Customer Rating: 
Summary: Beware! This accessory is hazardous!
Comment: Several other reviewers have commented on the tendency of this keyless chuck to wobble and loosen in use. In some 20 years of use of this accessory, I've also found this to be the case (the tool bit works loose during use about 1/3 of the time), but have also found that this is particularly dangerous at high tool speeds. I recently had the keyless chuck vibrate loose while using a cut-off disk. Despite the fact that I felt a vibration in the tool and hurriedly moved to shut it down, by the time I did so, the mandrel had walked its way nearly fully out of the chuck, bent sharply sideways, but luckily stayed stuck in the chuck jaws long enough for me to shut down the tool. Despite the fact that cut-off wheels are extemely light, the mandrel was dramatically bent to some 30 degrees. I can barely imagine at what velocity the mandrel would have shot off had it not snagged in the chuck jaws. Lightweight but high velocity objects can cause severe injury, so if you intend to use this thing, I recommend that you save it only for low-speed applications. Stick to the collet chucks for high speeds -- I personally have never, in some 20 years, seen one of these get loose while working with the Dremel.
Customer Rating: Summary: they got it right the second time
Comment: In 1994 I purchased a Dremel kit and a version of this chuck was included. I was quite excited as those who have worked with the fixed-size collets know how pesky they are, especially for small drill bits.
ohmi Vibration. I contacted Dremel Manufacturing and they, in 1995, had withdrawn this chuck as it was "too heavy" and "did not run true." They were glad to send me a package of fixed collets (but, having about fifteen different Dremels -- AC and battery), I have enough collets, thank you.
Several years passed and then I saw that the adjustable chuck was again provided. I have one and will get more ... Dremel has solved the 'balance' issues which, are mighty, given the mass of this steel and speeds of 30K RPM.
Also, I am a fan of the 50-bit box sets of carbide drills. When Harbor Freight sold these at half price, $4, I bought eight boxes. However, if you've tried these, you know that using such bits on metals, even 'soft' metals, they break easily.
Using the variable chuck I devised a solution. If you have ever tried to deal with a carbide drill, broken off in a drill hole that is critical, you will mightily appreciate this ... so ... for $9.95, check or Paypal, I'll provide instructions and 2 additional components that virtually eliminate breakage.
And, if you haven't tried such a drill, for $12.95 I will send the instructions, kit, and 3 carbide drills for you to try. Quite honestly, if you have not had the delight of using a carbide to drill, say, medium-hard steel, or even a printed circuit board, you will be very pleased.
W. Curtiss Priest, Ph.D.
Engineer
email: bmslib@mit.edu
