The Corners Don't Fit

[dusty]

I have a problem building boxes; boxes of any sort. It seems that I can never get then perfectly square. Try as I do, they never come out right.

A different thread got me to thinking about this so I decided to work through my problem in Sketchup. I sketched the side of a simple box (6x6x2) with miters and then duplicated the sides. This gives me four "identical sides" with no miscuts except for one. All of the miters are 44.8 degrees rather than what would be the intended 45 degree cut.

Only a small error of .2 degrees. That should not make a big difference.

When I put the box together (in Sketchup), I did one corner at a time. This is the way I normally assemble the sides of a box (because I never have enough of the right clamps). Doing it this way, I got three pretty good joints but the fourth was a bear (typical of many of my boxes.

[ATTACH]24135[/ATTACH]

My tiny .2 degree error accumulated to 1.2 degrees at the final joint. Mathematically, it is obvious but the question remains, "What can be done about it"?

Equally obvious - cut 45 degree miters. Treat that tiny .2 degree error as a big thing.

Get an Incra V120 Miter Gauge or learn to micro-adjust the Table Tilt.

[beeg]

I thought you have a incra v120 miter gauge? For it to be square, EACH CUT has to at a 45° cut, a 44.8° cut equals 89.6°. Are ya trying to cut a bevel miter?

[terrydowning]

Confirm that the outside length is exactly the same. The .2 difference will accumulate.

For miter cuts on boxes I use this


It's very fast and quite accurate. I've had the same blade in mine for 12 yrs and it still cuts beautifully.

[anmius]

I tilt the table using a wixey box and my miters come out just fine. But not only does the miter have to be 45 degrees, it has to be square across the board. Both have to be perfect for a perfect miter in all four corners.

[robinson46176]

I solved that problem years ago. I declared miter joints to be part of a great fiendish plot and just quit using them almost totally.
Too many easier ways to make a box.

Actually I don't have all that much trouble with them but I typically hand fit them often using sandpaper or a fine rasp.

If it makes you feel any better go to an antique shop and take an honest look at some nice handmade pieces. It didn't always work out for the old-timers either.


.

[charlese]

Assuming there is a box bottom already in place with a loose fit during a dry fit exercise - there are several methods to assemble the box sides as is, without a new miter gauge or "micro" learning, or trying to adjust to "micro" accuracy.

In this case, close is good enough!! The error as seen in Dusty's example is actually no error at all. It's just something that needs a different methodology.

First fix: Assemble all 4 sides at the same time distributing the angle error 4 ways. Use an inexpensive strap clamp. This should be used for the dry fit and also the glue-up. This type of clamp is also used to tie down things on top of a car.

Second fix: Trim one or more of the corner's 45 deg. cuts with a sander so they fit in a second dry fit.

Third fix: If three corners fit and one has a gap - cut a wood splint to fill the gap.

NOTE: Gluing up one corner at a time is asking for trouble. There is no sense making trouble when different techniques can solve the problems.

[Ed in Tampa]

I find most of my miter problems not so much on the angle of the cut but rather on the length of the boards. If they aren't exactly the same length no matter how perfect the 45 degree cut is they will not go together without a gap.

Also an old craftsman taught me a secret of the miter cut. Glue them together if there is a gap on the outside corner run the shaft of a screw driver over the corner. The wood fibers will bend and close the gap. No filler no noticeable difference when staining or finishing.

[fjimp]

The only way I have perfect luck with mitered corners is the Incra 5000 sled. Set up and checked with the machinist square the corners are perfect every time. Jim

[mgbbob]

The Dubby sled will take care of the problem but I don't think he has a model for the Shopsmith. I have one on my Craftsman 113.xxx saw and it works great. I think there must have been a problem with someone tilting the sled off the end of the table on a Shopsmith. I am thinking about building one with a locking miter slot and that should solve the problem. If you want it see it in action watch his video. Search for Dubby and watch the fun.

[edflorence]

I like the Shopsmith Miter Pro for boxrs and frames. Even if the corner cuts are not perfectly 45 degrees, the jig ensures that all corners come together to make 90 degrees. Mating cuts are always complementary. I have cut boo koo picture frames using the Miter Pro and then clamped them with band clamps and they have all come out square, so I never get concerned about if the corner is actually 45.

Granted there are times when a single cut must be 45 degrees, but for boxes and frames all that matter is that the corners be 90.