A Model Engineers' Fantasy Lathe Concept Design
Model Engineers' Workshop|April 2020
Alex du Pre shares his thoughts on what might make an ideal lathe
Alex du Pre

The editor’s challenge in MEW285 to design a lathe of the future certainly got me thinking. I am lucky enough to own a Myford Super 7B lathe, a design that is considered by many to be the ideal model engineering lathe and one that has stood the test of time. But it is not without its shortcomings and since it was introduced in the 1950s, technology has moved on. Electronics and computing are now being widely adopted in the maker community with the advent of affordable 3D printers, laser cutters and the like. Many people have fitted CNC upgrades to their lathes and mills and are exploiting the possibilities of programmable microcontrollers such as the Arduino, which have broad application in machine control. Digital read-outs (DROs) are a commonly used machine tool upgrade.

In this slightly tongue-in-cheek piece, I have set out to propose a concept for a thoroughly modern model engineers’ lathe that takes full advantage of this new technology but retains the convenience and versatility of the Myford. My main aim is to provoke thought. I don’t claim to have any particular skill in machine design and certainly don’t have the knowledge to design the electronics in detail. But as someone who has spent countless hours operating my workshop machine tools, I know all about their best and worst features and which accessories are useful, so I hope my ideas are grounded in some sort of reality.

Please hold on tight as I attempt to reinvent the hobby lathe.

Why is the Myford so good? And bad?

Let’s start with a few words about what makes the Myford a great hobby lathe and flag some of its limitations. I also own a combined lathe/milling machine, which is a good basis for comparison. The Myford is a compact and accurate machine with considerable thought given to convenience of use. The drive belts are easily accessible so spindle speeds can quickly be adjusted (I need two spanners, several minutes and a bucketful of patience to do this on my other lathe; consequently it usually runs at inappropriate speeds). The back gear allows a very slow, high-torque spindle speed and also offers a means of indexing the spindle for dividing operations. I love the clutch, which prevents a constant stop-start of the motor. The gearbox gives almost instantaneous access to a wide range of threads and feeds; the changewheels make this a 20 minute job on the other lathe, hence one I rarely bother with. The gap bed, slotted cross slide, power cross feed and flat bed are all great conveniences enhancing the machine’s versatility.

On the negative side, the Myford has a small spindle bore (bigger on later models) and it is not particularly rigid, needing careful levelling to remove any twisting in the bed. Minor transgressions, you might say, but when considered alongside the opportunities that modern electronics provide, its shortcomings appear starker. The range of possible threads is limited, and it requires spectacularly rare and expensive extra change wheels to achieve metric threads (on my imperial machine at least). It cannot work fluently across both metric and imperial without further accessories or errorprone calculations by the operator. Without the luxury of the quick change gearbox, you will spend your life calculating gear trains and juggling changewheels. Spindle speeds are adjustable only in fixed steps and the top speed is quite low. Accurate work by reference to the handwheel dials requires a certain amount of mental dexterity and memory. Above all, a range of expensive accessories is needed to permit jobs like long tapers, profile turning, ball turning, milling, repetition work and so on.

So, let us consider how a modern lathe could alleviate all this misery.

Electronics

I remember my university lecturer once saying that things which are very complex to achieve by mechanical means are often straightforward to achieve electronically. As a case in point, compare the internal combustion engine and gearbox of a petrol car with the motor and electronic speed control of an electric car; the latter has far fewer components and moving parts. So, on my fantasy lathe, I am going to do away with such horrors as gearboxes, change wheels and adjustable drive belts and achieve the same effect and more with electronics and electrical machinery.

My CNC fantasy lathe

My fantasy lathe, fig. 1, is primarily operated by CNC (Computer Numerical Control), which operates the X and Y feeds and controls the position and speed of the spindle (for reasons that I will come back to). CNC means that complex shapes can readily be achieved automatically without the need for some of the aforementioned accessories. The top slide also becomes unnecessary, so is gone. Goodbye also to the screwcutting gearbox and goodbye changewheels (hooray!). At a stroke, our lathe is mechanically far simpler, yet we can turn stepped parts, chamfers, tapers, curves, threads, radii and more with ease, thanks to the CNC. Furthermore, we can let the lathe get on with its work while we do something else, in theory at least, although there is much to be said for watching the machine work while we don’t have to. The range of cutting tools needed is also greatly reduced as a reasonably-pointy left-hand and right-hand turning and facing tool, a boring tool and a parting off tool will do for the majority of jobs. We don’t need that chamfering tool and all those nasty radius and profiling tools can also go in the bin. Think of the time saved making those!

The X and Y axes are driven by motors connected to zero-backlash ballscrews. Since a DRO is fitted, the positions of the carriage and cross slide can be measured by the electronic brain of the machine, so the precise position of the cutting tool can be confirmed and adjusted, without simply relying on electronically counting the steps of stepper motors.

The spindle is under CNC control too, so that screwcutting operations are fully automated via the synchronisation of the spindle rotation and X and Y axis movements. This also permits a spindle indexing capability that I will tell you about in just a moment.

Manual control and DRO

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