Matt,
I am new to wood working. I am trying to make a dado with a router. I am using a 3/4 inch straight bit with bearing in my 1/4 inch shaft Craftsman Router. Everytime I try to make a cut, only 1/8 inch deep, the width of the dado is greater than 3/4 inch !
Maybe 1/16 inch wider. I am running the router along a clamped straight edge. I have the motor pulled back quite a ways to allow only the 1/8 inch deep dado, but could there be enough play in the motor mounting to cause this much play?
Please offer suggestions. I am getting pretty discouraged with a simple cut. Thank you.
Replies
A 3/4" straight bit on a 1/4" shaft is prone to some flex and runout, especially if you are pushing it hard, but taking shallow cuts as you are, should get you around the problem.
It would help if you gave me a lot more details. The length of the bit's cutting edge, the bearing's location. When you take the cut, are you running the bearing along the straight edge, or are you running the router's base along the edge? Are you taking just one pass? Are you trying to get a 3/4" dado for 3/4" plywood, how are you measuring the width of the dado? What are you cutting the groove into? What are you using for a straightedge, how long is the cut? As you feed the router, which side of the machine is the straight edge on?
John White
Thank you so much for answering my question and taking the interest in helping me.
I am using a Bosch 3/4" straight bit with bearing that has a 1" long cutting edge. The bearing in on the top of the cutting edge near the shaft. I am running the base of the router against a piece of 3/4" plywood as a straight edge. I am trying to put a 3/4" wide dado, 1/4" deep into a piece of 3/4" plywood, 12" wide. For my test cut I was just going 1/8" deep. The straight edge is on the left side of the router as I push the router away from me. I only made a 3" long test cut to see what the dado was like. That is when I tried putting a 3/4" piece of ply next to the dado and found it was wide.
After writing my question I went on finewoodworking archive and found that maybe I should use a plain straight bit without bearing.
I also have a 1/2" bit of similar design as the 3/4" one. I guess I could use that and 'sneak up' on a snug fit for the plywood.
Thanks you again John. I will try whatever you suggest.
John
Some of my questions were a long shot, especially the one about trying to get a slot for plywood, but it paid off. Modern 3/4" plywood isn't 3/4" thick, it is thinner. All of the router bit suppliers sell special router bits that are sized for the true thickness of plywood, that's what you need. There are other approaches, such as the one you are thinking about, using a 1/2" bit and taking more than one pass, although that can be hard to get exactly right especially if you are making a lot of grooves. Another approach is to make a deliberately narrow dado and then thin down the end of the shelf to fit.John WhiteEdited 2/13/2008 12:40 pm ET by JohnWW
Edited 2/13/2008 12:57 pm ET by JohnWW
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