Need Some Mitering Help

[David Stone]

I'm replacing the trim and molding around my deck posts.  The posts are 5" x 6.5", square.    So, I measure and cut the molding -- simple, flat 1 x 3/4 with a profile (not angled crown) -- so that I've got 2 pieces with 5" interior faces and 2 with 6.5".  But when I install them, the last piece never fits, no matter how careful I am with the first three.  Sometimes the last piece is too long, sometimes too short, sometimes a gap, etc.

Is this just a question of my being more careful when I measure, cut and install? Or is there a trick here that I'm missing.  

(It's funny, a few months back, a carpenter friend came over to help me install some new windows.  When he was cutting the trim, I showed him how the laser on my fancy Kapex worked.  He turned it off.  Every piece was marked with a fairly thick pencil mark, he lined it up by eye/blade tooth, and every cut fit with no gaps.  He said, "do this every day for the next 25 years, and you'll figure it out.)

[Guest]

Two questions come to mind.

1. are the faces on the post all perfectly square to each other?

2. Are your miter cuts truly 45 degrees?

[Cooler]

Cut one piece at a time and transfer the dimensions directly to the stock (no ruler).  

A deck settles over time.  It is likely that nothing remained square or plumb.

[JGrout]

cut as you go do not cut and then fit. 

trimming is just what it suggests you trim to fit. 

Joe

[RPE1]

I use a razor knife (box cutter) to mark cuts.  Not a pencil.  Cut one piece at a time.  Make sure you are cutting the right side of the mark.

RP

[tomsteve]

Is this just a question of my being more careful when I measure, cut and install? Or is there a trick here that I'm missing.  

 

"do this every day for the next 25 years, and you'll figure it out."


if this is out in weather around wooden posts, id make em a little big. nail/glue the joints and tack in place. burnish the corners with a screwdriver to close gaps and knock down sharp outside corners.

[David Stone]

Thanks everyone.  I guess I'll do some more practice this weekend.

Oh, and here's a picture of what's been keeping me busy these past nine months:

[Guest]

That's better than mitering trim around deck posts any day.

[K. L. McReynolds]

The posts are not square nor is each side equal widths.

The way I do that job is to cut the first piece with the heel(short measurement or inside) of the miters the width of one side of the post. Easiest way to find that measurement is to lightly clamp a F clamp on the post and measure the distance inside the clamp faces.

You can cut the next three pieces the same way, but you will find often trimming is necessary because the faces of the posts are not 90 degrees from each other.

I've had to make shims for some really warped posts to get a decent look.

[David Stone]

Assuming the post corners are not 90*, should that affect the length of the trim pieces or the angle?  I.e., when "trimming to fit, should I play with the miter angle?