When I first got my printrbot simple, I used a lazy susan from the kitchen to hold my filament. This worked exactly as poorly as it sounds like it would. Lacking access to a laser cutter to make a wooden one or the money to buy a spool stand, I improvised one with the only building material I had: K'Nex. This is made with only red and yellow sticks, and purple, white, and red connectors. The structure itself doesn't have any wheels or axles, but the spool spins freely on the bar at the top.

This works for my Pet + filament spool, in the tall skinny spools with the big hole. If you have matterhackers filament, or other filament in wide spools with small holes, skip step 6 or use my other instructable.

Step 1: Parts List

That is:
28 yellow bars
18 red bars (there's only 17 in the picture but you need all 18
8 white connector wheels
16 purple cutout semi-circle connectors, but the blue slotted wheels will work too for all but the pairs on the bottom
2 red right angle connectors

Step 2: Bottom

Use four pairs of purple slotted connectors, one white connector, four yellow bars, and four red bars.
Put all the slotted pieces into pairs, then put four pairs in a square as shown. Use the red bars to connect them, then connect four yellow bars to the white wheel in a plus configuration and put the ends in the corner piece.

Step 3: Building Up the Cube

Use the assembly from the previous step, four pairs of purple or blue slotted connectors, two white connectors, eight yellow bars, and two red bars. Also use eight yellow bars, two red right angle connectors, and one white connector in preparation for the next step.
Insert four red bars sticking straight up out of the corner of the square you made in the last step and place the four new slotted pairs on the tops of the bars so that each is along the plane of the adjacent side of the cube (like in the first picture). Another way to say this is that the axis will be vertical and oriented so that you could make a square parallel to the one at the bottom. This is different to how they were aligned on the bottom face of the cube. Connect four yellow sticks to a white circle at right angles to make a plus sign, then do the same on the other white circle. Put these on any two opposite faces of the cube so that each connects to two red verticle bars, then use two new red bar to go across the top of the two other faces. If this is confusing for you, look at the pictures for this step and recreate what you see in them.
Connect two yellow sticks at 90 degrees using a red connector piece, and make another plus sign with a white wheel and four yellow bars in preparation for the next step.

Step 4: Reinforcing the Base

For this step, you need the right angle pieces you made in the last step, the plus sign you made in the last step, and the cube that you've been making this entire time.
Attach the two right angle pieces you made in the last step underneath the red bars. Snap the yellow bars into the two red connectors you just put on and the white connectors that have been there this whole time. This is a different type of connection than we've used in the other steps. The bar hits the connector at a right angle (it is normal to the plane formed by the connector) instead of laying flat and the connection is somewhere in the middle of the bar instead of at the ends like in all the other connections we've made. If you've never done this before, it takes a lot of force and feels like you're going to break the connector, so try on another connector using a hard surface first to get a feel for it. It should look like the picture when you're done, with the red pars poking out a little on all four faces and the white connector barely higher than the center of the cube.

Step 5: Making Two Halves of the Axle

For this step eight red bars and four white connectors. You won't need anything that you've built up to this point.
This part may make your fingers hurt, but having a hard surface to press against may help. Snap four red bars into two of the wheels so that there is a space on the wheel between each bar and each red bar is connected to both white wheels. It helps if you do this one bar at a time, connecting each to both white wheels before putting on the next. Make one more like this. On each, one wheel should be right at the end of the bars and the other should be a little more than an inch from the end of the red bars, like in the picture.

If you have a spool with a small hole, like matterhackers filament comes on, skip the next step.

Step 6: Connecting the Axle

For this step, you need four yellow bars and the two halves of the axle you made in the previous picture.
Line the two halves up so that the wheels at the very end of the bars on each one are next to each other and the empty spaces on the white connectors are lined up. Snap the yellow bars into these two wheels to connect them. It's easiest if you do it one at a time, and connect the yellow bars near the end instead of near the middle. When that's done push in the red bars one at a time so they meet in the middle, keeping the wheels as far apart as possible. See the last picture for how it should end up. This makes it so that the wheels are on each side of the spool which is better balanced than both underneath or one on the side and one underneath.

Step 7: Attaching the Axle

For this step you need all the pieces you made before and the last four yellow bars.

If you have a spool with a big hole:

Put four yellow bars on the outside wheels and connect them to the big cube's purple corner connectors directly above the red bars. This way, the spool won't hit the red bars when it's on the axle. You can take off one pair of the yellow bars and slide the spool onto the axle to load it.

For a spool with a small hole that the gears won't fit into:

Use the two halves of the axle that you made before, and connect it to the base as shown in the fourth and fifth picture. The loose ends of the red bars will be inside the spool and support it. You could push them farther out and use the orange straight connectors, but the way I did it there will be eight bars inside the spool supporting it and it won't bend as easily. To attach the spool, only attach one of the half axles, put the spool on, then slide the other axle inside and attach it to the base.

Make sure that the filament is coming off the top of the spool when you load it. This makes it easier for your 3d printer to pull. It's at a really good height for my printrbot simple, but if you want it taller, you can always scale up by using the next size bars. Happy printing!