Lathe Alignment Check


The next check is to mount the face plate and test the cross slide (actually the crosslide dovetail on the saddle) to see if it is perpendicular to the bed and headstock axis.

I have never skimmed my faceplate (bought from Chris Wood's excellent "Little Machine Shop"), as it clocks within 0.0002" as is. I did mark it to ensure I always mount it on the same alignment on the spindle.

Again I used J Latta's method.

With the cross slide in the middle of travel, set up the clock on about the centerline, then crank it full forward. Bring the clock into contact with the face plate, and zero it. Mark the spot on the faceplate with a pen or chalk. Now wind the cross slide full back, and rotate the face plate so that you are again measuring the same point. We know from the first test that the spindle axis is parallel to the bed horizontally, and by only using one point on the face plate, we avoid adding compounding variables.

I had to use the Mitutoyo 0.01mm DTI, because a small lever came loose on the verdict, and it was cold (2°C) on the balcony, so I didn't want to fiddle with it. Fig 4.

Fig 4. Crosslide FWD (Left pic.) and Rear (Right Pic).

As you can see, my saddle's dovetail is angled to cut concave by about 0.045mm over the 100mm of available travel (that's 0.0018 over 5 inches). Lathes are always set up to cut concave, as this ensures that a faced surface will sit flat and not rock. Nearly two thou is a bit much, but will have to be lived with, as I have not desire to scrape the dovetail of the saddle.