Discrete bolts/nuts

[chunkolini]

I.have to make a 2m diameter globe for a customer. Due to its size it has to be galved in two pieces.
I'd like the bolts holding it together to be as discrete as possible.
It will be made of hoops of 30x5mm mild steel strip curved along the flat side and doubled up along the joint.
Plan A use countersunk m8 bolts going into countersunk nuts.
I have seen these online. Can you buy them by length? Say 6mm?
Something like these.
I think they are called sex bolts.
Great name

 

[julianf]

I'm sure I've seen them in various configurations on Ali express.

 

[8ob]

I would look for a decent galvanizer that can cope with the 2mts diameter, sounds like a lot of grief to build in two parts.

Bob

 

[chunkolini]

I've looked at the localish ones, biggest tank is 1.3m in Cardiff
I'd prefer to do it in one piece.
But I imagine shipping both ways would cost a bomb.
Any suggestions?

 

[qwakers]

Why don't you have a large stud and nut in the middle on the inside and simply screw it together after?

 

[chunkolini]

It has to be hollow.
Internal structures would look messy

 

[Agroshield]

It will be made of hoops of 30x5mm mild steel strip curved along the flat side and doubled up along the joint.

If you have 2 x 30 x 5, the maximum length of thread plus two countersinks is 10mm.

At 8mm diameter, that is going to be nigh on impossible. In general, you would want a minimum depth of thread equal to the diameter of thread.

Draw a side view of the joint, to scale, and you see what you have to play with. It will be challenging to find suitable off-the-shelf fasteners for this.

----

Here is a possible mechanical/spring loaded idea: have the outer ring continuous with some small projections regularly around the inside. Drill holes in the inner ring so they slip over those projections. Make one single (kerfless) cut in the inner ring so it is not continuous but so that its ends touch when in place inside the outer ring. Spring it into place to assemble.

---

'countersunk barrel nuts' is another way to find the items.

 

[bletchmonster]

I would look for a decent galvanizer that can cope with the 2mts diameter, sounds like a lot of grief to build in two parts.

Bob

I went though this trying to get 2 meter teapots galvanised (mad hatter teapots garden).
Joseph Ash could do them, but then decided, because I couldn't take any where else, they could Roger me blind on price.
I cut the teapots in half and sent them to my usual galvers.
It was a faff but a day and half's work saved a few grand!!

 

[Morrisman]

How about tapping the inner part/flange/strip , and using countersink screws from the outside. No nuts required then, and far simpler.

 

[Gareth J]

As above, ditch the nuts and tap the frame. Bolt it up for testing with M6 in 6.5mm holes then, after galvanizing you have plenty of material left to finish/countersink the holes and tap the threads. Stainless bolts and cut/flap wheel the excess off.

Alternatively, what about celebrating the fasteners. Rivet it together with something that can be done cold? Copper?

 

[6ply]

Something like these.
I think they are called sex bolts.
Great name

You'll have more luck if you ask for a screw.

 

[tom2207]

sex bolts are known as book screws too ,,, Id be aiming for one piece and make it out of stainless , easier than galve , it will be round when you finish too , and probably will cost the same if you allow for messing about , a one piece globe will be all shapes after dipping , and as for a two part , I dread to think what it will look like , how about powder coat in zinc look ... just options

 

[Migmac]

Can be called Chicago bolts too

 

[Erie Fred]

Can be called Chicago bolts too

Yabutt...the OP is in the UK .....

 

[Hitch]

Joseph Ash in Telford would dip that in a one-er.

 

[Agroshield]

How about tapping the inner part/flange/strip , and using countersink screws from the outside.

If you tap before galvanising, it needs a super loose tap so the bolt goes back in after. If you tap after galvanising, how do you ensure corrosion-resistance?

With the heat and hence possible distortion from the galvanising, would the holes still line up afterwards?

Whatever we come up with has to be 'as good' as hot dip galvanising and also take account of the galvanising process.

 

[Hitch]

If you tap before galvanising, it needs a super loose tap so the bolt goes back in after. If you tap after galvanising, how do you ensure corrosion-resistance?

With the heat and hence possible distortion from the galvanising, would the holes still line up afterwards?

Whatever we come up with has to be 'as good' as hot dip galvanising and also take account of the galvanising process.

Pilot holes and tap after galvanising...

If you use a galv bolt, use an oversized tap.
The zinc on the bolts protects the hole, same as proper galv nuts and bolts, the nuts are tapped after galvanising.

 

[Wildefalcon]

Err, how sturdy does it have to be? BIG magnets do the job?

 

[sako243]

I've looked at the localish ones, biggest tank is 1.3m in Cardiff
I'd prefer to do it in one piece.
But I imagine shipping both ways would cost a bomb.
Any suggestions?

Perhaps speak to Mark @ CLH and see in you can dump it on one of their loads to the galvers. I've done that in the past with odds and sods. They send trailers up so it shouldn't be an issue size wise.

 

[Pond frog]

Have you contacted the galvanisers sometimes it’s possible to double dip items too big for the tank