Making a Wood Frame

ridley_2004June 2, 2008


I wanted to make a wood frame for a mirror for my bathroom. I purchased chair rail molding that I like and mitered cut the corners (45 degrees) using a compound miter saw.

The measurements were suppose to be 25.5" long and 21.5" wide. But I ended up with a gap in the bottom piece when I put the pieces together. The bottom piece seems to be off by 1/4" from the top but the top is square and has a tight fit.

What am I doing wrong?

Also, how do you mark your wood at a 45 degree angle as a cutting guide?

Thanks. Patty

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The measurement needs to be made at the inside corner of the chair rail---where the corner of the mirror sets. There is a formula for figuring the width of the molding and marking for the cut on the outside of the molding, but I keep forgetting that, so simply make the cut mark on the inside. I cut the molding upside down if it is flat enough---if not, I use an adjustable combination square to make a 45 degree line(across the mark I made on the inside in the correct direction of cut. I then use the 90 degree side to continue the longest end of the miter line across the outside---and make the corresponding 45 degree mark on the top---then cut just outside that line.

    Bookmark   June 2, 2008 at 8:06PM
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Handymac, if the angles are 45 degrees then the length on the outside edge would be the length of the inside edge plus twice the width of the molding. Is that the formula you're thinking of?

Patty, have you put the matching pieces (top and bottom, right and left) back to back against each other to see whether they are the same length? If they aren't then better measuring and cutting technique would be the answer to your problem.

It could also be, however, that the 45 degree detent on the saw is off a bit. An error of only a fraction of a degree could easily create a 1/4" gap over the 4 joints and nearly 8 feet of molding you're dealing with. If you've got the top assembled to the two sides, then measure the distance across the frame at the top and bottom to see whether the sides are parallel.

The last possibility is that one or more sections of the frame are warped, making the outer edge(s) concave and throwing off the angle of the miter cut even though it might seem correct right at the joint.

    Bookmark   June 3, 2008 at 7:01AM
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It is really hard for the novice to get perfect results in a job like this. Even slight errors in measurements and angles can cause all kinds of problems. As can a wall not being perfectly flat. The good news is that you probably have a bit of a "fudge factor" because the moulding overlaps the mirror. Nobody is going to know if overlaps by a 1/4" on one side and 3/8" on the other side.

The first step is to ensure you miter saw is dead on -- use an inexpensive combination square that is available at any hardware store to check.

Rather than trying to measure, mark whenever possible and cut everything a bit long and work back until you have it right. Start with one edge and get that piece right. Since you have an overlap, the short edge of the mitered piece will be somewhat less in length than the mirror. That number is kind of arbitrary but just cut it long and keep working back until you get where you want it. Once you're happy with that piece, cut the opposite piece using the first one to mark the second one. Again, go slow cutting the second piece until it matches the first piece.

Tack those pieces on the wall using a couple of small nails. You may want to pre-drill to avoid splitting. Make sure their overlap matches and they are exactly parallel. Then mark the other two side by flipping those piece over and marking the outside edge of the in-place pieces. Those marks will be the length of the outside of the miter. Again, go slow and creep up on your final dimension. It's better to make another cut than try to glue sawdust back on your piece.

That should get you pretty darn close -- enough for wood putty or caulk.

Of course, all of this presumes your mirror is square. Might want to check that first.

    Bookmark   June 3, 2008 at 7:38AM
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I get better miter joints using the table saw w/ crosscut sled. The table saw has less blade wobble.

To check the cutting angle, whether it is a 45 or a 90, make a test cut on a scrap piece and flip one side over and put the two halves back to back to verify if the angles are equal. Any error will be twice as evident. Also check for the bevel- that the blade is plumb vertically. Use a thick test piece for that.

    Bookmark   June 3, 2008 at 11:59AM
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My Dewalt miter saw has a blade that wabbles. Why is that? I have checked to make sure it is secure. Aidan M, I agree with your comments about miters on the table saw.

    Bookmark   June 10, 2008 at 11:04PM
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The slide arm wobbles. You can lock it in place to cut down on wobble if you aren't cutting very wide stock.

    Bookmark   June 11, 2008 at 1:22PM
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