Images representing different hobbies

Model Engineering

Ever since I was a boy, I was in awe of the working mechanical models to be seen in the pages of Model Engineer magazine or on television programmes like Bob Symes' Model World. In 1999 I managed to acquire both a daughter and a lathe, and against all the odds started my journey in model engineering.

You can buy my books including the Mini-Lathe, Norden: Building a Victoirian Steam Engine and The Home Workshop Dictionary using the links below:

Hardback and Paperback Books

 

                 

Ebooks and Kindle

                               

When you are making heavily loaded parts like crankshafts, gears, pistons or pivots you are likely to turn to one of the high carbon steels. These are generally more expensive than mild steels and more difficult to machine to a high finish, so you will only choose them when their special properties are needed.. Let's look at the commonest examples: EN16, EN19 and EN24. Their high carbon content allows them to be hardened through heat treatment, and the can be supplied in as-produced condition or in the T (heat treated) condition which has less stress and better machineability.

EN16

EN16 is also known by the European designation 605M36. It is a strong steel that is a step up from EN8 (see mild steels) in terms of its ability to withstand wear and shear loads. In smaller sizes it is usually supplied in the 'T' condition (heat treated) as EN16T which maximises its shock resistance and helps machineability.

Although it is stronger than EN8, it still has a certain degree of give which makes it a good choice for load bearing and stressed parts such as connecting rods. It is not too demanding to machine but you do need to use cutting fluid.

EN19

EN19 or 709M40 is a really strong steel ideal for gears and other highly stressed components. It is quite tough to machine and the use of carbide tooling is recommended but not essential. Use plenty of cutting fluid, especially with HSS. Unlike EN16 it is easy to polish to a good finish.

EN 19 is also available in heat treated (EN19T) condition. One specialist product are accurately drawn hard-chromium plated bars which can be useful for things like guide bars.

EN24T

EN24T, which is also listed as 817M40, is a very strong steel that is usually supplied in the 'T' condition. It is very wear resistant but this can be increased even further by induction hardening or nitriding. It can be hardened in the workshop by heating followed by oil quenching, but it should be tempered at a relatively high temperature to prevent brittleness. For this reasons sharp edges and corners should be avoided - it has less resistance to shock loads than EN16 and EN19.

It is a demanding metal to machine, but with carbide tools and high surface speeds you can achieve a very good finish straight from the tool.

 

See Mild Steels for more general purpose steels.

 

 

Mild steel is not a specific material, but rather a catch-all for steels (iron alloys) that have relatively low-levels of carbon. This means that generally they can't easily be hardened (unlike high-carbon steels) and they are relatively ductile (easy to bend). While this limits their applications, it does make them relatively easy to produce and they are especially suited to to 'drawing' or 'cold rolling' into sized bars and flats. They are also generally easy to machine.

Though mild steels have a low carbon content, they are still classed as 'carbon steels'. The 'mild steels' most commonly encountered in the UK are designated EN1a, EN3 and EN8.

EN1a

Also known by the instantly forgettable code of 230M07, you are still more likely to find 'bright mild steel' classified as EN1a. EN1a is available as round, square and flat bar with a good finish and fairly accurately sized (you can buy accurate ground bars as well). It is a great all-round material for parts that are not going to be highly stressed or subjects to high levels of wear. It might not be the ideal material for making machine tools for use in a factory, but is usually fine for making your own devices. It machines easily and gives a good finish, the variant EN1a Pb has added lead and is even freer machining.

It's low carbon content makes it virtually impossible to harden but it can be case hardened (although EN1a Pb doesn't case harden well). It should not be welded.

Bright drawn metal has a lot of 'locked in' stress. If you do any asymmetrical machining of EN1a bar don't be surprised to see it bend like a banana! This, rather than its relatively low strength, makes it unsuitable for parts such as crankshafts.

In practice, you are likely to find that EN1a is the most useful general purpose, inexpensive material for non-critical components but is best avoided for bolts, studs or high wear/load parts.

EN3

EN3, also known as 070M20, is a slightly higher carbon content mild steel that is suitable for welding and one of its main uses is for making steel fabrications. It has good machineability, but isn't quite as pleasant to work as EN1a, being best machined with a lubricant.

It is typically available as bright drawn bars and a hot rolled bars. Hot rolled steel is less accurately sized and has a poor finish but it is stress-relieved so it is the ideal alternative to bright bar for asymmetrical or heavily machined parts. It is also suitable for making lightly loaded fixings.

EN3 can be case hardened.

EN8

EN8, or 080M40, is actually a medium-carbon steel but it is usually classed as a 'mild steel'. It is stronger than EN3 but does not machine so well and a cutting fluid of some sort is essential to get a reasonable finish.It is generally available a bright drawn round bars.

Like EN1a and EN3 it tends to bend rather than break, which can be a useful property in situations where complete failure would cause a hazard. Unlike EN3 and EN1a it is reasonably easy to harden EN8 to increase its surface hardness and wear resistance, but it does not become as hard as high-carbon steels.

EN8 welds well and even fairly thick sections (up to 18mm) can be welded without preheating. It is a good choice for parts or fixings that have to bear moderate loads where going to a higher carbon steel would be overkill.

 

For applications where you do need extra strength see High Carbon Steels

If you model historic machines they will almost always have plain bearings. Plain bearings can also be the best solution for other purposes having performances equal to ball races whenever adequate lubrication is provided.

Although you will often read references to bearing 'brasses', the most common metals used for plain bearings are actually bronzes. Brasses are alloys largely of copper and zinc, and though they will serve as bearing materials for lightly loaded models the bronzes (which are alloys of copper with tin and other elements) are generally much harder wearing.

Potts Spindle with plain bronze bearings

A Potts Milling Spindle with plain bronze bearings

Let's look at two bronzes which meet most of the needs of hobbyists. They both have a similar dark, reddish colour and often bear a dark spiral pattern and feel very heavy.

PB1

Most hobbyists will instinctively turn to 'phosphor bronze' - usually  supplied as PB1 a very tough, hard and hard-wearing material that is ideal for heavily loaded bearings.

The downside of PB1 is that it is not a particularly pleasant metal to machine. It can produce tough, raggedy swarf but the worst problem is that it tends to 'close up' when drilled. This nasty habit can cause drills or reamers to jam and even break giving phosphor bronze a reputation for difficultly in machining.Some people even go as far as grinding drills with off-centre tips so they drill over-size to avoid these problems.

Rather than spoiling your best drills, is there an easily available alternative?

SAE 660 Bronze

Fortunately there is! SAE 660 is a bronze with a high lead content that both makes it a lot easier to machine and also helps it bearing properties. You can pretty much treat it like a free-cutting mild steel. It's not as good for extreme load bearing or very high speeds as PB1 but for 9 out of 10 (or more) hobby applications you are better off using SAE 660.

The good news is that SAE 660 is often rather cheaper than PB1, sometimes around 3/4 of the price, and is readily available from most metal stockholders.

As well as being available as drawn or continuously cast bars they are both available in tube form. This doesn't just save you some machining work, work the reduced weight of buying tube can save you a significant amount when buying what is one of the more expensive metals. Fortunately, we often find we only need a short end of material for bearing use and many specialist hobby suppliers will sell very short lengths.

'Oilite' Bushes

It's worth mentioning 'Oilite' bushes, and other similar bushes. These are made from sintered bronze and impregnated with oil to provide plain bearings that need minimal maintenance. Usually these should be bought in the size you need and may well prove to be a cost effective alternative to making your own bearings..

Bear in mind that the housing size should be carefully made to the right size for the bearing as if it is too tight the bearing will close up. You may often read that such bushes should never be machined, in practice they can be finish machined but a very sharp tool should be used to avoid 'closing up' the micro-pores in the material.

See also:

Mild Steels

High Carbon Steels

 

These change wheel tables apply to all Mini Lathes with:

  • Metric 1.5mm pitch leadscrew
  • Imperial 16TPI leadscrew

They also cover some slightly larger lathes with Metric 2mm pitch leadcrews sometimes referred to as 'mini lathes' but fo different design, including the SIEG SC4.

The tables cover most Metric, Imperial and BA threads.

Always do a check before cutting metal, as there is always a possibility of errors.

Download Mini Lathe Cahnge Wheel Tables Here

 

For the ultimate change gear experience, check out Brian Wood's book:

 

 

Fans of cult Canadian science fiction movie 'The Cube' can now live out the experience of escaping from a three-dimensional maze in their own living rooms!

Cube

This Cube is a 27 'room' maze with a 15mm ball bearing trapped inside. The' exits' are on opposite faces, one in a corner, the other in the middle so you can tell which is which. How long will it take you to move the ball from one exit to the other? Of course the catch is that the ball is permanently trapped, dropped in during the print process.

You can download the STL file of the cube and print your own.

As a 'clue' here's what the Cube looks like inside, credit to Moduleworks' free, simple and really handy STLview program.

Inside Cube

The example Cube was printed using the 'standard' setting of a Dremel 3D40 Idea Builder printer. Advice for printing your own is:

  • Don't use any supports - they will block the maze!
  • Make sure your printer settings can cope with bridges up to about 17mm long, this should be OK on most printers if you have the right settings.
  • Ideally use a 15mm ball bearing or a marble. One down to 1/2" or 13mm should not to come out of the holes, but any much larger than 15mm may get jammed. That said, bigger ball bearings make a more satisfying clunk as they move around the maze.
  • You can use a smaller ball bearing, but it won't remain trapped inside, which is half the fun of the object - something you can't take apart without destroying it!
  • The best time to put the bearing in the print is while the second or third layer is being built - pause the print and drop the ball through any hole that links to the layer below out of the way of the print head. If you can't pause then you will have to judge a moment when the print head is occupied elsewhere!
  • If you use a solid colour rather than a translucent one, the cube will be even harder to solve!

Finally if you print your own Cube, please post a pic online and share this page!