New designs for power feeding a lathe topslide

A full set of  illustrations from Stuart and Paul’s approaches may be seen by clicking the links below:

Use of CNC to aid the making process

Original top slide parts in Stuart Walker’s conversion

Paul Gammon’s approach to the powered topslide

If your lathe is not fitted with a taper turning attachment or is not CNC controlled you’ll need to use the topslide of your lathe with it set over at the correct angle to make tapered fitting parts. To achieve a nice smooth, even finish a slow power feed cut is a big help but such accessories are not readily available and some improvisation is needed. Several years ago I made up an external drive using a cordless drill and an 8:1 gearbox which, despite being somewhat cumbersome, worked quite well. Unfortunately, the gearbox has been incorporated into another project and I began to think of alternative ways of making a compact, self-contained unit which can be left permanently attached or easily removed so that the original set up can be restored. The new power feed is currently needed to make up two Myford type spindles, one for cylindrical grinding, the other for CNC hobbing.

I’d originally thought a stepper motor powered by a Division Master or the kind of digital divider being developed by Keith Burton and Kieran Wisely  would be the answer. As Paul Gammon has a similar lathe to mine and has been using a Division Master for quite some time, I discussed the matter with him at some length and we concluded that a standard compact, high torque, geared DC motor would be a better approach. We undertook some rough calculations to assess the required torque and speed, and concluded that between 1 and 5 RPM would be about right. A wide range of these geared motors can be found at Amazon and on eBay. We both developed different approaches to suit our own particular needs and method of working, and the following is a brief explanation of what was achieved.

Paul decided to bypass his manual feed facility and use a reversible variable speed motor to achieve a useful range of powered feed rates. The drive is in line with the leadscrew and an oldham coupling is used to accommodate any slight misalignment to provide a smooth feed. It’s quite a long extension but it easily clears the tailstock and doesn’t interfere with normal turning operations. Returning the topslide to the normal hand feed mode is fairly straightforward.

Alternatively, I decided to retain the hand feed option without removing the attachment and make the assembly more compact by using a geared drive with the motor mounted on top of the topslide. A shorter single speed 5 RPM geared drive is mounted in a cylindrical drive housing that can slide and lock the drive either in or out of gear. I could have introduced a reverse drive but prefer to do a more rapid move back to the start point by hand. As with Paul’s design, the original configuration of the topslide can easily achieved. At the same time, I’ve introduced a digital readout on the topslide which can be useful for tapers but it’s more useful for screw cutting with the topslide set over, as well as for offset drilling/milling with the Quickstep equipment.

The other reason for designing and making my attachment was to explore in more depth the capabilities of my CNC mill. I have to say I’ve become quite a fan and would recommend it to any members who are not using CNC. If you’re thinking about it and haven’t already done so, check out the excellent work that Alan Martin’s is doing to help members get to grips with the technology . Whilst much of my work was carried out using a manual lathe with digital readout, my 2D CNC mill was used for the following:
External profiling and inside pocketing of the switch housing,
External profiling of the slide clamp unit,
External profiling of the gear housing,
Drilling the screw fixing holes in the housings and cover plates.

CNC was also used for powering the table for the full depth gear cutting with a slow speed power cut and back-off, and rapid move back to the start point. Manual indexing was used, but if I’d had the kind of digital divider developed by the DG the complete gear cutting operation could have been fully automated even though my CNC mill uses a proprietary system that is incapable of directly interfacing with a Windows based system. Paul Gammon and Mike Sayers successfully demonstrated, some time ago, how a standard slotter can be fitted with a micro switched link to a Division Master to automate the process of cutting internal gears for Mike’s current model Bentley engine project.