Hi,
After experiencing a filament clog, I attempted to remove the hotend to clear it.
However, one of the 2 hex bolts had a stripped head (the right one, highlighted in the attached photo).
Thus the hex/allen key ‘freely rotated’ in the bolt head.
I tried various hex keys in case it was the key that was stripped and not the bolt-head. No joy.
I then tried using a ‘damaged screw head extractor bit’ in my drill, but the bolt seemed to be made of high speed steel. No joy.
My only remaining option appears to be using a Dremmel to score a horizontal channel in the bolt-head and then use a screwdriver to attempt to extract it.
I’m wary of doing this as it will damage the hotend, and may damage the toolhead.
Any advice would be very much appreaciated.
PS Great printer apart from the above and the cloud outage last week! 
Thanks in advance.
Glyn
If you carefully drill out the center of the head of the cap screw, with a bit that’s a little bigger than the hex key size (so, if you have a drill that’s around 2.5mm since I think that’s a 2mm keyway), the head of the screw will separate from the shaft. You’ll be able to extract the hot end and then grab the exposed threaded shaft with some needle nose pliers and twist it out.
Worst case, you drill a little deeper than necessary and take some material away from the bore in the hot end that the screw is going through. You should not be able to do any damage to anything else with this method.
Take a lighter and melt some plastic filament (higher temp strongest you have) push enough of the filament into the rounded hex to smoosh into the rounded hex area to pack it in. Cool it down completely, trim the excess. Take the hex key and heat up the tip enough to melt into the packed filament and then cool that down completely. Try and remove it!
If that doesn’t work, JB weld the hex key to the bolt and let it cure and spin it out. It shouldn’t be in there THAT tight.
I would not try the slicing a channel in it with a Dremel unless you feel compelled to. But that’s what I would try first.
Aluminum foil small strips build it up and find a replacement asap
Like the JB weld idea. I’ve had a stripped screw on my cooker for a couple of years and tried all sorts of things. JB weld ordered…
Yeah I have no idea if any of that would work but it’s just ideas before OP takes a grinding wheel to the nut lol.
I believe JB Weld may be your best bet. Even strong super glue may work to attach something to the bolt head to allow you to break the initial tightness of the bolt. If you take off the head of the bolt, you still won’t be able to remove the hotend, as the bolt shaft will still be in there. As the bolts go through the housing this is going to prevent you from pulling the hotend down to remove it. If you can get a small enough reverse drill bit, try that first if the JB doesn’t work. Usually bolts loosen and unscrew with them before the head is drilled completely off. It may be worth taking out the 3 bolts that hold in the extruder and remove the whole assembly so you can work on it outside of the printer. Worst case you may end up having to remove the cooling fan and hacksaw or dremel through the hotend where the bolt goes through. Obviously, this is going to destroy it but they’re cheap enough. Note that the bolts have a factory loctite on them and they can be tight. If you have a good square end hex tool which you can confidently tighten enough without damaging the internal hex, put some anti seize on the new bolts to make them easier to remove in future.
Is there enough room to grab the screw head with some vise-grips and rotate the screw out?
get an elastic band and jam it on the end of your allen key, it should grip and turn
Thanks to all who have posted with suggestions. It’s very much appreciated.
I bought the JB Weld epoxy resin (I was slightly dubious, as my GorrillaGlue epoxy has let me down a couple of times in other situations).
However, having patiently left the JB for over 24 hours, I’ve just extracted the hex bolt successfully. 
Cheers all, and happy printing!
Glyn
Had the exact same thing happen to me. This is what worked for me. https://www.amazon.com/Be91eiter-Extractor-Stripped-All-Purpose-Extension/dp/B09C5MNHQY/ref=mp_s_a_1_4?crid=1POT9DPBLEPIA&keywords=hex+extractor+set&qid=1693132903&sprefix=hex+ex%2Caps%2C145&sr=8-4
Also be aware that those screws have blue locktite so I unplugged the little hotend fan (not the part cooling fan) set it to 300 let it sit for like 20 minutes so it heat creeps up into the bolt loosening the locktite be very careful not to burn yourself. Use that set and my bolt came right out no problem.
Also you have to be extremely careful but your Dremel idea would work. Don’t put the slot all the way across. You only need enough to fit the screwdriver blade in.
Also maybe try to see if you can rock the hotend at all and see if that will loosen that screw a bit. Maybe enough you get it loose.
Two points:
If you are using the Bambu-supplied wrenches, stop! Get some quality wrenches of hardened steel that will fit the socket properly and are slow to lose the correct shape.
Avoid using a ball-end wrench whenever possible, especially for the initial loosening and final tightening of a screw. A ball-end concentrates the torque on six points that slide when the wrench is at angle, which causes wear and rounding of the socket. A straight hex will spread the torque over six edges, and will not move relative to the socket.
Just note I keep a set of left handed drills bits for these problems, as often the heat created frees up bolt and they spin out.I know this is no instant fix if you do not have left hand drills. I paid £8+ from aliexpress for a small set m42 cobolt left drills. worth having for future problems
Left or right twist doesn’t matter if you’re drilling off the head of the cap screw. If you’re using a left twist drill because that’s also the direction to turn the screw to remove it, then what you really want to use is an “Easy Out” screw extractor (which will turn counter clockwise like a left twist drill) and not a drill at all…
You need to drill a hole in the screw before you can insert the EZout. Using a left hand drill takes care of that, and about half the time it gets the bolt out all by itself, so that the EZout is not even needed.
Though they might exist, I’ve never seen an EZout small enough to use on a hot end screw.
They come that small, though not at Home Depot. Do a goog for mini or micro screw extractors.
I was just drilling screwheads out when this happened to me with other products. Luckilly, didn’t happen to bambulabs yet. And with this construction not like it will help a lot…
hi glyn
make up some super glue and baking powder dip your hex key in and push and hold until secure then un screw
superglue baking soda , mix and apply within 30 seconds