Joining aluminium tube.

[skipdiver]

I need to join some ali tube and would welcome suggestions as to the best way to approach this as i am a novice in all things metal. The join can be permanently fixed one side but needs to be detachable the other. I was thinking of plastic tube joiners, which you can buy with metal inserts for strength but i can only track down one company that does the size i require and they will only sell me 700 at a pound each, so that rules them out.

My preferred option is a piece of tube inside the main tube, i think it's known as a splice from what i can gather. The guy who fabricates them for me now uses this method but the piece he uses to join them has clearly been turned down on a lathe to a snug fit and i don't have that facility. The tube in question is 1 3/8" diameter 16g, which is 34.9mm OD and the inside diameter is something like 31.6mm. I have some 1 1/4" tube and it is a tad too big to slide inside, so the next option is 30mm OD, which i think may be a tad too sloppy. Is there any way i can slightly increase the OD with some kind of tape or shrink sleeving maybe? Alternatively, is there an easy way to slightly reduce the OD of the 1 1/4" without a lathe.

I have been frantically googling for days and am none the wiser as metalwork is a steep learning curve for me. Any help most gratefully received.

 

[marcros]

what is it being used for? How strong does the join need to be?

 

[skipdiver]

It doesn't need to be that strong. The bars i get fabricated now are joined with a piece of tubing about 6 inches long but of a heavier gauge than the 16g main tube , so that is sufficient for my needs.They are attached with 5mm machine screws.

I could ask them for advice but i doubt they would be happy to help me with taking business away from them.

 

[n0legs]

At my mate's fabrication company they cut a slot out of steel tube and squeeze it inside the tubes that need joining.
Get a disc cutter with a slitting disc and run a slot in the 1.25". The ali will squeeze up enough by hand to fit inside the bigger tube I expect.

 

[skipdiver]

At my mate's fabrication company they cut a slot out of steel tube and squeeze it inside the tubes that need joining.
Get a disc cutter with a slitting disc and run a slot in the 1.25". The ali will squeeze up enough by hand to fit inside the bigger tube I expect.

Yeah, i had thought of that option and will do that if there is no other way, but would prefer not to do that if i can find an easier way.

 

[MrTeroo]

How about carbon fibre tube with an od of 31.3mm?

http://www.easycomposites.co.uk/#!/...be/carbon-fibre-tube-roll-wrapped-28-5mm.html

 

[skipdiver]

That's a good shout MrTeroo. Cheers.

 

[skipdiver]

........until i checked the prices. Carbon fibre is about 6 times the price of ali. :shock:

 

[MrTeroo]

You didn't give us a budget figure

 

[skipdiver]

You didn't give us a budget figure

That's true and i'm not totally ruling it out as i only need short pieces, so i'll keep it in mind.

 

[marcros]

A bit crude, but would some masking tape, or gaffa tape not take up the slack with the slightly undersized tube? On the permanent side, you could even use a gap filling adhesive.

Or, get somebody to turn down the slightly oversized one. Dont tell your fabricator what it is for, just pay them to do a length of it. It is a single pass on a lathe, so shouldnt take long at all and could be done between centres.

 

[skipdiver]

Tape would work on the permanent side, no problem, but the other side needs to have the facility to part, which is why i was thinking of some sort of shrink sleeve. It needs to be just just so, neither too slack nor tight. Not sure of the use of shrink sleeve and how much glide it has. Tape would wear away eventually and look a bit cobbled together.

Suppose i could see if a local engineering firm could help me out.

How much does a metalworking lathe cost and how big are they?

 

[marcros]

how long is a piece of string?

But to be more helpful, my lathe will stand me at about £350, including the timber to make a stand, and a few bits of tooling. I would offer to help, but I have literally no experience of turning metal, and have only just set up the lathe. Give me 6 months and i may be able to assist.

How long is each jointing piece and how many do you need doing in a batch? Longer pieces need larger lathes, and the costs start to increase. Tooling also amounts up. If you are thinking of buying a lathe, just for this job then i would sub it out.

Could you put something on a drill and slightly sand/abrade the inside of the main tube? you only have a mm or less to remove, which is half a mm from each side, so it cant take long on aluminium.

 

[chaoticbob]

Skipdiver, if you have a way of spinning the 1.25" joining tube and it has enough meat on it I'd suggest that it would be better to sand down the joining piece rather than trying to fiddle with the ID of the main tubes. It's much easier to fettle outside diameters than inside. If the joining tube you have is too thin walled for that, you can buy solid 1.25 ali bar at about 30 quid a metre.
Or you could just buy an engineering lathe, job sorted....
Rob

 

[skipdiver]

Thanks. If i were to fettle the joining tube, i would get 1.25" in a thicker gauge than the 16 of the main bar. Can Ali be sanded down?

 

[mbartlett99]

Yes ally is soft as hell.

1 Mount in vice
2 long strip of emery tape - hold at ends, wrap around and saw at it
3 once you get close put inner tube in freezer, heat outer tube and smack it in

Or use smaller tube and epoxy secrue once dry with some grub screw.

FYI bicycle seat posts are availble in different diameters but it won't be cheap.

 

[skipdiver]

I intended to use smaller tube as it needs to come apart again. The problem is that the tubes i can get are either slightly too big or too small with a lot of play in the side that disengages. The guy who currently does them for me gets the larger tube and turns it down, i don't have a lathe and have never used one, so was looking for ways around it. I have been looking at small benchtop lathes.

 

[Jake]

Is it possible to flare that sort of aluminium and if so would that work for the intended usage?

 

[eddieperkins]

You can turn aluminium down on a wood lathe but would be best to use carbide tools

 

[chaoticbob]

I intended to use smaller tube as it needs to come apart again. The problem is that the tubes i can get are either slightly too big or too small with a lot of play in the side that disengages. The guy who currently does them for me gets the larger tube and turns it down, i don't have a lathe and have never used one, so was looking for ways around it. I have been looking at small benchtop lathes.

Presumably you're looking to save money by making the joining pieces yourself. If so it depends on how the economics stack up for you - one of the ubiquitous Chinese 'mini-lathes' (eg Sieg SC2/3) would do the job for sure, but would set you back a few £££s. I've made joiners between 3 metre lengths of ali tube to fly stage scenery with a similarly sized machine.

Ali is indeed 'sandable', but precisely because it's soft (and gummy) it clogs paper quickly, so it's a slow process and you get through quite a bit of wet'n'dry. It comes down to economics again - how highly do you price your time?

If you do decide to buy a metalworking lathe you shouldn't be intimidated by your lack of experience - it's far less of a black art than woodworking. IMO.
REgards, Rob