Fountain pen nib work, my story

There are a number of good videos from competent people that show you how to do that.
After watching and reading I did my own thing, of course. But we make mistakes and sometimes we learn from them.
First I did a little work on my Preppy. It was scratchy in one direction so I thought I should address it. Aligning the tongues on the nib was the first step. After very many tries I failed and gave up the strategy.
My second step was to "polish", more like grind the nib using ceramic. The back of a cup which was smooth enough for the task. I tried sandpaper 1200 but I only made it worse.
So back to the cup. After a lot of figures 8, circles in both direction and rocking the nib left to right, right to left, up and down, I came to an acceptable finish.
I also spread the tongues a little bit to make it wetter (this made it broader also). The last step was the polishing. I used a glass and done figure 8. The glass is smoother than the ceramic so it made it a little more paper friendly.
But after these experiments, I am pleased with the fountain pen. It does not scratch in any direction, it writes well with no feed problem, the ink keeps up with the nib regardless of speed or direction.
Of course, I did not stop here.
I had to tweak my other fountain pen the Faber Castell Loom.
There was a lot of voices in my head saying don't do it, for God sake DO NOT DO IT, but being the person I am I could not help myself.
I noticed a problem after I took it apart and reassemble it for the first time.
It wasn't writing as I remembered it. It was drier. If I was moving my hand quick to underline something or sign a paper the ink would not keep up with the nib.
I could not leave it like this knowing that is something wrong with it and the pen could write a lot better.
At a later time, I figured it out, how I managed to ruin the nice feel of it. The nib was not set properly from the factory and it had a slight wobble. Being my first serious pen I did not know I could just push it inside a bit more and I was constantly realigning the nib to the feed by pressing the tip of the nib to the paper I was using. This made the tongues to get closer and closer at the tip. I did this so I would not get ink on my fingers.
Anyway...

So I tried to make it wetter. I applied light pressure on the nib to spread it apart. But it didn't work very well. I fell the nib after a short time just takes its initial form. So I brought out the big guns.
The first problem, I do not have a magnifier glass
The second problem, I do not have a brass shim

But where is a way there is a solution.
First I took the nib out of the fountain pen and used the bathroom fluorescent light to see if the spread between the tongues is consistent. It shows very well, just put the nib in front of the light.
It has to be a fluorescent because is a source of light that does not blind you.
The tip of the nib was really close. So without a shim, I improvised. I picked up an old style razor blade and used it as a shim.
One important note. Be gentle! when prying the nib, I put a little too much pressure and I slightly bent one of the tongues (very slightly) to the left. Because of this, the nib would scratch a little bit as it grabbed the paper. To fix this I used something I do not recommend. Cover your eyes and ears, I used a plier and extra light touches as I couldn't straighten it by hand.
To check how I need to align it I did vertical up-down lines and horizontal left to right and vice versa, and finally a 45 degree angle. This way you can determine if one of the tongues is misaligned. Another method to check it out is using the camera on the phone plus a flashlight as you need a lot of light to focus well and see any imperfections, or just buy a cheap magnifier. I did finally buy a magnifier but after I went through all the trouble. It is much more fun this way.
Because the Faber Castell Loom has such a great nib I did not try polishing it in any way. I just checked the alignment after I made it wetter.
I am happy the pen writes very well now, and the feel of it in the hand is great. Also, I am glad I did not ruin it.

And before you get into nib work, make sure you have cleaned it. Also, consider that the nib will feel different on different papers and when using different inks. Some inks are more fluid than others.
Plus, never use Pelikan 4001 Brilliant Red, there is nothing brilliant about that :)