I have found that I never make anything out of round tube and I had a bender that wasn't doing anything. I made a set of dies for 20mm tube and it worked really good, so I thought I would make a set for 25mm tube and an instructable while I was at it.

Step 1: Making the Dies

You will need some of:

10mm plate
M12x 75mm bolts with nyloc nuts
25x5mm flat bar
6mm round bar
25mm square tube
a cheap pipe bender
welder, grinder, drill and other common consumables

How to get it done:

Grinding, welding and generally making anything in the shed could end up dangerous so please use caution and appropriate personal protective equipment.

Bend a horse shoe shape in a short length of the flat bar and also the round. This will determine the bend radius of the bender, the one I have built the radius is about 90mm.
Cut a bit of the square tube to push the centre of the die, it should only be as long at the bend radius (I stuffed this up in my example here).
Weld this into the flat then tie the sides of the arc to the side of the tube with a couple of small lengths of flat bar.
At this point you can weld this to one of your pieces of plate, cut these to extend 25mm beyond the centre part of the die.
The round can now be welded to the outside face of the arc of flat then cleaned up with the angle grinder.
Lay the other piece of plate on the other side and clamp it in place. Drill 3 holes around the arc and bolt the die together.
If you now take 6x 100mm pieces of flat then put a small bend about 20mm from the one end. With 2 pieces of 25mm tube cut to the same length of rollers that came with the bender. Arrange 3 of the small pieces of flat into a channel/funnel configuration and weld them centered onto the pieces of tube.
You can now install the slippers and die into the bender, put your length of tube to be bent into the die and start bending!

Its probably easier to follow on the video, I have struggled to put what I have done into words but I did record making the dies.