Hi there!



I need to get information on what is the minimal bending radius for 1.9''
(48mm) OD steel tube with 0.079'' (2mm) wall thickness where bending angle
won't be greater than 90 degrees. I'm planning on building my own tube
bender dedicated for this kind of tubing. Tube bender should be similar to
model presented on this page:
http://www.blindchickenracing.com/To...bingbender.htm



Since I live in Poland, having those tubes bent by someone else is not an
option. Locations where this job could be done are way too distant and
prices are too high. I've already spent some time trying to figure out the
bend radius by myself but I've seen too many different opinions. I tried
looking up this information on Pro-Tools website since I know they are
selling dies for benders but there is no die suitable for me. I'm interested
in minimal radius (CLR) that is possible without additional means like
heating up tube walls or filling tube with dry sand.



I hope this is clear description of what I need. Please forgive me if I made
any language mistakes - English isn't my native language.



Regards

Lukasz

If your bender is only half as good as your English, you'll have a
super bender.

Best of luck with your project.

Lewis.

****************

You could do a whole book on the subject but here is the condensed
version:

"degree of difficulty" is defined as the center line radius divided by
the diameter. 6 and up is easy, 4 is ok, 2 is hard, 1 is VERY hard. This
is really a function of how much the outer skin stretches in relation to
the neutral axis that runs near the center of the tube. You are at 4,
not too much of an issue.

"Wall factor" is the diameter divided by the wall thickness. The higher
the number,the more support you will need to keep the outer wall from
collapsing and the inner wall from crumpling. 10 and less is pretty much
self supporting, you are up at 24 to one, this will require substantial
internal support. You can do it with a mandrel, cerobend (low temp
metal) or sand. Sand is not very useful, it must be packed VERY hard.

The bend die you need will need to be machined. If you only need to do a
few (dozen) bends, you can make it from aluminum. A few hundred can be
done with mild steel. Thousands will require hardened tool steel. The
inner channel must be an exact fit for the tube, it must come up to the
center of the tube. The edge walls need to be at least 4mm,6mm would be
better. this means yours should be machined from a 60mm plate, a non
trivial chunk of metal! standard practice is to spin a disk with proper
groove, cut out the excess. Or cut it on a rotary table set on edge in a
mill using a 48 mm roughing mill. This is very close to 1-7/8" if you
could find a mill of that size it would be fast. Otherwise rough it then
use a boring head to get the last cut. Slow and tedious.

Try this site for some great information. You will need to register but
it's worth it.
http://www.toolsforbending.com/literature.asp

Good luck.

Lukasz Kucharski wrote:

Hi there!



I need to get information on what is the minimal bending radius for 1.9''
(48mm) OD steel tube with 0.079'' (2mm) wall thickness where bending angle
won't be greater than 90 degrees. I'm planning on building my own tube
bender dedicated for this kind of tubing. Tube bender should be similar to
model presented on this page:
http://www.blindchickenracing.com/To...bingbender.htm



Since I live in Poland, having those tubes bent by someone else is not an
option. Locations where this job could be done are way too distant and
prices are too high. I've already spent some time trying to figure out the
bend radius by myself but I've seen too many different opinions. I tried
looking up this information on Pro-Tools website since I know they are
selling dies for benders but there is no die suitable for me. I'm interested
in minimal radius (CLR) that is possible without additional means like
heating up tube walls or filling tube with dry sand.



I hope this is clear description of what I need. Please forgive me if I made
any language mistakes - English isn't my native language.



Regards

Lukasz

"Wall factor" is the diameter divided by the wall thickness. The higher
the number,the more support you will need to keep the outer wall from
collapsing and the inner wall from crumpling. 10 and less is pretty much
self supporting, you are up at 24 to one, this will require substantial
internal support. You can do it with a mandrel, cerobend (low temp
metal) or sand. Sand is not very useful, it must be packed VERY hard.


Thanks for your reply Roy. Thanks for lots of adequate information. The
website you recommended is very helpful. I decided to build 5 x OD radius
die just to be on the safe side. Unfortunately mandrel and cerobend are
beyond my reach. I wonder if it's possible to fill the tube up with dry
cement or maybe gypsum instead of sand. What do you think about this idea?
Small grain substance like gypsum or cement wouldn't be hard to pack tightly
or would it?.



Regards



Lukasz

In the tube bending world, bend radius of a round tube is ALWAYS
described as the centerline of the tube. Bend radius of a square tube is
ALWAYS described as the inside radius of the tube. Go figure. But using
the proper nomenclature makes it easier to get assistance with your
project.

On the hbobbist level, we have tried the sand route with a hydraulic ram
bender with marginal success.
http://www.harborfreight.com/cpi/cta...emnumber=32888
bends over about 40 degrees would kink. And this is for a tube with
heavier wall than yours. I think your idea of gypsum has merit. You want
something that will clump and not flow under pressure. You will need to
pack it very tight for a distance of at least 2 to 4 diameters past the
bend area. You will need to have some sort of drill powered spring
cutter to get the material out of there.

If you decide that you want to build a bender like the one you
mentioned, I think I would try and figure out some sort of mandrel
inside the tube. The point where the bending occurs is well defined,
about 1" from the point of contact with the straight die. Use a plug
mandrel about .005" to .010" (.1mm to .3mm) smaller than the inside of
the tube. It needs to be relieved a bit on the outside of the bend to
conform to the newly formed bend. With this design, the mandrel does not
move so it can be just a solid plug screwed into the end of a solid rod.
You will need to have it easily adjustable for exact placement as well
as well some sort of cam to pull it the first inch or two when you are
done with the bend.

Lukasz Kucharski wrote:
"Wall factor" is the diameter divided by the wall thickness. The higher
the number,the more support you will need to keep the outer wall from
collapsing and the inner wall from crumpling. 10 and less is pretty much
self supporting, you are up at 24 to one, this will require substantial
internal support. You can do it with a mandrel, cerobend (low temp
metal) or sand. Sand is not very useful, it must be packed VERY hard.



Thanks for your reply Roy. Thanks for lots of adequate information. The
website you recommended is very helpful. I decided to build 5 x OD radius
die just to be on the safe side. Unfortunately mandrel and cerobend are
beyond my reach. I wonder if it's possible to fill the tube up with dry
cement or maybe gypsum instead of sand. What do you think about this idea?
Small grain substance like gypsum or cement wouldn't be hard to pack tightly
or would it?.



Regards



Lukasz