I bought an R8 from B&H and used it mostly with heavier lens (RF24-105L, EF70-300 with nano USM + adapter). I used it in the same way as my RP and 6DII. Within a month, the grip got "loose", in the sense that if I hold the grip tight and tried to squeeze/move the grip, I could feel that the grip moved a little bit and it made some clicking/cracking noise. The noise/move seemed to come from where the grip part meets the top panel right around the shutter.
I did an exchange and also bought the extension grip hoping that it would make the grip structure stronger. I also then handled the R8 with more care, like not picking up the camera with my index finger right under the shutter. However, after a little more than a month, the grip is a little loose again, but this time it's just a little bit and doesn't bother me much (so far).
My RP's grip also gets a little loose after about one year's usage, but I can mostly fix the problem by adjusting the three screws (two on the side, one on the top panel). I can't achieve the same with my R8.
So at this point my personal conclusion is that the R8 build quality is not as good as I would like to have and even a little worse than RP.
What's your experience with your R8?
and
Update:
My replacement R8's grip became squeaky again after very light use (R5 is my main camera these days). Before my 1 year warranty expired I sent it to Canon. They said that the problem is the grip cover; R8 has a unique design that the grip cover itself is a separate piece and thus may get loose. They replaced the grip cover.
They didn't say it aloud because my camera was still under warranty, but I got the impression that this could possibly be a no-charge repair without a warranty. If your R8 (or even RP) has the same problem, you can give Canon a call to check whether the repair doesn't require a warranty.
Okay, some notes from me:
1. Have had R8 for 8 months, no issues at all, build seems solid, everything is tight, no real creaks or groans. 32000 shots and counting.
2. I have used the RF 100mm macro for most of my shooting so far with the R8. I recently got the RF 70-200 f/2.8 and am really loving it as well. These aren't the heaviest lenses, but they aren't super small or light either.
3. It sounds like you're gripping very hard with your right hand and basically making that the primary load path by which you balance the weight of the camera and lens.
4. I do component stress analysis professionally, so this isn't even fully conscious, but generally I use my left hand to hold the camera up under its center of gravity. This is the best way to hold it up in terms of preventing excessive loading.
5. I do try to be mindful of how I'm loading the camera and lens when I'm holding them. This probably isn't for everyone, but for instance when carrying the camera mostly by the lens, I internally note the contact forces of my hand - i.e. are my fingers exerting balanced loads, etc. For expensive equipment like this, how you hold something absolutely is important.
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For more of a deep dive on why using the right hand camera-body grip as the primary load path, especially for heavy and/or long lenses, here are the technical reasons, assuming the lens and body are held level to the ground:
1. The weight of the camera and lens must be balanced by the upward force from your right hand. This can be thought of your hand being a stationary support for the camera, which is trying to shear itself downwards out of your hand.
2. Because the grip cover is superficial, the shearing aspect of this loading will be a worst-case load on the interface between the grip cover and grip structure (I haven't done or looked at a teardown, don't know exactly how it's mounted).
3. Based on the weight and length of the lens, there is a moment applied. Basically a torque trying to pitch the lens downward in your hand. You can think of it as applied on the lens mounting ring as a force pulling directly outwards (parallel to lens axis) on the top half of the ring and pushing inwards (again parallel to lens axis) on the bottom half of the ring.
4. Continuing #1 and #3, there is also a vertical shear from the weight of the lens applied at the mounting ring (if you pretend the lens is detached). This applies two more torques to the body:
4.a. A "torsion" twisting moment, i.e. like if you take your hands on both sides of the body and try to twist them in opposite directions. This load and the lens moment from #3 are counteracted by your hand the same way - your index and ring fingers press down harder because the lens is trying to pitch down. The body also pushes into your palm.
4.b. A bending moment again like #3. This is less significant because the distance between your hand contact and the center of the lens mount ring is pretty small. However, it does try to rotate the body and lens counter-clockwise towards the ground (again, if you are holding the lens and body parallel/level to the ground). This pushes the right lower side of the body into your right palm and requires a bit more clamping from the middle and ring fingers.
5. All told, your right hand has to do a lot of jockeying if you are making it the primary load path to support the weight of the lens and camera. In addition to supporting the weight, there are all these torques to deal with. Depending on the placement of your fingers, you can easily grip in a way that adds more shear under your fingers due to contact angle/friction shear with the high normal force being applied. Since these weird torques are applied, it would also be very easy for you to be unconsciously compensating the sensation of the loading (which can include some weird loading on your wrist) with significantly more grip strength than is needed to compensate the load. This can of course cause issues as well.
6. Given that the grip cover is a nonstructural part and this type of hard grip is basically loading it as maximally as possible to shear from its mount and start to come loose, I'm not super surprised by the outcome.
7. As a comparison, if you hold the lens mostly under the combined center of mass of the camera and lens, the only load is (essentially): the small compressive force between hand and lens to hold the weight up vertically (probably with a much larger surface area i.e. lower stress on the surface).
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Finishing thoughts: from a shooting perspective, you don't want to load through your hand, especially with the R8. In my case, a ton of 1-1.4x macro outside and needing very low ISO to avoid clipping and chrominance noise, and trying to do handheld standing shots like this is very challenging. So, I am rather mindful of technique, and certainly this is some of my technical background, but how one holds and loads the camera is an important part of technique!
The more load you put through your right hand, the more tiny motion you'll have. The body is a dynamic machine. It's not a matter of strength - I can one-arm dumbbell row 40kg for 30 reps, for instance - a few pounds is essentially nothing. If you exert more force there, there will simply be motion. Imo, one should take as light a grip as possible with the right hand, particularly for a body without IBIS.
To be clear - I don't think one should have to approach a camera body from like a professional stress analysis perspective lol. I was just giving the full nerd rundown, because that's how I am. On one hand, I think it is possible to break almost any well-designed consumer electronic device with bad handling/load paths.
On the other hand, designs should try to accommodate this variation if at all possible. In your case, it seems you might be somewhat of an outlier in your handling. Given that it will probably save you headache AND give you better technique/shots (imo), I would just try to train yourself to hold under the center of mass (generally hand-under-lens). I would also try to be mindful of how hard your fingers press and where they press on things like this. I find it easy to over-grip things, and perhaps you might do this a bit as well.
Anyways this is probably the most over-written answer anyone could have mustered, so I will leave it there lol.
