This is not so much an instructable but rather a quick tip for those that wish to cut a reduced section on a long lead screw upon which to mount a bearing.
In my other instructable 'a good quality CNC machine' which was almost 1800mm long, I used stainless steel, 12mm threaded rod for the lead screws.
I needed to fit bearings at each end and therefore had to reduce the diameter from 12mm to the 8mm required to fit the 'roller skate' bearings that I used. The only way to do this was on my mini-lathe but any lathe with a hollow spindle will do the trick.
The problem with working with a long lead screw on a lathe was that the machine became uncontrollable due to the 'whipping' effect of the lead screw as it came out of the hollow spindle.
I overcame the problem by sliding a half inch (15mm od) copper pipe over the 12mm lead screw and inserted the end into the spindle opening. The mini-lathe has a 20mm bore through the spindle and the pipe/lead screw combination fitted quite comfortably but it may be necessary to fit some sort of plastic sleeve to accommodate larger spindle bores.
t was then quite easy to hold the pipe quite steady with one hand and completely eliminate the whipping effect. The soft copper of the pipe did not produce any damaging friction between it and the stainless steel threaded rod.
The drawing above is from my other instructable 'a good quality CNC Machine' which shews the stepped lead screw, bearing and how it was fitted to the machine. The DXF file for the clamp accompanies the instructable.
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