A door I'm trying to put a casing around isn't square. How best to work
out and cut the mitre angles for my top and side pieces? A large
protractor, or is there a device that fits inside interior angles (such
as inside the door frame) to measure them?
I have a device, not sure what it is called, it has a wooden handle
with a thin metal blade that folds out like a pocket knife that is
handy for finding angles, it is a pretty common tool, not hard to find.
You may encounter another problem, once you find the angles, the cuts
may not have the same face length. Unless it is horribly out of square,
it may be better to just cut the miters 45 and at least have part of it
Is that the one that has a slot down the middle of the blade? I bought
one of those in a tool-buying frenzy about ten years ago, and didn't
really know what it was for.
The trick there should be to take whatever the angle is and halve it, I
think. For example, if the angle is 92 degrees, cut each piece with an
outside angle of 46 degrees. Then the joined edges should match.
I think your tool is called a "T-Bevel". Not sure how it got its name, but
I've used one before and it helps for those angles that are only slightly
out of a square 90 degrees. Cut one piece at 45, tack it up and use the
bevel to determine the cut for the other side. I generally do the top piece
at 45 on both ends to the correct length. Then cut the 'legs', leaving them
a little longer than they need to be. They will have enough 'flex' in them
to be able to check the mitered cut, and re-cut a time or two if necessary.
Once I'm good with the miter, I cut the bottom of the leg square to the
If the jam is out more than a few degrees you are better off using a
protractor and making each cut half the total angle. That way they are the
same length on each side and the molding will line up better at the cut. A
bevel is still good for doing that.
You can use the 345 rule to check square and then use those measurements to
find the angle.
The 345 rule is, pick a corner and measure 3 inches one way, and 4 inches
the other way, and the ends of those two lines will be 5 inches IF that
corner is square. Of course you use larger numbers for larger corners (ie
multiply by 5 will mean 15, 20 and 25 inches if square).
Now if you don't get 5 inches you need to figure out the angle using the
Cosine Law. Much simpler just to use this online calculator.
The correct name is "bevel gauge". I call it an "angle guesser"
You fit it too the corner, tighten the clamp. Then all you have to do
(hah!) is bisect that angle. How to do that? I could at one time on a
planet long ago and far away explain it using geometry. Real world is
"Take a guess then make repeated cuts" with your your saw changing the
angle slightly each time until you get it right. Use scrap wood for
On Sat, 30 Dec 2006 12:41:38 -0500, Harlan Messinger
Is the top jamb level?... use a two foot level under the header jamb.
Speaking for myself. Take a four foot level to the top frame jamb and
mark each side jamb where the reveal is set (horizontal), adjust
reasonably, but keep level. Cut the normal 45 degree angles. and nail
the top casing.
Determine the reveal line at the top mark and mark a (vertical).
Measure and cut the side casing. Same 45 cut.
Doing the verticals from top down, adjust the casing a little to set
the reveal as best you can.... nail it... as you move down I take an
extra blade off at the bottom and not force the casing. If I can hold
it up, match the cuts and shoot a nail in it. I work my way down,
adjusting the reveal as necessary.
I have not failed. I've just found 10,000 ways that won't work.
Thomas A. Edison
Obviously I'm missing something. From what I see, the jambs are set
level and plumb (supposedly) by shimming them--and then they're nailed
into place. Once they're nailed, how can I shift them without taking the
Depends how many nails, and where they are placed. Sometimes you can
fine-tune reality with some hardwood blocks and a BFH. Stanley wonder bars
are great, too, if you have a solid header and jack studs to pry against.
Just how much out of square are we talking about?
If this is an interior door, I'd be inclined to rip the sucker out, and
reinstall properly. God invented Sawzalls and stubby steel-nail-cutting
blades for a reason. A couple hours work, tops. Even if you get lucky on the
trim angles, it will annoy you every time you look at it or use it. Exterior
doors are a lot harder, especially if they are trapped in brick or siding.
What I would be more concerned about, and nobody in this thread has
addressed, is why is the door out of square? Has it always been this way, or
is this a recent problem? Bad install job, or settled foundation? Does it
move around depending on time of year and weather conditions? How old is
house? I'd only be inclined to fake a non-square door on an older house with
no practical way to fix the underlying problem. If this is a modern
(mid-20th century or newer) house, and the floors and walls were level,
square, and stable, I'd definitely rip out, and reinstall properly, or
replace if the door was junk anyway.
I'm glad you asked, since I've measured the angles now. Figuring the
easiest way to measure a diagonal is with a rigid rule, I used a yard
stick with one corner on the header at 12 inches in, and the other
corner against the jamb. I found that the deviations are small in angle
terms: 90.62 degrees and 89.72 degrees.*
Why did I think the door was out of square? Because I had already cased
one door, and the pieces fit beautifully, but when I tried this door,
having mitered my three pieces of molding to 45 degrees, there were gaps
at the molding joints that I couldn't get rid of however I shifted the
pieces around the door. I figure (a) I was really lucky with the first
door and (b) 0.62 degrees is really quite noticeable. Also, small though
this deviation sounds as an angle, [80 * sin(.72)] shows that it makes a
difference of about an inch horizontally over an 80-inch drop to the floor.
I think I need to change my question. Now it's: what's the best way to
handle a tiny gap like this? Should I try to set my miter saw to cut at
45.3 degrees and 44.8 degrees, respectively? Or should I stick to the 45
degree detent and fill in the gap with something?
But a bit of trig tells me that in an 80 inch drop to the floor, this
is a difference of around an inch.
* THEN I found a leveling protractor in my tool chest, after all
this--and confirmed that any deviation of the jamb or header from level
or plumb is a fraction of a degree.
My experience is minimal, and I suspect that if I did this myself I'd
wind up worse off than I am now!
I'm replacing existing moldings, just to replace plan, flat moldings
with contoured ones. Come to think of it, the door doesn't fit too well
Built in 1974. Possibly just settled, though heaven knows a number of
things were evidently done poorly here.
I'd only be inclined to fake a non-square door on an older house with
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.