plan B for pulley/flywheel removal


New Member
Hello all:

I'm trying to remove the flywheel from the shaft of a scavenged treadmill motor (for use in a future DIY wind turbine). The joint appears to involve a key and keyway between shaft and flywheel, but reinforced by an in-line set screw with a hex socket. In hindsight, the socket must have been 3mm, but I fear I've stripped it out trying to loosen it with a 7/16" Allen wrench. I'd rather not destroy the joint by drilling the hex screw out, especially since I lack the tools and skills of a machinist. Is there some other option that doesn't involve paying a professional?

Thanks in advance,
Rob Capps


Photon Sorcerer
Have you tried driving in a 3mm hex key (or bit)?

"in-line", do you mean axial, concentric to shaft, rather than radial, in the flywheel and clamping on the key?
I assume this isn't in the flywheel, where drilling it out wouldn't matter.

Sometimes, penetrating oil helps, and sometimes hammering helps. I have a 1/2" drive tool I strike with a hammer to get philips screws to turn. The strikes may help relieve pressure on threads, especially for a set screw without head.

Bolts, I sometimes arc weld to a socket. The heat probably helps too.

A puller might get it off despite setscrew on key.


New Member
Thanks for the quick reply!

I've rounded out the socket so much with a slightly-too-small 7/16" key that the 3mm one won't "grab" the socket anymore.

"In-line" was my amateurish way of saying the set screw penetrates the flywheel perpendicular to the shaft, and is radially (like a spoke) aligned with the keyway. This radial alignment leads me to suspect the set screw is clamping the key in place, but I don't know this for sure. The set screw is approximately an inch and a half away from the end of the shaft, but I don't know how long the key inside the key-way is - I just know that it ends where the shaft does because I can see it.

I reckon I should have hammered the hex key in first, but I was both too optimistic and impatient for that. Live and learn.

Arc-welding sounds both intriguing and unnerving. I've never done it deliberately (plenty of times by accident). I'd be willing to try, but due to the small distances involved (less than 1/4" in diameter), I'd be worried about bonding the set screw to the flywheel. Not to mention damaging the motor coils and/or rectifier inside.

By "puller", do you mean a 3-jaw puller?


Photon Sorcerer
Arc weld is more practical for an exposed, rounded hex head, not hex socket. Brief hit of heat, rest of motor wouldn't get too hot. So long as ground clamp on shaft or pulley, no current flowing through windings or electronics.

EDM (electrical discharge machining) is a way to remove stuck parts. I've never done it, but had it done.

You ought to be able to drill the set screw with a drill the size used to tap the female thread. That's if you're trying to save the flywheel; if not, drill up to a clearance hole for the threads.

Yes, 3-jaw puller, or bearing puller, whichever you were likely to need to get it off once the set screw was out.



New Member
Often times, you can shock the hub with a hammer, and it will relieve the tension of the set screw enough that you could possibly back it out with whatever size you can get to grab. The tension is relieved by making a groove, or physically galling a trench that the set screw is setting in. The keyway tends to be very soft, and one can easily make some movement which breaks the tension.
There are also left handed drill bits which dig and rotate counter-clockwise. Sometimes you can get lucky that the bit will grab enough to back out. Hope this helps.


Solar Enthusiast
I would just drill it. You don't need the pully right? Even if you manage to drill completely through the shaft it should still be usable.


Staff member
A picture might help...
I have been pulling setscrews and keyway all month... im scrapping several hundred AC units in my shop...
Anyway, if the sets crew is locking a key in place, the key can be shattered... if you can get to the actual motor shift.
Keys are designed to sacrifice when bound, to prevent a fire, or destruction of components.
If however, the set screw locks to the motor shaft itself, it will need to be unscrewed, and it will be VERY difficult to use an easy out because the screw will be under compression, not tension...


Solar Enthusiast
Keep in mind... extractors are designed for bolts under tension... not compression like a set screw is.
I'm not an engineer, but all I know is the last Allen head bolt I messed up, I drilled a hole in the center and the extractor got it out with no problem.
Mind you, I've had extractors break inside the bolt and as the extractor is hardened steel it made the problem far worse.


Solar Addict
I'm not an engineer, but all I know is the last Allen head bolt I messed up, I drilled a hole in the center and the extractor got it out with no problem.
I’ve not had luck with extractor sets. I’ve always had to drill. Unfortunately with drilling, very difficult to get the center of the screw. Depending on how far off center, can knock a balanced part out of balance.

The last major thing I wanted to extract was a cam bolt on the crank shaft of my car. Using an impact wrench and cheap chinese made allen bits had rounded out the bolts. Ended up not being worth the effort for what I wanted to do. If I ever do need to get that off, I will use the weld method, or likely a new camshaft and gear will be cheaper than a welding kit.

Beside Drilling, I have had luck with heat and also CRC Freeze spray. An Impact wrench helps. If its already stripped, that probably won’t do much good. I use WD40, but doubt the effectiveness.

Most important though Once Your Build Commences Would be awesome to See a BUILD THREAD.

I’ve also had luck cutting behind the piece and picking away at something with a Dremel. I have a 3” Metal Cutting Disk I can get fairly clone and then use some sort of metal grinding bit to get the rest,


New Member
Thanks to everybody for chiming in; you've given me some great ideas to try. I couldn't have asked for a better welcome to this forum. And to chrisski: if this works, I'll try to take good pictures of the generator build as it progresses, then post them in a separate thread.

One other thing has occurred to me, though: the flywheel has a "threaded" (as opposed to smooth-rimmed) pulley built in to it, originally connected to the treadmill's drivetrain by a small diameter belt. In the spirit of K.I.S.S., I might just join this to the stripped-down rear tire rim of the bicycle with a suitably sized belt for the generator build. The gear ratio would be high enough, and I wouldn't have to fiddle with the set screw or keyed joint. The idea of removing the flywheel was in aid of furthering my kids' education about mechanical matters, but maybe simpler is better.


Solar Addict
I recently purchased a book off Amazon about building your own windmill. Although I doubt I will go that route, It’d be nice to get a junk alternator and attach it to a homemade turbane to see how much juice it could produce.

My goal is 250 wh or so a day. This matches the amount of power I would want to get from some places I take the RV.

Very little available out there about Wind Turbines. This forum here gets a post every two to five minutes, and I have not found a wind forum that active.