Simple Box Bottoms
How to Make Box Bottoms
In this article I’ll go over my process for making bottoms to fit into wooden boxes or cabinet drawers. There are multiple ways to tackle this process so don’t be intimated by a particular part of the process or a certain tool. I’m hoping this can serve as a guide to help you to build some really nice boxes of your own.
Prep Your Materials
Since we’re talking about box bottoms, it stands to reason that we need sides first. I often like to use mitered corners for my boxes so that’s what you’ll see in my example. While, I won’t go over exactly how to cut miters, you can check out my previous blog article on getting perfect miter joints and then come back to see how to add the bottom. My box is approximately 10” square (outside dimensions). The sides are approximately 1/2” thick. I know that I’ll need a bottom that’s at least 9” square. I like to start with a board that’s a little bit longer and wider than I need. I can always cut parts off, but it’s pain to put boards back together! I took a board that’s about 10” square and milled it down to around 3/8” of an inch thick. I find that I like my bottoms between 1/4 - 3/8” thick for most boxes. If the box is super small or really large then I may go thinner or thicker. This is completely subjective. If you don’t have milling tools like a planner, you can typically buy wood in different thicknesses. You may have to do some online shopping to find a place that sells boards pre-milled, but I know I’ve personally done it. After my board is to the desired thickness, I sand it using 120 grit and then 180 grit sandpaper. I do this before cutting the grooves to hold the box bottom.
Ideally, when I put the box together, the bottom will be thick enough that it doesn’t sound thin. If you don’t know what I mean, take a box or drawer and tap your finger on the bottom. The thinner the bottom board the lighter to higher the sound. While the sound has little to do with the actual quality, a weighty thud sound gives the feeling of quality compared to a hollow thin sound.
Cut Grooves
I like to have my box bottoms sit inside a groove that’s cut into the side walls. There are two primary ways to do this: a table saw or a router. For boxes with miter or rabbet joints I use the table saw. For boxes with box or dovetail joints I use the router. The only real difference is that a table saw cuts a groove in the board from end to end, creating an entrance and exit point. When you put the box together, the cut that it made when the blade entered and exited the board is hidden. But if you are using dovetails or box joints then you’ll see a giant hole in your box side. That’s why I’ll use the router for those joints. With a router, I can plunge the bit into the wood, cut down the length of my board, and then stop short of exiting the board. I still get a groove without the entrance and exit points. You can see me use this plunge method in my blog article about my rosewood box.
For this example, I’m using the table saw since it’s the most common method for me. I set the height of my blade to about half the thickness of my workpiece. This is subjective. You can do deeper or shallower if you want. After the blade height is set, I move my table saw fence over so that I have about 1/8” of material from the bottom of the sides to the bottom of the box bottom.
Once my table saw fence is set, I cut a groove in all four sides. This will give you a groove that is the thickness of your blade, so in my case a 1/8” wide groove. After each side is cut, I move the fence a little closer to the blade and lock it down. I typically move mine so that it’s almost 1/8” closer, that way my next cut overlaps the previous one. Cut all four sides again. Keep doing this until you get fairly close to the box bottom fitting into the groove. Do not try to cut a groove one side at a time, repositioning the fence for each box side. It’s virtually impossible to align your table saw fence perfectly four separate times. Every time you set your fence, remember to cut all four sides before repositioning your fence for the next cut
If my box bottom is 1/4” thick then I know that I need two full width passes with my 1/8” wide blade. I always aim for cutting my groove just a bit less than what I need. Then I see if my box bottom fits into the groove. If it doesn’t, I nudge the fence closer to the blade just a hair and make another cut. Then test fit it again. This allows me to sneak up on the fit. I want a snug fit. I shouldn’t need a mallet to put the bottom into place. It should take little pressure at all. You know you have it perfect when you can insert the bottom into the groove and turn the piece upside down without the box side falling off. That’s a friction fit! Remember, once you dialed in your fence, make sure to cut all four box sides.
Cut the Bottom to Size
The bottom fits into the grooves that we cut, but we need to cut the bottom to it’s final length and width. To do this I opt for zero measuring. I honestly don’t care how long or wide the bottom is, only that it fits with a little room to spare. I take some painter’s tape and tape my box sides together. I can then use a combination square to set the depth of my groove. I make a mark on all four sides. I know that I need to cut my box bottom so that it’s within those lines. Wood expands and contracts as the humidity changes throughout the seasons. Because of this I leave a little bit of wiggle room in the form of a small gap about all four sides. I don’t cut my bottom so that it’s perfectly on the line. I cut it a little bit inside the line. If my bottom expands then it won’t break the box.
The last step is to dry assemble the entire box. Insert the bottom, assemble the sides, and clamp the whole thing together, whether that’s with tape or actual clamps. Do this before applying any glue. You want to make sure that your box assembles together and that the bottom still fits into the groove and isn’t too big. If you have a joint that won’t close the your bottom is too big; cut it a little bit and try again. If you find that your bottom isn’t fitting into one of your four sides then take some sandpaper and sand the edge (the part that sits into the groove) until it fits.
There you have it, my process for making box or drawer bottoms. As I said, there are multiple ways to do this so get creative and come up with a process that works best for you and your shop.
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