Large drinks don’t fit in my car’s cup holders. My Chevy Malibu has two convenient cup holders in the front. But not convenient enough to hold larger based cups, like a large soda/slushy. I wanted a solution that didn’t involve holding it as I drove, or sticking it in the arm rest storage (and risking it spilling). I sketched up some ideas, and this Instructable is the one I wound up building out of wood.

Some of the rejected ideas involved PVC tubing and ABS reducers. Their sizes didn’t wind up working, and were less adaptable. I considered making a 3D design, but I don't have my own 3D printer and I already had wood lying around.

Step 1: Planning, Parts, and Tools

Planning:

Measure the diameter of the existing cup holder, and its internal height. Mine was 3” wide, by 3” tall.
Measure the diameter of the desired cup you want to adapt for (or just pick a larger but reasonable diameter). And decide on a new height (similar to the existing cup holder seems reasonable). I decided on designing it to hold a cup approximately 4” wide, and to make the height 3” tall to duplicate the existing cup holder height..
Plan for the outer diameter of the enlarger to be 1” wider than the cup you wish to accommodate. I want to accommodate a 4” cup, so my finished product will be 5” wide (this gives the outer ring a 1/2" diameter)
Choose your material. I had left over cedar decking (descent moisture resistance) scraps. You may want to seal it when you’re complete to help protect from moisture.

Parts:

Wood or other suitable material
- 5/4” cedar decking or other material
- ¼” plywood
Wood glue (or glue appropriate for the chosen material)

Tools:

Circle cutter
- Suitable drill and hole saws of the required diameters
  - I originally intended to use 5", 4" and 3" hole saws
- Or an adjustable circle cutter, such as a rotary tool with a circle cutter attachment (wound up working better for my needs, and can produce a greater variety of circle sizes)
Jigsaw (optional) if cutting a square or octagon for the outer diameter of the enlarger
Sand paper or sanding block
Rotary tool with sanding bit (optional). Makes sanding the inner diameters easier.
Pencil
Measuring tape or ruler

Step 2: Construction of Insert

Cut out circles to the diameter of the existing cup holder. Based on the thickness of the material you chose, you’ll need to cut multiple circles until the total thickness of those circles is close to the internal height of the existing cup holder. If the height is less, that’s okay; just want it tall enough to prevent it from rocking or falling out of the existing cup holder when the full enlarger is in place. A little taller in height would be okay as well, but won’t look as nice as it will elevate the base of the enlarger. However, depending on the layout around you existing cup holder this may allow it to clear obstacles. Plan accordingly. I chose to use a 3” hole saw for this step. I cut out three circles from scrap pieces of 5/4” cedar (I actually cut these when I made a wine rack prototype, the 3" circles were the left over scrap). Make sure to clamp the wood in place, and proceed slow and steady. Due to the thickness being greater than what the hole saw can cut through (and to avoid tear outs), I drill half way through for each circle and then flip the board over to cut through the other half (reusing the pilot hole lines it up for you). Using a 3" hole saw will actually result in a 2 3/4" circle. Close enough for my purposes. If you want the dimensions closer, you'll need to use an adjustable circle cutter.

Lightly sand the outer diameter as needed, to smooth it out. It’s not going to be visible when in use, so as long as it fits in the existing cup holder you shouldn’t need to invest much time sanding this part.

Step 3: Construction of Enlarger Section

This will require each piece to have an inner circle cut out, as well as an outer circle. You could substitute the outer circle as a square or octagon if you find it easier or more desirable. The outer circle (or square/octagon) needs to be at least a 1” larger than the inner circle diameter of the sized cup you wish to accommodate. In my case a 5” circle. If you use a circle cutter (they typically need a center hole) cut the larger circle first, so when you cut the smaller circle you can reuse the center/pilot hole.

5/4” Cedar was a bleep to cut with the hole saw. As I learned on a recent project, my cheap power drill isn’t suitable for this use. Use a high torque, lower RPM drill if possible. Less than half way through this step, I switched to the rotary tool with circle cutter. The huge advantage to this method is more adjustability to the hole sizes. The disadvantages of this method are ensuring the bit is long enough to cut through the material thickness, needing an additional pilot hole to get the circle diameter started, and having to reposition the clamps a few times.

I proceeded to cut two 5" circles out of the cedar (it actually left me with 4 3/4" circles, but close enough). If using the circle cutter you'll need to predrill a hole along the diameter for the cutting bit to fit in, to get the cut going. I didn’t have enough scrap to cut a 3rd circle successfully, but the total height of the two circles wound up being sufficient.

Now go back and cut a smaller inner circle out of the larger circles. In my case I wanted a 4" inner circle. I adjusted the circle cutter accordingly, and reused the center pilot hole. You'll again need to predrill a hole along the diameter for the cutting big to fit in, to get the cut going.

Your end result will be rings, with the inner circle large enough to accommodate the desired cup size. It left me with a 3 7/8" inner diameter.

Sand the inner diameter as needed, to smooth it out. Your cup will make contact with the inner diameter. If the cup is paper it could be punctured or otherwise damaged by any jagged bits within the inner diameter. Sand the outer diameter as well (weather you made an outer circle, square, or octagon) as a hand/arm could make contact with it while in use; and it will be visible. (You can see in my picture, I just glossed over this step as I mostly wanted to finish the project and test it out).

Step 4: Construction of the Joining Base

This will require a circle (or optionally square or octagon) cut to the overall intended outer diameter, in my case a 4 3/4" circle; but with no inner circle cut out. This will be used as a base to adhere between the two sizes of the insert and the enlarger. I originally planned to use the same 5/4” cedar for this step, but this would have unnecessarily raised the overall height. Instead I used some scrap ¼” plywood (1/4” hardboard may possibly work as well).

I used the rotary tool circle cutter on this step, partially for the smaller pilot hole but mostly cause the tool was already setup and ready to go. Again, predrill a hole along the diameter for the cutting bit to fit in to get started.

A light sanding of the outer edge should be sufficient.

Step 5: Connecting the Insert, Enlarger, and Base

You’ll want a glue suitable for the material you chose to build with. In my case a wood glue, and I already had Gorilla brand wood glue. Check the instructions for proper application. In the case of Gorilla wood glue, apply to a clean surface and clamp in place for at least 20 minutes for the bond to set. I lightly sanded the surfaces first.

I glued the smaller 3” (2 3/4") circles together all at once, and clamped them together for 20 minutes. Wipe up any excess glue after clamping, before it dries. One or two clamps should be suitable for this size, but I went with three (the wood looked slightly warped and I wanted the finished product flush with itself).

I than glued the 5” (4 3/4") circle/rings together all at once, and clamped them together for 20 minutes. Wipe up any excess glue after clamping, before it dries. Due to the cut out inner diameter, you'll want to use three of four clamps to ensure the rings are adhered flush to one another. The rings were slightly warped as well, so I planned ahead and found positions where they were most likely to be flushed when connected.

Next I glued the ¼” thick base to the 3” circles (or whatever size you created for the insert). You may find it helpful, using a pencil, to sketch a 3” circle (or whatever size matches your insert) onto the joining base; the center point of the sketched circle should be in center of the base. You could use a compass, but I just traced around a 3” hole saw. Using a similar number of clamps from the insert step, clamp again for 20 minutes centering the 3” circles inserts to the 1/4" thick x 5" base. Wipe up any excess glue after clamping, before it dries.

Finally I glued the insert/base unit to the enlarger. Use a similar number of clamps to what you used in the enlarger (rings in my case) step. Wipe up any excess glue after clamping, before it dries. Give it another 20 minutes to dry.

Step 6: Finishing Touches

This would be a good time to apply a varnish or seal coat to protect the unit from moisture. I delayed this step until after testing. Follow the directions on the product you chose to use. I’m thinking of just using a simple spray can of clear coat. But note, in outdoor applications I've found the spray-on clear coat to be almost useless.

Step 7: Testing

We were heading to the movies the night I was wrapping up construction. Cold night, but I opted for a slushy none the less. I refilled it before heading back to the car, and gave the new cup holder enlarger a try. The cup now fits. But does it stay upright? Are you a cop? I gave it a good test :) The cup did not spill, nor fall out. Everything stayed in place as I would have hoped.

The sad/funny part follows… rather than sealing the wood, I decided to investigate buying a stainless steel insert. I couldn’t find an appropriate size for what I had built. However, I did discover that cup holder enlargers already exist and are available for purchase :(