Hi Gang:
To improve the casting is just half of the job, you need to improve the runout on the knob. Both can be corrected with a file. Use some Persian Blue, coat the back of the know and run it up to the carriage. Look for where it rubs off the know and onto the carriage. File both spots down un till the Blue rubs off the whole knob and onto the whole casting. A bent lead screw will mess this up some, but it should help.
Carl.
On 04/06/2023 9:37 AM Quinn Golden <quinngolden@...> wrote:
When I rebuilt my SL, reducing the backlash as much as possible was a goal. However, there was a point of diminishing return as the hand wheel rubs against a rough uneven casting. With any flex in the screw train that gives a ¡°tight spot¡° as the hand wheel is rotated, exacerbating the problem. I tightened the hand wheel until it touched the casting, put on the nut and then tighten them together by hand, felt it then after a few tries gently tightened the nut. I had hit the ¡°sweet spot¡° that seems to work best. So short of machining that piece of casting behind the hand wheel to make it smoother, one needs to revert to the old primitive machining days of always moving your cutting tool into the work piece. Which is to say, you always back off a couple of turns on the handle and then go forward to remove the backlash and make your cut. ?I think that the casting is a poor enough bearing surface, so even placing thrust washers behind it would not illuminate the ¡°problem¡±. ?
That is to see if you consider it a problem, which I really do not. Anything that uses a lead screw into a tapped casting is going to have backlash. It is actually engineered that way.?
I have equipped my Unimat with dial indicators on both axis ?to enable me to see the backlash with every cut made.?
Carl