This has happened a few times to me now (with different g code files).
Please see image to illustrate my problem, its the spoil board and you can see the progressive down slope of the cut, not by design!
I was cutting out a part using a 1/4 down 2 spiral bit when things went bad. It started to move down the z-axis through my part, into the spoil board and eventually into a screw, breaking my bit. This was in white oak, 1/2 thick. 1800 mm/min feed rate.
Has anyone had this problem? Or any idea why it happened? Everything worked fine up to this portion of the cut.
Was the shank still in your collet at the same depth as inserted? If the bit never pulled out, then you lost steps on Z.
Upcut bits pull the router down, and can exert a lot of downward force when they start to auger. Edit: nevermind, i misread the original post that you used a downcut.
Did your bit run into a screw/bolt at the end? Edit: I really need to read it more carefully next time! I see you mentioned this in OP. my apologies.
Actually right…if the bit was pulled downward due to cutting too deep too fast, the Z could have slipped steps and just continued to go lower and lower
Thanks for the quick replies, I have uploaded my gpuff_box_lid.nc (31.1 KB) code (the .c2d file is not in my shop computer, where I am at the moment) for you to look at. I forgot to mention I have the Z-Plus.
Its possible that the bit was pulled down from the collet, I failed to notice when it broke and I pulled the bit out. I “think” it looked okay, but I kick myself for not looking closer.
I have had the exact same thing happen to me about 3 times. I even have a thread about it. I believe for me (and everything looks identical to your picture) it was the bit slipping down because it wasn’t tight enough.
Now, I’m not sure if it was the collet (I was using the high precision version), or dirt/dust in it, or just not tightened enough. I am leaning towards not tight enough because I was using 1 wrench and the button on the bottom of the carbide router. I have since bought 2 wrenches and I’ll be using them from now on to make sure it is tight. The benefit of 2 wrenches is you can tighten with minimal chances of messing up position on a tool change.
Those who mentioned slipping of the bit, it seems that is the case. I have run a few more tests and everything looks good. I’m going to start using the double wrench method to make sure its tight.
FYI: I’ve had it happen to me on a router table too (REALLY dangerous situation - because it’s climbing towards your hands). This is a common problem with collets. I always tighten fully…in this case, the collet was getting old and just couldn’t be tightened enough anymore (it was a 1/2" PC router). I replaced the collet and all was fine.
Make sure you snug it all up - don’t go crazy cranking on it - but just make sure it’s tight…and if it still happens even though the collet is clean, replace the collet.
A good way to do the double wrench tighten (and the loosen after the job) is to set them up so that you can squeeze the two wrenches together with one hand. This has a bunch of benefits, it reduces force on the machine, it saves your knuckles when the collet loosens and the wrenches suddenly move and I find it’s easier to judge a consistent torque as a grip strength.
