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.
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.
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.
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.
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.
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?
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.
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.
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.
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.
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.
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.
Since using a 1/2'' bit, try drilling say 1/4'' holes centered along the mortise first to eliminate some of the stress of the router bit. This way the router bit is only cutting 1/8'' on each side Ordinarily this shouldn't be necessary but on occasion and with certain lumber I found this to work out great. Extra work but will save the project.
Like Mad Mark said, if you don't have a plunge bit, the bit like does not have a cutting edge at the center of the end. So, you're going to be generating heat and working a lot harder back and forth to dig your way down. If you don't have a bit with an edge on the end, you're better off drilling a full-depth hole at either end and slowly working across, lower the bit in the end hole, go back across, lower the bit again, etc.
Yes it was a plunge bit with the two sharp edges, one along the bit another square to it at the tip of the bit.
I had no problem plunging it in and cutting the first 5 or so mortises. Then the piece started violently jerking. It was a
2×3.5×30" hard maple. It it were something smaller or weaker material the thing for sure would fly away from my hands or broke into splinters.
I think I should have lowered the router speed, it was at about 18,000 rpm.
Use a spiral bit for that kind of cut. That's your problem. Also, Bosch bits aren't really very good.
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