Lumen light R2 - screw on clear cap snapped

[Eloi (DynamOcean)]

Hello,

I have a set of 4 Lumen R2 lights. I opened the 2nd light in the daisy chain twice to be able to use 2 lights only and then back to 4 lights. When reassembling for the 2nd time, one of the screw on the clear cap snapped. I was using a screw driver but only finger tight. I have to admit however that at some previous point, the ROV was left not-rinsed during 4 days after a dive in salt water and some corrosion occurred in a few places.

Anyway, looking closely at the snapped screw (and the other screws two), it seems as if the end of the threaded part connected to the screw head is somewhat hollow. This means that the threaded part and head are connected by very thin metal. See sketch below for illustration.

Is this a know problem or just an isolated issue combined with corrosion?

I temporarily solve the issue by taking a spare Bluerobotics screw (dome mount I think) and cutting excess length. See photo below.

Can you confirm that the silver screws are stainless steel whereas the black ones are anodized aluminum?
Can I leave it like this or should I source a new aluminum screw?

From now on, I will just hold the hex tip (without screw driver) in my hand to screw the aluminum screws to make sure over-tightening is avoided.

[adam]

Hi @Eloi,

We switched to using aluminum in stead of stainless steel screws on the R2 lumens, primarily to reduce galvanic corrosion. Due to the thin material and tight clearances, the corrosion by the screws in the R1 lumens could cause concerning damage over time in certain environments. One trade off is the screws are a bit weaker than they were previously, due to the material used and manufacturing process. Over tightening can cause them to snap like this. We tighten them to 35 cN-m with a torque limiting driver in production, roughly finger tight.

You can replace it with a stainless steel screw, but corrosion is more likely to happen in the long term, especially if running in saltwater.

-Adam