On Sun, 09 Aug 2020 21:33:03 -0400, Paul
wrote:

snip


This is one of those instances where (for most of us anyway) 'a
picture speaks 1000 words'.

snip

But without a picture, we can make some simple statements.

Well ...

Gluing pieces end-on won't work. Not strong enough.

But the OP said 'a small piece snapped off' and we don't know what
load it would be under when it's repaired and all screwed up again?
The bit that broke off may not typically be under much load at all and
something like JB Weld on some clean breaks may well hold it
perfectly?

------X X-------
/

If you add a slab of material underneath, now there are
a lot more square inches of glue working for you. But
practical issues (how armrest fastens to tubular frame)
aren't going to work out for you.

------X X-------
/ XXXXXXXXXX
----------

*******

Sure, if that was how / where it broke (hence the picture). ;-)

It might be that the op would reinforce the back of that area with a
thin plate because the forces are only in shear, and as long as the
screws are kept tight ...

Say the arm has a hole at each end that provides the main support (arm
in tension) but a third / smaller lug that *just* keeps the arm
upright. The main tension screw becomes loose, allowing the full
tension load on a part of the arm not designed for such and ...

Now, if you aren't into your structural engineering you (one) might
not appreciate that and so assume the 3rd screw takes any real load in
normal circumstances.

When the armrests on the chair I'm sitting in failed,
I made new ones. The retention screws tend to
constantly loosen up.

Loctite?

But at least I have armrests.

;-)

Cheers, T i m