Copper Tube Bending kit for 3,4,5,6 and 8mm pipe

Copper Tube Bending kit for 3,4,5,6 and 8mm pipe

Hemingway’s Tube Bender Kit

Hemingway’s Tube Bender Kit was a Christmas present from my son Adam and his family. This followed a request for ideas for a present. So I sent him a link to Hemingways model engineering kits.

Adam came straight back and said why make one when he found a tube bender, already made, and cheaper,  on the Screwfix site!

I had to explain  to him that the making of the tube bender was as important to me as much as the finished tool.  Perhaps even more so than simply buying one. Even if you could find one for small diameter copper tube which range in size between 1/8th” (3mm), to 5/16” (8mm). Clearly not achievable by the Screwfix tube bender.

Starting 2020 anew, I decided that the 2″ scale Fowler Traction Engine by MJ Engineering will be the main project this year.  It has been promoted since the long running Postman Pat van project is completed.

I want to make sure that all the pipework on the Fowler is as neat as possible. There is quite a bit of  plumbing required hence the need for a tube bender and the Hemingway kit looked the way to go.

The Hemingway Tube Bending Kit.

The Hemingway Tube Bending Kit consists of bar stock, an excellent drawing and construction notes in the form of an article. Once I checked the contents it was time to consider whether to stay with the imperial measurements, or ‘go metric’. Sourcing copper pipe may be easier in metric so I plumped to ‘go metric’.

The use of a spreadsheet for measurement conversion was considered, but instead I just made a chart of measurements then annotated the plans accordingly,  also giving each part an identifier A,B,C etc.

Hemingway Tube bender – 7 parts.

To bend 1 tube size needs 7 parts to bend.  Since there are different diameter copper pipes you can bend (requiring 5 components each), making a total of 19 individual parts to machine.

They consist of:-

A.  Handle x 1

B.  Vice Block  x 1

C.  Slide Pin  x 1

D. Pivot Pin  x 1

E.  Formers

      1. 1 /8th”,   (3mm)
      2. 5/32nd”, (4mm)
      3. 3/16th”,  (5mm)
      4. 1/4″,        (6mm)
      5. 5/16th”   (8mm)

F.   Pressure Slide x 5

G.   Hooks x 5

A. The Handle.

The handle is a straight forward machining task where two holes are drilled before machining a slot between them.

It is a pretty simple task to make the slot however I did make a pigs ear of the radius at the end of the handle.  Due to misalignment of the rotary table it wasn’t as good as I had wanted. An unfortunate result which pre-dates a  Mach3 update where the position of a part/vice/accessory can be set very accurately, but more important, simply. A blog covering the centre, edge finding enhancements will follow soon. 

The radius end mistake doesn’t affect the operation of the tool in any way. Just very annoying!  Yet again proving you shouldn’t ‘push’ through a bad day health wise!

The hole used to locate the pivot was done with greater care, before it was reamed to size. Its worth the effort to get this right. Since when the formers are attached, they are secured tightly, but it has to allow the free and easy movement of the handle itself. At least this was carried out correctly.

B. Vice Block

A simple task to make.  I used hand files to finish it and it was a nice to reminder that hand tools still find an important place in the mechanised workshop!

As an aside some years ago I was fortunate enough to be given a set of high quality files from a retired engineer who worked for Jaguar cars at their Browns lane factory in Coventry, UK. A gift I was very pleased to receive.

While owning a Mk2 Jaguar and  until recently an XJ Sovereign, replaced with a Jaguar iPace (you can see I’m a big fan of Jaguars!) wouldn’t it be nice to think the files could have been used on my own Mk2 Jaguar when it was built?

C. Slide Pin

Looking on the plans the 1/32nd (0.794mm) thin piece of metal that acts as a spacer I thought this would be ‘challenging when turning on the lathe. The question in my mind was how durable it would be in use? However my fears were unwarranted and seems more than durable in use.  It needs to be accurate since it is key to ensure the pressure slide fits inside the formers.

Milling the two flats was simple enough.  A little fettling was done using those retired engineers files.

The slide pin fits in the handle slot and slides along to accommodate the different diameter formers.

D. Pivot Pin

A nice turning exercise that requires the pivot surface to be as good as possible for the handle to rotate easily. A recess is machined at the base for the vice block to fit in. Then drilled and tapped, using the Vice block as a drilling guide for marking out.

E. Formers (x 5)

The profile for the copper tube requires tool steel ground to match that formers size. A good tip from the designer was to take out most of the material with a parting tool before changing to the profiled tool steel.

In the end the task was easier that I thought it would be.  It was pleasing to see how good the fit was. The tops of the formers were then milled using the dimension table supplied. In the end I enjoyed making the formers most of all.

Each former has a hook to secure the copper pipe by means of a tapped hole in the former top. However it has to wait until the hooks are made since their location relies on where the copper pipe is when it comes between the former and pressure slide.  Not too difficult until the smallest 3mm former is tapped. It requires special care since the tapped hole is positioned inside part of the profile itself.

F. Pressure Slides

My methodology for producing the pressure slides was a major departure from the designers. After reducing the stock material to size each part was placed in the milling machine vice, on a set of parallels.

During the project I found a way to find centres, edges etc. of stock material with Mach3.  Now the centre position of the slides  could be accurately found.  I intend to produce an article on how this was achieved at a later date.

The pressure slides were then milled using  ball nosed end mills to produce the profiles required. This method avoided the complicated sounding method using a Myford vertical slide.

The last machining task was too mill each side at 90 degrees from the profiled top. It’s important to get this machined correctly,  since the sides allow the pressure slide to sit inside the former.

To hold the slides in the vice during the side milling a  transfer punch   of correct diameter was used to protect the edges of the grooves.

Following the drilling of the hole used to secure the pressure slide in place each slide was hardened.  After cleaning up, a file was used to confirm the process had been successful. The top edges have to do a lot of the work and hardening improves durability.

G.Hooks

The hooks have two holes drilled in them. One matches the diameter of the tube to be bent. The second is used to bolt the hook on top of the former. To find where to drill and tap for the securing bolt the former and pressure slide are used with pipe between them in the vice.

Placing the required pipe at 90 degrees to the top of the former the hook is placed over the pipe and the second holes position is transferred to the former. Now with the hook loosely bolted to the former it is possible to rest it against the pipe and scribe lines either side of the pipe.

The method of cutting this material away was to use a Dremel Speedclic disc. To get the slot as accurate as possible I had a spare MT3 arbour and drilled it to fit the shaft of the Speedclic.

By placing the hook in the vice with one scribed line parallel to the vice top the mill was advanced until meeting the drilled hole. Final adjustment was made by filing.

The slot allows the hook, holding the copper pipe, is then swung away to remove or adjust the position or twists in the pipe being bent.

Tube Bender in Use

The Tube Bender is placed in the vice and the required size set of Former, Hook and Pressure Slide attached to the handle (as shown in the video). It is important to stress that the pressure slide (which does all the hard work) is located just inside the the formers edge, but not tightened yet.

Copper pipe is then placed between former and slide, snug to the pipe and inside the former.

The hook is now swivelled into position and secured. All that’s left to do now is pull the handle around until the radius required is achieved.

If the copper tube is age hardened then you will need to anneal the sections you require.

It is easy to produce some complicated shapes by loosening the hook and pipe repositioned. On my first trial I was very pleased with the results. Using new copper pipe was a dream and little or no inside compression was seen.

The designer carried out considerable research which provided the dimensions of the formers and was a pleasure to build.. now where is that Fowler Tender…….

9. Future enhancements

Between finishing the project and completing this article I completed a planned enhancement. I powder coated the parts and this also will be covered in more depth now I’ve started to get the typewriter out again ..at least it shouldn’t rust!

Having tried all the sizes (3mm,4mm,5mm,6mm and 8mm) with new Albion metals copper tube, no undue pressure was required to bend pipe all the way around the former.

I have some older pipe in stock but noticed no difference in their use.

The end of the handle was turned to accept an extension piece if required. But it may as well have a nice hardwood wooden handle turned to fit.

Engraving each set of Hook, Pressure Slide and Former with their size may be a nice addition as well. Whilst engraving, perhaps a line at 33, 45, 60 and 90 degree mark could be considered.

One definite enhancement will be to make a box to store the tool. I did one with the inline boring tool and it does keep it tidy.

Inline boring bar set
My inline boring bar in its storage box

 

Hemingway’s Tube Bending kit – photo’s

 

 

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