Joining ali tube.

[skipdiver]

I'm a complete ignoramus with all things metal, so i thought i would venture over here to swarfland. :lol:

I have asked this question before but i still haven't found a suitable answer. I need to butt join ali tube and i'm not sure how to do this satisfactorily. The easiest way and my preferred choice would be to use a small section of smaller diameter tube as a spline if that is the correct term? The tubing in question is 1 1/4" which has an OD of 31.75mm and an ID of roughly 28.5mm. The nearest size tube to fit inside is 1 1/8" which also has an ID of roughly 28.5 mm and is too tight to slide inside nicely. I'm wondering if i bought a mini lathe to take some off the diameter, what would i be looking at spending on one to get decent repeatable results? The pieces only need to be about 6 inches in length i think.

Is there a better way to do it? I've seen all sorts of tube inserts both metal and nylon but i really don't know which route to take and my brain hurts now from internet searches. This is not a one off and is something i will need to do regularly, so am looking for a permanent solution. Also forgot to mention that it needs to be able to be taken apart and put back together by the end user, so nothing too complicated. Maybe some way of screwing the two parts together.

Any ideas would be most welcome.

 

[AndyT]

You might be better off stretching the end of one piece so the other will sit inside it.

Try a search for "tube expander". You'll find an assortment of tools, hand-powered or hydraulic, designed to stretch the end of soft metal tubing, quickly and consistently. Most are for the smaller sizes used in plumbing, but I expect you will find something big enough. (It's not something I have experience of, I just know they exist.)

For example, this one is nearly big enough: https://youtu.be/nsHeIkF8Gyw

 

[Rorschach]

Considering the size difference I am sure the excess would just be filed or sanded off for a nice tight fit. You could also warm one and chill the other and get an interference fit.

 

[skipdiver]

Tried sanding and it takes too long, as well as being too inconsistent. Interference fit no good either as it needs to be able to be assembled and disassembled.

Stretching is a possibility, thanks.

 

[sunnybob]

Whats the finished item?
There wont be much strength sideways, especially if you weaken the ali by stretching.

 

[kevinlightfoot]

Could you use a wooden cylinder turned to a snug fit ,maybe oak and then use brass round head screws to hold the pieces together.A turner will easily make you a load in no time.

 

[AndyT]

I just remembered these people https://www.bpfonline.co.uk/search.asp?catid=3101

You'd want to phone them and check, but the threaded inserts look like they could be the answer, with a bit of studding glued into one side.

Or indeed these:

https://www.bpfonline.co.uk/show_produc ... catid=2998

 

[SteveF]

could you cut slot on the inside one so that it compresses in outer one?

 

[skipdiver]

I forgot to say that i already have these fabricated by someone else and am looking to take over myself, as he is a bit unreliable, although he does a good job. He uses a piece of thicker gauge ali, 6 inches long, which he turns down to match the bars. I put my vernier on the joint piece today and it is 28.2 mm. 1 1/8" ali is 28.8, so i don't need to take a lot off.

I also forgot to mention that the bars cannot be pulled apart as they have cloth attached but still need to be collapsible. That is achieved by the joint being a sliding one which can be retracted fully inside one bar, hence the need for a good fit. Not too tight, nor too slack.

I am increasingly thinking that the best solution has already been reached and i am going to have to get a lathe and fabricate my own, though i know nothing of lathes and less about metalwork. Do like the wooden dowel idea though and that may well work. I will look into it. Splitting the tube is also something worth looking at.

Thanks for the link AndyT. I had already seen those and had them in my basket at one time but that would mean that the attached cloth, which is currently held on with rivets, would have to change to a removable arrangement, possibly press studs and that changes everything again.

Thanks for all the ideas chaps. i will have another search but can anyone tell me what sort of money i would need to spend on a lathe to get something decent. I would only need small centres, so a mini lathe would suffice. If i fabricate my own, it would soon pay for itself.

 

[TFrench]

If it's going to pay for itself, I'd just get yourself a mini lathe with a decent guarantee and a set of insert tooling. Minimum set up time, don't have to learn to grind tools, it'll instantly start paying for itself.

 

[skipdiver]

Cheers. Any recommendations?

 

[TFrench]

I've never used a mini lathe, but the SIEG ones get consistently good commments. Think Axi do one, and arceurotrade. I got my dad a set of indexable tools from RDG that he loves.

 

[skipdiver]

Thanks, will check them out.

 

[Rorschach]

If you go with insert tooling make sure you get tips designed for aluminium, if you use steel tips you will make one heck of a mess.

 

[skipdiver]

Ok, thanks for all the info. Will research before i proceed.

 

[skipdiver]

Right, been looking at mini and micro lathes for metal and as usual, the more i look, the more baffled i become and it doesn't help that i am a complete ignoramus with all things metal and haven't used a lathe since i was at school 40 years ago and that was a wood lathe.

I need to turn 6 inch lengths of 10g ali tube down from 28.8mm to 28.2mm and that is it. I'm not interested in any other kind of turning and this is purely a means to an end for one process. I need to do batches of about twenty, 2 or 3 times a year. Something as small as possible because i don't have a lot of room and it will spend most of it's time under a bench.

I have seen some micro lathes (there is a sieg one for sale near me second hand) but they are 125mm between centres. Is that the absolute limit, or is there a way to get a 6 inch piece done on one of those. Possibly doing one half, then spinning it round and doing the other? Does the tube need to be supported at both ends or just one end in the chuck?

Can someone recommend a way to do this as easily as possible. Is a lathe the answer, or is there a simpler solution? I'm clueless and floundering.

 

[ColeyS1]

How about hammer a threaded rod joiner in both ends ? Might be a bit of trial and error to find the right one- m20 ish perhaps ? Then threadlock in a short length of threaded bar and screw them together like a snooker cue. Perhaps a couple discreet grub screws might keep the threaded rod joiner in place or if it takes a bit of welly to hammer in, leave it at that.
Cheers
Coley

Sent from my SM-G900F using Tapatalk

 

[skipdiver]

Thanks Coley but i can't do that. The two pieces of tube have cloth attached to them, so it's collapsible, which is done with a sliding joint, which goes inside the two tubes. There is no play to turn the tubes or pull them apart. I've exhausted every idea and the sliding joint is the only solution, so i have to find a way of reducing the tube by about 0.6mm, so it slides inside the outer tube. The nearest stock size is 1 1/8", which is 28.8mm and is a tad too big. I am happy with the way the thing works, but i currently pay someone to do them for me and he is a bit unreliable. I want to take over the operation myself but am not au fait with metalwork and lathes. Thanks for the input anyway.

 

[J-G]

The Seig C0 (I presume that is the model you are considering) does only have 125mm between centres and although you could probably remove the tail-stock to accommodate your 6" tube I would be much happier supporting the free end properly.

Have you looked at the Osaki 300 which Cromwell have on special offer at the moment? I don't have any first hand knowledge of it but the spec is quite a bit better than the Seig with 250W motor rather than 150W, 300mm between centres which will easily accommodate your 6" (~150mm) tube and a 20mm head-stock bore (Seig has 10mm). It also has screw-cutting facility though this may not be of any interest currently - you never know what you may want to do in the future.

 

[skipdiver]

Thanks J-G. I had seen the Osaki on ebay but no idea of it's quality. We have a Cromwell Tool Store locally and i never thought of them, so that's a good reminder. Not being sure how lathes work, how is the other end supported? Is it a tapered tail-stock type thing? I don't know what is meant by head-stock bore, so that is something else to familiarise myself with.