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. 
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Was this with a one-wrench and spindle lock collet, or the dual wrench type?
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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.
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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
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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;
- Put collet spanners on spoilboard
- Put bitzero on the spoilboard or workpiece - to remind me to re-zero Z (I don’t have a bitsetter)
- Jog to tool change position
- Change tool
- Tighten collet, put collet spanners back in their home
- 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.
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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.
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Nope. This happened using a 1/4” bit.
Eeks. I’m unfortunately quite familiar. This happens to me specifically on my original Carbide3d 1/8 bits I bought in 2019 with my SO3. They’re upcut, which pulls them down into the surface and holy heck I have to tighten the schnikies out of them.
I don’t use them all that often, and due to this I do my Winston “monkey tight” method like I always do, and that’s when I remember, “Oh, I need to go ape-sh*t tight with these” after finding a new blemish in my wasteboard. Such a bummer when this happens.
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I bought the https://elairecorp.com/ precision collets for 1/8, 1/4, 4MM and 6MM. They have never let me down. Maybe you should replace your 1/8" collet if you have to tighten it up so tight. C3D also sells some as well.
I’ll second that.
Buying good quality collets and keeping them clean and smooth, including checking the taper inside the spindle / router and the nut has let me do less gorilla tightening with a decent grip on the cutter and minimised run-out.
I had the AMB Kress spindle for a while, the collets from AMB were decent, on the 2.2kW spindle upgrade I had to polish the inside of the spindle taper with some scotchbrite and buy a decent collet nut, after that the good collets don’t bind, release easily and grip cleanly.
Thanks for the suggestion. I just have the 1/8 C3D precision insert (not the full collet). So you remove the nut fully, then swap collets entirely every time you change shank diameters?
Could you post a photo of what you have?
A long while back ISTR we sold a 1/4"–1/8" reducing bushing, but it has since been supplanted by a precision collet:
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Ditto to most of what was said regarding this. I also follow a standard work flow which has helped reduce issues. Good, clean, collets and smooth tool shanks sure do help. I’ve also switched to mostly down cut bits which has eliminated the “grabbing and pulling the bit downwards as the Z travels upwards” effect of the wood on the bit caused by a collet issue or a dull bit. If the DC comes loose in the collet, it gets pushed upwards into the collet so the worst I’ve had to do is to rerun the job and maybe take a little more material off. Haven’t had a catastrophic failure since. The OP’s photo brings back painful memories of my past hard learned lessons.
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