Is there some sort of trick to keying a canvas?

First time working with a canvas big enough to need keys.  As I understand, they help tighten the canvas, which would be extremely helpful!   It's tight, but sensitive to humidity changes.

The keys keep falling out.

Is there some sort of trick to this?


https://en.wikipedia.org/wiki/Tightening_key

Ah ha!

I put mine in the wrong way, with the slant pointing away from the corrner.



I'm morning how many hours of my life (3) I lost to this problem.

Nope, that way of putting the keys in was just as bad.  They all fall out!

jacksons suggests we can use keys either way

Here is my theory

1. The staples they used over the join to attach the canvas is preventing it from stretching

2. The glue they used to neaten down the corrners of the canvas is preventing it from stretching

Or

3. The keys are too smooth.

One and two seem hard to fix.  So I focused on 3 and appled some hide glue (because easily reversable) to one side of each key and will leave it to dry.  This isn't to glue the key in place.  Instead, this liquid hide glue seems to stay slightly tacky for about 4 days and might provide enough friction when I insert them tomorrow.

Didn't work. Keys are too thin.

New theory.  Keys are too small or wrong shape.

User error is still on the table

I got a winsor and newton canvas and putting the keys in was a treat.  So easy!

As the canvas was overall loose, I first sprayed the back with water to moisten (but not too wet) the back, then let it dry a few days.  This got it most of the way there, but still a bit bouncy for my painting style.  So I put the keys that came with it in.

The keys were very snug in the slot, not loose like the opus canvas above.  I pressed them in with my thumb, but since I didn't have a hammer, I used a pair of heavy plyers to give them an enthusiastic tap.  None of the keys loosened or fell out as I tapped the others.  They all stayed in place as designed.

So, the first canvas has three issues I can see.
1. the keys are too small for the slots.  There's not enough friction for them to stay.  I think it's mostly too thin, but possibly too small in all directions.
2. they canvas is stapled across the expansion place - so the keys can't expand the stretcher, thus reducing friction and the keys falling out.  
3. the canvas was already tighter than needs to be - so the keys wouldn't have done any good anyway.  As I was painting on it, I was wondering if it's too tight and might cause problems later.  


So now I know what it's supposed to be like.  I wonder.  I have three more canvases from the same line as the first one.  Would it be worth re-stretching the canvas or at the very least, removing the staples that are in the way of the stretcher being a stretcher (it's just a strainer like this).