Dado cuts in plywood - Router Forums
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post #1 of 5 (permalink) Old 04-15-2009, 01:08 PM Thread Starter
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Default Dado cuts in plywood

I am planning a built-in project in our guest room closet. It will house a TV, Printer and have file drawers below.

My question is: What would be the best method to cut dados in the plywood sides? The unit will be about 78" tall, so cutting the dado on my table saw would be somewhat unwieldy. I want to dado the shelves and compartment dividers into the sides. How can I make sure the dados align exactly on each side? If I use a router: Would it be better to use a 3/8" bit with two passes (assuming a 3/4" by 3/8" deep dado) OR would I be better off using a 3/4" bid in one pass? Would a spiral bit work better than a dado bit? and finally (sorry for all the questions) What type of guide and router base would work best to accomplish the dado using a router?

I would value any and all advice.

John Lombardo
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post #2 of 5 (permalink) Old 04-15-2009, 03:28 PM
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Howdy BK,

I made a jig for Dados, but you can get away with clamping a straight edge over both of the cabinet sides.

Lay both sides of the cabinet on the flat and against each other, align them to ensure both are even then clamp them to your work table.

Decide what thickness the shelves will be, (1/2", 5/8" or 3/4") and mark where you want the shelves to be placed on one of the cabinet sides and use a straight edge to carry the mark over both sections. I mark the top or the bottom of the shelf not both.

Know this it is likely that your plywood isn't exactly 3/4" or 1/2", that it's undersized and you will need a cabinet grade router bit for the job. Standard 3/4" cabinet grade, AC and MDO plys are actually 23/32" check to ensure exactly what it is.

Take a test run against the straight edge on some junk to gauge the offset required to hit your marks on the cabinet sides then set accordingly on the sections.

Ensure that the cabinet sides once set for marking do not move prior to or during the dado process, check for alignment between each dado for safety

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post #3 of 5 (permalink) Old 04-15-2009, 03:38 PM
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Best bet, get some plywood bits. These are the exact size of ply. Using a 3/8" or even the 3/4" leaves room for error.

Plywood Bits - Lee Valley Tools


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post #4 of 5 (permalink) Old 04-15-2009, 04:32 PM
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Cut the plywood to WIDTH after routing for shelves. That way they will be sure to line up.

An easy way to cut right on dados for undersized plywood is to draw a line for the top or bottom of the dado. clamp a straight edge on that line. Place a scrap of your shelf material against that straight edge. Then, clamp another straight edge against the scrap. Use your 3/8 pattern bit to rout up one side and down the other.
Perfectly sized dados.

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post #5 of 5 (permalink) Old 04-18-2009, 01:28 PM
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nothing to add, cuz the 3 previous posts were excellent advice!! honest days work, for an honest days pay....
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