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Lorch lathe
Adding screwcutting to a Lorch


My Lorch is a precision plain lathe. That means that it was once precise, and that you lock down the saddle to make a cut, and to move the saddle you unlock it and you move it. Yes, you move it, by hand - you slide it to the left, or you slide it to the right. No lead screw, no power feed, no gearbox, no nothing. It does have a flat belt pulley with three diameters, but I haven't got around to making a matching drive pulley, the increments seem too close, and changing speeds with a flat belt is a pain unless you make guides for the belt.

This was my first lathe, and I liked using it. The cross slide screw and the top slide screw were silky smooth, and barring slop they were quite precise. And then I went and made up many attachments for it.

So when I wanted power feed to the saddle, and geared screw turning, I had to make it do the job. This meant a frame for change gears, a tumbler, a dog clutch, and a feed to the headstock end of the top slide screw.

Although it now seems antediluvian compared to the QC gearbox on my Bantam, it did the job for me in very limited space for a number of years, and was quite up to turning the 39mmx4mm thread for a spigot and a couple of backplates to match the spindle on the Lorch itself.

A general view of my Lorch plain lathe with the gear change frame, clutch and drive rod fitted. I will paint it I will !
The tumbler mechanism, with a train of screw cutting gears assembled on the banjo.
A view of the change gear frame with the dividing head fitted. The handle turns a large worm gear that meshes directly with the simple spur gear at the top of the tumbler mechanism. A worm on a spur would wear quickly in high speed power transmission, but when used merely for hand turning it should outlast me.
To disengage the dividing mechanism it is arranged to pivot on one bolt - the spring-loaded lock pin is adjustable to take up slack in the worm-spur engagement.
After a further gear set, primarily used to raise the level of the drive, the top slide screw is driven by the extendible rod. Each rod is made up from two or three parts, with internal springs to hold the connecting pieces in place. There is a gear mounted even higher, which is used when I want to drive my TP drill unit.
When a short connecting rod is required, I resort to the two piece where one end slides in the other, with one spring inside. For a longer reach, I use female links at each end, a central rod and two springs to hold the end apart and the connecting rod centralised.
The rod parts are held by the internal spring(s) against captive miniature ball bearings at each end. The UJs are home made, the pivots being half threaded 3mm rod.


Page updated on 12th June 2018

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