A MODEL ENGINEERING APPRENTICESHIP

Part seven by David Carpenter

The first thing to make clear about milling is that you do not need a milling machine. It is not that long since most model engineers did all their milling on their Myford lathe. Maybe they progressed to a home-built Dore Westbury which conveniently accepts Myford tooling. However, the advent of the inexpensive milling machine import has changed all that.

But you can still do plenty of milling on a lathe if you cannot afford, or find space, for a milling machine.

Its very simple, really. Hold an end mill securely in the lathe, clamp the work piece securely (probably in a vice, probably on a vertical slide), set the end mill turning at the required speed and cut away to your hearts content.

However, do take note of the word ‘securely’. Do not try to use an end mill held in a drill chuck, a lathe chuck, or even some types of collet. It will not be gripped  sufficiently, however hard you tighten the chuck, and when you start cutting, the end mill will wander out of the chuck and ruin the work. Only hold end mills and slot drills in collets designed for the job or ER series double sprung collets. This applies whether you are using a milling machine or a lathe.

A brief note about milling cutters. They come in all shapes and sizes, but the most common are end mills (which actually cut on the sides rather than the end!), slot drills (which can be fed downwards), and these days the throw-away tri cutters which can be used both to feed down and cut on the side. Then there are ball nosed slot drills that cut on rounded ends, dovetails cutters, T-slot cutters, and Woodruff key seat cutters. All of these are held in collets.

Other cutters used by model engineers are saw-type cutters, held on an arbor or mandrel and used to cut slots and similar types of operation, and specialist cutters for cutting gear teeth, for example.

Milling on the lathe using a vertical slide is actually quite good. Its quite a rigid setup (especially if the slides not being used are locked) as it does not have much in the way of overhang to worry about. It is overhang that causes problems with some milling machines.

You can test a milling machine for yourself with a dial test indicator fixed to the spindle and resting on the table. Pull the machine head and see how much movement there is on the dti. On a poorly built or worn machine there will be movement. So not much use for doing accurate work, then. Now wind the table along and see if it registers on the dti. Again expect movement on a worn or poorly built machine.

Which milling machine?

Unless you are only working in small scale and cutting materials that are not too difficult, do get something substantial. That’s the key to success in accuracy and finish. One of the problems is that milling machines take up a lot of space. A Bridgeport is great but not in a garden shed. Even a small industrial machine such as the delightful Deckel will usually be too big for the home workshop. For most of us the versatile ‘mill/drill’ type of  machine will be the choice. There are a number of imports (no longer quite so cheap, though) available from many sources.

These come in a wide range of sizes from the popular mini mills (currently around £700) to ‘proper’ knee mills (£2000 plus). Here is a small selection, from small (tho with larger tables and more powerful motors these days):

to popular medium size:
to large enough for most jobs.

Part one here. Part two here Part three Part four part five Part six Part seven

 
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Editor: David Carpenter