routing a dado for a shelf

I need to rout a dado for some shelves I am building. I use a straight edge to guide the router. The upright is about 24 inches wide and I need to rout a 3/4 inch dado.
Problem in the past is I always get one or two spots where the bit kicks away from the straight edge a litte.
Any ideas/techniques on how to prevent this?
George
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Use a straight edge to guide both sides.
-Jack

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I assume you know to rout in the direction such that the rotation of the bit is forcing the router against the straight edge.
You can use an undersized bit and rout twice, once on each edge of the dado. Of course, if precision width is important, then fence alignment is critical (but can be accomplished more easily with a spacer to align the fence the second time).
Greg
George wrote:

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Use two guides, one on each side. Use a 1/2" bit. Make one pass and then come back to do the other side and clean up any imperfections on the first side. Be sure to make the passes in the proper direction, but you already know that. Ed
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It isn't intuitive, to me anyway. I cut in the wrong direction watching the base move away from the guide wondering why I had to hold it so hard against the guide. A post had words that shouted, to me, USE BIT ROTATION TO FORCE THE BASE AGAINST THE GUIDE STUPID!! Now I "already know that". I used the "right-hand"rule" as a mnemonic when hand routing to determine proper direction.
wrote:

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Ed, What is the advantage of using a 1/2" bit vs. a 3/4 inch bit?
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then
first
already
With a 3/4" bit you are plowing through the cut in one or two passes depending on the depth. With the smaller bit, you plow through the first time but on the second and any subsequent passes there is more room for the chips and I find a cleaner cut.
Works well for me, but it is not the only way. Ed
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Advantage of using a 1/2 bit to route a 3/4 dado is that you make 2 passes, and if the router jumps a bit, the 1/4in lets it move without gouging the far side, you just go back and make another pass to correct the spot where it jumped
John
On 19 Jul 2004 12:25:25 -0700, snipped-for-privacy@yahoo.com (George) wrote:

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Your bit pretty well centered in the guide? If so, make a plywood jig with some 1/4" ply, nailing two parallel strips of wood to it, as far apart as the diameter of guide you will be using. That way you can attach a fence to butt it against the pieces you're routing, make stopped dados by nailing a couple pieces of your spacer at either end of the parallel strips, etc. As the router is contained between the strips, no problems with jump. You might even get a little wacky and try routing a sliding dovetail - same jig.
Those guides are great items, though some tend to think of them as pattern routing aids only.

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On 19 Jul 2004 07:23:36 -0700, snipped-for-privacy@aol.com (George) wrote:

http://benchnotes.com/Router%20Dado%20Guide/router_dado_guide.htm http://www.popularmechanics.com/home_improvement/workshop/2001/1/router_jigs/index2.phtml
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It is mainly a matter of practice, but...
If one side is less critical than the other, besure to put your straight edge on the critical side!
That sounds obvious, but it took me a major screw up to learn it.
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One very simple solution is 2 straight edges set the width of the router base apart.
John
On 19 Jul 2004 07:23:36 -0700, snipped-for-privacy@aol.com (George) wrote:

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If you rout on the correct side of the straightedge, you have to physically pull it away from the straightedge.

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What works for me is consider the right thumb the saft of the router bit and fingers the direction the bit is rotating. If the thumb point up rotation is counterclockwise and if down rotation clockwise. If down router is held against the nearside of the fence or board to be contoured and moved left to right, rotation PULLING the router tighter against the fence. Right hand rule from school days in EE.
wrote:

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You could also use a track that holds a router mounted on a slide which eliminates nearly all of the wavering.

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Very true but a wooden T-square takes about three minutes to make and has the advantage that it has a built in alignment pointer.

straight
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