You don’t need to grind a form tool just turn up a button harden and fix to a shank.

Fill the tube with fine dry sand and block both ends, that will reduce the kinking. If a second bend is to be made, repack the sand before doing it.

As you might expect, success bending copper tube improves with greater wall thickness, a larger bend radius, well annealed tube, and a former with close width constraint. I personally have had little success with sand filling (it always eventually still kinks for a tight bend radius). Cerrobend works the first time, but not so good with reuse, though I seem to remember there is guidance somewhere of what to do about that.

You can contrive an adequate former with a circle of ply etc. of the right radius and thickness clamped in a wood vise. Bending springs work well for plumbing pipe, but annealing is essential except for very gradual bends for adjustment of alignment, and there is a very definite limit for these thin wall tubes. Small diameter bending springs tend to be a pain.

One thing to appreciate is that with a proper commercial tube bender, the inner diameter of the former has to be the neutral axis, and the outside of the bend is progressively stretched using tension and an internal nose piece to avoid flattening. That is why tight bends are a challenge with amateur methods, and there is limited potential to replicate commercial results.

You may enjoy reading this article which tries various methods and endorses Noel’s method I think. No need for the luxury of the washer on the side – just stick it horizontally in a smooth-jawed vice.
Theory being pipes flatten when bending by squeezing out sideways  – so stick it in a groove so it can’t do it.
Make up one for each pipe size you might use?

Have loaded to my webspace – not sure of copyright issues – will leave it for a few days. Enjoy!
https://www.tonykendall.co.uk/SimplePipeBenderB.pdf

Definitely the easiest method I’ve seen – I’ll adopt it in future.

I did make a bender like this one –

https://modelengineeringwebsite.com/artisans_pipe_bender.html

It works well, but it’s a bit of a pain making all the different wheels (so I haven’t), worth having though for bending flat stuff for little brackets and things.