Sep 17, 2011

Compound lead screw arrived

Yes, it had arrived, and was not unbearably expensive: EUR 5.30 + VAT. It seems to be much better than the original one, the threading is nicer, and of correct size. The outer diameter is 7.90 mm along the whole screw.

After inserting it to it's place, the compound nut can now be backlash compensated. With the original lead screw it had 0.4 mm backlash in worst case.

Mentioned elsewhere many times that the scaling of the dials are confusing on this machine. On every dial the whole circle has 50 divisions, as if the screws would have 0.5 mm lead, but they have 1 mm lead in fact, so a whole turn causes 1 mm shift, while the dial counts 50.

Well, it's indicated that one division means 0.02, but who likes multiplying all the time. In case of the cross slide it is even more interesting to multiply by 4 if you count in diameter...

I use the machine since 3 months by now, machined different pieces of different materials, inner and outer threads etc. What I disliked so far:

1. The compound gib had to be readjusted from time to time, what is embarrassing.
My first observation was that the adjusting screws had peaky tapered end, so they can intrude deeper and deeper to the gib due to mechanical wear, increasing the backlash of the compound from time to time. I modified the screws to have a hemisphere like ending rather than tapered. This resulted a better behaviour, but let's give it some time. Otherwise if the compound is positioned so that only one single screw is "active" at the middle of the cutter rest (picture on the left), the compound has a slight backlash, while if two screws are "working" (picture on the right), it is just good.

The next idea is to put an additional screw between each existing one. I plan to do it, and will write my experiences in an upcoming  post.

2. I found the toolpost clamping lever too small, so changed to a bigger self-made one. Later I checked on the exploded view that the rod-shaped lever knob is a separate piece fixed with M6 thread to the clamp, so it would have been enough to change that to a longer one.