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Compound Miter Question

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Forum topic by johnhutchinson posted 10-22-2014 02:43 AM 1030 views 2 times favorited 27 replies Add to Favorites Watch
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johnhutchinson

1195 posts in 1093 days


10-22-2014 02:43 AM

Topic tags/keywords: compound miter question

I’m making another one of turtle boxes, and this time I want to get it right. In this first version, I added green felt to the underside of the shell to hide the miter gaps.

The angle between the top and sides is 45 degrees. So what’s the compound miter angle where a triangular corner meets a rectangular side? The nine shell slabs have the same thickness.

-- John - Central Ohio - "too much is never enough"


27 replies so far

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Loren

8303 posts in 3112 days


#1 posted 10-22-2014 02:54 AM

I can’t do this in my head at the moment.

You might consider building a cradle to hold the
work at 45 degrees. Then you don’t have to
set a bevel angle, just the miter angle and that’s
far easier to get dialed in. In cutting mouldings
on the flat, as you’ve noticed no doubt, when
you change either the miter or the bevel it
throws off the other setting, for want of a
better way to describe it.

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johnhutchinson

1195 posts in 1093 days


#2 posted 10-22-2014 03:17 AM

Thanks, Loren. If nothing else, the video convinced me that I NEVER want to install crown molding.

-- John - Central Ohio - "too much is never enough"

View tyvekboy's profile

tyvekboy

1340 posts in 2477 days


#3 posted 10-22-2014 03:38 AM

Crown molding is easy if you know the tricks.

I agree with Loren. That video was really good.

The same tricks in cutting crown molding could be adapted to your turtle pieces.
Looks like you have a lot of 22-1/2 degree cuts …

-- Tyvekboy -- Marietta, GA ………….. one can never be too organized

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johnhutchinson

1195 posts in 1093 days


#4 posted 10-22-2014 03:44 AM

tyvekboy: I know it’s not 22-1/2 degrees because that’s how I cut them the first time. That left the miters open on the underside of the shell. 22-1/2 is too great of an angle.

Next. :)

-- John - Central Ohio - "too much is never enough"

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JAAune

1643 posts in 1780 days


#5 posted 10-22-2014 04:08 AM

For small parts I like the cradle method Loren mentioned.

However, since we’ve got a Kapex which is super easy to dial in to the right bevel and we do larger scale work, I often mockup joints in Sketchup then extract the miter and bevel angles and take that info to the miter saw. Usually I’m close enough on the first cut to get a good joint.

According to my (untested) Sketchup drawing of that turtle joint, the miter is 30 degrees and the bevel is approximately 17.6 degrees.

-- See my work at http://remmertstudios.com and http://altaredesign.com

View JoeMcGlynn's profile

JoeMcGlynn

219 posts in 1817 days


#6 posted 10-22-2014 04:14 AM

the included angle between the two sides is 60 degrees

-- Blog: http://mcglynnonmaking.wordpress.com/

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stefang

15512 posts in 2798 days


#7 posted 10-22-2014 06:48 AM

First off John, I love that turtle box. I will have to make one of these as it is so cool. Apart from the discussion on getting the two settings for a compound angle just right or using an angled fence, there is one more option to insure perfect fits. That is to cut the parts slightly oversize at the desired angles and then use a sanding jig to perfect them. This requires a disk sander and a shop-made sanding jig. The jig I am familiar with and have in my shop is made for perfecting ring segments for segmented turning, which have to have perfect glue joints to look acceptable. A different jig would probably be necessary for your turtle segments. I don’t have a photo of my jig, but I will take one to send to you as a basis for further discussion.

-- Mike, an American living in Norway.

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johnhutchinson

1195 posts in 1093 days


#8 posted 10-22-2014 12:58 PM

I think I found the answer at this website … http://jansson.us/jcompound.html

When I went to the N-sided Box calculator, and entered 8 sides with a 45-degree slope, the blade tilt came up as 15.7 degrees.

So …

For the top, I need 22.5-degree bevels around the sides.
For the rectangles, I need 0-degree bevel at the bottom, 22.5 at the top, and 15.7 on the sides.
For the triangles, I need 0-degree bevel at the bottom and 15.7 on the sides.

Does that sound about right?

-- John - Central Ohio - "too much is never enough"

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TopamaxSurvivor

17671 posts in 3140 days


#9 posted 10-22-2014 04:14 PM

Wow, that is a great link you posted!

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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johnhutchinson

1195 posts in 1093 days


#10 posted 10-22-2014 04:40 PM

TopamaxSurvivor: I agree !!! I’ve filed that one away.

-- John - Central Ohio - "too much is never enough"

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a1Jim

115202 posts in 3041 days


#11 posted 10-22-2014 08:06 PM

I have that jig and had forgotten all about it,thanks for the reminder john.

-- http://artisticwoodstudio.com Custom furniture

View JAAune's profile

JAAune

1643 posts in 1780 days


#12 posted 10-22-2014 10:56 PM

The calculator from the website assumes a symmetrical miter joint but the picture of the turtle lid indicates the cuts for the side pieces are not the same as the cuts for the corners (otherwise the rectangles would taper to a narrower top just like the triangles). That means it’s not a symmetrical miter and the calculator is not going to give the proper angles.

I’m still sure it’s a 30 degree miter and an approximate 17.6 degree bevel for the triangle. The rectangles would be cut with the same bevel but with the miter set to zero degrees.

-- See my work at http://remmertstudios.com and http://altaredesign.com

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johnhutchinson

1195 posts in 1093 days


#13 posted 10-22-2014 11:10 PM

Thanks, Jacob. I’m going to do the same thing in AutoCAD that you did in SketchUp and look at the bevels. If I extrude solids beyond the intersection, and then slice on the miters, that should give me the bevels … I hope.

And just when I thought the mystery was solved. :(

-- John - Central Ohio - "too much is never enough"

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CFrye

8747 posts in 1303 days


#14 posted 10-23-2014 12:04 AM

I still have trouble with simple miters. :-(

-- God bless, Candy

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REO

889 posts in 1538 days


#15 posted 10-23-2014 01:42 AM

First and last: That is a fantastic box!!!

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