jmbfestool
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- Joined
- Jan 9, 2009
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- 6,646
Rick Christopherson said:It happens to me too, and you are correct--it is from being stupid. [big grin] It is not the chuck, it is the operator not inspecting the bit they just installed. Contrary to intuition, it is actually caused from the chuck gripping too well.
This happens with non-round shanks, like hex and tri-flat bits, and the operator closes the jaws by running the drill and holding the bit. The jaws have enough immediate grip that they will catch the lobes or points on the shank and begin tightening against them. A chuck with less immediate grip will allow the bit to slip a fraction of a turn to align the flats with the jaws.
If you have caught the lobes or points on the leading, or uphill side, the bit will stay locked in place while under load (e.g. while drilling), but as soon as the load is removed, the bit will relax in the jaws and re-seat the way it should have been set. This is what makes people think that the chuck suddenly let go of the bit--because it held it long enough to begin heavy drilling.
To stop this from happening, simply get yourself into the habit of looking at the flats of the bit as you begin to tighten the chuck.
P.S. The faster the drill is spinning while you are closing the jaws down (like going from a large shank to a small shank bit, and the drill is spinning really fast because you are too impatient [big grin]) the closer to aligned the jaws can be with the flats, while still being non-aligned. The jaws grip so hard, so fast, that they can grip the bit just barely skewed off the flats. However, in these cases, the bit usually pops loose as soon as you begin drilling--not after a lot of drilling.
The image below shows the jaws gripping a hex shank bit, but gripping it on the points.
I missed this post! This can only happen with hex and I always check I can even feel if it hits the corners thats how often I change my Hex bits. Clever isnt it! I do is so quickly I run the drill feel that is hasnt got the flat bits I then run the drill the other way quickly then front again some times I do it 3 times because I am doing it to quick and 2 times the chuck catches the corners.Often well nearly always if the chuck only grips the corners the bit wont be straight and would wobble so you know your self the bit isnt in correctly and would adjust it! Im sure alot of peole are aware of the chuck only gripping the corners!
Well thats why I used a large round drill bit as this can not happen! I didnt use a small bit cus you can get it of centre and only 2 of the grips on the chuck catch the bit which again while cause to wobble as its not in the centre! Using a large bit like I did non of the above can happen as their is no room for the bit to try and slip out of line basically the bit will always self align into the centre because it its larger size!
JMB