routing plywood

[tpolley]

i built a box out of 3/4 plywood and i wanted to rout a lip or whatever on the lid and the opening of the box so that the two would mesh together. i'm not sure if i'm using the right terminology so forgive me. anyway i used a 3/8 router bit and set the dept at around 1/4 inch or so. anyway part of the lip turned out fine but several pieces splintered and broke off in big chunks. i ended up destroying the box. i'm not sure what kind of router bit it was. can you not rout plywood or what??

 

[kbs2244]

It would be better to use a dado blade in a table saw.

 

[goodfellow]

Plywood is cross-layered and will tear easily with a router -- doesn't matter what kind of cutter. As stated, the best way to cut a "rabbit" is to use a dado in a table saw.

 

[boiler7904]

Dado blade in a table saw would be best choice.

Multiple shallow passes are better than one deep pass if you had to use a router.

 

[charlie_nj]

You didn't say what type of bit or what brand bit you are using.

A dado blade in a table saw will work, of course, but a router with a good carbide bit, like a CMT or a Freud, can readily be used to cut a quality dado or a rabbit on plywood. With a high quality bit, the only place tearout should be a problem is at the end of the cut and this is easily alleviated by clamping a piece of scrap the same thickness as your plywood to your work. Tearout at the end of the cut can be a problem with a dado blade too, unless you do the same. With the router you have to use a quality carbide bit, cheaper bits will result in much more tearout.

 

[Vicegrip]

If you can't make the cuts with a dado blade make many shallow passes or use a back up board. Clamp a scrap board on the face of the target wood to prevent splintering out. Cut both boards at the same time.

 

[ears]

Also remember to run the router in the right direction. Imagine a picture frame, inside the frame move the router clockwise, outside the frame counter clockwise. "Clock box" is how I was taught to remember this. I roundover plywood a lot for fiberglass and dont have tearout problems.