Issues with router table extension and sacrificial fence...

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Forum topic by MattyMattAg posted 06-11-2014 01:48 PM 984 views 0 times favorited 13 replies Add to Favorites Watch
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38 posts in 483 days

06-11-2014 01:48 PM

Topic tags/keywords: help router bits

So I have been using my new Grizzly 1023 TS and love it, but this past weekend I finally got around to trying out the router table extension. I mounted a Dewalt router underneath and slipped in a 1/2” dovetail bit with the intentions of making a sliding dovetail joint on butt-ends for a bookshelf top I’m making.

Forgive my lack of proper jargon…

Making the female end was easy and I was able to make that portion of the dovetail centered on the edge of the oak board I was working on. But, when I went to make the male end, everything went wrong…

I was pushing the board into the spinning bit, so I know I was feeding it the correct direction. But the oak board kept splintering and half way down the 4’ board, the router bit head snapped off the shank. Luckily it didn’t fly around the shop and just fell on the table, but it scared me a bit.

I guess my question is why would that have happened? I was running the board the correct direction, and the board was between the fence and the bit, making the male end of the dovetail like I thought I should.

The only thing I didn’t have was a sacrificial fence. Some videos I’ve watched have shown guys making the male end of a sliding dovetail joint with the outer part of the bit cutting the wood while the inside part of the bit is hidden by the fence. Other than dust collection, what’s the difference in the way I did it, using the inner part of the bit to cut, as opposed to using the outer part of the bit to cut with a sacrificial fence?

-- If Jesus was a carpenter, what better profession could there be?

13 replies so far

View Bill White's profile (online now)

Bill White

3907 posts in 2959 days

#1 posted 06-11-2014 02:10 PM

Sounds like you were taking a cut that was too big for the bit. Hogging cuts just won’t work well.


View j_dubb's profile


196 posts in 808 days

#2 posted 06-11-2014 02:26 PM

Holy smokes, man. Good thing the bit just dropped off.

There might’ve been several contributing factors at play. As Bill said – perhaps you were trying to take too much at once? Even so, I wouldn’t expect that to result with the friggin’ bit head snapping off. Was the bit extremely dull? Cheapish brand? Perhaps you were feeding the board too fast? Was the collet absolutely unequivocally tightened sufficiently around the bit itself?

-- Josh // "If trees could scream, would we be so cavalier about cutting them down? We might, if they screamed all the time, for no good reason." - Jack Handey

View ChefHDAN's profile


565 posts in 1849 days

#3 posted 06-11-2014 02:34 PM

Matt, were you going from left to right with the board or right to left? Feed direction changes from the bottom of the bit to the top, on my table setup, I would have pushed that left to right with the set up you described, (though my fence has two wings, and I would not have cut the way you described), sounds like you were climb cutting and the trapped force of the tear out against the fence snapped the bit, because you made the full cut in one pass for the dovetail dado.

View WhyMe's profile


314 posts in 560 days

#4 posted 06-11-2014 03:06 PM

One reason it snapped the bit was because you were feeding the board between the bit and fence. The bit should be sunken in the fence. That way there is no trapped pressure pushing outward from the fence by the work piece against the bit.

View MattyMattAg's profile


38 posts in 483 days

#5 posted 06-11-2014 09:29 PM

My 1023 has a right wing router extension, and I was feeding the piece from the front of the TS to the back, or left to right when standing on the right side of the TS. I made sure I was feeding the piece slowly, taking off a small amount each time, and that the cutting half was cutting into the feed and the freed half of the bit was moving away, or with the direction of the feed.

I guess that answers my question on why I need a sacrificial fence. The bit was a Craftsman bit… not the best quality but not the worst by any means.

-- If Jesus was a carpenter, what better profession could there be?

View TheFridge's profile (online now)


2786 posts in 485 days

#6 posted 06-11-2014 09:43 PM

Oak don’t play across the grain.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View mantwi's profile


312 posts in 895 days

#7 posted 06-12-2014 04:11 AM

You were feeding the workpiece the wrong direction. A router that’s used freehand rotates counterclockwise. When a router is inverted the bit is now spinning clockwise. When you tried to feed the work between the fence and the bit it was pulling the workpiece forward and caused excess pressure that snapped the shank. It takes a lot of pressure to snap a 1/2” shank by the way. As already suggested you need to feed the workpiece against the rotation of the bit and burying the bit is a sacrificial fence face is the safest way to accomplish this. I’d also remove the material to be wasted to within an 1/8” of the finished cut with a handsaw. You definitely need a sled that rides against the fence and acts as a backer board to prevent the inevitable tear out you’ll get without one. Look at the way your feed a hand held router into the work. If you feed it right to left (or clockwise) you are feeding against the rotation of the bit. This is the correct way. If you feed it left to right (counter clockwise) the bit will be grabbing the work and propelling itself. That’s a climb cut and it’s a very unsafe practice. The one exception is when you want a super smooth surface right off the cutter you leave a 32nd or so remaining on your initial pass then use the climb cut technique to remove the rest. Because the depth of cut is so shallow you can control the feed and safely route in the wrong direction. Remember when you turn a router upside down it changes the feed direction. God bless and be safe. By the way, Craftsman bits are terrible. In fact just about everything branded Craftsman that has to do with woodworking is low quality. If it doesn’t have a lifetime guarantee don’t buy it from Sears tool department.

View mantwi's profile


312 posts in 895 days

#8 posted 06-12-2014 01:03 PM

Wait a minute, or is it left to right or maybe? It all depends on which side of the bit you are working from. Just make sure the cutter is facing the workpiece no matter which side of the bit you are approaching. I’ve been routing the inside edges of door frames for days and on the inside the feed directions different from the outside . This is confusing, like I said just make sure the face of the cutter is moving into the ….... never mind. You’ll figure it out. I sure can’t unless I have a router in my hand.

View bowedcurly's profile


514 posts in 728 days

#9 posted 06-12-2014 01:24 PM

if you had the board between the bit and fence it will pull the board you should be vertical with your board using a tall fence I think could be wrong though you can hog some out with the tablesaw, it will make it easier to rout I think

-- Staining killed the wood<<<<<>>>>>Dyeing gave it life

View MattyMattAg's profile


38 posts in 483 days

#10 posted 06-12-2014 01:38 PM

Yeah, I’m pretty sure if the router is facing up and the bit is spinning counterclockwise, then when you face the router down, the bit is still spinning counterclockwise.

I was feeding the board into the front face… or towards the cutting edge as described above.

After reading the responses, I think my issue was twofold… 1) trying to take too much material at one pass & 2), not using a sacrificial fence, causing too much sideways pressure on the bit.

-- If Jesus was a carpenter, what better profession could there be?

View ChefHDAN's profile


565 posts in 1849 days

#11 posted 06-12-2014 06:11 PM

Matt, Mantwi has the right of it in his second post, it depends on what side of the bit you’re using to cut, I typed mine quick earlier and didn’t explain it well. Let’s just eliminate the fence question and say you were using a bearing guided bit, with the bit spinning, you would feed the stock into the edge of the bit closest to you from the right side to the left side. If you were to use the side of the bit furthest from you would feed from the left to the right to avoid the climb cut, If you ever cut a rabbet in a picture frame or a case frame for a back, you’ll see this real quick as you go around the blade. Look at router fence plans like this

the “wings” or infeed and outfeed fences can be adjusted to fit the spaces near your bit and you don’t have to sacrifice the fence portion unless you need ZCI for the bit, plus you can get a bit of topside dust collection!

View MattyMattAg's profile


38 posts in 483 days

#12 posted 06-13-2014 03:14 AM

Chef, great explanation and I can honestly say that is what I was doing. Facing the bit with the bit spinnging counter clockwise, I was feeding from left to right on the far side of the bit… meaning the board was running between the bit and the fence.

I need to find some fence plans, most definitely!!

-- If Jesus was a carpenter, what better profession could there be?

View runswithscissors's profile


1609 posts in 1024 days

#13 posted 06-13-2014 07:14 AM

A simple mantra to repeat in these situations is, always feed into the carbide. Well, that’s mostly true, but there are occasions when a climb cut is called for. Also, I’ve always heard that it’s a no-no to feed between the bit and the fence.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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