I am building a bed frame. Like a fool, I thought 2 x 4 lumber was actually 2 x 4 inches. Now I have a gap that is .5 inches too wide on either side of my frame. I'm wondering if there is a good fix for this without reordering more boards.
It is not feasible to sand down a wooden member by a whole half of an inch.
- If something is too long then cut off the additional half inch using a saw.
- If something is too thick (wide) by the half inch then rip saw off that extra thickness or use a planer to remove it.
- If you cut something too short you will have to go get a replacement piece and re-cut that to the proper length.
You have learned a valuable lesson here. Plan out everything in advance carefully by making sure you understand what is needed and materials are available.
A picture would help, but I believe that you're planning on putting your 2x4 somewhere that you now need a full 2" or 4" to fill.
I'm not sure where sanding comes into play here, but yes, you absolutely could sand a 1/2" off of a piece of wood. It will take some time with a belt sander and even more time if you're doing it by hand. (On the bright side, you'll build a good bicep that way!) You may run into issues with keeping the newly sanded face exactly parallel to the non-sanded face, though, so keep that in mind. Marking your desired width on two opposing faces of the board and sanding the down to that line on each face should do the trick.
Since you mention "ordering" more wood, consider going to (or calling) a local lumber mill or woodworker's lumber supply house (not your local big-box hardware store) and tell them what you need. Since you're just using SPF lumber, they might be able to mill up an actual 2"x4" out of something inexpensive.
If you're simply looking to fill a 4" gap, you may consider buying a 2x6 (1-1/2 x 5-1/2) and ripping that along its length to your desired 4" actual measurement. This won't help much if you're looking to fill a 2" gap, however.
Another option, which will involve disassembly, is to run the 2x4 thru a table saw to remove the extra 1/2". A 10" table saw won't be able to do this in one pass as the blade doesn't rise far enough to cut thru 4", but flipping the board and doing a second pass isn't too inconvenient.