Manky Monkey Motors

Well, maybe not profit.  I have read all sorts about bending tube and pipe in simple "clarke" benders. Some of this information is contradictory.  So I have decided to do a little experimentation and put the results up for discussion. Maybe we can collectively come to a "best practice" result???

So I have started with 1" mild steel ERW pipe.  Thats 1" Internal diameter, 1 3/8" External diameter.

I bent it to 90 degrees in a single operation with the wheels in the outermost position.  The results were underwhelming.  The image is below.

oooop,s  kinky  ::)

So I made a few changes.

1. I filled the pipe with sand. This was acheived by
   a. Sealing one end with insulation tape, - yes the pressure at the end will be that low!
   b. Filling the pipe with water
   c. Carefully putting wet sand into the open end until the pipe is full of sand and the water displaced
   d. Sealing the open end with tape


2. Modifying the bender.
  a.  Drill a hole into the former centrally  below the forming curve
  b.  Create a strap to fit over the pipe that can be secured with a bolt through the hole at (a)
  c.  Weld a nut to the top of the strap and fit a bolt so that the pipe can be held firmly in the former.

The logic behind this modification is that the pipe rises out of the former as soon as the bend starts, so the pressure is not exerted in a progressive manner around the inside edge of the bend as it forms.

To make the test as tough as possible the idler wheels were placed at the most internal setting, and the pipe was bent to 90 degrees, the results are below.

there are a few things to comment on here. 

We did not use a bolt to hold the strap in place, but a bar, this slipped out towards the end of the bend which may have reduced the efficiency of the hold down strap

The bend seems to be heading in the right direction, but the idler rollers are now causing a problem. The pipe appears not to have moved through the rollers but instead dug into them.

Others have suggested putting some form of load spreading shim between the idler rollers and the pipe.  That will be the next addition to the test bed.  We will also lubricate the pipe.

After that we will experiment with progressively moving the idler rollers in (rather than starting at the innermost position)

Indeed :)

its a crying shame that my dad passed away a while ago  as he was an expert of the old school and could even cut a pipe to lenth before bending it and after putting it through the bender it would come out within 1/16 of an inch of where it should be  and that was on pipe ranging from 1/2 inch upto 8 inch  it was an art to watch

i still have his  TUBELLA hydraulic bender upto 4 inch  he had a screw wound bender before that

Hi Andy,The tube you are using is only 3.1/6"wall,So you can't expect to get a good bend no matter what you try.To get anything like a decent bend you'll need 2,5mm wall thickness.

Hi Hunter.  This is an experiment in getting the best from what I currently have to find the best set up for the bender.  I have some CDS coming on Friday.  However, As the current pipe is 3/16" wall thickness that comes to about 4mm does it not, certainly it measures over 3 mm????  Or are you saying that the wall thickness needs to be thinner to get a decent bend? - i'm confused now :) ( Always actually )

no you was right first time round the thicker the wall the better the bend. is good to have a play before hand,no point in wasting the good stuff. ;)

Please keep going with this. I will begin building a new frame for a project later this year and your experiences will be invaluable to me. Keep bending that tubing!! ;D

Andy I was going to try cutting some larger pipe to work as sleeves on the bit you want bending, I invisaged the 'sleeves' would be on the rollers but I have never got round to trying it. I thought that may eliminate the marks made by the rollers. This is just my logic though so may be total rubbish :)

tbh, looks like the corners are too sharp to me, are you actually gonna use 90 deg bends any where?

what did you expect trying 90deg bends on the inner roller settings,? its gonna leave roller depressions doin that, start from the outside in,like u said...

buy yourself an engineering book, itl show you how to bend pipework like spanners dad, its not hard once you know,
you may have probs bending cws in a erw set up bender, cws will react differently to erw, it may flatten even more, so all these experiments may be useless anyway, get extra cds and try with that

If you have a little time on your hands have a butchers at THIS THREAD (http://www.britchopper.co.uk/forum/viewtopic.php?f=28&t=6326) It not on here but it shows a wealth of information on bending tube etc etc. How to do it accurately. How to stop the kinks and also how I built a V8 trike.
I have been bending tube for the best part of 30 years and most of my experience is show in the thread. I will gladly answer any questions you have.

My best advice is to purchase a good quality bender. In fact the one in the build is for sale as I have just bought a slightly better one.

Hi Guys. Yeah, Digger, I rather expected that, What I am trying to do here is find out how for myself how the various parameters interact with the kit I have, so i understand how things work together.  My thinking is to get to a point wher I know what can and can't be acheived.  And maybe the next guy to buy a bender knows more about what to expect than I did when I bought mine.

I would like to bring the front frame up perpendicular to the road, that will require a pair of 90 degree bends, apart from that, no, I won't need 90 Deg or sharp bends.

Haggis, that is a facinating thread, looks like an good evenings time to read through it all.  And thank you I will certainly ask :)

The CDS arrives tomorrow - So I shall be having a lot of fun this weekend :)

great thread of the v8, the yokes and forks look very smart indeed,      andy i only had two nearly 90 on the lower frame rails the cds kinked a bit so i give it a dam good gusseting :o which insedently made it look better.

Sorry Andy, to late posting 1.24am and to much meds,Head shot,
 I think i made a miscalculation :-[

Andy,somehtings wrong here! That cant be ERW! It looks totally cr*p!

 school table leg ? ? ?  ;) :D

Its painted which makes it look bad, I got 24 meters of it for £20 from a local scrap metal place.  Ive been using it for practicing welding, bending and and so on.  I just took delivery of 12 meters of beautiful brand new cold drawn - about to go play with that :)

theres one for sale in the for sale sect says its great for erw not so good on cds if you get your steel from a steel stock holder ask for bending quality  when ordering   remember if the frame is not 100% its your life  at risk sounds a bit harsh but thats the  way it is   the clarke bender comes with six formers in the frame there are six holes where the rollers go  this in not by coinsidence when using the small former use  the holes closest  to the center and  and when using the large former  use the holes at the endsthis will give the correct radius of bend  with out kinking  to avoid dents where the rollers touch the tube cut a small piece of tube you are bending an d cut it down the length into three pieces use one of these pieces in between the rollers and the tube it will spread the pressure and not dent the tube hope this helps  andy b

Hi Andy. Yes, I fully agree with the safety thing. In the end I decvided to sitch this stuff I have and use some proper stuff (From K steels in Rawtenstall BTW). Funnily enough we made the peices for the rollers this afternoon. Just have to make a nice packer for the bending former now.  I have steel sheet, and Lead here, gonna try with the lead to see how that behaves.  Pics will follow.  I am hoping that by carefully working all this out I can end up with a decent result with the CDS I got frok K's  Thanks for the advice :)

Whose Kaye?? ;D ;D ;D

if you cant get 90 deg bends, buy some and slug em to straights,
90 deg can still be achieved with a bigger diameter former (for same dia pipe though) it,l lessen the chance of kinking, though i doubt you will be able to get hold of, (or want to buy) such a thing easily, and it might not go with the trikes shape

Hi everyone.  *** SUCCESS ! ***
After a lot of trial and error I have managed to find a way of getting a near perfect 90 degree bend in both ERW and CDS using a cheap clark type bender. There is still one more experiment before I feel I can say with confidence “this works” – but I am very near (see below). 

Thank you to everyone who made comments / posted links etc - it has all been invaluable to my understanding. I am sure there is still much more to learn :)

A few extra components are used to get these results with the bender, these are:
•   An adjustable clamp
•   A pressure shim
•   A bending shim
•   2 roller followers

Here is the technique I have been using:

Create a pressure clamp.
a.   Drill a hole into the former centrally below the forming curve
b.   Create a strap to fit over the pipe that can be secured with a bolt through the hole at (a) – This needs to be a high tensile bolt or it will bend. I used the inner of a rawlbolt.
c.   Weld a nut to the top of the strap and fit a bolt so that the pipe can be held firmly in the former.

Create a pressure shim
•   This shim will go between the pressure bolt and the piece to be bent.  This stops the bolt point pressure dinging the piece in.
•   Cut a short length of pipe / tube with about a 45 degree arc, and spread it so it follows the Outside of the work piece

Create a bending shim
•   Take a length of tube / pipe sufficient to line the bending former.
•   Cut a 110 degree section out of the tube / pipe.  I did this then chopped the length off as its easier to handle in that sequence
•   Put the open slot of the piece over a piece of same diameter tube and wallop it with a hammer to force it open. Eventually with care the cut tube will nestle nicely on the outside of the piece to be bent

Create roller followers
•   Both rollers have a follower between the roller and the work piece
•   This is formed in a similar manner to above by cutting down the length of a tube to create 2 X 180 degree pieces
•   These are opened up to fit by the delicate use of a big hammer as above.

Fill the pipe with sand. This is achieved by
•   Sealing one end with insulation tape, - yes the pressure at the end will be that low!
•   Filling the pipe with water
•   Carefully putting wet sand into the open end until the pipe is full of sand and the water displaced
•   Tamp down the sand inside the pipe / tube with a wooden dowel
•   Put in more sand
•   Seal the open end with tape

Assembling it all
Pretty much as it seems, I oiled everything that moved as they went together

Technique
The bending shim starts off straight below the work peice, and ends up bent into the bending former.  As the bend is started the work piece will move down into the bending shim. I regularly took up the slack with the pressure shim and bolt.  Eventually the forces reverse, and the centre of the work piece will try to rise out of the former, thats when the pressure shim does it's work.  I started on the outermost roller, then move in one set, then moved in again, and I took my time

Results
The pictures below shows the components assembled with a length of CDS in the bender bent to 90 degrees.

Concerns
In each instance I started with a straight bending shim and allowed it to bend down with the pipe / tube.  I have not yet tried a second tube bend using the preformed bending shim.

here are the results. They look pretty good in real life :)

they look way better than mine. i suspect ur a genius.   nice

very nice tight bends

As I was reading through I thought this needs pictures, as I got further down I found the pictures :)

Amazing how I can get the complete wrong end of something, where you have been saying drill a hole through the former I was thingking it was inside the radius and couldn't imagine how it would work. Seeing the picture it is under the former and makes perfect sense :)

Well done Andy

Cheers guys. Now I feel I can finally start on the frame :)

Aw,and I was looking forward to a Rennison explanatory video!! ;D

OK Rod. Once I have proved the resue of the former we will do one :)

what size tube is that? ie od and wall?

I bend up some stuff I found laying at the back of the garage, its 33.7 od, and 3mm wall or thereabouts, but it will bend over 90 degrees with one of them clarke benders

I built a frame with it and hammered the crap out of it for a long time, and no problems