Q Re Strength of 1/4" vs 3/8" Fasteners

I've wondered about this from time to time, and now I have a situation where I need to know whether the difference in tensile strength matters.

I'm setting up a Pocket 4K with an Easrig Minimax. I plan to use an Easyrig Quick Release, which comes with both 1/4" and 3/8" studs. The first photo shows a Minimax + Quick Release in use. The second photo, borrowed from a post by Mark Wyatt, shows a Quick Release stud on a top handle.

Easyrig has designed its Quick Release for use with all Easyrig models, one of which supports a maximum load of 32kg (70lbs). The Minimax supports up to 7kg (15.5lbs). I expect my camera, lens and accessories to weigh no more than 4.5kg (10lbs).

My question is whether it makes any practical difference whether I use a 1/4" stud and socket or a 3/8" stud and socket. I should note that I plan to try the Quick Release mounted directly to a socket on my 8Sinn camera cage as well as on a top handle. I'm satisfied that the cage and top handle sockets, and my top handle mount, are themselves strong enough. If I can use a 1/4" socket, I have more options for attaching the Minimax.

A quick search, by no means exhaustive, on the difference in tensile strength between these two sizes of fastener suggests that it doesn't matter whether I use 1/4"-20 or 3/8"-16.

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Easyrig Photo.jpg (247.83 KiB) Viewed 3093 times

Mark Wyatt Photo.jpg (259.46 KiB) Viewed 3093 times

A quick note:
Even though bolts may be rated for certain loads, please keep in mind that dynamic load may be much greater than static load.

Hey Rob,

For that setup, I am using the 3/8" (just to be on the safe side). That means I have 3 x 1/4" for the Smallrig top plate connected to the top of the camera, 2 x 1/4" for the handle connected to the top plate, and then 3/8" quick release adapter. I am sure the 1/4" would probably be ok, but screws definitely do break, though I expect the Easyrig quick release is of high quality since it really needs to be (hopefully, haha).

If you have the option of using ⅜” that works for you in terms of clearances and balance where your ⅜” are positioned, I’d go for the larger screw as Marc suggested. You’re right though that the ¼” give you more mounting points so you do need to be convinced that ⅜” is going to give you your preferred mounting point position. I had a similar issue with my Shape cage for the BMPCC4K where the ⅜” I wanted to use for the BT Titan Arm would not work in conjunction with the best balance for my Top Handle. So I had to use ¼” but it’s been fine nonetheless.

Thanks for the input. I'll try to go with 3/8", just wanted to see if the idea of using 1/4" would raise red flags.

I expect the Easyrig quick release is of high quality since it really needs to be (hopefully, haha).

Being new to Easyrig, and reasonably paranoid, I've already thought of how I might set up a safety wire Thanks for the details on how you've set up your Minimax.

I had a similar issue with my Shape cage for the BMPCC4K where the ⅜” I wanted to use for the BT Titan Arm would not work in conjunction with the best balance for my Top Handle. So I had to use ¼” but it’s been fine nonetheless.

As you know, I use a Titan Arm myself. Very interesting to know that 1/4" at the camera end of the Arm is working fine to support your Blackmagic Video Assist.

Even though bolts may be rated for certain loads, please keep in mind that dynamic load may be much greater than static load.

Will do, although I don't anticipate using the Minimax in a way that would cause large fluctuations in stress on the stud and socket.

.

It all depends upon the metal chosen for the bolt. When you see the size of critical fasteners used in aircraft, you will quite literally perceive a developing weakness in your bowels if you are about to take flight in the aircraft.

My personal preference is for the larger diameter bolt. I can find them conveniently in a hardware store and trim them with a hacksaw, file and vice to my heart's content. I need not fret so much about strength and yield strength of the metal. However, the strength of the bolt may become the least of one's concerns.

On the BM URSA Mini upper and lower mounting points, especially the upper, the attachment bolts are loaded by tensile and bending forces, the worst load state. With machined broad flat surfaces on mounting points and accessories, loading upon bolts is mainly tensile. The attachment point mating surfaces are castwork and not machined flat on the BM URSA Mini.

If third party accessories are not correctly designed to compensate, particularly for the upper attachments, they will impose bending loads upon the attachment bolts and the supporting threaded pillars they fasten into. In that circumstance, the bolts might break or instead spread the narrow walls of the threaded pillars loosening the helicoil threads which may then come out.

Top-mounting cheeseplates look sweet but may cause false re-assurance. Some things you should be seriously examining :-

Is the cooling airflow compromised? If you continuously run the CPU too hot, you may not reach the 10,000 hours or so it is supposed to work before laying down.

What provision is there to share the dynamic loads with the base mount attachment points, especially lateral and front-heavy? With a mattebox, heavy lenses and heavy batteries, you may be really pushing it unless there is bridged support between the lower and upper attachment points.

The URSA Mini alloy casework is adequate but with the outboard leverage of stacked attachments things change. If your agile cammo goes leg-up, is pulled into a faceplant by a rampant steadicam or some fool hangs a toe in a cable and pulls a tripod over, your camera may become a parts donor for the sleasy likes of me after the top and/or front casework is broken out.

In that circumstance, a bolt failure in overload may become a blessing.

It all depends upon the metal chosen for the bolt.

Just came across this video. Johan Hellsten, inventor of the Easyrig, and his friend Christer the Pizza Man, test the strength of the Easyrig Quick Release and its bolts/studs

I think that Easyrig includes 1/4"-20 studs with the Quick Release because it's comfortable with people using them, at least with the Minimax, which has a maximum load capacity of 7kg (15.5lbs). If there's an issue, it's 3/8" vs 1/4" sockets on my cage and top handle. I'm comfortable with the materials quality of my 8Sinn cage and Wooden Camera handle.

If I have a weak point, it's the 1/4"-20 socket on the top of the Pocket 4K, which is one of the two attachment points for the cage. As Pocket 4K owners know, Blackmagic warns about the strength of this socket. Next time I purchase a camera, I'll pay more and get one that's built better. In the meantime, this is not something I can do anything about.

Thanks to those who commented. It's helped me think this through.

1/4"-20 can take a lot of direct pull, it is more question for the thread and attachment point over all on the camera and how direct pull that is.

Also fatigue is something to consider.

Over all it is good to consider fail safe. That is if one connection breaks, there is still something preventing catastrophic fail.

Thanks Kim, good to have the view of someone who makes camera hardware. I'm going to take a wait and see attitude toward a safety wire, but it would easy to run one, although a bit of a nuisance, from my base plate to, say, my belt.

Yesterday, I did a rough setup of the Minimax with the Pocket 4K. I'm using the Easyrig 3/8" stud. However, if it helps fine-tune balance, I'm prepared to use Easyrig's 1/4" stud and a 1/4" socket. The following post and the one after it explain the setup: viewtopic.php?f=2&t=105319&start=300#p732570

The main issue with 1/4” is the amount of turning force needed to solidly attach a plate to a camera which can damage the often flimsy camera side esp as the thread depth is not very much. Once you are just dealing with threads on a cage you can crank them down with much more force as the surrounding metal is much more substantial and the threads are deeper. Anybody with mechanical experience should be able to size up by eye what thread diameter is suitable for a particular load and 1/4” is fine for small cameras when not subjected to much dynamic load on a static tripod but anything more and it’s looking pretty undersized....

Bigger the better with this kind of engineering.

The way the cooling works by the way, is that the middle aisle where the 1/4 screws are is SLIGHTLY higher than the sides so any cheese plate attached there has a built in gap for air to escape. It doesn't close it off, same on the bottom for that matter, unless you rest it on a cinesaddle in which case watch how hot you make your camera after 10 mins

I REALLY WISH THEY'D USE 3/8" ON THE BOTTOM

But that said, it's worked ok for me on various high G rigs. I have seen some people yank the thread out of the bottom of the camera through over tightening the 1/4"s, and need a helicoil repair.

JB

QUOTE: John Brawley.

The way the cooling works by the way, is that the middle aisle where the 1/4 screws are is SLIGHTLY higher than the sides so any cheese plate attached there has a built in gap for air to escape. It doesn't close it off ------

I should have been clearer in my responsive comment. There remains small side-clearances when a wide cheeseplate is fixed to the top. The unused holes in the cheeseplate will also pass some airflow if an accessory is not sitting broadly on the cheesplate. The need remains for users to make sure that the inlet and outlet spaces are not impeded.

It does not take much to stall airflow from an axial-flow fan. The mesh necessary top and bottom already imposes some restriction. A significant path for airflow is from the front as well as the sides. A slight breeze from front-on may initially help purge air from the space between a broad cheeseplate and the casework.

There may be reached a point where stronger wind pressure from the front will stall the airflow through the camera if a broad accessory is mounted close to the top and acts as a scoop. Airflow into the bottom vent ingests through the sides of the lower airspace if the shoulder mount is fitted so a front-on breeze will not introduce an equal counterpressure into the lower vent.

I realise my comment is pedantic but I think users need to be mindful of the airflows and heat management. One assumes that BM did some smoke testing or even thermal image testing to see what happened before they released the cameras.

I REALLY WISH THEY'D USE 3/8" ON THE BOTTOM

I think the basic issue is that the Pocket camera bodies are plastic without a metal/magnesium skeleton. It isn't clear how much, if at all, using 3/8" rather than 1/4" for a socket addresses this, and it may encourage people to think that the sockets are stronger than they are.

This is the warning in the Operation Manual for the Pocket 4K 1/4" socket on the top of the camera. Perhaps the bottom socket has some kind of metal reinforcement, but if not the top socket probably gets particular attention because it's where users add accessories:

warning.jpeg (362.15 KiB) Viewed 2532 times

Being a believer that all genitalizations are wrong.
I will say this, things are only as strong as it's weakest link.

As someone who has spent a good deal of my working life suspending objects, I would suggest that you do include a safety, secondary system. This will give you peace of mind.

As someone who has spent a good deal of my working life suspending objects, I would suggest that you do include a safety, secondary system. This will give you peace of mind.

I've come around to that point of view. I don't trust the Pocket 4K sockets, and re-reading the warning in the manual reinforces the concern. Using an Easyrig, your hands are on the camera most of the time anyway, but I think that it may be possible to run a safety wire that won't get in my way.

I don't trust the Pocket 4K sockets

Are you not using a full cage on the Pocket 4K?

I don't trust the Pocket 4K sockets

Are you not using a full cage on the Pocket 4K?

The camera's two 1/4" sockets are the attachment points for the cage. Not being a structural engineer, I'm unsure how much a cage "fixes" the warning about the accessory socket. Yesterday, I learned that the 6K Pro has the same warning. Don't know what's "Pro" about that.

The camera's two 1/4" sockets are the attachment points for the cage.

I can only speak about the cage I have on my Org BMPCC.

Once you have placed the camera into the cage all the pressure points are taken of the camera body(if using a full cage).

To my thinking if you attach anything to the cage be it from below as gimbal, tripod etc. The cage is what is attached to the support device and the same goes for if the camera is suspended from above,
The cage takes the weight.

The 2 X 1/4-20 top and bottom keep the camera in place in the cage.

I could be wrong.

The cage takes the weight.

The 2 X 1/4-20 top and bottom keep the camera in place in the cage.

I could be wrong.

The practical reality is that I'll be using the Easyrig, not just with a US$1300 Pocket 4K, but with a zoom lens and follow focus worth about $5,000. I don't trust the Pocket 4K sockets. I have to think through exactly what could happen if the sockets fail.

A safety wire would also address a failure of the Easyrig line itself, although I've yet to see a report from an Easyrig owner about such a failure. That would add the cost of my monitor ($1000), put at risk my Titan Arm ($265) and sometimes put at risk a Schoeps microphone ($1800), although the Cinela windscreen on the mike ($250) would probably protect it.

It adds up. I'll decide over the next few days whether a safety wire is helpful, and convenient enough that I'm happy to use one. If a safety wire doesn't get in the way, I'm reminded of what an elderly neighbour used to say about chicken soup for a cold: "Couldn't hurt"