Denford Software & Machines

Hi

Next on the menu was the gearbox. The oil level sight glass showed golden coloured oil that looked clean. This was deceptive. There was a thick layer of black tar like sediment in the base of the gearbox. More gunk to clean out.

Opening the gearbox is simply a matter of removing the selector lever and then unscrewing the front cover. Inside is a nice selection of cogs, dogs and shafts.

In use, raising the selector lever lowers the gear that engages with a long spur gear running across the width and along the bottom of the gearbox. The gear slides along a shaft to the position defined by the selector knob. An interlock pin prevents the knob being rotated when the selector lever is away from the neutral position. The spring loaded plunger fitted above the selector lever simply covers the interlock pin when the selector lever is away from the neutral position.

Lubrication depends on oil pick-up from the lower gears. Some parts of the gearbox had little or no oil. I suggest slightly overfilling the gearbox by a couple of mm on the sight glass.

The internal rack engages with a gear on the selector knob and this slides the gear along the shaft to the right position.

hmmm - looks like copper-slip(R) in there

is that teeth shavings ?

Hi

The stuff on my finger just looked like dirty sediment. The oil may never have been changed before. I don't know what sealant was used on the cover. I used silicon gasket in a tube. All the paint inside and below the oil line is stripped off. There were fine metalic particles but nothing more than might be expected from a 27 year old gearbox. No shavings or broken teeth.

The gearbox is not sealed. The gear drive for the lead screw is exposed within the headstock. I guess over the years, dust has also slowly invaded and combined with paint, oxidised oil etc.

The following images show some more detail about the inards
.
Before refitting the cover, the rack and selector lever must be placed in known positions so the knob and lever can be correctly refitted.
The rack is slid fully to the left, and the selector lever shaft is in the full down position. This position is held by engaging the feedshaft and using friction to hold the gears up in the correct position.

When refitting the cover, the cover must be lifted up against the screws to stop the pinion binding with the rack. I refilled with straight 90 gear oil, not EP.

Here is a close up of the feed/thread table on the gearbox.