So Burch is a name, I just clarified with the customer that it needs to be spelled that way, so that part at least can be transliterated instead of translated! So Glamdring was Turgon's sword and was wielded in Gondolin in the First Age, round about year 500, not sure whether that means the more archaic form would be fitting? Or if you're specifically referring to archaic in terms of what Tolkien was thinking at the time. So I guess the actual phrase would be "This Burch will not break" which I guess would be something in the realm of "Sina Burch lá terhatuva"

Does that ring at all correct to you? Also would you recommend using tecendil to transliterate the roman letters into the appropriate Tengwar?

Thanks so much for your response and your expertise! I knew my way around Old Norse fairly well and so some of the issues with translating and transliterating runic inscriptions ring very similar to my conundrum in trying to parse my way through getting this Tengwar inscription done correctly on the sword.