ge_rik wrote: ↑Wed May 16, 2018 1:51 pm
Is there something I can do to aid the bending process - or can anyone suggest a more effective design of jig (which would be within my capabilities as a kitchen-table modeller)?
No Metallurgists here in Aust., they re-invented themselves as Materials Engineers years ago. I worked with them for most of my career and some of it rubbed off...........
Heating the 1.5mm rod won't make much difference to how easily it bends unless you take it up to red heat, which will anneal it. At which point it will have the mechanical properties of soggy spaghetti......
The metallurgical issue is that the wire is work hardened when it is drawn to size and only partly annealed afterwards, so it is a bit springy. When you bend it, it tends to bend back a bit when released (referred to as springback by metallurgists). It has to be bent past the nominal angle, so it will spring back to the correct angle. With a fixed pin jig like yours the other pins prevent the wire being bent far enough to get the correct final angle.
So......
1. The jig needs to have removable pins, so it works the same way as a jewellers wire forming jig.
2. The wire needs to be pushed with a flat block so it only bends where it passes around a pin. The block should be metal for preference, but hardwood will work.
The way bending coupler loops in a jig with removable pins would work is as follows -
- Bend the short locating arm at one end with pliers and push into the hole in the jig.
- Fit the first pin into the jig and using a couple of blocks to keep things straight, put in the first bend, pushing far enough that the wire comes back to the edge of the second pin hole.
- Fit the second pin and make the next bend using the two blocks to keep things straight until the wire lines up with the edge of the third pin hole.
- repeat with the other two pins until the coupler loop is formed.
- To form the last locating leg, you will need a right angle cut in the corner of the jig, so the wire can be pushed down to form the last angle.
- Remove the pins, then remove the coupler loop and start all over again.
-You may need to clamp the wire down as you go, so it doesn't twist as it is formed.
Being me, I'd make the jig in metal and have screw in pins. I've not made anything like it in wood, but I'd make the following observations for a kitchen table job......
Make the pins out of steel nails and use a thick block of hardwood. The holes for the nails need to be deep and a sliding fit on the nails, so the nails will be well supported against side load. Using a softwood like pine would be unlikely to last long enough to do the number of loops you need to make, as the holes will slowly get enlarged, allowing the pins to move out of line.
Wood is a pig of a material to drill accurately for making jigs, especially with a hand drill. If you can find a suitable size block of a dense plastic like Tufnol, it would work better for making a jig.
I hope that all makes sense.
Regards,
Graeme