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When I first encountered the Scalextric 4 Schools competition I was tempted to dismiss it. When I initially viewed the formula it appeared that the size of the cars themselves would not allow deep engineering thinking as they felt too small. Three years further on I am starting to wonder if I will ever plumb it's depths.

From a teaching point of view it is manor from heaven unlike many projects it has been described as being an onion, you no sooner remove one layer then you discover another.

This was one of these good ideas encountered by accident. We had been trying to make tyres for a long time. We initially tried wheelchair and pedal cycle innertubes cut and stretched over laser cut acrylic hubs but this proved to be useless. We postulated many solutions but most died on the drawing board.

When I finally encountered Multibase the solution was obvious and it opened up a whole new level of engineering practice.

At Keystage 3 I would be introducing these additional pieces as future expansion as the basic car build will absorb the students fully without getting into the finer detail of engineering design. However a look at where the project may extend is always inspiring.

At keystage 4 I would first look at the bearing which is almost a brass bead pressed into the acrylic chassis (You need to be using the Boxford Ladder chassis for this to work). The Acrylic chassis will heat up with the friction of racing and after about 4 minutes will start to plasticise and add drag to the rear axle placing additional stress on the motor and gears, it can eventually result in the back end seizing up. Brass bearings like we are using were common in the world of steam engines for over 100 years and with correct lubrication can last thousands of miles under the loads expected by British Rail. I myself have seen ships gearboxes with 13ft diameter gears arrive back at David Brown Gear industries for new white metal bearings with no sign of a ball bearing in the whole unit. Needless to say any modern gearbox would utilise the advantages of a ball bearing unit.

The manufacture of the wheel is very much governed by the shape of the tyre you are going to make the two halves to match each other but it is worth noting at how the diameter of the wheel is slightly larger than the diameter of the hole in the tyre to ensure good friction.

Finally the elastomer - I have found a video about elastomers to help students understand there use it is not the elastomer we are using but shows why they were developed. Elastomers are still relatively new and as such not much information is held on the web. What we are doing is very cutting edge.

At Keystage 4 there are any number of project areas covering tyre shape, tread pattern, removal of bumps or ensuring rotational accuracy. Also removal of dirt or grease before racing (Often done with upturned gaffer tape). The potential improvements to try and gain a racing edge are enormous.

 

 

Resources
 
 

Wheels

The project will cover the manufacture of wheels, tyres and bearings for the scalextric project taking it to another level of engineering.

 

Initially we will discuss the axles, the standard scalextric axle is just below 2.5mm and has knurled sections on the rear axle to help the plastic wheels and gears to grip the shaft.

I selected 2.5mm silver steel as a replacement as this would have the strength and would also make an interference fit with the gears, if you fear slip a little bit of scratching of the surface with a file would achieve the same result as a knurl. The rod is available from most hobby engineers or tool suppliers in 300mm lengths and should be about 45p per length.

 

We will then move on to the turning.

The wheels can be turned on any of our lathes, however, to drill the axle hole the standard 5mm drill is too large. To solve this I bought a Stanley pin chuck which is supplied with a 6.35mm shaft I slipped a 6.35mm to 10mm conversion collet (Boxford Part Number TCL-17-024) over the shaft so that it fits the position taken by the 5mm drill and collet.

I then purchased a selection of drills in 0.1mm steps from 2.3mm to 2.7mm these in conjunction with the pin chuck allows you to create holes in soft materials like nylon that give the type of interference fit you desire. Wheels produced in aluminium will benefit from being the closest sliding fit you can achieve then drill 2.3mm at an angle and tap 3mm from the back of the hub and fit a 3mm by 6mm grub screw.

Bearing

Screw

Wheel

Profile

Scalextric Wheel Lathe Profile File - Download

Wheel Bearings

Next we will discuss the wheel bearings.

Two designs have been made depending on how your chassis is designed.

The first being Brass Bearings which are designed to go into the ladder chassis with larger holes or any wishbone arrangement hence the do-nut shape.

The same profile could be cut in Nylon, PTFE or Steel. Depending on what characteristics you are trying to achieve.

Bearing

 

Bearing

Scalextric Wheel Bearing Lathe Profile File - Download

Flanged Bearing.

Front Bearing

Front

Scalextric Front Wheel Bearing Lathe Profile File - Download

Tyres

I have two designs for the tyre moulds the first the two halves of the mould are identical, this produces a tyre where the join is round the middle of the tread, which means that if there is any flashing from over-injection it is right in the middle of the tread and very hard to remove.

First Mould

First Mould

Scalextric First Mould Design - Download

Machining of the mould.

Manufacturing

The second design makes the mould split down the side of the tyre,

Second Design

Scalextric Second Mould First Half Mould Design - Download

Scalextric Second Mould Second Half Mould Design - Download

 

The act of injection.

Injection

Moulds

 

Car with finished Tyres, Nylon front bearings and brass rear bearings, Turned aluminium wheels and silver steel axles.

Car

Car with body attached.

Car