# Newb. Question - broken router bit



## oilman87 (Mar 4, 2014)

Hey all, first off - been following this forum for a while and THANKS to all for the great content. It's been a great help for a newb like me.

Here's my issue:
Just got my router table set up with a 3/4" straight bit. Set it up for a 3/4" x 3/8" deep rabbet. On my first pass with 3/4" plywood, the piece kicked back on me (or so I remember). I shut the router down and discovered my bit had cratered (see pics)!

Admittedly I am new to routing but I did have the workpiece firmly against the fence and was using a benchdog push block. Also, bit was 1/2" and router is PC 7815 running @21,000RPM

Was this cut too aggressive? Is my setup flawed? Just want to make sure before I get a new bit and try this all over again. Thanks all and sorry if this is a dumb question with an easy answer.


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## Semipro (Mar 22, 2013)

Hello and greetings to the router forums,
First would you please give a first name, like to keep thing friendly.
I not sure but are you telling us that you broke that bit,I see nothing that would have cause that, a 3/8" deep pass may have been a little deep but nothing that would have cause that, were you feeding from right side of table to left, were you holding tight to fence and using down pressure as you cross over the bit. Possible you have a bad bit ( could you have drop this bit on the floor before use)
That is a whiteside bit so if it new should be replaced,they are good bits but sometimes things go wrong


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## jw2170 (Jan 24, 2008)

Hi Oilman, I may be losing something in translation???

broken router bit - bit cratered?

a 3/4" straight bit. - bit was 1/2"


did the cutter actually break or did the carbide come off?

The router speed may be OK , how was your speed of feed?

3/8" deep cut with 3/4" cutter should not be a problem.


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## old55 (Aug 11, 2013)

Welcome to the forum.


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## BCK (Feb 23, 2014)

welcome aboard.....


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## Quillman (Aug 16, 2010)

On close inspection, 2nd pix, the plies look very much like bacon.
(Smoked or just ordinary off the butcher, shelf bacon, it makes a difference.)

Now really, the problem: Speed and depths of cut kill.
3/4 x 3/8 is waste-able but demanding.
Take it as fast you can with a new cutter, and you can easily break it.
Bad cutter? I doubt it, WMC q.c. is as good as it gets but a remotely possible, nevertheless.
Prevention: With your big machine, keep the waste to <3/8 x 3/8 and I'd be taking only 1/2 of that. And slow down. Let the feed rate = cut rate, don't exceed that. And that takes practice.
Routers


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## oilman87 (Mar 4, 2014)

Thanks for all the help. Sorry for the confusion: "cratered" is an oilfield term for broke but it was the carbide cutter that broke. It was a 3/4" bit with a 1/2" shank. Had workpiece up against fence and pushing down with my push block. If anything I thought I was going too slow as I didn't want to screw anything up on first pass!

As Quillman suggests I'll take smaller bites on the next go around. I just didn't realize with as beefy of a router and bit that I would have issue in plywood taking all in 1 pass.

Again, thanks for all the help!
Chris


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## Quillman (Aug 16, 2010)

7518, one of many routers capable of breaking bits.


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## Nickp (Dec 4, 2012)

Might this kind of thing happen because of the glue in the laminates heating and hardening as it cuts...? Not solving Oilman's problem but just asking for my own education. Should routing laminates be handled differently in general...?


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## Quillman (Aug 16, 2010)

The glue will definitely cause wear lines where they are but not break a bit.
Since the plies are presented at so many angles, it's about the same as routing at 45° to long grain. As such, it is a labored cut and should be wasted as end grain, sparingly/pass.


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## MAFoElffen (Jun 8, 2012)

+1 with Pat.

I thought that was an aggressive cut. Since you usually consider that the rule of thumb for a router's depth of cut by two different methods:
- One is by 1/4" at a time...
- Another measure on the cut is by 1/2 the diameter...

...And that cut was 3/8" deep by 3/4" across.

If, because of the profile, a wide cut is needed, I try to compensate/adjust for that with less of a depth of cut... and vice-versa.


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## Nickp (Dec 4, 2012)

Quillman said:


> The glue will definitely cause wear lines where they are but not break a bit.
> Since the plies are presented at so many angles, it's about the same as routing at 45° to long grain. As such, it is a labored cut and should be wasted as end grain, sparingly/pass.


Thanks, Pat...


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## bob156235 (Jun 14, 2009)

*Too Much of a Cut?*

I've been woodworking all my life and continue to learn. It is not that often that I experience something I had not given thought to, at least briefly before the operation. Breaking a 1/2" shanked, 3/4" dato bit while taking a 3/8" deep cut in Fur plywood is NOT something I would ever consider unless I was using inferior bits (seconds, cheap, unheard of brands, etc.), or dull bits (see Router Bit Trouble Shooting). 

I've got a big Triton in a table and hog out large panel profiles in one pass in hardwoods and do not break bits. I've _burned_ bits prematurely, but that's due to slow feed rates. My experience and (limited, I admit) knowledge forces me to conclude the bit was defective, of low quality, or dull.

Could breakage have been prevented by taking less of a cut? Of course, but I cannot get my head around the fact that it broke because too much wood was being wasted. Can someone chime in on this thought?


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## whimsofchaz (Jun 6, 2013)

Since you are new I would give the following advice. Take smaller cuts until you get used to your table and bits. The only other thing not mentioned is the possibility of some other debris being caught by the bit. Whiteside makes good bits. I have the exact same bit. You will learn to feel a bit or wood struggling. I have also started cutting with a loose collett. Scarry. A piece of steel spinning at 22,000 rpm on a loose collett. Good luck with your project.


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## Quillman (Aug 16, 2010)

"Could breakage have been prevented by taking less of a cut? Of course, but I cannot get my head around the fact that it broke because too much wood was being wasted. Can someone chime in on this thought?"
********************************************
I think you've been lucky, working on the fringes.
You treat a router like a shaper. Routers are trimmers not hoggers.
Whence the depths of cut exceed the cut rate, a cutter can break or bend.
If you have the power and the cutter has the modulus, you can plow with impunity but the cosmetics and dimensionality of the cut will be compromised.
You mention a slow feed rate that has burned your cutters. Is that not because you simply can't feed the work any faster? In that event, you have exceeded the cut or chip ejection rate.
Why stress your equipment like that?

Note these cuttings, no chatter no burns, metal, wood & plastic.
And appreciate, the 1/2 life of most cutters occurs at ~300'!
At 20'/min that is not a lot of cutting. It is not a bad idea to take light cuts and extend cutter life.
What % of your total time on any given project is spent routing? Maybe 5-10%?
So if you double that time, what are you out? In production? Then a whole new approach is warranted.


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## alaskagypsy (Jan 31, 2009)

You mentioned kick back??? What side of the fence was the bit in reference to the wood??
Kick back easily happens if you have the wood between the fence and the bit. You didn't say where the bit was in reference to the wood.


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## bkukyjt (Mar 6, 2014)

Thanks John for your very timely reminder about dropping router bits, it certainly is a hidden danger especially at 21000 rpm! Brian


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## bob156235 (Jun 14, 2009)

*Breaking Bits and Other bad Things*

FROM: Quillman... _"You mention a slow feed rate that has burned your cutters. Is that not because you simply can't feed the work any faster? In that event, you have exceeded the cut or chip ejection rate."_ 

No Quillman, it isn't that I cannot feed faster, _but it does seem you can't draw conclusions faster!_ Neither do I treat routers like shapers. Until a year ago, I used both regularly and often. I only mentioned that because the router (when properly sized) or bit (when properly maintained) can plow door component profiles in one pass without struggle, damage or increased hazards when operated by experienced journeymen. 

I've dulled bits because I've slowed feed rate around cathedral-topped panels and other uniquely shaped panels and rails where fences cannot be used. A 3-1/2" diameter bit is threatening when I pass the panel's curved end grain across its bearing, as does even a 2" diameter coping/profile bit as I move the rail through tight radii. On the other hand, slowed feed rate helps to reduce tearout, especially on difficult grainned woods like Hickory or curly Maple: _go too slow, it burns,_ _go too fast it tears_. The feed "sweet spot" blurs even more where changes in direction must occur - stopping briefly at inside corners will burn the wood and prematurely dull the bit. 
NOTE the tight radii of the panel and rail below. 








If feed rate is not increased on these woods or shapes, heat builds and the bit dulls expodentially - ultimately shattering the carbide. Engage this link - Router Bit Trouble Shooting - to better understand this phenomenon.

Leaving no burns on the plywood does minimize a dull bit probability, but the bit itself, apart from the wood, may also show signs of heat damage. Another cause for the chip could have been when the peice kicked back into the cutter as shown on the ply.

In any case, it just goes to show that we all must keep on our toes when working around machinery - always expecting the unexpected and being proactive to prevent injury or damage by the unexplainable.


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## TomE (Dec 17, 2010)

alaskagypsy said:


> You mentioned kick back??? What side of the fence was the bit in reference to the wood??
> Kick back easily happens if you have the wood between the fence and the bit. You didn't say where the bit was in reference to the wood.


Looking at image 3, the bit was making a full width cut with space between the fence and bit. (Note the sliver of uncut stock on the fence side which disappears just before the apparent problems.)

I suspect that the stock 'got loose' just enough for the bit to grab and kickback resulted, chipping the carbide.

Depth of cut is not horrible but probably should have not gone for full width of cut in single pass.


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## Quillman (Aug 16, 2010)

"No Quillman, it isn't that I cannot feed faster, but it does seem you can't draw conclusions faster!"
**************************************
You're right, my assessment was made without all the facts.

Notwithstanding, you're making my case. A 3.5" cutter, tho ordinary these days, used to be a small shaper cutter. In the 60's & 70's a 1/2" round over was considered about the limit for a 2-3 hp router. Almost all subbases were made with just 1.2" cutter holes.
Achitectural cutters, 45°  glue cutters, finger joint bits, panel bits, were all in the provence of the shaper. Not any more. 
Trying to make them work in the router is folly. You, no doubt, are very skilled at getting the most out of your machine and cutters. But, in my view, a router should not see a cutter >1.75" in length or diameter. But who the hell am I? A 1000 Frenchman can't be wrong, safe routing sir.


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## gmercer_48083 (Jul 18, 2012)

Picture #3 shows the diameter of the bit was pulling the wood both against and away from the fence at the same time. When you have the fence adjusted so the cut is deeper than 1/2 the diameter you no longer have the bit helping you to pull the wood against the fence as you feed it. What happened to you is that the extra 50% of the (diameter) bit caused the wood to move slightly away as you were feeding it creating Kickback. If you make this type of cut and cut no more than 1/3 of the diameter this type of kickback is unlikely.


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## Mike (Nov 22, 2004)

Any router bit will kickback in this situation and kickback is what caused the carbide to break. When making a cut like this with a fence you should limit it to less than half the bit's diameter on an edge. This cut would of gone smoothly if it had been made in two passes.


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## bbandu (May 12, 2014)

I was glaad to come across this topic as I have broken router bits in the past and now this info just confirms what I thought I was doing wrong. Trying to make to big a a cut at one time rather then doing it in more the one pass.


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## RainMan 2.0 (May 6, 2014)

bbandu said:


> I was glaad to come across this topic as I have broken router bits in the past and now this info just confirms what I thought I was doing wrong. Trying to make to big a a cut at one time rather then doing it in more the one pass.



I bent a router bit when it caught to much plexi once . Amazing how fast a piece of material can fly threw the air when it's propelled by a bit going 21,000 rpm


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