Hand built bespoke bicycle frames in the heart of the Wiltshire countryside - dmoframeworks@gmail.com.
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Wednesday, 4 July 2012

Top Tube Bending - Complete!

Having researched tube bending companies on Google I compiled a list of likely candidates (about 7 in all) - the first of which was a company called Pipecraft based in West Sussex (http://www.pipecraft.co.uk/).

I spoke with a chap called Andy who was so helpful I didn't even bother phoning the other companies on my list!

Having discussed my requirements (and essentially because I am generally interested in all things engineering) we decided that it was probably best for me to pop down and visit Pipecraft with my tubing.

This enabled me to watch and learn about the process of forming the tube and also served as a splendid opportunity to get a proper feel for their manufacturing capability for use on future projects.

In the end Andy rolled my 4130 tubing on a ring roller, we experimented with both sand filled and empty tubing and it turned out the bend was so shallow sand was not required to support the tubing - see pics below:

Andy in action on the ring roller!

Andy (with mesmerised Dad in background) demonstrating a tube mitreing belt sander.

All in all an excellent visit, 5 shaped top tubes and lots learnt about tube bending, shaping and fabricating.

Everyone at Pipecraft couldn't have been more helpful and I couldn't have wished to work with a more open and generally welcoming group of people - contact them for all your tube shaping needs ;) 

Monday, 2 July 2012

Tube Bending Pre-Work!

One of the design features of the Element frame is a very slightly curved top tube.

There are various reasons for this design choice the main ones being:
  • it results in slightly more vertical compliance in the front triangle - aimed to provide a more comfortable ride over multi-day events while maintaining lateral stiffness and hence frame responsiveness.
  • it enables a slightly larger frame bag to be fitted to the frame (essential for balanced bivvy bike setups)
  • finally, and arguably least importantly, it differentiates the frame from anything else currently on the market!
 In order to achieve this "shaped" top tube it was necessary to cold form the tubing - I did a lot of research into this with various techniques being suggested including:

  • fill the tube with soapy water and freeze it prior to shaping (the soap apparently acts to stop the ice crushing and cracking up under load).
  • fill the tube with Bendalloy prior to shaping
  • don't bother filling the tube with anything
  • fill the tube with water and then pour in fine sand - the water acts to ensure no air is trapped in the filled tube.
In the end I decided to sand fill one tube and to not fill one tube and test bend them back to back.

In order to stop the sand coming out during shaping it was recommended I bung the ends of the tube with wood.

For this I turned to my friend Piet from work who not only has a wood lathe but is also pretty handy at using it!!

We used some old South African railway sleeper wood (Piet is originally from SA) and proceeded to turn the bungs on the lathe - see pic below:

Piet in action on the wood lathe!!
The finished bungs prior to parting off and finishing.
The bung in situ - job done!

Many thanks to Piet for showing me how to make the bungs on his lathe, putting up with my slightly optimistic manufacturing tollerences, and for providing some splendid Portuguese red wine to oil the wheels of creativity!!

The next step is to take the tubing to a company called Pipecraft to get it bent.