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Miters, miters, miters…

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Blog entry by Don posted 08-22-2007 05:08 AM 4097 reads 1 time favorited 10 comments Add to Favorites Watch

[I posted this as a comment here.]

A beautiful joint with no end-grain showing and really simple – right? NO!

Well the first part is right – they are attractive, but making a good miter joint is not as easy as it looks. And they get more difficult than just matching two 45 degree cuts together – there’s the compound miter joint that introduces another angel, or the mitered dovetail joint, and many other variations – all difficult to make.

I can always make a three-sided picture frame with perfect miter joints – it’s adding that fourth side where everything can go pear-shaped.

The problem is one of compound errors. What looks to the eye like a perfect 45 degrees, may actually be 45.05 degrees, or 44.95 degrees. Three pieces fit together well, but when you add the fourth piece you see you are out by .15 degrees.

If you can’t get your saw set up perfectly, there is hope. Make a sled with a 90 degree block split by the saw blade as close to 45 degrees both sides as possible. If you are out on one side by a little, you will be out on the other side by a compensating amount. Keep track of your pieces, mark them A & B cuts and make sure that you fit an A cut to a B cut all the way around.

Result? A PERFECT MITER CUT FRAME!

-- CanuckDon "I just love small wooden boxes!" http://dpb-photography.me/



10 comments so far

View WayneC's profile

WayneC

12290 posts in 2754 days


#1 posted 08-22-2007 05:21 AM

Very nice sled. One way to adjust the miters is this.

-- We must guard our enthusiasm as we would our life - James Krenov

View Don's profile

Don

2599 posts in 2833 days


#2 posted 08-22-2007 05:25 AM

Yep, and a way to bu**er them up is this. LOL

-- CanuckDon "I just love small wooden boxes!" http://dpb-photography.me/

View Douglas Bordner's profile

Douglas Bordner

3966 posts in 2720 days


#3 posted 08-22-2007 05:35 AM

Ah, the duality of planes in a nutshell. In one man’s hands, a way to create a glass-like sheen on end grain.
In my hands, a torn-grained, edge-chipped-off fiasco. Thanks for reminding me about that jig Don. I just generally despise miters, but they are so versatile, and look so good on your boxes, I’m going to have to make that jig.

-- "Bordnerizing" perfectly good lumber for over a decade.

View Karson's profile

Karson

34876 posts in 3057 days


#4 posted 08-22-2007 05:36 AM

Don:

If the “A” board is always on the left side and the “B” board is always on the right side then the blade being not exactly 90 Deg with the surface will always have its out of alignment being compensated by the wood being cut on opposite sides of the blade.

I had a person who makes segmented bowls show that trick when sanding segments to be glued together.

If you make another of your 90 deg sliding sleds, but set the blade at 15 degrees then the two pieces will be 90 degrees but the corner edge will not be straight up and down, but will match perfectly. An interesting design modification.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware karson_morrison@bigfoot.com †

View Don's profile

Don

2599 posts in 2833 days


#5 posted 08-22-2007 05:45 AM

Thanks, Karson.

I think we are saying the same thing. The principal of ‘self-compensating errors’ works with a number of cuts.

I like your idea of tilting the blade at an angle – this would be a scarf-miter.

-- CanuckDon "I just love small wooden boxes!" http://dpb-photography.me/

View Karson's profile

Karson

34876 posts in 3057 days


#6 posted 08-22-2007 05:53 AM

I realize we were saying the same thing. I just wanted to point out by using a larger “out of alignment” cut would still give a flat 90 deg angle piece of wood.

I had not known the term scarf-miter, something new I learned at 11:50 PM the day was almost over without be able to say that.

Not really true I was working on a vacuum storage system for the last 2 weeks (vacation in the middle) and i still had a vacuum leak. Almost all gone but silicone glue helps to plug vacuum holes by letting the vacuum suck the glue into the small holes.

The leak is still about 7in of Hg loss of pressure over 6 hours.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware karson_morrison@bigfoot.com †

View Thos. Angle's profile

Thos. Angle

4435 posts in 2619 days


#7 posted 08-22-2007 06:29 AM

Don,
I’ve got a sled just about like yours. I made removeble faces from 1/2 inch MDF. I can adjust the angle with playing cards under the faces. That’s if and when they are out of square. I also use PC stick on sand paper, 110 grit next to the fence. It really holds. this is a good thread for the new guys because nothing is more frustrating than miters. Dang, I still need to make that shoot board!!

-- Thos. Angle, Jordan Valley, Oregon

View Bob Babcock's profile

Bob Babcock

1804 posts in 2742 days


#8 posted 08-22-2007 07:57 AM

The 1st thing I’m going to do for my boxes is to build that jig. Thanks Don!

-- Bob, Carver Massachusetts, Sawdust Maker http://www.capecodbaychallenge.org

View Tony's profile

Tony

978 posts in 2687 days


#9 posted 08-22-2007 08:29 PM

Very simple, but an excelent idea. I have been struggling all my life using a single miter to cut.

By the way your maths are a little out the error is 0.15° (3×0.05° error per joint)

-- Tony - All things are possible, just some things are more difficult than others! - SKYPE: Heron2005 (http://www.poydatjatuolit.fi)

View Don's profile

Don

2599 posts in 2833 days


#10 posted 08-22-2007 11:48 PM

Thanks, Tony. I’ve corrected my error above.

-- CanuckDon "I just love small wooden boxes!" http://dpb-photography.me/

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