If you have ever used helping hands to hold electronic components, most are quite tricky to positioning the exact location that you require. One solution could be this excellent DIY build by Tim Gremalm, who has mounted to helping hands on an adjustable aluminium rail for easy positioning.
“This is a pair of helping hands I made for soldering. Ordinary clamps and holders are so flimsy. The base is a couple of articulating arms that is ordinary used for dial clock holders at CNC machines.”
Helping hands are available in a wide variety of different designs with some being more effective than others. Personally I think this design using the sliding aluminium rail and custom-made clamps and hinges is properly one of the best I’ve seen to date.