I have just bought a Portass Model S, in good overall condition apart from a bodged repair to the lead screw nut. A threaded bit of brass joined onto the existing nut by a flat plate. The repair piece is badly worn and probably not even the correct thread. As such there is a lot of backlash.
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I have identified the thread as left hand square thread 5/8'' – 8TPI (1/8'' pitch).
This seems to be an outdated thread, I can only find Acme screw of these sizes.
My question is should I make a new lead screw with Acme rod and bush the nut, then thread it to suit.
Or is there a metric equivalent that would maintain the lathes thread cutting abilities?
I'm struggling to find a UK supplier of Acme rod, but I have found a tap for rethreading the nut.
Thanks.