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This project uses the elastomer multibase I have inlay bought the natural colour so far as I wanted to use it both as the school rubber and also for the Scalextric tyres.

Depending on your facilities at Keystage 3 I would either allow the pupils to laser cut their silhouettes or perhaps Hegner them. You can at a pinch use MDF but it needs sealing to stop the elastomer bonding with it. I must admit to not yet having found a foolproof way of making more than 2 erasers out of MDF.

As we discuss the possibility of designs I would point out to the pupils that when we are dealing with a silhouette the impression of the subject is all that is required, I usually had some wooden animal silhouette toys to display this. I have included a video but it does not employ the best shapes I have seen.

The "How its made" series has a video about the manufacture of erasers but I have yet to locate it.

At keystage 4 you could introduce the use of a metal rectangle as this allows the production of far more detailed moulds. It also allows pupils to hone their needle file skill. It is possible to make moulds that have negative draft angles as the elastic nature of the material allows it to be pulled out of even a bad mould when cold.

 

Resources

Eraser

Boxford offer a taster day which introduces the Scalextric 4 Schools project to both pupils and teachers.

I was pleased to deliver the first of these to the year 9 pupils from Bradford Grammar.

Whilst I was there Mike McKay the current head of department introduced me to this elastomer project for which I instantly requested permission to plagiaries.

I have added very little to the basic project and as such must pass all the kudos back to Mike.

Once I saw this material and it's characteristics then gave me the idea of making a number of projects out of this compound one of them being the Scalextric Wheels, I also tried to come up with as many projects for it as possible which would make a whole school solution for the one material and could negate the need to change the material in the injection moulder.

We will come back to the Scalextric Tyres and Other projects in pages to come.

In the mean time.

The elastomer know as - TPE TES A5005 BASI MULTIFLEX

It is available in 10kg bags from Azelis Plastics UK


www.azelisplastics.co.uk

 

At a cost of about £85

As most projects only weigh a few grams the whole thing should last quite well.

 

The concept is brilliant, pupils are given a small piece of MDF that fits perfectly into one half of the injection mould.

They take this away and either with a coping saw, Hegner, Laser Cutter or CNC router cut a silhouette of the pupils choice.

The MDF is then sealed to stop the elastomer sticking to it, we used cellulose sanding sealer and just before injection dabbed the mould with french chalk to act as a release agent.

When the silhouette is ready the MDF is placed in the mould in the injection machine.

 

CR Clarke

CR Clarke Injection Moulder In our workshop.

 

Empty

Mould prior to the insertion of the MDF

Pre Mould

Mould with MDF Inserted

(We use a CR Clarke machine) and the elastomer is side injected into the void.

Mould With Sprue

Moulding With Spru.

On cooling the Eraser is removed from the mould and trimmed . Approximately 5 to 6 Erasers can be easily made without undue wear on the mould.

 

SeaHorse

 

Sea Horse Mould with finished example and empty mould.

SeaHorse

SeaHorse

Sea Horse Mould - Download

Dog

Mould

Dog Mould - Download

Head

Head

Head Mould. - Download

Blank

MDF Blank - Download

 

Making the Injection Mould Blank.

The Boxford moulds are made from free cutting aluminium. The blank is - 76 mm diameter by 30mm thick

Blank

The additional thickness allows for the re-machining of a second or possible third mould project after the first becomes obsolete or worn.

 

Using the Boxford 190 / 300 with the 3 jaw vice fitted.

First skim the block to ensure it is flat and level.

Mould

Skim File - Download

Pop

Then run the following drawing

Back Mould

with these settings.

Based on the tooling being :-

Tool 01 - 2mm Slot Drill

Tool 02 - 3mm Slot Drill

Tool 03 - 4mm Slot Drill

Tool 04 - 8mm Slot Drill

Tool 05 - 10mm Drill with 45 Degree Rake

Tool 06 - 25mm Tipped facing cutter.

Set 01

190 Screen

Ste 03

Injection Mould Back - Download

Finished Cutting.

Finished

 

Machining the second side of the blank.

 

When fitting the job back to the 3 jaw chuck it is necessary that the four holes are positioned so that when the blank is placed into the injection moulder the entry point is correctly located at the top.

To achieve this we need a jig which locates into the four holes and uses the jaws to lock the position front to back.

Jig

Jig File - Download

Pins File - Download

Locked

The second side needs to be skimmed and then machined with the following settings.

PP

Depth

Tooling

 

When finished it should look like this

BlankTop

Top

Blank Back

Back

 

Using the Boxford A3 "M"

It must be an M model to machine metal other models may suffer damage if this type of machining is undertaken.

The first part of the machining can take place using the bracket with offset nut position.

Bracket

The drawings and settings remain the same as on the 190.

To help with the machining of moulds Boxford has created a jig to hold part machined blanks.

Blank in jig.

CR Clarke also sell ready to finish blanks that follow the same profile. These will also fit the jig and can be machined in the same manner.

Finished

 

CR Clarke Blank

CR Clarke

 

Making The MDF Mould Half.

The MDF piece is in mould terms a relatively simple piece of machining.

The depths are.

6mm for Pink

5mm for Red.

MDF Mould

Making The Side Injection Half.

The Side Injection is also in mould terms a relatively simple piece of machining.

The depths are.

6mm for Pink

4mm for Blue.

MDF Filler

 

Finished Moulds

FMoulds