Dremel 4000 quit working

The power “switch” is a sliding lever that engages a microswitch (which does the actual switching). However the design of this is so %#*@ dumb as to make one despair for the state of the human intellect. If this happens again, get a small hammer, slide to the “on” position then give the body a sharp love tap right above the speed control dial. If it then comes to life you’re a victim of bad design. If you look at the picture of the dremel 4000 electrical assembly replacement picture earlier in the thread you’ll see a black box on the left. That’s a microswitch. The blue plastic “on/off” switch we humans operate is nothing more than a long strip of plastic that reaches all the way back to press this microswitch. The trigger on the microswitch is nicely rounded so that something sliding over (and travelling down the long length of the component) can easily operate the trigger. However, in the dremel the microswitch is mounted sideways so the blue plastic on/off lever (which is soft plastic) has to scrape up over the side of the trigger that has a sharp right angle. The trigger is also soft plastic. To make things extra schmart the microswitch isn’t actually screwed on to the housing, it’s only gripped by a ridge molded into the inside of the housing. So one of 3 things may be happening when you slide your power switch: 1. The plastic has been scraped off the blue lever by the sharp corner of the microswitch’s trigger, 2. The plastic has been scraped off the trigger itself, or 3, the microswitch isn’t being held securely so instead of the lever depressing the trigger, the whole microswitch part moves. All of these failure modes are covered by whacking the side of the tool just above the speed selector dial.

bkm sure sounds like you are on the right track. Only thing I would have done different is to check the switch assembly for simple on-off function to see if that is going to be the issue. You so want to make sure that your brushes are okay and check the resistor which goes to the motor from one of the brush assemblies. One weak spot of these is the plastic switch that is activating the microswitch on the switch assembly. Make sure that it is properly activating.

My Dremel was either intermittent or died when under any load. An air blow out/clean made no difference. Brushes were basically new. I disassembled the unit and noticed a tiny piece of metal fell out. This turned out to be part of one of four slide contacts between the circuit board/switch assembly and the external main coil assembly. These 2 main parts connect together via 4 pins and 4 sliders. Two had broken so the contacts were loose at best but mostly non-existent. I was able to give it a McGyver fix with thin slithers of metal that help to maintain the contact. How did this happen? I do not know. My Dremel is out of warranty but has not had that much use. Well ,fixed and useful for now.

Hope that description helps someone else fix their Dremel.

i have a dremel 4000, it cuts out very often, but more so if im using the flexicord, i have tried all the possible fixings people have put up here, and it still happens, if i leave it for 10 mins or so it works for 5 mins again, i get the fact it’s obviously over heating but for no reason_{, people have said its not designed to be used extensively}, then whats the point of it being in existence, i had an older dremel for about ten years and it never had a problem, and that did much more work than my newer one, its just out of warranty, but i think ive got the answer, dremel have started to use sub standard parts, in england they use free visible wires while in the states they seem to have a closed section that clips into the back of the commutator housing, is there a difference in quality between the two, other than its easier to take apart and refit as opposed to the english part, as an example i used my old dremel to sand uprights in a set of bannisters, it was running solid for the two days it took to do the job, my newer one would now take a day to do half of a single upright,,, not impressed dremel, take note and solve these problems, or make the price more compatible to its ability,

My Dremel 4000 is working when used by itself but for some reason it doesn’t spin the flexshaft (Dremel 225) when it’s connected anymore. Any idea what might be causing this?