Instructables
Picture of 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.
 
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Step 1: An overview image

Picture of 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.

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

Step 2: First steps

Picture of 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

Picture of 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.

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!!

Phil B (author)  judee.norton28 days ago
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.
Creativeman2 years ago
Good job, as usual! I see you are on 222, and way over 2M views! Wow, you are a busy man!
Phil B (author)  Creativeman2 years ago
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!
Phil B (author)  Hiyadudez2 years ago
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.
Phil B (author)  Lutzboater2 years ago
Thanks. I hope itt is useful to someone.
shazni2 years ago
Is the hole positioned to clamp?...what is the purpose of the hole?
Phil B (author)  shazni2 years ago
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.
stroland Phil B2 years ago
Great idea Phil, let us know how it turns out in use.
John
Phil B (author)  stroland2 years ago
My daughter-in-law sent a photo of the baseboard corner the dog chewed. I looked all over the Internet and in one of the big box home repair stores. Nowhere can I find baseboard molding like what they have. If I cannot find replacement molding, there is no point in ripping out what is there. The damage is not too extensive. I am planning on building it up with wood putty, then filing and sanding it as many times as necessary, then painting it and calling it good. So, after all of the effort to plan and make my miter box, I am not planning to take it on the trip to my son's house. Still, it was a fun project and someone else may be able to use the idea. I may even be able to use the miter box in the future.
stroland Phil B2 years ago
Any chance you could make a replacement piece? I have used "scratch-stock" but it was a small, simple piece. I have also used epoxy putty because it was in a wet environment. I realize your piece is not in that type of locale.
I continue to use epoxy because my only attempt to use wood putty did not turn out nearly as well as with the epoxy. In fact I just completed a repair on a tombstone vase. Half of the bottom piece was missing and I made it by using a file since it was much too heavy to mount on a lathe. It actually turned out well. I should have taken pictures.
Phil B (author)  stroland2 years ago
Thank you for the idea.
Phil B (author)  stroland2 years ago
In a couple of days we will be driving to our son's house where I plan to use this miter box. I may be able to post about how things worked right away. If not, it will be about ten days from now before I will be able to tell how things went.
Goodluck Phil B2 years ago
You need a smaller C-clamp! A 'quick grip' type clamp could be turned over with the bar portion down. Or drill another hole where a clamp you have will work.
rimar20002 years ago
Great work, Phil, you publish always useful things.
Phil B (author)  rimar20002 years ago
Thank you, Osvaldo. I expect it will require a little practice to learn to use well, but, I think the basic principles are trustworthy.
Bill WW2 years ago
Nice project, Phil, thanks.

Couple of questions:
What software did you use for the overview image?
How do you see to cut to a precise line, as you need to do when cutting moulding?

I have a neat hand miter saw that I found in the trash and rebuilt. Would be glad to make it available to you, especially if your son's houste is an hour drive north of your shop.
Phil B (author)  Bill WW2 years ago
Bill,

The overview image was done in Google Sketch-Up. If you have not used it, it is free and there are quite a number of video tutorials. I do not use it enough to learn and remember more than a few very, very basic things.

I can turn the miter box upside down so I can match cut marks scored on the molding with the path the saw blade will follow. I can also shine a flashlight through the opening made by the blade to align the marks on the molding. And, I could cut the molding a quarter inch or so long, turn the miter box over and compare the mark on the molding with the actual cut, then move the molding slightly, clamp it, and make the final cut.

I am sure there are little modifications I will make after more experience using it. I am already thinking of a couple of ways to support the end of the molding near the saw blade. One would be a pedestal that would elevate the miter box a small fraction of an inch. It would be just enough to support the end of the molding by the weight of the miter box. I have also thought about a 1/2 inch dowel that would cross between the sides of the miter box near the end to be cut. I would use a thin shim or two between the dowel and the molding to make the molding secure.

We will be driving to my son's house in Idaho on Friday. Thank you for the offer of a traditional miter box. I actually need two pieces of molding to make a total length of six or seven inches. For that I will likely need to buy an eight foot piece, so I can make quite a few mistakes until I get it right.
Bill WW Phil B2 years ago
Thanks Phil. I have seen some other great Sketchup drawings here. I tried it once, years aro, guess I should get back to it.

Don't know how much you are into woodworking, you might check this Instructable (of mine) on sharpening http://www.instructables.com/id/How-to-sharpen-your-woodworking-tools-with-sandpap/
Phil B (author)  Bill WW2 years ago
Thanks. I looked at your Instructable and left a comment, as well as a rating.
Great job phil 5 stars!!!
Phil B (author)  coolbeansbaby682 years ago
Thanks, Jim. Thank you for looking.
Goodluck2 years ago
Love this, even though I have a miter saw. I need to make one to cut scarfs in long pieces of lumber and a miter saw doesn't get to that angle (~7º relative to the fence).

Both sides of your workpiece should turn out fairly smooth since it is well supported by the "zero clearance" slot through the box.

One last thing, marking the angle you want to cut is great advice. I have cut many, many unmarked pieces in the wrong direction.
Phil B (author)  Goodluck2 years ago
A smaller "C" clamp is certainly an option. In my response to BillWW I mentioned a couple of things I am also considering to be certain the end of the molding near the saw blade does not move. I may also cut more holes with a hole saw so I have more options on where to place a "C" clamp.

Not only are the cuts smooth, especially with a 40 tooth carbide tipped blade, but pushing the saw slowly will make for a smoother and better cut.

I have had the same problem you mentioned. I get confused and cut my last, barely long enough, piece in the wrong direction. I always mark the cuts on miters to reduce greatly the number of times I cut the wrong way.

I think you could make a version of this miter box that does not tilt the saw away from its normal 90 degree cut, but uses a fence designed to hold the work vertically on the work piece's edge and the fence is at an angle of about 7 degrees relative to the cut line of the saw. The saw would ride over the top of the fence with guides to keep it cutting in a straight line. The width of the piece to be cut would be limited by the depth of cut offered by the blade. I can try to make a graphic if this is not clear.
Goodluck Phil B2 years ago
I was thinking the fence would be oriented ~7º relative to the workpiece and the saw's foot would slide along as yours does. The foot would be set 90º to the blade.

We're probably saying the same thing, just using different words. Po-tay-to, po-tah-to.