I am a newbie. I have had good luck with my Pro XXL except for one thing (well, mainly one) - when I try to cut out a piece with a 1/4" end mill and a profile path, the bit keeps coming loose from the collet. I have the spindle from Carbide. I have tried different bits, inserting as much of the shaft as I can and still get through the material (usually 3/4") and tightening as much as I can, but the bit still keeps coming loose in the middle of a cut. What am I doing wrong? Bit speed? Defective collet? Thanks in advance.
How are you securing the endmill in the collet?
We recommend using the button only to hand-tighten so that things will stay in place while one fully tightens w/ a pair of good quality wrenches (13mm low profile and 22mm stubby).
Reducing the cutting forces will help as well — avoid cutting slots as narrow as the endmill as much as is possible — add geometry and cut as a pocket down to tab depth or the penultimate pass.
If you continue to have difficulties, let us know at support@carbide3d.com
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Just curious - do you entirely remove the collet and nut at each bit change, or are you removing and sliding in a new bit with the collet and nut still attached to the router?
I ask because I could envision issues like what you’re describing if there was a little dust trapped in the collet (or between the collet nut and collet), when tightening down on a bit.
Early on I discovered that I had to take the collet out entirely and clean the collet, nut and socket at each bit change because a bit of fine dust gets drawn up in there. I keep a small brush handy for this. It’s just become part of bit change procedure for me.
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I had a bit come loose once. What I noticed is that there was a lot of debris up in the router. I thoroughly cleaned out the router with air and have made sure to clean the collet every bit change.
I have not had this happen since.
I also try to not over tighten the collet.
The above is what I have done, others may disagree, but it seems to work for me.
I had problems as well. It turned out for me that “good quality wrenches” didn’t include the ones received with the machine. Buying new wrenches was the key for me.
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You only need to insert the bit to length of the collet. If you bottom out the bit in the router shaft vibration can occur. The c3d collets are about 3/4 inch long so best to insert no more than an inch. Clean collet and router shaft with solvent like brake cleaner. Cover spoilboard below router to keep mdf from swelling. You can mark bit with marker ar 1 inch to aid in insertion. The mark is also a good visual to check if bit has slipped.
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GDon is correct. I usually hold my bit with only .75 showing above my fingertips while inserting the bit into the collet.
The one thing I forgot to mention. At least until someone mentions something else. 
Thanks to all! I bet the problem is debris on the collet. I have been slipping one bit out and another in without removing the collet.I will try all your hints and let you know if I still have problems.
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