A Miter Box for a Circular Saw





Introduction: A Miter Box for a Circular Saw

I need to replace some baseboard trim in my son's house a day's drive from my workshop. I do not have a miter box, but I do have a pretty good circular saw. 

The photo shows the miter box I made for my circular saw. In the photo I am testing it with some 1 x 2 furring strip. In use the saw slides across a table with the saw shoe against a fence. See the next step for a Google Sketch-Up view of the miter box.

Step 1: An Overview Image

The miter box is an inverted "U" made from 1/2 inch plywood.  The wider section toward the upper left of the graphic is the table on which the saw slides. The narrower piece on it is the fence to guide the circular saw. The hole in the side was conceived as a place to insert a "C" clamp, but is too close to the saw. It works well for holding the molding while clamping it in place from the end of the miter box near the lower right corner of the graphic.

  • 1/2 inch plywood
  • Finish nails
  • Glue
  • Screws
  • Table saw
  • Rule
  • Square
  • Hammer
  • "C" clamps
  • Hole saw

Step 2: First Steps

I made two pieces of plywood cut to 5 x 24 inches. In the photo a third piece of plywood 5 x 12 inches is being glued to one of the pieces 5 x 24 inches. The finish nails hold the pieces in place until the glue can dry. The other piece 5 x 24 will be glued and nailed in place to form the "U" box.

Step 3: Add the Table

Cut and glue a piece of plywood 12 x 12 inches over the open portion of the "U" box. This will be the table on which the saw moves.

Step 4: Add the Fence

I used a square with longer legs to make a reference line on the table portion. Then I used a rule to measure so I could position the fence where the edge of the saw's base plate or shoe will be. After attaching the fence with "C" clamps, I used two screws to fasten the fence to the table portion.

Step 5: Establish the Cut Line

As soon as the miter box was ready I set the saw to 45 degrees and made a cut across the table. This will aid in positioning pieces of molding for cutting. (I had not yet cut a hole with the hole saw.) 

Step 6: Test

I am using two pieces of furring strip lumber. It is relatively straight. The "X" mark on each represents the top of a piece of molding for cuts that need to be a mirror opposite of each other, and not the same cut made twice, then flipped over. The pencil lines indicate roughly where the cuts will be to make a mitered corner.

Step 7: Making the Cuts

The photo shows one of the furring strips clamped in place for cutting. The end has been pulled into the miter box far enough that the saw will cut through it without removing too much and without failing to cut enough. The "C" clamp is enough to hold the furring strip snugly enough. I paid attention to the pencil marks from the previous step so the saw cut follows them and I do not make a cut the opposite of what I intended. When the first piece was cut, I inserted and clamped the second piece for its cut.

If need be, I could insert a piece of molding from the opposite end of the miter box, although I do not yet have a clamping system worked out for that arrangement. As it is, the finished side of the molding will be facing downward. That means the cut will be cleaner because the teeth of the saw blade will cut the finished surface of the molding as the teeth enter the molding, not as they exit it.

Step 8: The Result

It is a little difficult to hold two pieces inside a square and take a photo, but you can see the miter cuts make a tight corner.

I did discover the click stop on my saw's tilt setting is not quite as accurate as I would like. When I travel to my son's house to replace the two pieces of molding damaged by a young dog chewing on them, I will take these furring strips along to make some test cuts before cutting the actual molding. 



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I am female, 65 years old, single, and in the process of remodelling a very old mobile home I got for a song. My projects are endless---today, I I had planned to frame my bathroom window. After determining that I CANNOT "eyeball" a mitered corner (lol, wish I could post the results so everyone could have a good laugh), I had the brilliant idea of building my own miter box, but no clue how to do so. I googled it, saw this, built this and my window is perfect! Now I'm seeking out projects that need corners! Very good job explaining and showing just how (and why) it was done; I am pleased and proud of my work! Thank you so much!!

Wow! I intended to use mine, but did what I needed to do another way. You actually did it. I am pleased it worked for you. Sooner or later a cut will be just a tiny amount off and the miter will not be as perfect, perhaps because corners on walls are not always exactly square. For times like that, you may find this very useful.

Good job, as usual! I see you are on 222, and way over 2M views! Wow, you are a busy man!

I retired in June and my wife has a few "honey-do" jobs for me. If something requires unusual problem solving, it has a good chance of becoming an Instructable. Thank you for looking.

I would love to be retired and just build cool things all the time. Too bad I'm only 16 :-(

Awesome job on this though!

Retirement will come sooner than you think. I remember being 16 and anxious to be 18 or 21. The older you get, the faster time seems to pass.

Time is like the toilet paper roll: the closer it gets to the end, the faster it goes. Nice project.

Thanks. I hope itt is useful to someone.

Is the hole positioned to clamp?...what is the purpose of the hole?

Originally, I intended the hole to accommodate a "C" clamp for holding the molding in place, but I made the hole without measuring and the clamp would be in the way of the saw. The hole is handy for supporting the piece of molding until I can get the "C" clamp on it as shown in the introductory photo. I may experiment with grasping the molding with my fingers to support the end near the blade when cutting. The blade is far enough away that it is not physically possible to get my fingers near to the blade. Thank you for looking and for your comment.