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Will this work?


bishbosh
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I have a push bender for pipe / tube. One of the issues with this type of bender is ripples forming on the inside of the bend.

I have seen small diameter extension springs for sale to use as mandrels for bending copper tube. I was thinking of extending the principle to roll cage size tube / pipe using a spring similar to the good old fashioned chest expander spring of old!

So, two questions:

1. Do you think it would work? and

2. Where would one find such a spring? I would reckon on an OD of 39mm and a free length of about 300-400mm. The wire would have to be fairly meaty too I would expect.

Ideas? Opinions?

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No. Sell it on ebay and buy a draw type bender with the proceeds plus a bit of spare cashishe.

(Ok, maybe, but still read the the previous sentence).

I'm not convinced you could find the right square cross-section profile spring in a large enough size, and that you could generate sufficient force to withdraw it from a bend even if you could find / make it.

Spend the extra 100 and get a decent bender. (Nice idea though!)

Al. :)

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The spring idea is a no goer unfortunately.

The real answer is to use quality pipe/tube, quality bender and former, however, I saw a video ages ago where a chap had the same problem. He used the sand technique, but used a very interesting way of ensuring the sand was tightly packed. He capped one end of the pipe, then stood it on end and first filled it with water. He then poured the sand in. As the sand went in it settled to the bottom and began displacing the water. Eventually the pipe was filled with damp sand with no voids and was capped. The bends were then perfect.

I have never tried this technique myself, but have successfully bent pipe with a cheap bender on thick walled pipe with a decent former

Regards

Diff

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I was about to suggest this.

Fill with sand, packed hard, and weld the ends of the pipe closed. Then bend it.

I've never tried this but I knew someone who did this with 3" pipe and bent it with some heat.

We are having some 65mm NB steel pipe bent at work this week using this method.

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Thanks for the replies folks.

Al - I like the idea, but I don't believe your maths!! :lol: The H3PR will fetch £200 tops on the bay so where do you get a draw bender with die for £300?

Jase - you're just a big girls blouse! Practice with some rice pudding skins!! :P

Les - the former is a Tubela former that fits the pipe incredibly tightly - it wont actually go in to the former by hand and needs to be jacked in.

This may of course be part of the problem but the main problem is that the tube is CDS. Now before you all start sucking your teeth, I know that a push bender is not ideal for CDS, but needs must and I only need to do a couple of gentle bends (the angle between the front and back of a hard top roof)

I am not convinced that I could get the sand sufficiently well compacted to be of much use for such a small change in volume.

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Just a word of warning....

If you are filling the tube with water or damp sand and capping it afterwards, then make very sure not to heat it excessively. The water vapour expands and fractures the tube - with possible devasting consequences for nearby humans....

The old way of bending tube consists of filling the tube with compacted DRY sand, then heating the tube to red hot and the doing the bend. However, this procedure is probably not applicable for CDS.

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Thanks for the replies folks.

Al - I like the idea, but I don't believe your maths!! :lol: The H3PR will fetch £200 tops on the bay so where do you get a draw bender with die for £300?

Jase - you're just a big girls blouse! Practice with some rice pudding skins!! :P

Les - the former is a Tubela former that fits the pipe incredibly tightly - it wont actually go in to the former by hand and needs to be jacked in.

This may of course be part of the problem but the main problem is that the tube is CDS. Now before you all start sucking your teeth, I know that a push bender is not ideal for CDS, but needs must and I only need to do a couple of gentle bends (the angle between the front and back of a hard top roof)

I am not convinced that I could get the sand sufficiently well compacted to be of much use for such a small change in volume.

I bent some 45mm CDS approx 40 deg' with a push bender, Then threw it away and ordered two lengths of tube bent as I needed from North. My effort wasn't good by any standard. Im sure North, P&P or any of the cage makers will do whatever needed if you speak to them. Mine only cost a few quid. If its a one off job, Much cheaper than buying a new former, never mind a bender.

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Want to borrow a decent bender?

Al.

Very kind Al, but it really is just two bends in two tubes I already have (which already have another bend in). As this bend will be directly over a supporting "stool" I think I will give it a go with sand and some heat to the tension face. If the inside of the bend ripples a bit it wont matter too much as it will be welded to the stool.

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If you don't think the sand will work then fill it with lead.

Steve

or maybe unobtainium...???? :lol:

The stuff he's refering to is cerabend, solid at room temperature liquid at about 85 degrees.

The sand technique only works if you cap the ends pack it very tightly using really realy fine ash type sand then "dent" the caps in to pack it even tighter.

From my experience bish you just won't get a decent bend on cds with a push type bender.

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For gentle bends of this type ,fill the tube with some of that kiln dried sand from wicks (the sort you brush into block paving) though dont add water.Cap the end & gently heat & bent to suit.Very easy & effective.When specials are needed in industry this never fails us.Good luck.

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Well, tried the sand method with an offcut of tube. Tamped it down in layers, capped it off and dented in the caps.

Bent at a shallow angle the same as an empty tube. As the angle increased the tube just folded up. :( I think for that method to work you need to really compress the sand hard. Even after my tamping efforts I could hear the sand if I shook the tube. :(

Anyhow, I have managed to bend the tubes I needed to with absolutely no distortion as the angle was so shallow. :rolleyes:

Just the "X" in the roof to do and the rear stays and I am done. :rolleyes:

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  • 4 weeks later...
Well, tried the sand method with an offcut of tube. Tamped it down in layers, capped it off and dented in the caps.

Bent at a shallow angle the same as an empty tube. As the angle increased the tube just folded up. :( I think for that method to work you need to really compress the sand hard. Even after my tamping efforts I could hear the sand if I shook the tube. :(

Anyhow, I have managed to bend the tubes I needed to with absolutely no distortion as the angle was so shallow. :rolleyes:

Just the "X" in the roof to do and the rear stays and I am done. :rolleyes:

I have acheived a good bend by mixing water with sand and pouring it into the tube - the sand eventually displaces all the water making it well compacted.

see this video - (not me but you get the idea)

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