wide dado with table mounted router

[Mark Visconti]

I've got a train of thought "what is the better way to do this task and are both options asking for trouble?"

I need to cut a 3/4" wide dado that is 5/8" deep. Due to the state of ductwork and other tools, I want to do it on the table router (everything is a nail right now).

I have a half inch and 3/8 inch straight bit and I used the 3/8 to cut an initial dado. Now I'm concerned because it looks a little like a climb cut and I don't want this 6' piece of 2.5x2 to rocket off the router.

Assuming I can do the rest of the dado like this, is it better to widen the dado with the existing dado to the left of the bit or with the dado to the right of the bit? (From outside to the fence with an imaginary line intersecting the cut area the difference is Wood, gap, bit, wood, fence or wood, bit, gap, wood, fence)

Maybe I'm over paranoid but with two options, I'm torn over whether they're both safe or one is better than the other.

A rabbeting bit would be a better option, but I'd rather just use a straight flute that I already own.

So, does it matter and why? I think the gap to the right of the bit would reduce the chance of a climb cut, but if the piece comes off the fence and touches the bit, it could pick up some momentum from the bit. With the gap to the left of the bit, it seems like a climb cut (wood trapped between fence and bit).

Mark

[Jason Beam]

It CAN matter, yes. Your instincts and spidey sense are spot on here. Climbing would be bad and could send the piece flying or the bit gets busted. The right way is to avoid the climb cut - if that means flipping your workpiece around and feeding the other way, that's all fine and good. You want the teeth of the blade to impact your direction of travel - that is, feeding against the rotation. It's less dramatic if the bit is over 50% burried, but I still wouldn't risk that. Go against the flow if you can.

[Peter Quinn]

[QUOTE=Mark Visconti;988575]
Assuming I can do the rest of the dado like this, is it better to widen the dado with the existing dado to the left of the bit or with the dado to the right of the bit?

Do it to the left of the bit in a router table if possible. With a piece that big and a bit that small in multiple passes you can reasonably do it either way, but to the right is both a climb cut and holds the wood captive between the fence and bit so any movement in the stock will place stress on your router and bit, danger exists there. On the bright side if things get away from you it will send the board away from the infeed direction toward the outfeed direction where you should not stand.

Seriously, move the fence back, take additional passes to the left of the original pass as viewed from the infeed position and avoid climb cutting when possible even with small bits. Make sense? Try to imagine a cut with a bearing guided bit set flush to the fence. Where would the wood be placed? Always to the left of the bit. Keep it that way even with a dado in the center of the work.

Next time you need to do this consider a shim on the fence and a 1/2" bit, multiple passes for depth. Set the bit height to 1/4" above the table, secure a 1/4" piece of MDF the length of your fence with a slot to accommodate the bit. Set the right shoulder of your dado with the shim in place. Make your first pass, pull the shim fence, make your second pass, viola, 3/4" dado. Replace the shim, raise the bit @ 1/4", repeat the original sequence until your dado is complete. Your hands, wood and router will all thank you for not hogging out that much wood in one or two passes.

[Mark Visconti]

Thanks. Makes sense. I originally thought I would just do a dado beside the existing one, but just moving the fence will let me do a more traditional cut and then everything is like routing with the bit at the fence.

[glenn bradley]

Thanks. Makes sense. I originally thought I would just do a dado beside the existing one, but just moving the fence will let me do a more traditional cut and then everything is like routing with the bit at the fence.

Correct. Never trap your piece between bit and fence. How long is the cut and what is it in? The reason I ask is because plywood often has some bends. Your table does not.

If the material is not real flat, you must force it to ride reliably past the bit and across the table. Not a good practice; the force part I mean. You will get inconsistent depth on your cut if the material is not as flat as your RT. DAMHIKT. A hand router is better for long dado's in plywood as the relatively small base follows the hills and valleys. Short cuts are not a real problem.

[Mark Visconti]

Yeah, a hand router was obvious, but I'm too stubborn to unmount/remount it in the table. A second router is on my list.

It's oak, and since I already have a slot cut, it will follow the same bend Depth of cut could be questionable (I have one piece that is a bit not straight), but I think I can work around it.

[Richard Wagner]

I appreciate the warnings that this thread provides but I always have problems envisioning what is being said. "Do it to the left of the router bit." Left as seen from the in feed side I assume. If I read this correctly, the previously cut dado is between the blade and the fence and the work piece is being fed left to right.