Author Topic: Another small radius pipe bender  (Read 3157 times)

Online Vixen

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Another small radius pipe bender
« on: May 16, 2021, 05:46:47 PM »
I decided to have a go at making a small bend radius pipe bender specifically for 5.0 mm copper tube. I based my pipe bender on the design used by Steve "Old Bill" to bend the external pipes on his 1909 Mercedes aero engine.

It did not take long to make, using offcuts and scrap pieces from the 'come in handy one day' box. There are one or two changes to the "Old Bill" design; I use two bolts on the adjuster to stop the slide bar from rocking, Similarly I added a third roller for the same purpose. This bender is designed to bend 5.0 mm copper pipe around a tight 5.5 mm internal bend radius. However is can easily be adapted or modified for other sizes of pipe or bend radii.

The 5.0 mm diameter groove in the slide bar and the rotating bit were made with a 5.0 mm ball ended cutter. The 10 mm AF hex was quickly done by indexing on the 4 th axis unit. The three brass rollers spin on hardened steel shafts, but this is realy not necessary to harden the shafts as they do such little work.

The pipe bender can easily be adapted for other tube/pipe diameters by machining a different diameter grove in one of the other faces of the slider and making another rotator with an appropriately sized groove at whatever bend radius is required.






A few 90* test bends pointed out the need for an internal bullet to prevent the 5.0 mm copper tube from flattening on the outside. A piece of angle iron was used to anchor a length of 4.0 mm steel rod inside the copper tube. The steel bullet rod needs to be clamped sufficiently far away from the bender to allow for a long length of stock tube.




In the photo below; the bend on the left was made from, as delivered, hard copper pipe without the central bullet. You can clearly see the flat on the outside. The middle bend was made the same way after the copper had been annealed (heat to bright red then quench in cold water). The flat is much reduced but still there. The final bend on the right was made with annealed copper and with the internal steel bullet rod, as you can see the bend is perfectly formed without the dreaded flat on the outside. The internal bullet is positioned inside the copper tube just short of where the bend commences. Somehow it prevents the outside of the tube from collapsing inwards




The bending part was easy, once the bender was set up properly. Not so easy was getting the second or third bend in the correct place or at the correct angle to the previous one. Lots more copper pipe found it's way into the scrap bin until I eventually discovered the knack.





Mike
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Offline Kim

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Re: Another small radius pipe bender
« Reply #1 on: May 16, 2021, 05:50:50 PM »
[copying my question from the other thread - sorry about that]

... The final bend on the right was made with annealed copper and with the internal steel bullet rod, as you can see the bend is perfectly formed without the dreaded flat on the outside. The internal bullet is positioned inside the copper tube just short of where the bend commences. Somehow it prevents the outside of the tube from collapsing inwards

You really got a nice bend there!  I'll have to remember this technique.

So, is the bullet rod the exact internal diameter of the tube you're bending?  And what shape is it on the end?  Does one assume its 'bullet' shaped since that's the name of the rod?

I would have thought the 'bullet' needed to go in the end of the jig that turns, so the bullet could stay tangent to the part of the tub that is bending.  But in your jig, it looks like it is in the stationary part of the tube.  Is this right?  Or maybe I'm not following it very well?

Thanks,
Kim

Online Vixen

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Re: Another small radius pipe bender
« Reply #2 on: May 16, 2021, 06:08:14 PM »
Hello Kim,

I thought it best to make a copy of the pipe bender in it's own topic so as not to clutter up the Mercedes build log.

To answer your questions:

The bullet rod needs to be a reasonably close fit to the copper tube but not a tight fit. Initially I turned a bullet shaped end which I thought would conform to the bend radius. It seemed to grab the tube, so I cut the end of the rod off flat with a tiny radius to stop it scratching. The internal bullet is positioned inside the copper tube just short of where the bend commences i.e. at the point where the tube is tangent to the rotator. If the internal bullet is too far inside the bend, the pipe buckles and kinks. You may need to do a couple of 90* test bends to find the sweet spot.

And yes the bullet rod is held stationary. The copper pipe is pulled over the bullet rod as the bend forms.  The bullet rod does not enter the bend, it just stops the copper pipe from collapsing. With this design, the copper pipe is pulled and stretched round the bend, it is not a simple case of being bent.

Mike
« Last Edit: May 16, 2021, 08:36:35 PM by Vixen »
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Offline crueby

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Re: Another small radius pipe bender
« Reply #3 on: May 16, 2021, 08:40:53 PM »
So if the slide bar moves with the tube, how is the bullet rod held in place? Looks fascinating - gotta make on of these...

Online Vixen

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Re: Another small radius pipe bender
« Reply #4 on: May 16, 2021, 09:05:14 PM »
Chris,

Out of the picture to the left, there is an aluminium block clamping the bullet rod to the angle iron. The bullet rod remains stationary,  The slider and the copper tube move to the right as the pipe is pulled and stretched around the rotating part. This is not a simple bender, it stretches the pipe round the bend. Not sure if the inside gets compressed.

The length of the bullet rod and the angle iron depends on the stock length of copper pipe. It's always best to start with the stock copper pipe as long as possible.

The copper must be fully annealed before you start bending. The process of stretching the pipe around the bend quickly work hardens the bent bit of pipe, while the straight bit remains soft. These hard and soft patches makes it difficult (impossible?) to correct a badly positioned bend. Best to scrap that piece and start again.

Mike
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline Kim

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Re: Another small radius pipe bender
« Reply #5 on: May 16, 2021, 11:02:49 PM »
Ah! I see.  I was originally thinking that the copper tube was stationary and the tube was bent around the die.  But the tube actual slides on the bullet rod and the OTHER side rotates with the die to pull the tube.  That's quite ingenious.  I now see what those bearings are doing.  I hadn't even noticed that block that slides with the tube before.  Yes, even though your post clearly talks about it - it didn't click with me till reading your reply.

Thank you for the additional explanation.  It really helped me follow.  This is a really neat bender!
Kim

Online Vixen

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Re: Another small radius pipe bender
« Reply #6 on: May 16, 2021, 11:34:28 PM »
Hello Kim,

I was taken by this clever design since I first came across it in "Old Bill" (Steve's) build log for the 1909 Mercedes aero engine. So all credit should go to Steve, unless he copied it from somewhere else.

Have a look at https://www.modelenginemaker.com/index.php/topic,8649.msg199318.html#msg199318 starting at reply 191. Steve calls it a mandrel bender, has a much better explanation than mine.

Mike
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Sometimes, it can be a long and winding road

Offline Kim

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Re: Another small radius pipe bender
« Reply #7 on: May 17, 2021, 05:14:18 AM »
Sure enough!   I didn't remember that till I went and looked through "Old Bill's" build.  With that refresh, I do recall seeing Steve's build.  But I guess it takes repetition for me to cement an idea.  Thanks for YOUR rendition of this.  It helped me get my head around it better.

Thanks,
Kim 

Offline fumopuc

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Re: Another small radius pipe bender
« Reply #8 on: May 17, 2021, 08:06:13 AM »
Hi Mike, a very interesting concept.
I have been fascinated form Old Billīs post some time ago also.
Good to know that it was not to difficult to copy the concept.
Sure better as my "desk decoration sand" (0,1 mm grain size) inside a tube for bending.
May be one day.....
Kind Regards
Achim

Offline Chipswitheverything

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Re: Another small radius pipe bender
« Reply #9 on: May 17, 2021, 10:14:29 PM »
Many thanks for writing up the details of this effective tool, also for the link to Old Bill's bender of similar type.  Will bookmark it with a note left among the pile of bits that for far too long has been my dismantled ( for painting ) Major beam engine...  It needs pipework with some tightish bends.  Could also be exactly the thing if the Stuart triple castings ever arrive at needing piping up !!   Dave

Online Vixen

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Re: Another small radius pipe bender
« Reply #10 on: May 18, 2021, 01:53:43 PM »
This is how I set up and use my small radius pipe bender for 5.0 mm copper pipe. The first photo shows all of the bender clamped in a vice at the dirty end of the workshop




The second photo shows the bullet rod positioned a fraction to the left of the bend centre line. The bender is quite sensitive to the position of the bullet rod so you will need to experiment. Note: I have also machined the position of the bending plate to be closer to the bend centre line than the Old Bill version.

I have marked the position of the start of the bend onto the annealed copper pipe, before moving it in to position and installing the slider bar.






It takes very little effort to bend the annealed copper pipe. I make the bend in one slow and continuous movement. I usually push on the slider with my left hand (when it's not holding the camera)




Then I mark the position of the end of the first bend and also the distance to the start of the second bend before moving the pipe into the new start position. Remember to rotate the copper pipe if the two bends are at an angle to each other.




I think I may have discovered the subtlety in how this bender works. The annealed copper pipe is held between the half round groove in the slider and the half round circular groove in the rotating part with the bullet rod up the centre. Everything fits tightly and totally constrains the annealed copper pipe both inside and out.  When the bend commences, it pulls and stretches (extrudes?) the outer edge and sides of the pipe into the tight bend. The stretching immediately work hardens the bent part of the copper pipe, making it strong enough to resist the flat forming on the outside of the bend. The softer unbent part of the pipe being held open by the bullet bar.

The bent section is noticeably harder than the straight unbent section. You can use this to your advantage. The soft straight section will twist easily if you need to correct the angular position of the two bends.

I also discovered that trying to rectify incorrectly positioned bends does not work. Best to start again with a fresh length of annealed pipe, so be prepared to get through a lot of copper pipe whilst you experiment.

I will shortly post some of the bending I have achieved, back on the Mercedes W165 log

Mike

« Last Edit: May 18, 2021, 03:08:33 PM by Vixen »
It is the journey that matters, not the destination

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Offline crueby

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Re: Another small radius pipe bender
« Reply #11 on: May 18, 2021, 02:01:24 PM »
Great sequence and explanations, thanks!

Offline Kim

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Re: Another small radius pipe bender
« Reply #12 on: May 18, 2021, 05:14:37 PM »
Yes!  Really appreciate the detailed step-by-step on how you use it.  Very helpful!
Kim

Offline Mcgyver

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Re: Another small radius pipe bender
« Reply #13 on: May 19, 2021, 01:53:19 PM »
Those bends look great!

It definitely needs to be a mandrel bender to get the small bends.  I notice your mandrel is just rounded over, whereas the build I did called for a bullet shaped mandrel with the radius put on the bullet matching the inside tube radius.  Thinking about it, I wonder if it matters as the critical part is to support things right at the tangent of the bend (much of the  bullet is well past the tangent)....but the designer of the one I made I think knew what he was doing and spec'd the bullet shape.  hmm.

Photo's of my build here https://www.modelenginemaker.com/index.php?topic=10063.0  ....I go on about the adventure, but the bullets are shown about halfway down.  I was able to get a 1/4 centre line bend in 1/4 tubing.  I didn't try annealing it, just ran it as it came out of my tube straightener, and it seemed to make a pretty good bend.

Online Vixen

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Re: Another small radius pipe bender
« Reply #14 on: May 19, 2021, 03:26:03 PM »
Hello Mcgyver.

I remember your post and your pipe bender from last December from that catchy title.

I was impressed with the robustness and complexity of your version of the bender, I can see why it took those six months to make.

The inspiration my version of the bender came form the "Old Bill" bender. I did not have any plans, just Steve's photos for inspiration. I made mine, from aluminium scraps, in a single afternoon.

Yes, the bullet bar or mandrel as you call it, has a small radius rather than a full bullet shape matching the inside diameter.     Worked for me...as they say.

Mike

« Last Edit: May 19, 2021, 03:43:33 PM by Vixen »
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

 

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