3/8 to 1/4 bushing resistant ?

[jk0592]

Well, I received my first LF camera last week, a Cambo monorail. Of course, the tripod socket is 3/8 inch, my 40 year old tripod has a 1/4 inch thread. So I installed a 3/8 to 1/4 bushing in the tripod socket. The camera is held in place, does not seem to vibrate.
My concern is that the coupling to the tripod is solely due to this bushing. The weight is not so much of a problem, but somehow i think that the torque applied to the bushing might cause the threads to collapse.
Should I worry or not ?

[BrianShaw]

I wouldn't worry. I've had cameras with bushings on tripods for many years an dnever had, nor heard of, a bushing failure.

[BrianShaw]

... of course just as I write this I'm sure someone will say the opposite, or have a story about how their camera fell to the ground due to a bushing failure. ;)

[lenser]

In decades of use, the only "failure" I've had was when I installed a bushing and over-tightened it with a screw driver, causing one edge of the face to chip off. I could have left it in and used it as is, but simply backed it out with the screw driver (the reverse side remained untouched) and replaced it with a second bushing. If you can find brass alloy, I think they are better than the steel, but both work beautifully.

[Bill_4606]

Quick answer... For properly tightened joints you are just fine with the bushing and 1/4x20 bolt.

Slightly longer answer... Where you get into trouble is taking the joint apart and putting back together. The larger thread size is quicker and less likely to cross thread.

Even longer answer... The tensile stress surface area of the larger is twice as much as the smaller so having the larger in the softer material, I.e. aluminum Deardorff base, has advantage, and bushing it down to a smaller steel tripod base is just fine. Since the proof strength of a 1/4x20 low Grade 2 bolt is around 1,000 kilo/sq. in. The smaller bolt will manage 100's of pounds of equipment so I woudn't worry about that.

Bottom line: see quick answer.:)
Cheers,
Bill

[Leigh]

A very rough calculation for the 1/4"-20 thread, assuming the bushing is common aluminum (6061-T6) with 3/8" engagement...

The pullout force would be about 1500 pounds.

The value for the 3/8"-16 thread would be roughly twice that value.

- Leigh

[C. D. Keth]

I've never had a problem. I stick to brass so if anything gets marred or otherwise damaged, it's the cheap bushing.

[E. von Hoegh]

Well, I received my first LF camera last week, a Cambo monorail. Of course, the tripod socket is 3/8 inch, my 40 year old tripod has a 1/4 inch thread. So I installed a 3/8 to 1/4 bushing in the tripod socket. The camera is held in place, does not seem to vibrate.
My concern is that the coupling to the tripod is solely due to this bushing. The weight is not so much of a problem, but somehow i think that the torque applied to the bushing might cause the threads to collapse.
Should I worry or not ?

Not.

[E. von Hoegh]

Even longer answer... The tensile stress surface area of the larger is twice as much as the smaller so having the larger in the softer material, I.e. aluminum Deardorff base, has advantage, and bushing it down to a smaller steel tripod base is just fine. Since the proof strength of a 1/4x20 low Grade 2 bolt is around 1,000 kilo/sq. in. The smaller bolt will manage 100's of pounds of equipment so I woudn't worry about that.

Bottom line: see quick answer.:)
Cheers,
Bill

The cross sectional area (minor diameter) of a 1/4-20 bolt is .028 sq. inches, that of the 3/8-24 bushing is .0818 sq inches, less the area of the 1/4 inch hole =.05 sq. in, or.0318 sq.in.. , very nearly the same area. For the proof strength of 1000 kilos/ sq. inch you cited the actual proof strain would be 61 lbs for the 1/4-20 bolt. The actual tensile strength of even low grade steel is much higher.
For the OP, don't worry.

[Dan Fromm]

Um, I've had one problem with those damned bushings that has nothing to do with strength. Some will go all the way into the 3/8" hole, with nothing protruding. These allow the tripod mount or whatever to make full contact with the tripod head. Others don't go all the way in, allow a little wobble because all that contacts the tripod head is the bushing's head. If not real wobble, frightening imaginary wobble.

[BrianShaw]

Oh, good point Dan. I had to apply a bit of file to a bushing once because it "bottomed out" prematurely. I seem to recall that was on a Rollei accessory -- a panorama head if memory serves correctly. Filed the thread end o fthe insert just a tad for a perfect fit. Re: a couple of earlier postings about over-tightening... don't do that... it is bad news almost every time.

[Steve Smith]

Another option if the bushing protrudes a little is to make a rubber plate to fit between the camera and tripod.


Steve.

[Leigh]

If the bushing is too long, file or grind the leading end to shorten it.

- Leigh

[Dan Fromm]

If the bushing is too long, file or grind the leading end to shorten it.

- Leigh

With the ones that give me trouble, length isn't the problem. They're made to go into a countersunk hole, the holes I have aren't countersunk.

[Leigh]

They're made to go into a countersunk hole, the holes I have aren't countersunk.
So countersink them. It's a $5 tool.

The countersink should be very shallow. Any significant reduction in thread length will weaken the threads.

If you prefer you can grind off the slotted face (the countersunk portion), but then you must re-cut the slot for the driver.
Depending on the specific bushing, this approach might damage the finish or external appearance.

With a little more effort you can remove the countersunk portion of the bushing, restoring a cylindrical profile.
Run a 2-inch 1/4"-20 bolt through the bushing with about 1 inch protruding at the inner end.
Chuck that end in a variable-speed power drill (masquerading as a lathe).
Run the drill at relatively low speed and take off the unwanted metal with a file.
Be sure the drill is turning the proper direction for the file to cut the work.

- Leigh

[jk0592]

Well, I am glad that basically there is no problem in using the bushing, as long as one is extra careful when setting up and/or removing the camera from the tripod. The pitfalls and the required corrections have been discussed. I had no idea that such complications could arise.

The level of help, the transmission of experience, and the technical hindsights are indeed incredible here. I hope that one day i will be able to give back what i learn...