered the original wires and replaced them with some thicker gauge wire.  I also tacked the wires to the underside of the LED circuit board with silicone adhesive, for strain relief.  Keep track of which lead is the negative one, and which is the positive.

Solder wire to each of the switch terminals.  If you are using a SPDT switch, be sure to use the normally open set of contacts.  Apply a small piece of shrink tubing over each soldered terminal.  The polarity of the leads does not make any difference in this case.

Measure the wire lengths by holding the components up to the case.  Cut, strip and tin the LED and switch wires.  Then solder to the PCB, and trim all leads short on the bottom of the PCB.  You can now install the batteries and test the LEDs.  If they do not light, examine all connections.  The likeliest error would have been to swap the LED leads.

Cut four small pieces of double-sided foam tape, and attach them to the underside of the LED array, on the areas of the board between the surface mount resistors.  Then mount the LEDs into the handle.  Install the switch using appropriate washer and nut, and tighten the nut securely.  Finally, using more double-sided foam tape, mount the battery assembly securely into the handle.

Attach the battery cover with two #2 screws.

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