Hendo's dome gauge -- nice idea

[Hendo]

(Essay No 33⅓)

Dome gauges – there are many ideas out there – perhaps the simplest, a bit of wire fixed by a screw or nail to the centre of the cooking floor.

For my project, the centre of the cooking floor for some reason did not coincide with an intersection between bricks. I was concerned that if I drilled a hole in the centre (close to the edge of a brick), it would lead to a chipped corner, and I had had enough of those laying the floor (too heavy handed with the rubber mallet!).

So I decided to:

1. put down a temporary MDF floor to assist in laying the first ring of bricks at the correct diameter;
2. fix a ball/socket joint to the centre of the MDF floor;
3. fix a dowel/rod setup to the ball joint like other members have recommended to test for correct diameter, course by course.

After many sleepless nights, I came up with the idea of using a photographic tripod ball head, fixed upside down to the MDF with a barbed T-nut, and a ‘dowel’ fastened to the ball head by an appropriately threaded bolt.

But what threads do tripods use, you may well ask? It's a choice of Metric (France, Germany etc) or Imperial – probably Whitworth (BSW) at a guess. Now I’m no betting man, but I would have thought that the first person to design a camera tripod mount would have been Continental (ie a metric thread), rather than a Brit or American. But wrong! The threads on the tripod mount are either ¼” (more common) or ⅜” BSW. So I’ve learnt yet another thing during the course of this project. I daresay it could have been George Eastman who decided on the thread, and camera tripod mounts will consequently be the same forever!

So I purchased a ⅜” bolt and ¼” T-nut, drilled out the end of a scrap piece of timber and glued the bolt (after decapitating it) into the end. A few quick calculations led me to realise that I had to compensate for the height of the ball head centre above the floor, so I rigged up a system of a packer (for slope) and end stop (for internal diameter) to check that I’m doing things more or less correctly. The only problem is that both the packer height and end stop distance must be altered each course.

Pics below are self-explanatory. And yes – I know, don’t tell me – the ancient Romans would not have done it like this – but I’m inexperienced. Well at least I chose an Italian ball head! If it survives the build, it will deserve pride of place on my new tripod!

Cheers, Paul.

[wlively]

Hendo

Very nice and original idea.

[dmun]

Originally Posted by Hendo

I would have thought that the first person to design a camera tripod mount would have been Continental (ie a metric thread), rather than a Brit or American. But wrong! The threads on the tripod mount are either ¼” (more common) or ⅜” BSW. So I’ve learnt yet another thing during the course of this project. I daresay it could have been George Eastman who decided on the thread, and camera tripod mounts will consequently be the same forever!

Yep, camera mounts are quarter-twenty. Thats what we call NC (national coarse) in the US, and it was standardized by the Society of Auto Engineers in the last century, and used to be called SAE threads. The interesting thing was that it was standardized from existing shop practice, rather that first principles. I've worked on clocks from Mass. made in the early 19th century that used standard NC threading. It's quite different from whitworth, which has 55 degree face angles instead of sixty, and a rather aggressive radius on the top of the thread. The differences seem trivial until you start to fit parts together. The British never really standardized these things across industries.
Manufacturers stuck stubbornly to their traditional practice.

The inch was never standardized until an international conference in the 1950's, where it was declared 25.4mm exactly. That's right - it's a metric measurement. It meant very little change to the US, but bigger changes for the other parts of the english speaking world.

[Les]

Paul - I believe there is a saying "Necessity is the mother of all invention". Very clever! For those that take this approach, you can purchase an in line ball joint for around $4.00 at this site. Keep your tripod in one piece so you can take pictures of the build

McMaster-Carr

Les...

[nissanneill]

Yeh,
good one Paul. You should have made your job a little easier by referring to that idea in Russell Jeavons book for positioning the dome bricks, but his cost much less sleep than yours by using a pin (rather than a tripod ball joint), and a folded right angles piece of metal on a rod.
Good to see you underway again.

Neill

[james]

This is a very good thread that has received good reviews, and Paul thought it would be a good idea to move it to Tools, Tips and Techiques. I've made it a sticky thread, so it will be read frequently.

Here it is. Thanks Paul.
James

[jeff]

James,
From my perspective as an Old Fart, this site certainly appears different from the one I know and love;viz. ExplorOz. (A touring/4wd forum for Australia, in which I have no financial interest,apart from being a dysfunctional member).
Mate, thanks in large part to you and your people, the 'soldiers' are set. Alas, Russell Jeavon's book , whilst inspirational, appears shy in the area of the brick gauge.
Never mind, all good,...and thanks Mate: Bloody inspirational.
Yours in awe.
faithfull,old serf's Dog.
Jess.

[givearats]

Very nice...

[Xabia Jim]

I resurfaced this as a bit of a tribute.....Adios amigo.....via con dios.

[Dutchoven]

Definitely worth bringing back...both the idea and the individual...
All the best all ways
Dutch