I have a chair that has a knob with a screw in type extension (about 1/4 inch
in diameter). The threads on the screw in portion of the knob became stripped,
and I obtained a new knob. However, the opening where the screw in extension
belongs has become damaged and it needs to be rethreaded. I am pretty sure
there are tools that will rethread the opening, and I am wondering if they are
adjustable or if I have to buy a specific tool for the specific sized opening
that I am dealing with.
Also, if it is simpler to just take the chair to a hardware store and get this
small opening rethreaded I would be happy to do that. I just don't know where
to start, and am looking for good tips.
The tool you need is called a "tap". The sizes of taps are specified by
diameter and threads per inch...1/4 x 20 for example. You also need a tap
wrench to hold the tap.
The socket in your chair may or may not be able to be rethreaded depending
on how much metal there is. You will have to enlarge it by drilling to the
next size bolt thread. For example, if the old thread was for a 1/4 bolt
you will have to drill it out to use a 5/16 bolt. The drill you would need
to use is *smaller* than 5/16 though so that when tapped there is sufficient
metal in the hole for the tap to cut threads.
An easier solution for you may be to get an epoxy that sets hard, turn the
chair upside down, pack the existing hole with epoxy, insert the new knob,
wipe off excess epoxy and let the epoxy cure undisturbed for 24 hours.
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Thanks a lot for your help. The chair I am dealing with only cost $25 at
Sam's Club, but it has been a good chair for more than three years. The socket
where the know extension goes seems to be damages only at the beginning (the
extension did not reach very far into the extension). Is there some way I can
just get it started without changing the thread size--buying several tools to
fix the chair doesn't seem to be worth it. Also, the expoxy may not work
because the knob does not go that far in.
I'm taking a WAG that this knob may hold some essential part of the
chair (like the backrest) in place, in which case you want the fix to be
STRONG, or someone may get hurt, like if it fell off when they leaned back.
If that's it, you might want to take that knob down to the hardware
store and see if you can find a bolt with the same sized thread, but
somewhat longer threads, and a few washers to stack under the bolt's
head if need be.
You can probably get the bolt you buy started in the mangled hole by
filing its tip down slightly, and maybe even filing a couple of grooves
at the tip to turn it into an erzats "self threading" screw.
If that works, you'll be tied down to using a wrench to tighten it, but
if it's like most chairs, it won't have to get adjusted very often.
Better safe than sorry...
My name is Jeff Wisnia and I approved this message....
Take the knob to the hardware store and get a tap the same size
as it. Carefully screw the tap into the hole after putting a
little oil on the cutting threads. Screw it in 1/2 to 3/4 turn,
then back it out half that. Keep doing that untill the threads
are clean. Chances are, that will do the job unless the threads
are too messed up.
The next best step would bew to helicoil the hole. If you have to
buy it, the helicoil set will cost more than the chair, but it
would be a permanent fix.
I don't think the epoxy idea would last very long.
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