A MODEL ENGINEERING APPRENTICESHIP

Part six by David Carpenter

Next, the lathe.

The answer to your first question is: “the best you can afford!”

How good you are at producing items with hand tools will depend on how well you develop your skills. For machined parts you need good gear, too.

Its not that long ago that if you were a serious model engineer you had a Myford lathe. It was designed to do just about everything you needed in a small space. Briliant.

Sadly they were also quite expensive and the competition was from cheaper and lower quality lathes. Then came the revolution. New lathes at a fraction of the price came in from, initially, Taiwan, and later China, The early ones weren’t great to be honest. Today they are mostly okay and range from mini lathes  to Colchester equivalents.

A word about mini lathes (above). They are small. They will not be much good if you are into building large locos, traction engines, and large stationary engines, or anything else where you need to chunk lumps off iron castings or turn large and heavy items.

Chinese mini lathes (which come from a variety of factories) have sold like hot cakes in recent years around the world. They are cheap as chips. And have an enthusiastic following. There is no end of helpful information on the internet.

For what you probably finish up spending on a cheap import you might find a decent used Myford from someone at the local model engineering club who is giving up.

New or old, buy from established dealers. Don’t buy the ‘bargain’ on ebay from a bloke who does house clearances (unless you really know what you are about). And just because something has a good brand name remember it is probably 50 years old and poorly maintained. The original Myford company used to take such old iron as ‘part exchange’ and generally it finished up in the skip, being uneconomic to restore. The same things today are on ebay for hundreds of pounds!

Second hand machines can be terrific value and often come with loads of goodies. If you need size and great precision you can find toolroom type lathes at affordable prices (these should be properly mounted on a concrete floor). Remember they are likely to be worn.

Beware some of the stuff on ebay. A lot of it looks dire. Probably no better is something just re-painted. Never part with cash until you see and collect the machine. Take someone with you who knows what to look out for.

One other factor in choosing a lathe is what other machine tools do you expect to have, and how much space do you have? There are examples of people doing great things with micro lathes like the Sherline or Unimat housed in a cupboard! A Myford lathe does not take up much space and it will do everything that otherwise you would also need a drilling machine, milling machine and even a slotting machine.

Installing your lathe should be straightforward. Read the instructions! Just make sure there is comfortable space to stand in front, and that both ends can be accessed, especially the headstock end.

For those with deeper pockets there are some good new larger lathes to be had from main dealers like the Warco gh1230 geared head machine (below) and some of the goodies that come with it. 

A good lathe will have installation instructions available; have a look at these before you buy. They will tell you a lot about owning the lathe.


We are not giving a shopping list for accessories and tooling for your lathe. Its best to get things as you need them. Sufficient to get you going are a three-jaw chuck, drill chuck, some cutting tools (High Speed Steel tools are fine for most uses) and a toolholder.

Let’s get started.

First thing. Where is the ‘stop’ switch. Remember that!

Are you suitably attired to work with rotating machinery (no loose clothing or unrestrained long hair and wearing eye protection)?

Yes? Then let’s make something useful.

When you were making the dice, it was probably difficult to know when you had drilled the holes to the right depth. You can make life easier with some depth stop collars.

As with the dice, there are no drawings. But do make your own drawing before you start. Its good to make things on paper first!

You are going to make a circular collar in mild steel. It is 18mm diameter with a 10mm hole in the centre. It is 8mm thick. A hole will be drilled in the centre of the outside edge through into the central hole. That will be tapped to give a 2BA thread to take a grub screw (a headless screw with a hexagonal hole to take an Allen key).

Buy a short length of, say, 20mm dia or 3/4in dia free-cutting mild steel.

Hold a piece of the bar in the lathe self-centring 3-jaw chuck with about 25mm protruding.

Place a turning and facing tool in the lathe tool post. Adjust the position of the tool so that it can cut along or across the bar.

The tip of the tool must be at exactly the centre height of the lathe. Just how you do that will depend on the toolpost on your lathe. If the tool height is adjustable, that’s OK. If not you will have to put pieces of metal packing under the tool to bring it to the height of the centre of the lathe. As a guide set the tip of the tool level with the lathe centre in the tailstock by swiveling the toolpost into position. When you are happy that the tip of the tool is close to centre height, tighten the holding bolt and return the toolpost to the cutting position.

Move the lathe saddle until the tool point is almost touching the front face of the bar in the chuck.

Select the correct spindle RPM and start the lathe. You will need to look this up in tables to suit your lathe tool, but around 400 rpm should be OK.

With the lathe running gradually move the saddle towards the workpiece until the tool just touches. Slowly withdraw the tool away towards you. It will remove some metal as you do. When clear of the work piece, advance the tool 0.25mm towards the chuck using the cross-slide. Now face the tool across the end of the workpiece right to the centre. If that has not cut completely across the face, repeat the process.

If there is a small piece in the centre, which has not been cut, you will need to raise the tool slightly. If a small bump is left where the tool has cut above the centre, the tool is too high.

With the tool now at the exact centre height, take a final light skim of around 0.1mm, which will give a good finish. Stop the lathe.

Now move the tool away from the bar and then slightly towards the chuck. Re-start the lathe and move the tool towards the outside of the bar until it just touches, and then move it away just past the end of the bar. Using the top slide, move the tool in by 0.5mm and take a cut along the bar around 15mm. Stop the machine and measure the new diameter with your micrometer. Repeat the turning process until you reach a diameter of 18mm.

Next you are going to drill a hole 10mm dia. If you are using standard jobber drills, first place a no 2 centre drill in the tailstock drill chuck. Drill about half way along the taper. Replace with your 10mm drill and drill a little over 10mm deep. Put a slight chamfer on the outside edge to remove the sharp edges. The correct way to do this is to use the top slide at an angle of 45deg. For speed, a touch with a file will suffice (be very careful when using hand held tools near to a rotating chuck!). Put a light countersink on the edge of the hole using a countersink cutter or larger drill.

We now need to cut off the machined part a little over 8mm thick. The easiest way for a beginner is to cut it off with a hacksaw. Of you can set up a parting off tool in the lathe and use that, again making sure it is on the centre line.

Now put the cut off piece in the 3-jaw chuck with a short length (say, 3mm) of the sawn edge protruding. All you need to do is to face off the piece, and lightly chamfer the hole and outside edge. You are working close to the chuck here, and great care is needed. The commonest mistake for beginners is to catch the chuck with the tool or the edge of the top or cross slide. The other one is to leave the chuck key in the chuck and then starting the lathe.

All that remains now is to to drill and tap a hole for the grub screw.  Hold the collar in the drill vice by gripping the flat sides. By eye, make a centre punch pop in the centre at the top of the collar. Start the hold with a no2 centre drill, then drill 4mm dia through one side of the collar (take care not to break the drill when it breaks through into the centre hole). With a 2BA tap held in a tap wrench position it vertically in the 4mm hole. Turn it clockwise (keeping it vertical) until it breaks through into the central hole. Remove any burrs created by the tapping process. Thread a 2BA grub screw into the hole.

And that’s that. You now have a drill stop collar for drills of 10mm or slightly smaller. Just slide it onto the drill bit at the depth you require, fix it carefully in place with a grub screw, and use it to drill holes to the required depth.

You can repeat the process to produce sets of stops of 3,4,5,6,8,10,12mm bore. Design them so that they are all 8mm thick, and have wall thickness of 4mm. For an imperial set the bores can be 1/8,3/16, ¼,5/16,3/8,7/16,1/2in.


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

 
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Editor: David Carpenter