DIY Network

Avoiding Miter Mistakes From "Ask DIY Home Improvement" episode DADH-211

Sloppy cuts made for bad miter-joints in this molding.

Q (from Dave in Memphis, TN): I don't like the molding in my office. I want to replace the molding, but don't know how to make accurate miter cuts. Can you help me avoid the mistakes?

A: (from DIY woodworking and refinishing expert Bruce Johnson) From the photo, it appears that some inaccurate cuts made for bad miter-joints and gaps in your molding. It also appears that attempts were made to fill the gaps with wood filler.

The best way to make precise miter cuts: a table-saw sled and miter-jig.

A miter joint is formed by the 45-degree cuts made on the ends of adjacent boards so that the boards can come together to form a 90-degree angle. Examples include boards used to make picture frames or where molding pieces come together at the corner of a room.

For bad miter-cuts, wood filler can sometimes be used to effectively conceal the problem if the wood is to be painted so that the filler will not be visible. If the wood is to be left natural or stained, it's critical to cut good, tight miter joints.

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As seen in the picture-frame samples, an imprecise cut results in a mitered corner with gaps where the edges don't meet properly (figure A). A proper miter-cut yields a tight corner and a nearly invisible line where the boards meet (figure B).

Figure A

Figure B

Miter Techniques and Tools

• A crude method for cutting miters is to use a miter-box (or guide) and miter-saw combination (figure C). These tools may be sufficient for basic cuts, but if a precise fit and neat appearance is desired, this is probably not the best way to go.

• A better way to make miter cuts is with a power saw such as a chop-saw or, better still, a table saw.

• Table saws typically come with a miter gauge with a range of angles marked on them (figure D). The angle can be set and locked to 45 degrees for cutting miter-joints.

  Figure C

  Figure D

  
  

• To improve the precision of the miter gauge, the back side of the guide (figure E) already has holes for attaching an extension.

• A straight piece of wood acting as an extension to the guide (figure F) provides a greater contact surface with the cutting board. This makes it easier to make the angled cuts.

  Figure E

  Figure F

  
  

  	Figure G
  	Figure H

• But even the miter-gauge with an extension is not the perfect solution. Particularly for long boards, the gauge and guide may rock or wobble, resulting in less precise cuts. The best way for repeatedly making precise cuts is to use a table saw with a miter-jig or sled.

• This sled was made from pieces of particle board, with two strips of wood glued to the underside that fit in the guide-grooves on the table saw. The guides ensure precise movement and prevent the sled from shifting as you cut. A carpenter's square was used to position two guide pieces on top of the flat surface at 90 degrees (figure G). A straight slot was cut right down the middle of that angle. The slot then serves as a guide for making perfect 45-degree cuts.

• By installing the sled on the table, setting the piece of wood in place on the guide and pushing the sled across the blade of the table saw (figure H), perfect 45-degree cuts can be made time after time.
  

RESOURCES :

The Wood Finisher: How to Finish Everything, From Decks to Floors to Doors
Author: Bruce Johnson
ISBN: 0345372972
Ballantine Books

The Weekend Refinisher:
How to Make the Most of Your Furniture-A Step-by-Step Guide
Author: Bruce E. Johnson
Publisher: Ballantine Books
ISBN: 034535866X