Bending brake pipes

citronut · Unread post by **citronut** » 11 May 2009, 19:30

i find the 3.5 copper knicle pipe bends quite alright without a pipe bender as long as you dont bend it realy sharpe

regards malcolm

Brigsygtt · Unread post by **Brigsygtt** » 11 May 2009, 19:41

No need for a pipe bender, As citronut said it bends very easily just don't go too sharp or it will kink.

XantiaMan · Unread post by **XantiaMan** » 11 May 2009, 19:43

Copper pipe no problem as already said

AndersDK · Unread post by **AndersDK** » 11 May 2009, 20:07

Backing up previous statements on the issue as well ...

addo · Unread post by **addo** » 11 May 2009, 22:56

I've got a little tube bender made by Record, that goes down to about 3.5mm.

A mate who is more "redneck" uses mandrels that come to hand - in his case, usually a beer bottle.

citronut · Unread post by **citronut** » 12 May 2009, 08:12

addo said
"uses mandrels that come to hand - in his case, usually a beer bottle."

i hope they are full or you might get your bends in the wrong place's

regards malcolm

addo · Unread post by **addo** » 12 May 2009, 09:58

Does my opinion count?

It's not absolutely necessary, and will only provide a bend of fixed radius up to about 120°. Still - it does make some swishy looking runs of tubing! I also have the next size up bender, for old-school metal fuel lines.

ellevie · Unread post by **ellevie** » 12 May 2009, 13:19

2.5D bending

In pipe bending machinery jargon they say that "Tight Radius Bending" for copper starts when the bend radius is about 2.5 times the tube’s outer diameter. So 3.5mm x 5 = 17.5mm is the corresponding diameter of a suitable cylindrical bar around which you could bend the pipe.

As it happens the rear arm bearing bolt for a BX or Xantia etc has a diameter of 16mm so if you have an old one of these knocking around it would be ideal for the job.

addo · Unread post by **addo** » 12 May 2009, 23:36

What David's talked about is the minimum radius you can bend the tube into, safely.

It's two and a half times the pipe diameter. So - if you have a 3.5mm pipe diameter, the minimum radius is 2½×3.5mm.

That's 8.75mm

Since that's radius, David was looking for examples of a tubular shape you could bend the pipe around. So he doubled the radius to get a forming diameter of 16.5mm - this is the same as multiplying the original formula by two:

2½×3.5×2 = 5×3.5

Cheers, Adam.

AndersDK · Unread post by **AndersDK** » 13 May 2009, 12:51

addo wrote:What David's talked about is the minimum radius you can bend the tube into, safely.

It's two and a half times the pipe diameter. So - if you have a 3.5mm pipe diameter, the minimum radius is 2½×3.5mm.

That's 8.75mm

Since that's radius, David was looking for examples of a tubular shape you could bend the pipe around. So he doubled the radius to get a forming diameter of 16.5mm - this is the same as multiplying the original formula by two:

2½×3.5×2 = 5×3.5

Cheers, Adam.

Except that 2½×3.5×2 = 5×3.5 is not 16.5.

but more precisely a bit more : 17.5

ellevie · Unread post by **ellevie** » 13 May 2009, 14:27

Sorry Mike and thanks Adam for explaining it better. Yes I doubled up from 2.5 to 5 because the diameter is twice the radius.

I did have some 3.5mm pipe and a rear arm bolt to hand so I tried it out before posting. I also did one just by bending it around the large segment of my index finger which gave a slightly larger radius.

As you have lots of pipe you could experiment with even smaller diameters to see at what point the pipe begins to kink, but to be honest even the one I did with my finger looks fine to me.

addo · Unread post by **addo** » 13 May 2009, 23:13

AndersDK wrote:Except that 2½×3.5×2 = 5×3.5 is not 16.5.

but more precisely a bit more : 17.5

Showing my tradesman's rough approach again.

As a fellow charpentier once said "If you can't fit your finger in the gap, it's fixable"...

ellevie · Unread post by **ellevie** » 14 May 2009, 08:38

Very useful things digits.