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Cross-slide extension and thrust bearing mod

March 2010

Though the mini-lathe is within the limits of the work size I use to do, there are times when a bit more cross-slide travel is useful. Without a cross-slide extension the maximum stock diameter that can be machined over the cross-slide is smaller than swing over cross-slide.

Mini-lathe cross slide extension

Here are both assemblies. The original and the new cross-slide extension I made that allows about 20mm additional travel. I've made a full new assembly with a longer leadscrew (M10x1mm left hand thread), a longer spacer and a new handwheel. The shape of the new spacer is to allow the leadscrew assembly to be bolted to the saddle from outside, to avoid the need to fully disassemble it. Have made it this way as for using the taper attachment the cross-slide leadscrew has to be removed.

I haven't found a way to be able to bolt it to the saddle using the existing tapped holes on saddle, so ended drilling and taping two new holes on the saddle to bolt the assembly with M4 SHCS.

To allow the additional cross-slide travel, the saddle has to be milled. Fortunately this mod was planned long time ago and the needed milling work on the saddle was made when I did my first mod to the mini-lathe, improving the saddle fit. So now the work was simplified.

Parts for cross slide extension

To eliminate play the spacer was bored for a thrust bearing to fit into it. Thrust bearing is a SKF 51100 (10x24x9mm). On the rear end of the spacer, bored and polished a bearing surface for the leadscrew to run on it. Both the bearing surface and the thrust bearing are grease lubed.

Parts for cross slide extension

The dial was bored to 21.5mm and the handwheel was made with a longer end with 20mm OD and a groove for a O-ring. The dial rotates on the O-ring which gives the necessary friction to keep it in place, while it is easy to reset the dial. The handwheel was made with a keyway, as the leadscrew, and a 4mm key is used to allow the lock-nut to press it onto the thrust bearing. The end of the handwheel is a little longer than the dial, so it protrudes to contact the thrust bearing.

On the picture is also the lock nut, which is maybe the most important component to remove play. It was made with 19mm OD and 12mm longer and drilled and tapped to M8 thread. Two small 2.5mm blind holes on front were made to use a spanner to tighten the nut. A M8x6mm set screw is used to lock it.

Thrust bearings on mini-lathe cross slide

The handwheel was bored on the front side to 20mm-12mm deep for the lock-nut to fit into it. The lock-nut fits the threaded end on the leadscrew and it is tightened with a spanner on the two small blind holes. The length of the threaded end of the leadscrew was adjusted so, when assembled, it threads on the the lock-nut by 6mm, leaving 6mm for the set screw to be also tightened on the lock-nut. When is it tight, but not excessively, the M8x6mm setscrew is tightened on the lock-nut. As the setscrew is pressed onto the leadscrew, the nut is locked.

If the leadscrew has still some play, or if it is hard to rotate the handwheel, the lock-nut must be adjusted. This setup works amazingly well and the handwheel rotates very smooth. Kind like a volume dial on a stereo.

To check play on this assembly, I have tried to measure it with the dial indicator point on the rear end of the leadscrew. While applying a considerable amount of force puling and pushing the cross-slide handwheel, couldn't measure any play on the dial indicator.

Excessive cross-slide play on this mini-lathe was always caused by the absence of a lock-nut. I never had reasons to blame on the cross-slide leadscrew nut, as Sieg's mini-lathe owners use to. This lathe has a cast iron nut on the cross slide leadscrew and all I did was to enlarge the two M4 threaded holes on the nut, used to bolt the nut to the cross-slide, to M5 thread. Have made it as I found that M5 SHCS fit snug on the counterbored holes and this way can't slide on holes anymore.

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