Internal door handles keep coming loose every month! Carpenter has been out 3 times already

[Newdoors]

Had new (solid wood) doors put in throughout the house for about 6 months. It seems every month, one or a few of the doors’ handles keep coming loose. We’ve had the carpenter who fitted them out about 3 times already. Supposedly ‘bolted’ them at the last visit but, yet again, it’s started to loosen again. (Screws loose, handles wobbly).

1. Can anyone think why?

1. How many times is reasonable to ask the carpenter to fix it? It must be just as annoying for him as it is for us!

Are the handles working normally otherwise? Are you rough with them?

My guess would be that either they're defective or have not been fitted properly or the wood is too soft.

@FayCarew yeah, they work fine. Only once has it got so bad that the door jammed shut. We aren’t rough with them in any way, just normal every day use.

At what point do I stop contacting the carpenter to come out again? He supplied the handles and doors as well as doing all the labour so I don’t know why it isn’t working, even after coming back to fix it multiple times😕

Longer screws?
Oil/wd40 the mechanism so it doesn't need yanking?

What does the carpenter say?

Google 'loose door handles'?

Been here but OH dealt with it.

Is it the woodscrews that fix the mechanism to the door or the grubscrew that holds the lever to the mechanism/spindle (excuse my descriptions)?

If it is the woodscrews coming loose, are the doors solid oak as these can be very hard? OH used a different woodscrew and it never happened again.
If it is the grubscrews coming out then they can be tightened with a bit of Loktite.

I would be asking him to change them all for a completely different type of handle.

My guess is the wood expanding and contracting with temperature change - I.e when you put heating on. This small movement is working the screws loose. In terms of fixing it I’m not sure. The carpenter must surely be the expert here? Bigger screws? Some sort of wood glue to hold it more firm?