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Calculate Near Size of Compound Miter Frame

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Forum topic by Divotdog posted 02-25-2020 04:14 AM 411 views 0 times favorited 10 replies Add to Favorites Watch
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Divotdog

75 posts in 4118 days


02-25-2020 04:14 AM

Topic tags/keywords: picture frame compound miter length of pieces question

Hey after searching online I need a little advice. I am making some picture frames of varying sizes and I want to make them with compound angles.

The problem is they will be made to varying specs (picky folks). The thickness, width and slant angle of the wood will all vary.

Now, I have no problem making these frames, except for the usual glue-up nightmare. But I tend to waste material by guestamating instead of maybe just allowing a little extra.

So – anybody have a calculator which can produce the length of sides based on thickness, width and angle. These formulas are commonplace for “flat” miters but not compound as in molding.

Thanks for reading this rambling mess.

-- David, Dallas,Tx - golf weather is warming up but it's cool in the shop.


10 replies so far

View Madmark2's profile

Madmark2

1006 posts in 1264 days


#1 posted 02-25-2020 04:41 AM

InvCos(angle°) x flat miter measure. Cos is 1 at 0° (flat) and 0 at 90° (vertical). This scales the miter length which is initially the stock width. Add twice this number to the inside length to get your overall length.

Factoring in stock thickness is the same but with sin(angle°). Which is 0 at 0° and 1 at 90° as the thickness scaling.

Add both above for the perfectly theoretical measure.

The reality is you’ll cut long and be finish sanding the miters and using a little gap filler no matter what. LOL

-- The hump with the stump and the pump!

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birdman

20 posts in 4209 days


#2 posted 02-25-2020 06:08 AM

Thanks, Madmark2, for your attention. As you know, when wood is cut at two different angles (compound miter) there are new angles formed. The calculation needed involves finding the sin and the cosine of these angles. But I have not studied trig in a while, to say the least!

But I already have tables that tell me the required angles based on the bevel. I am looking for a means of knowing the starting length for each piece, considering these angles and the width & thickness of the pieces.

So I was hoping to find a webpage with a calculator since these calculations all change with the specs I mentioned above. Yes, I am lazy. But that’s why I have lots of power tools.

Thanks, man.

-- DavidP - still count on my fingers and toes - not for math, just inventory!

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Madmark2

1006 posts in 1264 days


#3 posted 02-25-2020 01:45 PM

You’ve got the formula. One computation for the miter, on for the thickness. Add both to your inside measure. The calculator function on your PC can solve it.

-- The hump with the stump and the pump!

View theart's profile

theart

162 posts in 1230 days


#4 posted 02-25-2020 02:15 PM

Inside length plus twice the width is the high limit. The addition of a slant will decrease the outside length, but not by much.

View Divotdog's profile

Divotdog

75 posts in 4118 days


#5 posted 02-25-2020 03:49 PM

Thanks, Quote.
But this is sort of a ballpark figure isn’t it. Because the greater the bevel, the greater the length of each piece.

-- David, Dallas,Tx - golf weather is warming up but it's cool in the shop.

View splintergroup's profile

splintergroup

3430 posts in 1898 days


#6 posted 02-25-2020 10:55 PM

Plenty of on-line calculators available for those opposed to going old-school and breaking out the slide rule 8^)

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Divotdog

75 posts in 4118 days


#7 posted 02-28-2020 04:41 AM

“Plenty” but I have not found one. Would you mind providing a URL?

-- David, Dallas,Tx - golf weather is warming up but it's cool in the shop.

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Divotdog

75 posts in 4118 days


#8 posted 02-28-2020 05:30 AM

Just to be clear —. I am not looking for an angle calculator, 45 degree, compound miter degree or otherwise.

I just think it would be handy to know the outside dimensions of a frame that’s made with compound angles in relation to what’s being framed without “sneaking up” on the fit.

-- David, Dallas,Tx - golf weather is warming up but it's cool in the shop.

View jacww's profile

jacww

58 posts in 1683 days


#9 posted 02-28-2020 02:36 PM

Deleted

TonyC

View Lazyman's profile

Lazyman

4789 posts in 2063 days


#10 posted 02-28-2020 03:51 PM

Maybe a crown molding calculator?

I’m not really following why you would need or want a compound angle for a frame. It seems like the joint would be even weaker if the surfaces are not “flat” in at least one plane. I guess I don’t understand what you are trying to do.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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