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Dremel 400 speed fluctuates during useeg slows down then speeds up again

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My Dremel 3000 makes a grinding noise and fluctuates speed while in the low speed range. Why is this?

I have one that I must keep pressing ******* the speed control with my thumb during use otherwise it is hopeless except at or near maximum. The potentiometer is of poor quality.

Jan 02, 2017 | Speed Washing Machines

1 Answer

Dremel rotary tool variable speed, low speed speeds up after short use. Will brush replacement solve this issue?

How stable is your line voltage? The SCR phase control used for speed control is more sensitive to line voltage changes at low speeds than at high speeds. Brushes should be changed when they are worn down to about 1/2 of their original length. Much more than this and they don't have enough tension to properly contact the commutator ring. Check with power off when the tool is cold and slowly turn the chuck by hand to feel the resistance. Run it a while and let the bearings warm up. Turn off power and turn by hand again. If it feels looser when warm (which would cause it to speed up at slow speeds), the tool might need to be disassembled and bearings oiled. I use Dexron automatic transmission fluid to lube most motors. Wipe down any excess.

Nov 14, 2014 | Dremel Variable - Speed Multipro Rotary...

1 Answer

Fluctuating speed

With the motor being new and the "hot electrical" smell, I would say the motor control board, which sends the speed command to the motor, would most likely be your issue.

Apr 03, 2014 | Proform XP 580 Trainer Treadmill

1 Answer

New Dremel 7700 not working on higher speed

I'm having the same issue. Can't find any more nformation to fix it

Jun 21, 2013 | Dremel 7700-1/15 7.2V Cordless Two-Speed...

1 Answer

2001 Chevrolet Silverado 2500 6.0 idles too fast.

May be a cooling sensor issue . If you can hook a scan tool to it and watch the coolant temp pid while idling high it may show a fluctuating reading .

Feb 20, 2018 | 2001 Chevrolet Silverado 2500

1 Answer

Is the Dremel 400 XPR unreliable or are the users expecting to much from the tool? I like the looks of the tool but I will probably end up with a 4000. I've been using a cordless tool but it keeps...

It's heating up and tripping the internal overload. They do that to prevent the battery from overheating.
The cordless are nice but they have limited applications

Feb 23, 2011 | Dremel 400 Xpr Rotary Tool

1 Answer

Stop turning on lower speeds

mine does that also at lower speeds under, you might have to increase the RPMs. You might also want to try for assistance and they also have a toll free number for tech support.

Jul 06, 2009 | Dremel 400 Xpr Rotary Tool

1 Answer

Running slower than it originally did

blow out the ducts on the side and if that is not it replace the brushes.

Jun 05, 2009 | Dremel 400 Series Xpr Rotary Tool Kit with...

1 Answer

Dremel scroll saw 1672 16'' two speed scroll saw slow motor

Go to or call toll free1-800-437-3635 and tech service might be able to get you a schematic and wiring diagram. It does sound as though the switch is either wired incorrectly or put in upside down. If I have helped you on this would you please take the time to rate me accordingly and Thank you

Apr 03, 2009 | Saws

1 Answer

Dremel 400 xpr stopped working. checked brushes looked ok but replaced with new ones. still not working. tool is still fairly new with only light to medium use.

It could be the fuse between the brush and variable speed control switch. I have the same problem and found the fuse blown. I am hoping that I can replace the fuse without having to buy the complete speed control unit which is about $17.00 from Dremel. If yours is still under warranty you could send it back. If I can find a fuse for mine I will let you know where to get them. joatmontag

Mar 31, 2009 | Dremel 400 Xpr Rotary Tool

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