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How easy is to break a router bit ?

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Forum topic by 716 posted 02-08-2016 12:57 AM 701 views 0 times favorited 20 replies Add to Favorites Watch
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716

502 posts in 382 days


02-08-2016 12:57 AM

My brand new Bosch bit lost a part of carbide tip after drilling mortise in hard maple in first couple of minutes.
1 1/4” deep mortise in three passes so about 3/8” cutting depth per pass. I admit it was my fault as a straight bit should not have been used here, still the bit should not have failed so easy. Or should it ? The router (also Bosch) did a great job refusing to continue cutting as if it knew something was wrong.

-- It's nice!


20 replies so far

View gfadvm's profile

gfadvm

14940 posts in 2155 days


#1 posted 02-08-2016 01:06 AM

I would try to return that bit. It looks like it got hot (or maybe just dirty). Hard maple is tough and I would probably have taken shallower cuts. That said, it shouldn’t have broken unless it had been dropped on the concrete.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View jap's profile

jap

1251 posts in 1519 days


#2 posted 02-08-2016 01:09 AM

I would have taken 1/8” passes.
Less likely to break the bit, and leave a better finish on the walls of the mortise.

-- Joel

View Bobsboxes's profile

Bobsboxes

1107 posts in 2129 days


#3 posted 02-08-2016 01:11 AM

The smaller straight router bits, 1/4” single carbide, more so than the double carbide 1/4” are very easily broken. They seem to heat much more than the bigger bits.

-- Bob in Montana. Kindness is the Language the blind can see and deaf can hear. - Mark Twain

View TheWoodRaccoon's profile

TheWoodRaccoon

364 posts in 395 days


#4 posted 02-08-2016 01:17 AM

gfadvm seems to be right, there is dicoloration of the metal usually present when it’s overheated. 3/8 inch per pass is too much, especially in hardwood. 1/8, or 3/16 inch at most per pass. A spiral upcut bit would have been the optimal choice, as they clear the chips and cut better thus reducing heat. I would try and return it, and use the moneyto get a good spiral upcut bit.

-- still trying to think of a clever signature......

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TheWoodRaccoon

364 posts in 395 days


#5 posted 02-08-2016 01:18 AM



The smaller straight router bits, 1/4” single carbide, more so than the double carbide 1/4” are very easily broken. They seem to heat much more than the bigger bits.

- Bobsboxes

Yup, there’s less metal to be heated, so it heats faster, like a knife edge would during heat treating.

-- still trying to think of a clever signature......

View bondogaposis's profile

bondogaposis

4034 posts in 1816 days


#6 posted 02-08-2016 01:36 AM

3/8” is way too big a bite in hard maple, that bit got too hot. Smaller bits build heat faster, take smaller bites 1/8” is about right for hard maple.

-- Bondo Gaposis

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716

502 posts in 382 days


#7 posted 02-08-2016 01:38 AM

It’s all true. However this a single 1/2” bit. The tip got burnt apparently after the failure as dull metal was spinning in the wood.

-- It's nice!

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TheWoodRaccoon

364 posts in 395 days


#8 posted 02-08-2016 01:48 AM



It s all true. However this a single 1/2” bit. The tip got burnt apparently after the failure as dull metal was spinning in the wood.

- 716

There’s no way to know for sure which came first, weather the heat caused the failure, or there was a failure that caused the heat. Were you plunge cutting?

-- still trying to think of a clever signature......

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716

502 posts in 382 days


#9 posted 02-08-2016 01:51 AM

Of course there is way at least for me as I was tgere, I did not see any burning when changing the cut height. Then all of sudden burnt wood and messed up slot in a $25 of material piece. I cut it on a router table.

-- It's nice!

View JAAune's profile

JAAune

1644 posts in 1782 days


#10 posted 02-08-2016 01:59 AM

That bit isn’t designed for plunging. If you were doing that without ramping it (moving sideways while plunging) it would put a lot of stress on the bit and may have caused the break.

-- See my work at http://remmertstudios.com and http://altaredesign.com

View MadMark's profile

MadMark

978 posts in 918 days


#11 posted 02-08-2016 02:43 AM

Was it a plunge bit? If it was just a straight cutter there is no carbide on the top so when you try to plunge there is a spot that just has to burn/wear down.

M

-- Madmark - Madmark2150@yahoo.com Wiretreefarm.com

View bigblockyeti's profile

bigblockyeti

3668 posts in 1186 days


#12 posted 02-08-2016 03:01 AM

I don’t think 3/8” per pass is too much, as you stated, it is a 1/2” bit. The key is keeping the feed rate slow enough not to break the bit and fast enough to not burn the wood. This rate will slow as the bit dulls over time. It is unlikely heat would have caused the failure, the brazing rod used to attach carbide teeth and blades to saw blades and router bits has a very high melting temperature, the carbide itself has a way higher melting temperature than even the steel used for the body of the bit or blade. If the bit was unable to evacuate the chips, you could have a mechanical overload that would cause the carbide to fracture. Carbide looses very, very little strength even at temperatures that would be considerably higher than anything used cutting would could be allow to escalate to.

View knotscott's profile

knotscott

7216 posts in 2841 days


#13 posted 02-08-2016 03:47 AM

It depends on the bit. It’s very easy to break a 1/4” or smaller bit, and is easy to break 1/2” bits that taper to 1/4” or less, but I’ve never broken a bit that’s 1/2” throughout.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

View doubleDD's profile

doubleDD

5237 posts in 1508 days


#14 posted 02-08-2016 04:23 AM

Next time try a relief cut on the table saw first, even one cut would relief a lot of stress on the router bit.

-- Dave, Downers Grove, Il. -------- When you run out of ideas, start building your dreams.

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runswithscissors

2189 posts in 1490 days


#15 posted 02-08-2016 04:38 AM

I trashed a 3/8” straight bit with a 1/2” shank doing the same thing in beech. Not as hard as maple, but still a pretty dense wood. I was drilling out much of the waste in 1 3/4” X 7/8” through mortises. I built a rough “bridge” that I clamped under the mortise area, so the chips would have somewhere to go. It was going fine until the last mortise (out of 24), at which point it started shedding carbide, and of course the bits of carbide in the wood helped demolish the rest of it. No damage to the work, thankfully.

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

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