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I turned on my compact router with a tongue cutting bit installed. Immediately after I hit the on switch I heard grinding noises and felt the router try to wobble out of my grip. I turned off the router as fast as I could and to my shock and horror saw the bit was making contact with the side of the base. I was holding the router in the air when I turned it on, and I feel extremely lucky I didn't end up in the hospital.

I need to have a better understanding of how this happened and what I did wrong before I will be comfortable using a router again. My googling hasn't yielded any results and I was hoping somebody here might have an idea.

Notes:

  • As far as I can tell, nothing was touching the router bit when I turned it on. For better or for worse I was holding it in the air. Part of a clamp holding the work-piece in place was sticking up into the air near the router, but I did not see any damage to the clamp that might indicate it had been struck by the router.
  • I'm using a makita compact router with plunge base (the plunge base doesn't fit on the router anymore, but the router itself seems OK)
  • Here's a link to the router bit I was using
  • Here's a two star review for the bit that sounds really familiar (found after I started drafting this post)
  • It's possible I did not tighten the bit enough, but prior to this incident I had successfully cut a tongue on a different work-piece without issue. I did not adjust the collet tightness in between.
  • I typically try to position router bits so they are about 1/4" away from resting against the bottom of the collet.
  • I had my speed setting at 3/6 when I turned on the router. The manual says this is about 17,000 rpm.
  • I haven't been able to find any max RPM ratings for this bit.
  • Obligatory: I am new to wood working. Thanks in advance for your wisdom, patience, and mercy. I was really enjoying this hobby up until this scare.

Picture of bent router bit and gouged router base

EDIT: After reading @blacksmith37 's comment. I put the offending bit in a vice and used a socket wrench to try and bend it. It bent easily and eventually snapped. video image taken after video linked above image taken after shank snapped

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    Yeah, I would not want to be anywhere near a 2" router bit on a 1/4" shank that only cost $16. Especially if it was spinning! Aug 18 '20 at 23:57
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    Wild guess after reading review of the other failure also :The steel shaft was not heat-treated and is soft. At the very high router RPM a slight imbalance causes bending stress. This guess could be tested with the cutter in a good vise and trying to bend the shaft with a large pliers or other tool . The fact that presumably a very hard shaft bent as much as shown is suspicious. Aug 19 '20 at 0:03
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    Hi, welcome to Woodworking. Yikes! I hope you were wearing your brown pants yesterday ^_^ While I share some of the reservations about the bit type (specifically, large diameter, narrow shaft) I'm not so certain 'better' heat treating would have been desirable here. While the damage to the base is unfortunate I feel a snap, followed by the bit being ejected at a tangent at about 100mph might have been slightly less desirable! I feel the important point re. the bit itself and its mode of failure was that we can't know — without unequivocal knowledge of failures [contd]
    – Graphus
    Aug 19 '20 at 6:19
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    of other bits, of various price points — what the ideal heat treat for a shaft like this actually is. Our gut feeling of where the heat treat should land (i.e. the temper colour) might be way off, somewhat similar to conventional screwdrivers which were tempered much softer than most imagine (blue, not tan or brown). Now all this aside, the ideal running speed for a bit of this size is slow, since the large diameter means the edge is moving very much faster than on a smaller bit. And with a 1/4" shaft I would always err on the side of caution anyway, because of the potential for overloading.
    – Graphus
    Aug 19 '20 at 6:26
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    Apropos: woodworking.stackexchange.com/q/2942/5572 (Even though this looks like a manufacturing flaw, the fact is that large diameter, large mass cutters need to be run slower. Good manufacturers will tell you the max RPM for each tool they sell [or tool size]).
    – jdv
    Aug 19 '20 at 15:50
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According to this chart from Woodcraft, you were probably in the correct speed range for that bit.

The real issue is that you are asking too much from a 1/4" shank router bit of this type. You'll notice that all of the reputable vendors (CMT, Whiteside, Freud) all use 1/2" shank for this type of bit. Small routers have their place, but this type of work isn't it. Look for a bigger router that takes both 1/4" and 1/2" bits. A fixed base router such as the Dewalt 616 of 618 would be a step in the right direction.

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  • Thanks for this insight @LeeG! I'm really tempted to switch this to the accepted answer. My only hesitation is I bought a similar bit with a 1/4" shank from Rockler (which I assume is a reputable vendor). The price tag was significantly higher, and the grooves it cuts are 1/2" instead of 5/8". My newbie brain interprets this type of bit as being just on the edge of what can be done with a 1/4" shank. Aug 28 '20 at 18:00
  • Ehhhh. I'm going to switch to this. @blacksmith37 I really appreciate your technical knowledge and input on this, but it does really seam like newbies (such as myself) should be discouraged from buying this wide of a bit on a 1/4" shank. I'm switching to this answer for all the newbies thinking about buying wide bits for their small routers. Aug 28 '20 at 18:11
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The low strength of the shaft as shown by the original failure and subsequent bend test, shows that the shaft was never hardened . So do not use this brand either because of poor quality control or poor planning. A shaft like this should be "hardened" , roughly to Rockwell C 35. This is about the hardness of socket or end wrench.

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Same thing happened to me yesterday. How I ended up here.

I was cutting out a 1/8"x1/8" groove. I only mention that, cause no way it was stress. Barely using the bit. I hate 1/4" shanks, after yesterday, I know even more why.

Same router as you. Nearly the same setup.

I was using the battery operated version. 3ah battery. Always in it. It runs low I charge it. Do other stuff for 15 minutes. Just keeps the compact compact, only reason I've always followed that.

Ran a bunch of practice cuts. Ran two of the four doors. Got to the 3rd, battery died.

I ended up putting in a fully charged 6ah battery to finish the job. Popped it in turned it on and thought, in hindsight, wow that sounds a lot more powerful.

Found where I left off, ran about an inch, and POP!

I bought a cabinet door. Happened to be working for an engineer on this job. He is convinced, I am too, it was speed and heat.

That new battery upped the speed somehow. Both 18v batteries. 🤷🏼‍♂️. But, that bend was heat and the bit getting just off kilter. No other explaination.

Happened to have a spare arbor. The one I bent was a whiteside. So, not cheap.

Got everything all set back up and knocked the speed down by half. Sounded about the same as the setup with the 3ah battery. Somehow that 6ah also doubled the speed, heated the bit, and it got just a bit off center and went out if control.

Just glad it was only wood that messed up. Keep those bits at low speed is my takeaway.

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