Tag: Improvements

It being once again time to tweak the mini-lathe’s cross slide and compound backlash …

The M3 slotted setscrew locking the cross slide’s DRO collar to the feed screw shaft had come loose:

Although it has a cone point, presumably to center the slot in the feed screw, an M3 cup point hex setscrew works just fine:

A hex socket is much easier to tighten securely.

The handle sits against a black washer that looks like it should rest against the aluminum spacer covering the DRO shaft, but it doesn’t. Contrary to what I originally thought, that gap doesn’t contribute to the backlash (given a tight setscrew!), but a filler shim makes it look less like an afterthought:

What does contribute to the backlash is a loose adjusting screw holding the follower nut against the feed screw:

The mini-lathe manual (page 17) and online references give the tedious process required to adjust the two cap screws and the setscrew to remove (nearly all of) the backlash. While I had the screws out, I took the opportunity to dribble oil through the cap screw holes onto the feed screw along as much of its length as was reachable.

Adjusting the gib screws is also a good idea, as is renewing the oil along the ways.

With all that done, the cross slide moves easily without slop and the backlash is a tolerable 0.1 mm.

The compound feed screw does not have any backlash adjustment, so fitting a suitable shim between the handle and the DRO spacer is essential:

That one looked nice, but was somewhat too thick.

This time around I could laser-cut and 3D print shims (16 mm OD, 10 mm ID) in a variety of thicknesses, some combination of which would surely fill the gap without binding:

The gnarly clear rings over on the left are the original punched-and-trimmed PETG shims. The fabric-looking ones are PTFE sheets intended for heat-press transfer machines, which Mary has used as a slider sheet to let fabric move easily over her sewing machines. The black one in the middle is 1.5 mm acrylic.

The bright white rings are 3D printed from a few lines of OpenSCAD code:

Washers = [0.5,0.6,0.7,0.8,1.2];

for (i = [0:len(Washers)-1])
  right(i*20.0 - 40.0)
    tube(Washers[i],od=16.0,id=(10.0 + HoleWindage),anchor=BOTTOM);

Print them with 0.1 mm layers in PETG, add a PTFE shim or two, and fiddle about enough to get minimum backlash with reasonable turning force.

The compound feed screw now has 0.16 mm of backlash, which is as good as it’s going to get.

Right now, the only thing preventing the handle from turning on the shaft is the chunky lockwasher gouging both the handle and the cap screw in the end of the shaft, with the side effect of putting far too much pressure on the spacer shims. I want setscrews in the handles bearing on flats filed in the feed screw shafts to put those awful screws + lockwashers out of business, which seems like a good Sherline project.