Threading 2mm wall tube

[Thrashsmith]

Hi folks, I have one of my least favourite jobs coming up...curved curtain poles for an oast house. To give clients the ability to add/remove curtain rings I usually roll them from hollow tube and socket the finials into the ends, then drill the tube and tap a thread so a grub screw can be tightened up against the finial tenon to keep it locked in.

Ideally I'd use 20mm x 2mm wall tube but I've had no joy before with threading the 2mm wall as the thread just strips as I tighten up the screw, I've tried with 3mm, 4mm and 6mm screws. I have however managed to thread 21.3 x 3mm wall tube before, but I'd prefer to use 20mm O/D tube. Part of the reason being is so I can use 20mm solid bar to forge the finials from, and then the shoulder of the tenon would flow seemlessly into the tube diameter. I'm aware that there's 22mm diameter solid bar which would flow well against 21.3mm tube, but I'd rather stick with 20mm and 20mm.

Can anyone offer any tips or tricks for threading the 2mm wall tube? I don't want to weld nuts onto the back face of the tube. Sometimes I overlook answers that are staring me in the face! The only thing that's springing to mind at the minute is to drill all the way through the tube and thread the tenon and switch from grub screws to a pan head slotted screw - but that's becoming a bit of a faff.

 

[piman]

Hello Thrashsmith,

drill through both the finial and the tube and use a bolt to secure them, alternatively drill and tap the finial and use a screw through the tube to secure the finial,. The latter is more fiddly but neater.
What larger companies do to thread thin wall tube is to pierce a hole rather than drill. This drags metal inward and gives more meat to tap. I imagine it need some power though to do that?

Alec

 

[bigegg]

can you use a self tapper, rather than a screw?
or a bigger hole in the tube, and a threaded hole in the finial?

 

[Hitch]

Clearance hole through the tube, say 6mm, then drill and tap the tennon M5. Just us a button head to lock it.

 

[8ob]

A small rivnut would work on tube.

Bob

 

[Hood]

Flow drill?

 

[pedrobedro]

Put a hole in the tube and thread the solid part of the finial that goes inside it ? Screw through the tube wall into the finial.

 

[wyn]

Bolt through the lot and thread the supporting bracket.

These are a few i made last year, solid bar though. Everything is hidden behind the bracket

 

[merryman]

I used to work for a seat manufacturer and they had the same problem on tubular seat frames. Fitted an aluminium end plug and drilled through one side of the tube and into the end plug, then drove a Mills pin into the hole, flush with the tube. If the plug ever did need to come out, you drove the pin further in.

 

[gordon stephenson]

Nice job Wyn, Like it a lot.

 

[8ob]

Flow drill?

Every day is a school day, even at my age

Bob

 

[8ob]

Bolt through the lot and thread the supporting bracket.

These are a few i made last year, solid bar though. Everything is hidden behind the bracket


View attachment 168822


View attachment 168823

@wyn Were they made for Geoff Capes ?

Bob

 

[hotponyshoes]

On the tube you want to put the thread in,
Say you want an m5 thread:
Drill a 3mm hole, put a m6 nut behind the hole, get a small bit of 4mm bar (cut 10mm of shank off the end of a drill bit)
Put the bar on the outside of the hole and push it through the tube and nut with a pair of mole grips to form a collar.
A bit of lube helps and you can either tap the round on through or pull it back out with mole grips. A bit of trial with the sizes and you should end up with enough depth to run a tap through.

 

[Kent]

How about black pipe and pipe threads ? Straight coupler turned or ground on The od?
it's all cast steel so you can weld ends on grind etc. 3\4" or 1" nominal bore ? Will roll a treat also

just a change that might work real well ?

 

[wyn]

@wyn Were they made for Geoff Capes ?

Bob

They were the small ones.

The one below had 20mm round bar ends in the same shape and was 4m long.

The second pic was 20mm round in adifferent shape but held on the same.