A bent and buckled nib will make an otherwise pristine pen valueless and the repair is no easy matter. Nib repair is one of the most time-consuming and difficult parts of pen repair but if you can’t straighten nibs, or at least the simpler ones, it will cost you in replacing nibs or having someone else repair them for you. I use excellent tools provided by Laurence Oldfield:
https://www.penpractice.com/page3.html
I cannot recommend them highly enough. They are not cheap but they are money well spent.
Before I discovered Laurence’s set I made do with what came to hand. For the concave part I used a boxwood pen rest which was hard enough to take the pressure without damage. The convex part was a polished length of a bolt of the right diameter. The most difficult part for me was to make the tool to press down on the nib. In the end, after much thought, I chose a six inch nail with the point cut off, rounded and polished to perfection – a lot of work. It had to be absolutely flawless as any imperfection in the tool would be transferred to the nib under the pressure needed to straighten it. Those make-do tools did the job for a while but I realised their temporary nature and was on the lookout for something better.
Whatever tools you use, the best time spent on a nib is not in using them but in studying the damage to the nib and planning how to go about straightening it. A loupe is essential here.
When you have decided how to proceed, whether to apply most pressure to the top or underside of the nib, don’t rush matters. The less you have to work the nib the better as it hardens the metal and changes the characteristics of the nib. Once the worst of the bend, or bends, have been reduced, it will take some adjustment on both sides of the nib to complete the repair.
I’m no nibmeister and there are nibs I can’t fix. I’ve seen the work of those experts and I am astounded by what they can achieve. I’ve seen nibs that have landed point first on a hard surface, resulting in a propeller shape, made absolutely perfect by those highly skilled hands. I can’t come close to that. I know my limits. If it’s a common nib in that state it goes in the scrap box and I find a replacement. A nib that is bent in more than one axis is a difficult repair but not impossible. It takes more time and success is not guaranteed.
I’ve found that professional tools help a lot but if nib repair is not something you do often it may be that the outlay is not justified and you can use whatever is available with some adaptation. That’s part of being a pen repairer.