I can identify with you on your problem also having just done my first threads, internal & external , not without some hair pulling &manual reference into the early hours and some reruns!
I have an S7b but the ML& should allow the deflection of the topslide to 30 deg. The point is where does the 30deg measure from? In my ignorance & inexperience I moved the top slide round to 30deg mark, it is indexed on the S7. Then gaily cut away using about 40rpm. I advanced at about .002" , this seemed OK and didnt tear too much. I got to thread depth & offered up the part to fit - NO!! Looking at the cut thread it was laid over to one side , I had an angle effectively of
60deg on the right hand side plus 30 deg on the left. I had to reposition the topslide to 60deg on the index and all was well. This is all to say and I suppose it is obvious really that the 30deg or 27.5 deg is off the line of the crossslide travel. I just looked at the index marks and assumed it would be right
Another experience I had was with the poor thread profile I cut initially. This was down to me using the tumbler gears to reverse the saddle and not the motor . In the end I didnt disengage the half nuts at all, even on the Whit threads and all was well. The use of the tumbler gears to reverse put the tool out of sync with the work each time. My threads cut were 20x1.00 metric external and 9/16 x 26 internal
I suppose we all learn by our mistakes
Mike "Martin Whybrow" wrote in message news:ybrrd.358$ snipped-for-privacy@newsfe2-gui.ntli.net... Just tried my first bit of threadcutting on my ML7 this evening, making a drawbar for my Sturdimill, 5/8" UNC thread. I originally intended to use the setover method as recommended by Chris Heapy, amongst others, but I discovered that I cannot set the topslide to 30 degrees (what would be 60 degrees as the zero is with the topslide at 90 degrees to the crosslide). Am I missing something with this method or is it a limitation with the ML7? I ended up going in at 90 degrees using the crosslide and taking small cuts (.010" at first, finishing with .002") and ended up with a good finish, but it looks very aggressive doing it this way. Martin.