The shaft lock button operating properly is critical to your success in securing an accessory in the tool. If you can no longer tighten or loosen the collet nut properly, you should send you tool to us so we can help you with a repair. Here's our service advice – seat and then tighten the accessory properly. Don't over-tighten your collet nut. As you hold down on the locking button to over-tighten the collet nut, you risk elongated the hole the stop pin fits into. To loosen that overtightened collet nut, you will have to put excessive pressure on that some hole, in the opposite direction. Develop the good habit of verifying that your accessory is securely held in the tool, and never push the locking button down when the tool is turned on; doing so will damage the hole the stop pin goes into and the stop pin itself. This condition can be repaired, but this is generally user error, and not a matter of warranty.