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Deskpilot

A short story, then a long journey

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Deskpilot, the aluminium tubing size you have quoted is possibly American-sourced 7/8" tubing, which is actually 22.2mm.

Thruster88 is onto it, thicker wall tubing is the way to go, the thicker wall aids greatly in preventing splitting.

Performance Metals in Sydney can supply a 6061-T6 tubing in 7/8" diameter (22.2mm) with a wall thickness of 0.120" (3mm). Their catalogue number is PSAT2230.

 

http://www.performancemetalsaustralia.com.au/round-tube-6061-T6-aluminium-stock-list.php

 

However, Performance Metals indicate they only supply full lengths of this tubing - 5.2 to 7.3 metres.

If I could source a short length of this material locally (Perth), I reckon I could produce the bent shape you require - although the general rule of thumb for maximum bend radius for aluminium tubing, is 3 1/2 inches.

I'll do some more searching locally and see what I can find. I'll also ask my local muffler and exhaust lads if they can bend 7/8" tubing with their power bender - these benders are the best you can get, for producing smooth radius bends.

Edited by onetrack
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For the small amount of extra weight in a joystick, I wouldn't worry about using thin walled tube, I'd rather it was strong anyway.

 

In which case Capral sell 22.23 (7/8") tube with a 5.99mm wall, it's a 6061T6 grade (marine structural) and comes in 6m lengths which would cost you about $40 (Capral Material No. 851607). If you let them know you only need a metre and speak to them nicely they might let you know who they last sold (or regularly sell) that size to, and you might be able to get an offcut from them instead.

 

With that size and wall thickness you wouldn't need a bender to shape it, you could just bend it cold in the crook of a tree or round a mate's bullbar - don't use your own bullbar it might leave marks and scratches on it 😉 . Seriously though, add a bit of padding and a car towball also makes a handy bender for that sort of job.

 

Half a metre of that size and wall thickness tube only weighs 400gm, so it's not a big weight penalty for quite a lot of improved simplicity and strength.

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I can't agree at all, that the 6061-T6 aluminium tubing with a 5.99mm wall thickness will bend easily.

6061-T6 grade is not easy to bend - it's heat treated and tempered, and it's highly resistant to bending - as you would expect from material designed to form structural members. To bend it, annealing would be required.

The T6 treatment number means the tubing has been solution heat treated and artificially aged, to achieve maximum precipitation hardening. This results in high strength aluminium with stabilised properties and dimensions.

 

Strategies for bending 6061-T6

 

I have been snooping around my contacts today, to try and dig up some aluminium tubing of 22mm diameter. It's non-existent amongst my salvage and scrap contacts, we went through racks and racks of offcuts looking for it.

What I did do, was order a length of thin wall 22.23mm tubing from Capral. This is the old imperial 7/8" sizing, and it has a wall thickness of 1.42mm, or 0.056".

It wasn't in stock, it has to be brought in from the warehouse and it won't be available for pickup until Friday. This stuff is 6060-T81 grade, the General Purpose grade used for extrusions such as window frames.

 

It's a drawn tubing, not extruded, so it is far better for forming purposes. It has more than adequate strength for a control column (160Mpa minimum tensile strength), but is soft enough not to crack when bent, as the 6061-T6 is likely to do.

Capral state that you can bend this grade and dimension of tubing to around 70mm (internal) radius. That makes it highly satisfactory for the planned design as produced by Deskpilot.

 

Come Friday, I'll pick up this length and experiment with bending it, utilising packing it with fine sand, and ends blocked off with wooden plugs.

I'll have a talk to my local Muffler and Exhaust lads - if they have a former for their mandrel bender that can do 22mm, I reckon we'll be laughing.

 

 

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12 hours ago, onetrack said:

I can't agree at all, that the 6061-T6 aluminium tubing with a 5.99mm wall thickness will bend easily.

6061-T6 grade is not easy to bend - it's heat treated and tempered, and it's highly resistant to bending - as you would expect from material designed to form structural members. To bend it, annealing would be required.

The T6 treatment number means the tubing has been solution heat treated and artificially aged, to achieve maximum precipitation hardening. This results in high strength aluminium with stabilised properties and dimensions. ....

 

 

 

Ah well, if it can't be done, it can't be done -

 

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If you get tired of mucking about with sand you could try one of these -

 

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Wow guys. thanks for you interest in my 'little' problem. Looking forward to the results of your trials, what ever the wall thickness. Mine was 1.2 mm and I bought an internal spring mandrel. What I didn't have was the anchorage and pulling power.

 

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HITC - I'm not saying bending 6061-T6 can't be done. All I'm saying is, there's a risk of cracking, if that grade of aluminium is used, and it is difficult to bend it, because it resists deformation.

One has to remember that when bending tubing, the outer wall section is stretched, and the inner wall section is compressed. This produces serious distortion and stresses.

The material used, has to have satisfactory properties, that are able to handle the distortion and stresses produced.

 

I bent a piece of thin-wall (3/8" x 1.2mm) stainless tubing to 100° a few days ago - a 4000psi pressure washer lance - in a normal plumbers copper pipe bender.

 

Stainless steel pipe is difficult to bend because stainless steel work-hardens as you bend it, making it harder and harder to bend, as the bending goes on.

And of course, with thin wall tubing, the risk of flattening the tubing is ever-present.

 

I filled it with used sandblasting garnet (very fine sand) and plugged the ends with tight-fitting custom-made plugs made from Bottlebrush wood.

Bottlebrush is some of the toughest wood you can find, it makes excellent pipe plugs, and you can hammer on it without it shattering or breaking up.

I had to secure the bender in a vice to prevent the handles from bending, but otherwise, the operation went just fine, and produced a perfect bend.

I used a smear of molybdenum disulphide low-viscosity grease to lube the tubing, this stuff has excellent EP properties.

 

I'd estimate the 6061-T6 in your photos has a far bigger radius bend than the 75mm radius that Deskpilot is requesting in his diagram.

Yes, the inserted spring is also a useful method for preventing tubing wall distortion, but I believe plugging with sand produces a better result - and you don't have to struggle with spring removal after the bending operation.

Then there's the problem of finding a spring that is a perfect fit for the tubing one is proposing to bend.

Edited by onetrack

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Deskpilot, you need formers to produce a good result when bending - and mandrel formers, such as used in the muffler and exhaust industry, are the best.

 

You can sometimes get reasonable success, with large-radius bends, by not using a former, but it's a risky approach. 

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A bloke by the name of David Lazenby, who is a former Lotus, F1, and Indy 500 chief mechanic, has produced a very neat little manually-operated mandrel tube bender, which can produce a very neat bend without major distortion, even in thin wall materials.

He points out that the general rule of thumb for bending, is that 4 times the diameter of the tubing is the normally-accepted minimum radius for bending.

But the bender he has designed will produce an excellent bend result, that has a radius as little as 2 times the diameter of the tubing.

 

Useful-Tools UK

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54 minutes ago, onetrack said:

.... I'd estimate the 6061-T6 in your photos has a far bigger radius bend than the 75mm radius that Deskpilot is requesting in his diagram. ....

 

Then your estimate would be wrong, I just measured it, the pictures I posted show a 90° bend with a C/L radius of 71mm.

 

BUT - you need to re-read DP's request (it's near the bottom of page 3) - he didn't ask for a 75mm radius, he asked for a 75mm offset with 'best radius possible' bends.

54 minutes ago, onetrack said:

All I'm saying is, there's a risk of cracking, if that grade of aluminium is used, and it is difficult to bend it, because it resists deformation.

One has to remember that when bending tubing, the outer wall section is stretched, and the inner wall section is compressed. This produces serious distortion and stresses.

The material used, has to have satisfactory properties, that are able to handle the distortion and stresses produced.

 

It'll crack if you try and bend it too tight, but I bent it quite happily to a 71mm radius with no indication of cracking, or more to the point being an aluminium alloy, no failure in compression on the inside of the bend.

 

No, actually 'that grade' (6061T6) isn't difficult to bend, it's easier and far more predictable than lower tensile grades if you know what you're doing, though it does take more force, naturally. Of course it resists deformation, so does a banana, it's all a matter of scale isn't it?

 

Fortunately I did remember about the stretching and compressing and distortion and stresses, and gladly I did choose a material with satisfactory properties, which could handle the distortion and stresses ... but thanks for the reminder anyway, I am getting older so I might have complete brain fade one day I expect 😉

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HITC - No need to take any personal offence, re my opinion of the difficulty of bending 6061-T6. The 'net is full of images, of less than satisfactory attempts at bending aluminium tubing, and 6061-T6 in particular.

If you have had good results, it's because you have used very thick wall tubing, and you have also used a good quality mandrel bender with tight-fitting formers.

 

Deskpilot - I acquired the 22.23mm (7/8") tubing on Friday afternoon, and made an initial attempt at bending a 500mm section, utilising my 1/2" steel pipe bender former.

I studied the 1/2" steel former and concluded it is very close to the 7/8" aluminium tubing in profile. I thought it would suffice for the aluminium tube bending, but I was wrong.

Despite packing with used garnet and exercising care, I didn't obtain satisfactory bends in the tubing, I ended up with some rippling on the inside radius, and some flattening on the outside radius.

I've put this down to a less-than-satisfactory fit of the tubing in the former, and possibly, inadequate packing of the garnet. I should have rammed the garnet to ensure maximum compaction.

 

I paid a visit to my local muffler and exhaust shop in the hope that they would have 7/8" dies for their power bender. Unfortunately, despite their helpfulness, I was out of luck, their dies don't go down to 7/8".

 

The next step, I'm going to acquire a set of HVACR ratchet mandrel benders, which have tight-tolerance formers and followers. I reckon these will produce a satisfactory bend result in the aluminium tubing. Stay tuned for further developments.

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15 minutes ago, onetrack said:

HITC - No need to take any personal offence, re my opinion of the difficulty of bending 6061-T6. The 'net is full of images, of less than satisfactory attempts at bending aluminium tubing, and 6061-T6 in particular.

If you have had good results, it's because you have used very thick wall tubing, and you have also used a good quality mandrel bender with tight-fitting formers.

......

I didn't take any offence - maybe you missed the 'wink' at the end of my comment? I was just somewhat bemused at your regular egg-sucking tutorials - I guess you might have been a school teacher in a previous life.

 

Yes, of course you will have far better results with thick walled tubing, which is why I suggested it to DP in the first place. And, no, I didn't use a good quality mandrel bender with tight fitting formers, the part I posted pictures of was simply bent around my bullbar as I described earlier. Having had to 'make do' in the bush a lot of my life I have a passable understanding of what will work and what won't, since I've tried most things at one time or another.

 

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