Tag: Mini-lathe

The hulking 1/2 inch Jacobs chuck is grossly oversized for most of the holes I poke in things spinning in the lathe. I already have several smaller Jacobs chucks for the Sherline’s 1 MT spindle, so I got some Morse Taper Sleeve Adapters for the mini-lathe’s 2MT tailstock. They’re longer than the “short” 2MT dead center:

Because they’re longer, the tailstock ram loses nearly an inch of travel it can’t afford.

So I hacksawed the taper just beyond the opening at the tang and faced off the ragged end:

The steady rest jaws don’t match the Morse taper angle, but they’re way better than assuming the nose of the Jacob chuck can hold such an ungainly affair.

The short 1MT taper on the drill chuck doesn’t extend to the opening: when it’s firmly pushed into the socket, there’s no simple way to eject it. So, drill a small hole for a pin punch to pop it out:

I hate hammering on tooling, which means I must eventually enlarge the hole to clear a 5 mm bolt, make a square-ish nut to fit inside the slot, and gimmick up a plug for the 1/4-20 socket in the 1MT taper (used by the Sherline mill drawbar). More work than I want to take on right now, but it’ll provide some Quality Shop Time.

If the truth be known, I also got a 3/8-16 thread to 2MT adapter for the mid-size Jacobs chuck seen in the pictures, thus eliminating the thread-to-1MT adapter and plugging the chuck directly into the tailstock. The 1MT adapter will come in handy for the least Jacobs chuck; although LMS has a 0JT-to-2MT adapter, the less I monkey with that tiny taper, the better off we’ll both be.

After dismantling the tailstock to apply the tweaks, it was grossly out of alignment, as seen from the top:

Seen from the side, the tailstock center is way too high:

No surprises there.

The object of the game is to make the tailstock bore collinear with the spindle bore in all four degrees of freedom:

• Front-back
• Up-down
• Yaw angle
• Pitch angle

The first step is to match those two points, then measure the angular error.

Loosen the (new!) screws holding the tailstock top & bottom castings together:

I set them snug enough to prevent casual motion and loose enough to allow adjustment with gentle taps from a plastic hammer. Tapping the top casting forward lined up the dead centers horizontally, leaving only the vertical alignment.

Then I clamped the tailstock’s bottom casting to the lathe bed:

Loosening the screws a bit more let me tilt the top casting to the left and slide a brass shim between the two castings, adding just a little more height to the left side to move the tailstock center downward.

This could do any or all of:

• Correct a pre-existing pitch angle so everything is fine again
• Pitch the tailstock ram axis out of line with respect to the spindle axis
• Confuse the issue

I started with a 6 mil = 0.15 mm shim that didn’t quite do enough and a 16 mil = 0.4 mm shim was a bit too much. Pinching a brass shimstock snippet between the centers show how they match front-back and don’t match up-down, with the tailstock center now too low:

Some back-and-forth fiddling showed a 10 mil = 0.25 mm sheet came out about right:

With the two linear degrees of freedom accounted for, measure the yaw angle by comparing the position of the tailstock ram’s far end:

With its near end:

Note: measure the offset by sliding the tailstock along the ways, not by retracting the ram. Reassuringly, the ram slides out parallel to its axis.

Measure the pitch angle, similarly:

As it turns out, the far end of the ram is 5 mils down and front from its base near the tailstock. Over 1.5 inches of travel, 5 mils works out to 0.19°.

Although it’s a small angle, the huge Jacob chuck supplied with the lathe puts a typical drill 125 mm from where you see the tailstock dead center’s tip. In round numbers, the drill point will be 16 mils low-and-front,  about 25 mils radially off-center, which agrees reasonably well with what I actually see:

Because I don’t do much turning between centers, I retinkered the alignment to put a point held in the drill chuck on center. Deep hole drilling won’t work quite right, because the ram extends along those 0.19° angles, but it’s Good Enough for now. It’ll be much easier to correct the yaw misalignment than the height mismatch.

Those of you who read image metadata surely noticed the pix aren’t in ascending temporal order. Verily, this was an iterative process, with pix happening all along the way.

Filling the mini-lathe’s tailstock ways with epoxy made it slide easily and lock firmly. Some upcoming projects urged me to perform The Canonical Mini-Lathe Tailstock Upgrades, as shown nearly everywhere on the Intertubes and detailed in various HSM articles.

For unknown reasons, the screw clamping the tailstock’s top and bottom castings together threads into the top casting from below:

Although it’s faintly possible you could adjust it by reaching up from below the bed, it’s easier to just drill out the threads for a clearance fit around a 5 mm SHCS:

The drill went through the tailstock so easily I think the hole had been capped with body filler, which would eliminate the need for a bottoming tap.

Then build a square nut from a slice of 7/16 inch square stock:

… and be done with it:

If the tailstock ever needs more adjustment range, I can knock those corners down a bit.

The screw clamps the castings vertically, with a second screw under the tailstock ram handwheel forcing the top and bottom not-quite dovetails together horizontally. I replaced both with 5 mm socket head cap screws:

Tightening a cup-end SHCS against the square not-a-dovetail tends to shift the upper casting; the original screw had a narrow pin end to reduce the torque. Having brass rod close at hand, this seemed easier than machining the screw:

The little tip comes from using a square-ended cutoff tool. Purists will dress the tool at a slight angle to cut off one side first. Of course, which way one dresses it depends on whether you want the remaining stub on the stock or the cut-off part. Sooo, I still have a square tool.

The tailstock has a cam lock handle clamping a square-ish plate against the bottom of the bed ways. Unfortunately, the manufacturer cut the plate with a dull shear, producing two beveled edges:

Flipping it over dramatically improved the clamping action, although I must eventually scrape the paint and grunge off the bottom of the ways. While I had it off, I turned a small aluminum bushing to replace the pair of washers:

The plate hangs lower toward the rear because the clamping bolt isn’t in the middle. The tailstock originally had a mighty spring holding it level, but the spring tended to snag against the front side of the bed, so I removed it.

The lever handle actuating the tailstock cam lock had no stops and rotated freely counterclockwise when loosened. The tailstock casting had enough meat for a 5 mm threaded brass insert in a useful location, so I drilled a suitable hole:

The vacuum hose slurped up the cast iron dust, which is a Very Good Idea.

Butter up the insert with JB Kwik epoxy, slide into the hole, wipe off most of the excess, then pause to admire the result:

The lever stopper won’t win any design awards, even though it’s a dramatic usability improvement:

The finger-tight nut serves to lock the SHCS in place against the lever’s impact. I conjured a small bumper around the head from a rubber foot intended to fit under a random box of electronics.

Pushing the lever leftward to the stop lets the tailstock slide freely and pushing it to the right clamps the tailstock to the bed. The cam’s limited rotation keeps the plate close enough to the underside of the bed to prevent it from tipping left-to-right as the tailstock slides, so it no longer snags.

While I had the tailstock up on jackstands, this is what the ram thrust bearing looks like:

The flange over on the left bears against the steel disk on the right, with no real thrust bearing to be seen. A dab of grease improved its disposition.

Now, to realign the thing …