After seeing a plea form a local General Medical Practice for PPE, which they are desperately short on. It occurred to me that I could utilise surplus stock form my place of work, Nottingham Playhouse Theatre.
So with the permission of the Chief Executive for a donation I precured the items I needed, took them home and started to work.
I believe that this method of making a Face Shield can be made with tools really available in most household toolboxes and craft kits. With easily available materials.The headpiece itself lightweight comfy and can be wiped down.

Supplies

Closed cell foam between 9 and 12mm in thickness; such as Eva Foam, Plastazote,Yoga mats, camping mats or foam floor tiles.
A4 clear plastic sheet.
Elastic, I used 25mm wide.
Masking tape.
None repositionable double sided tape.
Contact adhesive.
Cable/zip ties.
Safety pins

Step 1: Tools

You will require;

A metal Rule.
Fine nib marker pen.
Sharp knife such as a scalpel, snap blade, craft knife or stanley knife (box cutter)
Set Square.
Scissors.
A wig/hat block. Do not worry if you do not have one of these, something round and head size will do. For example a biscuit tin, tupperware or a piece of plastic pipe.
Hole punch or ring binder paper punch.
A bradawl, gimlet, knitting needle basically something to punch a hole through the foam with.
Wire snips; these are for cutting the excess off the cable ties, you could also use the scissors or knife. Something to make a circle, a pair of drawing compasses will do but I used the tin lid from a posh biscuit tube. Using this meant I could score around it with my craft knife.
Cheap paint brush, pallet knife, or paint/glue spatula for the contact adhesive.
A respirator mask. This is for when applying the contact adhesive, if you cannot get a suitable respiratory then please do this process outdoors.
A chalk or a white maker; this is for making the glue line on the elastic. I had a surplus of black elastic, I have some white elastic on order for the next batch so I will not need this next time.
An A4 piece of paper.

Step 2: Cut and Mark Out the Foam.

Each Face Shield comprises of 3 pieces of foam. I have found that cutting out ten of each at a time is a good working number but this depends on how many you can make with the materials at hand so reduce or add as required.
You will need;

One strip cut to 390mm by 30mm
One strip cut to 335mm by 30mm
One piece cut to 20mm by 30mm
Next mark out a line at 50mm from the end on the two strips and a two lines from the center that are the thickness of your foam.
Now turn over the larger strip and mark a centre line.

If you are would like to make multiple face shield form then I have worked out you can make 88 units for one standard sheet of foam. Please see the PDF Attached for instructions.

Face-Shield-Foam-1-to-10-at-A4.pdf
Download

Step 3: Cut and Mark the Elastic Strips.

Cut 25mm elastic strips to 370mm long and mark a line from both ends on both sides 40mm in.

Step 4: Cut Out the Foam Parts

Using your sharp knife cut out all these components. If you have a metal edge square then this will be helpful at this time but by hand and eye with a steel rule is fine.

Step 5: Apply the Glue.

Realign the cut strips on a scrap, flat sheet of board, I have used some plastic sheet material but cardboard, PLYwood, MDF etc. will be perfect. Using the masking tape to temporarily fix them to the board and mask off the line markings.
Next apply the contact adhesive to the center and two side areas of the foam stips, both end sides of the elastic and the 30mm sides of the 20mm cut pieces.

Step 6: Assemble the Foam and Elastic Parts.

Following the steps in the photographs t step 6;

Connect the the 30mm part at the center of both the 390mm and 335mm strips, being careful not to accidentally touch the glued end of the strips. There should be a 10mm strip of glue on the foam after the end of elastic
Next attach the glued end of the elastic to one of the 390mm glued ends and pinch the end of the 390mm to the 335mm sandwiching the elastic.
Bring the elastic around to the other side of the foam and repeat the sandwiching process.
Apply a bit of pressure to make sure the glue hold firm.

This is the peak and headband.

Step 7: Preparing the Visor

For then next part you will need a crystal clear A4 sheet of plastic. for the face shield I have made so far I have managed to source 250 micron acetate and 0.5mm poly copolyester also known as PETG. The photo references for this build is the PETG version. The PEGT comes with an added protective film on both sides but I prefer working with the acetate for speed and lightness. In the end as I am receiving donations it really does not matter so long as the conclusion is right.

First mark a line along one of the long edges 30mm in.
Gently run your sharp knife along this marked line, just cutting into the film but not the plastic (some plastics will not have a film so ignore this). this line will be where the visor attaches to the peak
Peel off the 30mm strip.
Mark a point 20mm and 20mm in form the side on visor edge, on boths sides.
Punch holes at these points with the hole punch.
On the opposite edge mark a curved edge on both sides and cut along this line with a pair of scissors or a sharp knife.

EDIT:
If you do not own a hole punch, then you could bind or clamp between a couple of pieces of sheet material such as PLYwood and drill through with your drill set to a low torque.
A further option and I think better option I have been working on, is to do away with the double sided tape (step 8) and place four holes along the top of the visor plastic.See image last image in this step for hole positioning. Another idea for hole making is to use a ring binder style hole punch, one punch for both holes on either side. I will try and fine my punch and upload a photo.

Step 8: Final Assembly.

Place your peak on a the head block.
Pinch in the elastic so the peak and headband fit snug around the circumference of the head and pin in place with a safety pin. The length of elastic should be large enough to fit most heads, even fitting over other headwear and then the safety pin can be used to shorten the elastic to the desired hatsize of the wearer. If you know the hat size of the intended wearer you could always cut the elastic to fit before gluing into place.
Mark a center point on the top edge of the visor. I have used a srtip of A4 paper folded in two.
Use the same folded strip of paper, match up with the center line on the front of the peak that you drew during Step 2 to mark lines on the peak front piece at each end of the the paper strip. (I'll take better photos of this process when I make my next batch). It is between these two points on the front of the peak the double sided stick tape will go.
The reason this is marked now rather than the mark out stage is because the glueing stage can produce a few inaccuracies. If the double sided tape is too long this will not only look messy but will be messy, sticking to hair etc.
Cut and stick a length of double sided tape between the two side mark points across the center front of the peak. before you peel off the tapes protective paper, give it a bit of pressure with your fingers to make sure is is firmly stuck down. (Again I will add more and concise photos of this process after may next build)
Now remove the double sided tapes protective paper and carefully match up the visor to the the front of the peak
Apply finger pressure to make sure the connection between the visor and the peak is strong.
Next, with your pointy tool, pop a hole at the place of the two holes you punched in the visor but only pierce through the other strip of foam.
Feed a cable/zip tie through the hole and close it over the top and around the first strip of the peak. Do not over tighten as this will tear through the foam. (Once again, I will take better photos of this process on the next build)
I have found through trial that the cable tie prevents the plastic from wanting to pop away. I am looking at other types of fastener such as nylon rivet, maybe even completely replacing the need for the double sided tape. If anyone has any success then please let me know.
Snip off the excess cable/zip tie.

YouTube video of me building a Face Shield link here; https://www.youtube.com/watch?v=cEbf4yPBD2k

EDIT
My new preferred method of attaching the visor to the peak is to just use four Cable/zip ties doing away for the need of double sided tape. This method would make it easier to clean or replace the visor is maintenance is needed.
Please so the new four tie MkIII visor image in this steps photos

Step 9: That's It You Are Done.

Give them a clean down.
Bag them.
Then get them to your nearest frontline healthcare provider. Them's the real heroes :)

Step 10: Amendments and Alterations

I have now done away with the double sided sticky tape favoring four cable ties instead.
Some of my masks are have teddy bear/doll nylon arm clips as I have had a donation of an amount of these. They gave a larger surface area then the cable ties so will not be prone to tearing through the foam or visor. This is just an option as personally I have thousands of cable ties but only a few arm clips.
I have now taken to dipping the finished Face Shields in a disinfectant / water bath, leaving them to dry naturally and bagging them once dry.