Oh the joys of not tightening the bit in the chuck enough!

Well this happened today and learned another lesson from experience. School of hard knocks.
I guess I didn’t get the chuck tight enough and during the cutout of my desk signs it dug in deep to the spoilboard and ruined my work piece. :man_facepalming:t2:

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Was this with a one-wrench and spindle lock collet, or the dual wrench type?


Ouch! I’m glad to hear the only thing injured was your project. Are you using a single wrench lock collet or dual wrench collet?

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As others are pointing out, always make sure you are using two wrench and one hand method to tighten the collet. The harder or deeper the material I am cutting the tighter I make the collet. I tighten mine pretty darn tight.

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One wrench and spindle lock. Afterwards I tried to recall if I even tighten it or not. I think I just got ahead of myself trying to get it done.

C3D recommends using the lock button and wrench only for initial tightening. After you get the bit where it wont fall out of the collet then use the two wrenches. The reasoning is if you pull hard enough on the wrench with the stop button you could break the casting out. I had a HF side grinder that I was using and was putting a new blade in. I had the stop button pushed and the nut for the blade would not tighten. The whole casting had broken out. I was able to complete the project by holding the blade with vice grips to get the nut to tighten. After the project I threw it in the trash and bought a good Dewalt one.


Glad to hear that the bit and collect did not fly off into your shop and become shrapnel. Before running a job, I forgot to remove the gator clamp from the spindle. The wire wiped across my belly as the spindle spun up and tore a hole in my work shirt. Hurt like hell, though. I now have a checklist that I run through before initiating a job. Also, from then on, every CNC I’ve owned has been in an enclosure.

Reposting Carbide 3D’s machine operating list for our new members and seasoned members (myself included) who may sometimes become a little too comfortable with our beloved machines. Machine operating checklist

Also, sharing @WillAdams and @robgrz excellent ebook. Introduction - Shapeoko CNC A to Z


For some time I had a sticker on the front of my machine which said “Probe Z” and one on the spindle which said “Tighten Collet”. I decided to follow a consistent order and after a while I got it into muscle memory that bit change was;

  1. Put collet spanners on spoilboard
  2. Put bitzero on the spoilboard or workpiece - to remind me to re-zero Z (I don’t have a bitsetter)
  3. Jog to tool change position
  4. Change tool
  5. Tighten collet, put collet spanners back in their home
  6. Re-zero Z, put away bitzero

Sufficient iterations of this sequence has got me to the point where when I get out of sequence it feels wrong and I tend to reset to ‘did I tighten?’ and ‘did I zero?’

It’s also worth remembering to pull the collet out and clean / blow out the inside, outside and slots in the collet to ensure that it grips the bit properly and that dust and chips in the slots aren’t stopping the collet closing properly.


I have to correct you on this one. @Julien compiled that excellent ebook.


Yep, I have very familiar looking gouges in my work surface and parts. I use 2 wrenches and clean the collects but even then that isn’t enough on some pieces especially if I’m cutting deep or going fast. It still loosens and causes bedlam. I suspect it is the C3D routers themselves. I have two other working routers setup in a router table and I’ve NEVER had a collet become loose.

Ive had that happen a few times. Even if you tighten, sometimes it loosens.

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You’re not using a collet reducer, are you? I always had this problem with 1/8 inch bits in my 1/4 inch collet with a reducer. Got a 1/8 inch collet, been fine since.


Nope. This happened using a 1/4” bit.