Shank to base question

Hello all, I was hoping I could ask if anyone could give me some advice on what is probably a non-issue for most of you.

Lately, I've been having trouble attaching my ring shanks to the base and keeping it 100% perpendicular.
I believe that the majority of the problem is coming from when I file off/down the shank to allow for soldering to the base.

At the moment, I hold the shank in a ring clasp, then hand file by eye, trying to keep it all straight and true.
Which, for me, is hit and miss.

Is there another way I could be approaching this? Or should I just keep trying to improve what it is I'm already doing, so it's more hit that miss.

I'll include a little diagram to help explain..

Attachment 13300

A inexpensive quick solution place the ring shank in a vice (with suitable protection e.g. copper) just slightly above the jaws and use the jaws as a guild for your file, keep practicing by hand and you will soon get the hang of it or you could purchase one of these
https://www.cooksongold.com/Jeweller...ing&channel=uk

Yes, dozens of ways to skin a rabbit.
My way is to put medium sandpaper flat on the bench, grip the shank firmly between finger and thumb, and draw it repeatedly in one direction only.
Check half way through that the angle looks good, giving you time to correct it. Dennis

Thank you both, I appreciate the advice.
I think I'll try both methods and see which one feels the most achievable for me.

China: I do have a smaller version of that mitre jig, but I've only used it on unformed sheet or wire. Can it be used on a formed shank somehow?

Yes depends on how wide the band is, just open it up and place the band so it misses the little cut outs, tighten up and it will hold secure and square

Thank you China. I'm a having a little bit of a hard time picturing what you mean, but will experiment this evening.

I was taught to get an even level using a base plate and sand paper. It’s often difficult not to roll a file doing it the other way round. You could start with the file and then finish the other way round if you get me

So many approaches, genuinely appreciate the help.
I ended up using the mitre jig approach China suggested and it worked a charm!