Pushing a router bit to the breaking point

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... actually past the breaking point.
1/4" straight carbide bit (Craftsman), kinda long (more than 3/4"), being used to cut a slot in 3/4" pine, using my old Craftsman router (1/4", old-fashioned little one). I was cutting along, carefully regulating the feed rate so as to only slow down the motor a little bit, thinking how much stress that bit was taking. Sure 'nuff, after cutting about 6-7 slots about 15" long, the bit just broke off. Didn't go flying at all, but just landed on the table under the router in a pile of wood chips.
So obviously this is my bad. I was even thinking as I was making that last cut that maybe I should be doing this in two passes.
So what're the rules of thumb for how much stress is too much for bits like these? The bit seems well-made, so I don't think I can blame it. Now I'm thinking of making that same cut in two passes (~3/8" depth of cut each). Would that be un-stressful enough for the bit?
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RE: Subject
It's a "finishing", not a "hogging" tool.
Plan accordingly.
Lew
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Indeed. Wrong bit for the job. That is more a job for an 'upcut' spiral. I find that one can lean into those a lot more as it is all about chip-ejection. A straight bit can't get out of its own way because the chips have nowhere to go but towards the back of the cut.
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with straight cutters, I don't cut deeper than the width of the cutter in any single pass.
your opinions will probably vary (yowpv?)
jc
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David Nebenzahl wrote:

A general rule of thumb is to cut only as deep as the diameter of the router bit. For a 1/4" diameter bit the maximum depth os a single pass would be 1/4" cut.
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I'd add another thumb to your rule, and not cut deeper than the smaller of the bit or shank diameter.
R
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With a straight cut bit I don't go more than 1/8" per pass.
Take more, shallower, cuts, and the job will go faster because you won't be fighting the tool.
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On 5/10/2009 5:04 PM Dave Balderstone spake thus:

Good suggestions so far, including the one about using a different tool (spiral cutter).
I notice one thing that happens is that there's a lot of fairly high-frequency chatter when you use a tool like this to "hog" wood, less with shallower cuts. It doesn't show so much on the cut, but I can sure hear it. I wouldn't be surprised if this vibration contributes to early tool mortality (all that flexing and stuff).
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Vibration is bad, period.
By taking lighter cuts, the cuts themselves are faster with less stress on the tool and on me.
Say I want to cut a fair number of 1/2" x 15" slots (let's say 10 for arguments' sake, or 150 linear inches). I can zip through those inches with a light cut (say six 1/8" passes) pretty damned fast with hardly any stress on the tool, the bit or my hands pressing the pieces against the fence.
Trying a deep cut, I'm not only stressing the router and the bit, but my hands and arms are going to get tired, and if I back/slack off at all, I just know the damned piece is going to come away from the fence, and I better hope that where I wanted that dado isn't visible in my finished project, because if it is, I've just made scrap wood.
In other words, the hurrier I go, the behinder I get.
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On Sun, 10 May 2009 20:01:38 -0600, Dave Balderstone

I've made more scrap as a result of impatience than from all other causes combined.
Tom Veatch Wichita, KS USA
An armed society is a polite society. Manners are good when one may have to back up his acts with his life. Robert A. Heinlein
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Amen.
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Tom Veatch wrote:

understand the virtue of patience.
A boat under sail has a rhythm that is insync with nature.
Try to rush things, you WILL make a mistake.
Make a mistake when single handing, chances are pretty good you ultimately end up DEAD.
Chances of finding any remains, SLIM and NONE, more likely NONE.
You quickly learn to be patient.
I find it is also a pleasant way to enjoy life while sailing.
YMMV.
Lew
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Lew,
It's hard to be patient when you are falling off the backsides of waves in a 10 foot sea at 2AM.
You had better be patient though. :-)
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"Lowell Holmes" wrote:

I hear ya, but I'm of the school that gentlemen don't go to weather, that's part of being patient.<grin>
Lew
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instances, my adam's apple would be in my mouth.
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"Lowell Holmes" wrote:

Being a "cruiser" rather than a "racer", I get "there" when I get "there", as the saying goes.
The party can wait or not, makes no difference.
Lew
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Lew Hodgett wrote:

the things that differentiated a sailor from the common man.
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That may be the description for an aged sailor, but in their youth, it also has to do with proving they have hair on their chest.
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On Sun, 10 May 2009 18:24:29 -0700, David Nebenzahl

I'm sure you're correct with that observation. Things don't vibrate without flexing and stress reversals from those cyclic deflections are prime contributors to fatigue cracking and failure.
Tom Veatch Wichita, KS USA
An armed society is a polite society. Manners are good when one may have to back up his acts with his life. Robert A. Heinlein
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wrote:

clearing. However, by taking much lighter passes with a straight bit, you may find that the chip clearing becomes moot. lighter passes produce less chips which are less likely to get jammed in a shallower grove. In other words, they become self clearing. And straight bits are cheaper!
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