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I have a number of 1930's glass doorknobs which are loose, not at the set screw, but between the glass knob and the brass holder. Nearly every knob in the entire house has the same problem. They all have a steel thread, a solid brass compression member, and a glass (or perhaps lead crystal) knob.

I know I can purchase reproductions, but can I save these? Here's a photo:

vintage glass and brass doorknob repair

The one on the left rattles but is usable. The one on the right is to illustrate the construction and show a prior owner's repair (the dent is a hammer mark). That one had cracked glass, got looser and looser with time, until the glass broke off completely.

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If you can figure out a way to inject epoxy through the threaded hole to secure the base of the knob, without getting any on the threads, that should secure the knob adequately. –  bcworkz Nov 25 '13 at 2:39
    
Agreed,@bcwork. The usual problem I've seen is allowing the shaft to be threaded too far into the handle base, spearing the glass and forcing it off the base. There are some fairly clear sealants (nearly optical quality) (NOT silicones, usually), as well as the encapsulating grade epoxies. –  HerrBag Nov 25 '13 at 2:57
    
I'd need a time machine to undo any spearing damage. But since every single doorknob has failed in the house, I don't think that's the only problem. I've been inventing various methods to get the epoxy down without affecting the threads, but wanted some validation or better ideas. –  Bryce Nov 25 '13 at 11:16
    
Once you get the epoxy through, use a cotton swab saturated in denatured alcohol. Repeat until clean. –  HerrBag Nov 25 '13 at 12:47
    
Note the the glass is actually in a dome shape, and the inside silvered to form a mirror. This model has no protection against threading the shaft too far (that action first scratches the silver, then breaks the knob). –  Bryce Dec 9 '13 at 7:39

2 Answers 2

Try #1: Liquefied MDI adhesive.

For my first attempt I assembled hot water, a thermometer, glue, Diphenylmethane Diisocyanate (MDI) glue, and a straw. The MDI is a thick glue, so the trick was making it thin enough without creating toxic fumes:

glass doorknob gluing

  1. Extended glue with straw
  2. Heated water to 120F to liquefy the glue. Dropped knob in water to activate glue and heat metal.
  3. Turned glass knob to be as loose as possible, to allow glue to flow.
  4. Carefully poured glue inside, and "swished" it around.
  5. Dried the threads as best as I could.
  6. Turned glass knob to be as tight as possible to "clamp" the MDI glue.

MDI is an expanding glue, and indeed I had over-expansion which almost created a huge mess.

Also note the caution from customer service at Gorilla Glue:

Dear Bryce,

Heating Gorilla Glue before using it will thin it. The safest way to do this is to put the bottle in a cup of hot water; do not boil bottle on stove top or put into a microwave. If heated to approximately 120°F, the viscosity of the glue will be like water, and application is very easy. Foaming is reduced a little. However, please note, that the elevated temperature also increases the probability of releasing MDI fumes, so this requires good ventilation.

Sincerely, Mary Ellen Customer Support Representative

The repair held but it was a fair amount of trouble.

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+1 for research and documentation –  HerrBag Dec 11 '13 at 0:36
up vote 3 down vote accepted

Try #2: Cyanoacrylate

This worked much better. The local hardwood distributor carries super thin "super glue". Turn the knob in the usual direction to set it tight, then apply glue to the glass/metal junction (it will wick right inside). Keep acetone handy in case you dribble. Scrape excess off with a small screwdriver. Done.

super thin Cyanoacrylate

What will we do when local stores no longer exist? Sigh.

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