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How do I measure for miter cuts?

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Forum topic by Purrmaster posted 02-18-2013 09:35 AM 16044 views 5 times favorited 30 replies Add to Favorites Watch
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Purrmaster

800 posts in 781 days


02-18-2013 09:35 AM

I know this is going to sound like an incredibly stupid question and I apologize in advance for this.

I’m trying to make a “frame” around a piece of wood. In this case it’s about 12 inches wide, 14 inches long, and 3/4” thick.

Basically I want to have some pieces around the thing with miter joints. The miter angle will be 45 degrees. To hide the end grain. But I can’t figure out how to do it.

I can’t make the frame pieces to the exact dimensions of the piece (12 by 14). Because when I make the 45 degree angle cut everything will be too short. If I make it too long it won’t fit together.

I was originally going to use compound miters but my tiny, pea brain couldn’t figure that out at all.

The “frame” pieces will be about 3 inches wide and the same thickness as the rest of the project.

I have a compound miter saw and a table saw so making the cuts shouldn’t be hard.

I’m going to have to figure out how to do this at some point or another. I’d like to make a custom size picture frame which would require the same technique.


30 replies so far

View Monte Pittman's profile (online now)

Monte Pittman

14588 posts in 1026 days


#1 posted 02-18-2013 10:03 AM

The outside of the edge will be the length of the center piece plus double the width of the board. Example would be on th 14” side using 3” wide edging, would be 14” plus 6” for 20”. When I started out this seemed complicated for some reason as well. As usual our minds over complicate things.

-- Mother Nature created it, I just assemble it.

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Handtooler

1097 posts in 820 days


#2 posted 02-18-2013 11:03 AM

Monte or others, Wanna go into how to take care of rabeted inside edges to receive inserts such as pictures on compound mitered frames? Cut rabets first and then the frame, the rabets turn out slanted when assembled. cut miters first and rabets are puzzling. And do you use a specially gigged shooting board to dress corners of a compound mitered frame stock to dress the edges for a more precise fit. Please expand on this thread for me also. Thanks!

-- Russell Pitner Hixson, TN 37343 bassboy40@msn.com

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JesseTutt

811 posts in 799 days


#3 posted 02-18-2013 04:28 PM

I am definitely not an expert on this.

Here is what I do:

1. Cut the pieces extra long.
2. Cut a miter on the end of piece 1
3. Cut the correct miter on the end of piece 2
4. Position piece 1 correctly on the picture (or wood)
5. Use piece 2 to mark where I need to cut the miter on piece 1.

I usually make the cut in step 5 a little long and then sneak up on the exact length through multiple trimmings.

As I said above I am certainly not an expert on this.

-- Jesse, Saint Louis, Missouri

View Handtooler's profile

Handtooler

1097 posts in 820 days


#4 posted 02-18-2013 10:02 PM

Jesse, Have you rabeted pieces and cut compound miters; or which ever way its done to end up with a flat rabet to install a picture, mat or panel from behind the frame? I’v sucessfully done flat rabeted frames just as you have described cutting the rabet on long stock, then cutting pieces 1,2,3,4 long and mitering back. You are right on.

-- Russell Pitner Hixson, TN 37343 bassboy40@msn.com

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JesseTutt

811 posts in 799 days


#5 posted 02-18-2013 10:03 PM

I have never figured out the math for compound miters. I lay the pieces flat (2-d).

-- Jesse, Saint Louis, Missouri

View Monte Pittman's profile (online now)

Monte Pittman

14588 posts in 1026 days


#6 posted 02-18-2013 10:15 PM

I will have to go home and cut it then I can figure out how to explain it.

-- Mother Nature created it, I just assemble it.

View Doug 's profile

Doug

26 posts in 782 days


#7 posted 02-18-2013 11:00 PM

You can start by cutting a miter on the end of your molding or “frame” piece. Line this mitered corner up on the outside corner of your piece. Once you have done this, mark the inside corner of the next miter. Continue all the way around until your done.

If you dont want to do that, make a miter on one end, then measure the horizontal distance from the inside corner of the miter to the outside corner of the miter. You can use this number to add onto the length of your piece to make the next cut.

View Purrmaster's profile

Purrmaster

800 posts in 781 days


#8 posted 02-19-2013 12:13 AM

At the moment I’m trying to do flat (2D) miters. If I want to make a picture frame, the inside dimensions of which would be 36” by 24” there has to be a way to calcuate this.

View waho6o9's profile

waho6o9

5082 posts in 1265 days


#9 posted 02-19-2013 12:46 AM

“I can’t make the frame pieces to the exact dimensions of the piece (12 by 14). Because when I make the 45 degree angle cut everything will be too short. If I make it too long it won’t fit together.”

I’d check your miter cuts with an accurate miter gauge because if your width is 12 the
inside miter measurement will be 12 by definition. If I understand you correctly.

View kdc68's profile

kdc68

1996 posts in 965 days


#10 posted 02-19-2013 12:49 AM

Purrmaster – Measure the backside of your frame pieces from the outside edge to the rabbet, then double it, then add it to 36”....do the same for the 24” side. Lets say your frame pieces measures 1-1/4 from the outside edge to the rabbet. That would be 2-1/2” when doubled. Overall outside dimensions would be 38-1/2” x 26-1/2”

-- Measure "at least" twice and cut once

View Dallas's profile

Dallas

3047 posts in 1175 days


#11 posted 02-19-2013 02:45 AM

Maybe pictures would help. Are you trying to cat a miter and have a rabbet that the piece will fit into?

I’m sorry, I’m just having a difficult time seeing this in my noggin.

-- Improvise.... Adapt...... Overcome!

View CharlieM1958's profile

CharlieM1958

15706 posts in 2907 days


#12 posted 02-19-2013 03:48 AM

Purrmaster: Why worry about doing the math to calculate the outside dimensions? If one side of what you’re framing is 36”, just make two marks on your frame piece 36 inches apart, and cut your 45’s outward from those two marks.

(Hint: I always cut a tad long because it’s easy to trim a hair off. Adding a hair…. not so easy.)

-- Charlie M. "Woodworking - patience = firewood"

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Purrmaster

800 posts in 781 days


#13 posted 02-19-2013 09:44 AM

Assuming I did the image upload right, the above images should give you an idea of what I’m trying to accomplish. And failing miserably at. I finally found my digital camera.

The first image shows the piece I want to make a mitered frame around. The second image shows me trying to accomplish this with regular 45 degree miters. The third image shows my original attempt to do it with compound miters.

View Pat Gornet's profile

Pat Gornet

12 posts in 682 days


#14 posted 02-19-2013 10:48 AM

I’m going to see if I can remedy the answer. What Monte Pittman said was correct. If you want the inside of the frame to be 8 inches in length then, with a board of 2 inch in width, you would add the width times 2. so with a 2 inch wide board the out side of your frame will be 12 inches.

However, if you want to account for the rabbit that you set the picture into then you have to do a bit more math. If with the same board you cut in a 1/8 rabbit then the space that the picture will be resting in will be the length of the inside edge plus a 1/4 inch (that’s twice the rabbit size) making the total space for the picture 8 1/4 inches In the picture below on the right side, that’s a 1/8 indicating the size of the rabbit.

if you wanted the space for the picture 8 inches, then you would make your frame 1/4 smaller. so instead of 12 inches you have 11 3/4.

Now my math mathematical to this is the following. (you will have to used this equation for both sides of the picture frame.

(length of picture) + 2[(width of board)-(width of rabbit)]= (outer length of frame)
or
length of picture) + 2(width of board)-2(width of rabbit)= (outer length of frame)

in a prettier version with
picture length=P
board width=B
rabbit width=R
Total=X P+2B-2R=X
or P+2(B-R)=X

and to apply that to the situation i was talking about earlier with
picture length=8
board width=2
rabbit width=1/8
Total=X

8+2(2-1/8)=X
8+2(1 7/8)=X
8+3 3/4=X
11 3/4=X
or
8+2(2)-2(1/8)=X
8+4-1/4=X
11 3/4=X

But honestly, if you have the picture in front of you it’s a hell of a lot easier to go by eye and pencil marks.
Hope I helped
~Pat

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Kaleb the Swede

1211 posts in 658 days


#15 posted 02-19-2013 10:58 AM

Pat that was one of the most helpful comments I have seen. As a new wood worker this process has always confused me. What you and Monte just said clears up a lot of head scratching I have been doing lately. Thanks a lot!

-- Just trying to build something beautiful

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