being a 1mm pitch you will need to set the gearbox to a 3mm pitch.To get the three threads to align exactly you need to be able to access the change gears that engage the main spindle to the gearbox .hopefully the main gear on the spindle will have a number of teeth that will divide into three.It is very important that there is the ability to rotate the work piece 120 degrees in relation to the first thread. Once the first thread run is cut and to size advance the change gear position by 120 degrees[one third].Cut the next thread run to size ,and then advance the change gears to the next third.In theory very easy but in practice can be frustrating. You will need to calculate the actual cutting depth,side clearance and finnish each seperate pitch to exact tolerances otherwise the finished item will not fit together or will be sloppy.A good thread cutting chart ,book
or the internet should have the calculations necessary to enable you to cut each thread accurately.You will need to obtain a thread cutting tool that is small enough to cut a 8mm internal thread, you could grind a tool to do a external thread as long as you are accurate.i would do a couple of practice threads to get used to all the possible problems and disasters that more than likely will occure.Hope this helps any problems or questions don't hessitate to ask. Cutting this thread can be daunting [especially a 8mm diameter ] but percieverance and patience will see great satisfaction if successful
Laurie Imms
LGI Engineering Ltd
Hikurangi
New Zealand
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