Augmented version of the article "When is a door not a door?", published in Lowflying, April 2015.

For those who read it, I'll spare you the terrible joke again, please skip the next line.

For those who missed the terrible joke, the answer is, "When it's a jar!". It wasn't that funny when I was a toddler.

Anyway...

I have a problem with standard sidescreens: The soft plastic is prone to scratching and damage if you stow them in the boot (when you find yourself miles from home on an unexpectedly lovely day); also at junctions, roundabout entries and through climbing right-handers, the framework sits in my sight line.

So when, early in 2013, I saw a picture of a Japanese Caterham with a frameless piece of glazing attached to the top of a half door, with door hinges bolted directly to the glazing, it set me thinking...

My first step was to procure a sheet of 3mm (not 4mm as I wrote in Lowflying - brain fade!) clear polycarbonate. Polycarbonate is used for safety glasses and goggles, helmet visors, riot shields, bullet-resistant glazing, etc, so it’s perfect for a sidescreen. It’s also fire-resistant, which I hope will never come in handy. I sourced mine from http://www.polycarbonateshop.co.uk but a search will find a variety of suppliers, with a 1m square sheet being plenty for two SV sidescreens (more like three plus change - polycarbonateshop will also cut a sheet down to your chosen size, but as delivery is a large proportion of the cost you may as well have plenty for experimentation).

Notes first:

Be aware that the polycarb "sawdust" created will be small, viciously sharp particles that your jigsaw will fire at you at significant velocity. Decent eye protection is an absolute must.

Leave both protective films on the polycarb for as long as possible and certainly while ever you're cutting and drilling the sheet. Once you remove it, attempting to make further adjustments with the jigsaw is pretty much guaranteed to scratch the plastic as swarf gets trapped between the jigsaw's baseplate and the polycarb. This will annoy you immensely. Ask me how I know... Pretty much, so long as you've peeled back the edges so they're not trapped, you can leave the protective films on until you've put the completed door back on the car and you're ready to drive away.

Finally, unlike some plastics, polycarb is not suitable for heating and forming - you're limited to a flat sheet, so you can't (for example) make a profiled wind deflector. **Edit** - This is not strictly true, I have since learned. It can be cold formed with enough force, although will spring back significantly from the bend you attempt to put into it. Additionally it can be heated to assist this if you're very gentle with the application of temperature - too much heat and the plastic will bubble, becoming opaque, which is not much use for a window.

Method:

Cut the old glazing out using a Stanley knife (with a fresh blade) - cut as close as possible to the black fabric without touching it. Then, cut the black fabric of the frame itself, at the rear corner and just back from the front top corner (see pictures). Note: Leave an excess length of the edge piping at both cuts; you can use this to provide a neat finish later. I wish I’d thought of that before cutting the first one...

I left the A-pillar to retain the weather protection between sidescreen and windscreen and because this retains the correct locations for the hinge bolts.

Next, slice the stitching between the two faces of the sidescreen fabric for a couple of inches from both the remaining ends, such that you can fold these back and get in far enough to cut the steel frame away with a hacksaw. You can get the knife in between the two pieces of fabric to cut the stitching - make sure you do this very carefully!

With the top and rear of the steelwork removed, reseal the two faces of the fabric using impact adhesive and stitch the edges back together, including the piping you left spare for this. When stitching, don’t try to push the needle through with your thumb - you will get perforated and the needle will bend. Use pliers to hold the needle near the pointy end, push it through and then as soon as you can, pull it from the other side.

Frankly, at this point, if what you want is a half-door with no glazing but still retaining a comfortable armrest and without the need to fix additional poppers or the like to your car, stop. Your work here is complete.

However, assuming you want some amount of window too, read on...

For cutting the polycarbonate, a jigsaw fitted with the finest toothed blade you can find gives a smooth cut edge that doesn’t need much finishing and you can cut tight turns where necessary.

Initially I made just a quarter light panel, drilled to use the four bolt holes that the hinges use, plus the two holes that the mirror was previously attached through (my mirrors are now on IVA mounts but this should work with door mirrors as well). These are all M5 bolts; obviously you’ll need to replace the old bolts with new, longer ones. IIRC the hinge bolts are originally 12mm; 15mm doesn't appear to be a standard M5 bolt length but 16mm is and that's what I've used all round.

This was surprisingly good. A half door alone cuts about 75% of the cockpit turbulence you normally get with a windscreen but no doors or roof; the quarter light cuts out most of the rest. After an hour of spirited blatting with it, my face was only just starting to become a bit chilly.

Note, picture shows the door before I'd sealed the ends of the fabric.

Back in the workshop (back garden), I cut a full sized panel - well, nearly. A slight miscalculation meant it’s a couple of inches shorter than planned on the bottom edge, at the rear. Whilst measuring up I also fitted the half hood and allowed about half an inch of overlap at the top.

I drilled two new holes in the metal framework at the (new) top edge of the sidescreen - plenty of care is needed to get these central in the metal strip (that you can’t see...), and also to avoid all the swarf disappearing into the sidescreen. To prevent overly stressing the glazing, I used plastic “top hat” washers through oversized holes for all the bolts along the bottom of the polycarbonate.

The end result is a much-improved sidescreen that doesn’t deform or scratch anything like as easily when abused, and has no blind spots.

If you use a full hood you may want to be fussier with the dimensions at the rear, but as we only use a half hood it’s not critical. If I were to remake the glazing I would also make it a fraction taller towards the rear - at higher speeds there’s enough flap in the half hood that the tail end of the glazing sometimes escapes to the outside.

Note, picture shows the door before I'd sealed the ends of the fabric.

Overall? Well, at no point in the last year have I thought the factory windows were better in any way, and if I do ever damage the glazing, it’s a few quid and half an hour’s work to replace the panel, rather than the cost of a whole new side screen.

With just a couple of minutes with an 8mm spanner and an allen key, I can swap between a half door, a half door with quarterlight / wind deflector, or a full door as you'd use with full weather gear, all the while retaining the comfort of the armrest.

It also gives, I think, a slight improvement to the "look" of the car when the roof's off, because, well, who doesn't like a frameless door window?

Matching passenger sidescreen to follow...