D-Special Sphere rebuild

[Buttercup]

Bob - If you are getting metal to metal contact then there is something very wrong with the construction of the diaphragms you are using......

.........The upper right photo shows a standard Desmopan diaphragm.
Steve

I'd suggest there's something wrong with the diaphragms YOU are using.

All my original red/green/white marked original diaphragms always behave perfectly as I described.

If these new fangled after market ones don't, I'd suggest they were not designed properly, or the manufacturer did not set the dies up properly in the injection molding machine and the diaphragm has come out too thick.

The original design of the 2 part spheres was well thought out for accurately repeatable manufacture. The elasticity of the diaphragm, and required compression was all planned. There was no need for operator guesswork... how tight is tight enough?

 

[Citroenfan]

Bob, If you indeed have 'original' units in factory sealed packages I would not touch them at all - as they would have to be at least 35 to 40 years old by now. But if that is you experience, that is your experience. Have never seen it myself. And that has been with both the Desmopan units as well as rubber ones supplied by reputable suppliers in Europe as well as the US (rubber ones only). And as the spheres built up with them last just fine, I would have to say their manufacturing is not suspect to me.

As to 'how tight is tight enough' - 1/3rd to 1/4 turn from first contact. Simple. As for the factory - I am sure it was all automated and that a specific torque was dialed into the equipment.

Steve

 

[Buttercup]

Bob, If you indeed have 'original' units in factory sealed packages I would not touch them at all - as they would have to be at least 35 to 40 years old by now. But if that is you experience, that is your experience. Have never seen it myself. And that has been with both the Desmopan units as well as rubber ones supplied by reputable suppliers in Europe as well as the US (rubber ones only). And as the spheres built up with them last just fine, I would have to say their manufacturing is not suspect to me.

As to 'how tight is tight enough' - 1/3rd to 1/4 turn from first contact. Simple. As for the factory - I am sure it was all automated and that a specific torque was dialed into the equipment.

Steve

And that torque is.............
Very slowly increasing as the elastomer is compressed,
And highly variable, dependent on factors other than elastomer compression, like thread condition and lubrication.

The only reliable measure of correct elastomer compression is a physical dimensional measurement, designed and checked during manufacture.

That is: The designed space for the elastomer. This is machined into the female hemisphere, it is not dependent on any particular measurement of the male part. With this known space, correct compression is achieved repeatedly by sensing the rapidly increasing torque as the metal faces meet.

If these "new kids on the block" making diaphragms, don't realise this, OR, realise it but don't inform their customers of correct tightening technique, they are not to be trusted.
Its reasonably common for small qty after market specialty parts to be designed/manufactured by people who don't study the application well enough to appreciate the detail of the original part

 

[pottsy]

Sorry guys, I got sidetracked by a Mother (mine) needing a visit to hospital. I wasn't ignoring this amazingly educational and spirited conversation, just wasn't able to respond yesterday.

I certainly never expected it to go to 4 pages, and potentially beyond!

I now feel I know a lot more about how to approach this task, (not to mention spheres in general) and the main gist seems to be that I'm on a slightly wrong track.

Citroenfan, that's where the pdf's become valuable as it's a lot easier to revise ideas on a computer screen than in the metal.

I love the bracket in the video. Simple but effective. Can I assume that any locking screws, unless they be grub screws which are already pointed, need to be slightly pointed to grip firmly? I'm thinking some Unbrako machine screwes through the edges of a clamping ring.

As far as using a chain wrench on the wide band is concerned, the cutaway posted above seems to show the wide band as being almost the strongest bit in the half of it nearer the sphere neck. Surely clamping on here wouldn't cause any kind of shrinkage?

Revision 6 will look very little like revision 1, that's for sure.

Keep it going lads, I'm sure we're all happy to learn from such mentors as your venerable selves!

Cheers, Pottsy

 

[GreenBlood]

Keep it going lads, I'm sure we're all happy to learn from such mentors as your venerable selves!

Cheers, Pottsy

Have a look at about 1min into this video, now that's a serious bit of metal. Unfortunately it doesn't show how the other half is gripped.

https://youtu.be/Dsn-Ku83PHU

Cheers
Chris

 

[Buttercup]

Unbrako, hollow cone pointed grub screws.



They grip a significant area of the rim, without pushing a large dint. They leave a neat circle rather like a 0 number punch.

I use M8 size with 4mm allen key, don't need much tightening, never slip.

 

[Buttercup]

..................As far as using a chain wrench on the wide band is concerned, the cutaway posted above seems to show the wide band as being almost the strongest bit in the half of it nearer the sphere neck. Surely clamping on here wouldn't cause any kind of shrinkage?................

Cheers, Pottsy

By "shrinkage" I mean a temporary reduction in size within the elastic range, caused by high circular clamping pressure. Small but enough to bind the thread so it feels tight.

Grub screw clamps avoid this, however only 3 or 4 will tend to push the rim into a triangular or square shape. That's why it better to use 6 or 8.... each one does not need to be very tight to contribute to overall tool grip, and reduces the tendency to push the rim out of round.

The video showing the ViseGrip chain wrench, shows it to be annoyingly fiddly to attach, also (and yes I have one, and have used it before making better tools) it needs very high tightening to get grip, because the links of the chain are quite hard steel with a curved shape.... naturally very slippery.

 

[pottsy]

Have a look at about 1min into this video, now that's a serious bit of metal. Unfortunately it doesn't show how the other half is gripped.

https://youtu.be/Dsn-Ku83PHU

Chris

You're not kidding! Here's a frame grab. Interestingly, this tool seems to be gripping on the bottom half of the wide band, potentially the strongest part if I'm interpreting the cutaway diagram correctly.

Cheers

 

[pottsy]

Semi Success!

After a lot of false starts, hammering and swearing, I've finally managed to create a tool that seems to work, albeit only 50% of the time so far.

Allow me to elucidate. I have four two-piece spheres here for reconditioning. One is the failed one from the reco set I bought in 2005 and the other three are replaceable damper types from an old car that I scored a few bits from.

The failed one and one of the oldies have yielded to pressure and are dismantled.

The other two are resisting fairly hard!

Interestingly, the three oldies of unknown history and heritage were all still holding pressure. I don't know how much as I didn't want to adulterate my pressure tester with whatever scunge may have been in there, but they all three took a while to slowly de-ressurise once I opened the top bolt.

I've got some diaphragms coming from Roger the Guru so after a clean up, and possibly a paint, I can maybe arrange some re-pressurising at some stage.

One of the obstacles in the way was re-learning my previous skill with an arc welder. It's some years since I've used this, but it is a bit like riding a bike, just not as painful when you fall off, metaphorically speaking! The reason for this was the beefiness of the metal I was welding and reluctance to change the settings on the MIG, already aligned for 2CV panel work.

The first few welds were atrocious, but after a while I got the hang of it again. Very satisfying since none of my freshly welded bits have moved or broken so far during the fairly strenuous activities of the afternoon.

Pictures will follow once I've charged the camera battery and stopped swearing and limping! (The long bit of pipe I was using as a force multiplier struck me a glancing blow on the leg out of spite! You'll get yours Jimmy! )

Cheers for now, chaps. Pottsy.

 

[Buttercup]

My sympathies regarding the relearning of stick welding...... But you really should pluck up the courage to fiddle with mig settings.

After a while you get to know good small medium and large settings on your own machine.
With practice you will be able to reset and get it right first time.

If you are using gas with the mig (and I always do, and always recommend it) turn the gas flow down to a minimum that works.
Most people waste a lot of gas with flows way higher than needed. Also it is possible to get porosity in the weld from having too much gas..... as the high flow sucks air in behind it.. like a Venturi. If you hold the nozzle near your ear (but not pointing into your ear...'cos the wire feeding out will do some damage) you should hear a solid puff as it starts then a very gentle hiss of gentle flow. if you hear a constant whoosh.... thats too much.

Anyway.... really play around with some scrap..... get used to it... then chuck out the stick holder.

Sympathies on the banged leg too...... it certainly dulls any sense of achievement.

If a sphere has some pressure in it... then it should be holding NO fluid. You can rinse the neck and valve with kero or turps, blow it dry, then use your pressure tester.....without contamination.