HF wouldn't mark the workpiece, Your work return is 100% isn't it????? have you tried direct to your clamp, also at the dinzie end they sometimes just drop to bits on the conection........... Your tungsten isn't really contaminated not like a touchdown or no gas.......
Fingers I'm in Norris Green - I'm waiting to hear if I;m dropping a bike off at a mates house for an engine rebuild tomorrow night - otherwise I'd bite your hand off! I'll Pm you my tel number and if the bike falls through (not literally!!) I'll drop you a bell.
That is if you will venture into Norris Green?
For clarity I am from Aughton near Ormskirk and moved here due to cheap house prices - I am not a wayne roonie type character!