Good day everyone. I have had the unfortunate experience of the screw holding the support plate for the upper works of the lantern to the fount breaking off in the nut. Please see photograph. I have filed it flat and will attempt to remove the screw with an extractor ( I believe its called an "easy-out"), but should this fail, is this nut soldered to the top of the fount and if so, is it viable to remove and replace with a new nut?
I measured the broken off bolt at 4mm. However, having used an extractor, the hole is now much bigger. Its almost as if the screw went into a threaded "sleeve" inside the nut that is on top. Seeing as this is brass nut, I was wondering if one could solder another nut on top of this one to be able to assemble the lantern again?
Another thought running through my head is to try and re-thread the nut and use a coupling nut to create a new threaded part for a screw. I believe this type of extension is called a "jack screw"
You could also try a helicoil. Yes, the thread is M4. Remember that this is a blind hole and not to drill through into the tank. Doesn't help much with holes in pressure vessels.
Thanks for the information everyone. It's so nice to know that there are people willing to help out there. I will probably use a combination of methods as suggested by the members. I have managed to get all of the old screw out by drilling it out to 4.8mm. Next, I will get a 6mm plug tap and re-thread the nut as deep as I can for a brass standoff sleeve as per the method used by ROBB055. Then soft solder the brass to the existing nut to prevent it working loose. I should have my new threaded portion on the inside of the standoff sleeve to enable me to attach the screw from the support plate. Everything will depend on the success of tapping a new thread into the existing nut on the fount!
I think I have found the cure for this problem. I used an M6 self-tapping threaded insert. Inside thread is M4. Drilled out the hole to 5.5mm and all seems to be as tight and sturdy as the day it was made. The picture (sorry for blurry photo) shows the insert before I gradually shortened it from the front (cutting side) to get as far into the non-tapered threads as possible. I then filed the insert down to required height and reassembled the lamp.
