Why not making a simple arch+wall and rotate it by 45�? 

problem with that is that rotating it would result in all the brushes being off-grid and probably have gaps, creases, and overlaps. 

And why not making a wall and rotate the negative arch by 45� and substract the brushes? 

Im gonna retexture the map you posted and compile it and try it later, but looking at it in notepad I dont understand why the lightning has a 'mangle' and a 'target'. I mean I have tried both of these techniques but not together at the same time, mainly cause the tutorial said to use 'target', 'mangle' or 'angle' - one or the other?!!?

Also you have light entities with:

{
"classname" "light"
"light" "400"
"wait" "1"
"mangle" "0 -90 0"
"angle" "70"
"origin" "-96 -88 384"
}

Surely you could ditch the 'angle' and write

"mangle" "70 -90 0"

Hehe - I was thinking I'll probably end up just using the hack for the lightning anyway cause it sounds better!

Also if I had some small func_trains following a path round in a circular shape (a six or eight edged route), I could source some info_notnull lighning in the middle using the CastLightning style entity, and then target the trains using the 'enemy' key... - voila - Half-Life intro style scene! 

Substracting is just as evil as rotating. 

Just make the shape by eye - all of these fancy tutorials and techniques for making quake-friendly curves dont give true curves anyway. A true circle wouldnt hit a 1*1 grid anywhere (potentially). Use wedge shaped brushes to make the shape, or four-sided brushes with a clipping tool for example. If you can get all of the edges on the grid you can go back and re-make the shape using less brushes. 

If you make the arches as simple as poss, say with two wedges in each corner, rotate by 45 degrees, then use vertex manipulation tool to line the points up on the grid! I dont think you would get any illegal faces because its 45 degrees all the way. 

The thing about the fancy methods is they let you build it once and know for sure it'll work, letting you copy it throughout the level. Also you can make much more complex shapes, like helix' multiple curves etc. Look at the very first room in czg07c to see a good example.

And it's much cheaper for vis time. 

I have an .rmf called acurve.rmf full of pre-fabricated curved shapes. Its soo easy to use them for whatever.

The problem is that rudl needs it to be 45 degrees rotated. Thats a pain cause although you could fit all of the points onto a 2*2 grid or whatever, you might find yourself with illegal faces, which worldcraft will render ok, but by the time its been through a Qbsp.exe its gonna distort the shape - you might end up with small gaps between brushes. 

http://files.myopera.com/christig/albums/391747/angledarch.png

1: Make your arch.

2: Rotate your arch 45 degrees.

3: Scale your arch in the X/Y plane by 1.060606... , OR up so the bounding box is 1.5 times larger than the original arch.

4: Snap to grid 1/4 of what the original arch snapped to (IE if the original was on grid 8, snap to grid 2) 

FYI, angle and mangle keys are not related to each other in a light entity, angle is spot light cone and mangle is spot direction.

Now you seem to be mixing up lighting with lightning ... ;) 

Dont listen to me anybody - I'm only ever speculating.

Rudl - Listen to czg, im only speculating here but I would say he knows about 50 times more about gemetry than I do. Maybe 52 times more...

AguirRe - I did not know that. So increasing the 'angle' of a light which already has a 'mangle' increases the size of the cone. Whats the default 'angle'? 

I cant even spell the word... 

Default is 40 degrees in QuArK...

Go experiment. 

Sorry, the "mangle" key in the info_lightning_targetted isn't needed. I forgot to remove it when adding the "target" key. "target" will always override "mangle", because having a "target" specifies the end point exactly. "mangle", isn't as precise, saying that the endpoint is up to 600 units in this direction, depending on whether you hit something. Not to mention "mangle" doesn't do anything in the current release of quoth anyway.

And yeah, what aguirRe said about the lights. You should only need the knave.wad file to make it compile, worldcraft throws the others in for fun. It's a texture set well worth having. 

Thats a cool method it's
exactly
http://www.picupload.net/f-10678b14ddc0b4e218414f35bdbec898.png

1,060660172...

and it must be built over a square 

no works with other arches too 

I usually put in 1.06060606006 because it's easy to remember and Ogier doesn't do more than four decimals precision anyway. 

It's possible to set the Number of decimals in Quark.
5 is the dafault value 

Better to scale by exactly 1.375, then shear to 45 degrees, and then use the clipper. Stuff is guaranteed to stay on grid this way. 

It seams that Preach's map lightning trap worked, so I tried putting my targetted info_notnulls back in an seeing if it would work. You see its not that it dont work at all, it makes the sound of lightning firing for a second, then nothing. So I took out my lightning ents and info_notnulls and put them in another simple room map with a simple brush trigger_once, and long and behold it worked!!

So now I'm think it something to do with my triggers (trigger_relays) - trigger_counter counts three buttons getting pressed, then fires a relay with a "delay" "1" and a message, then fires another relay with a delay that fires the lightning...? 

Did you enable the light "toggle" field ? If it is not the case, you are not able to switch on/off the light. and BTW, it only work with light of style 0 AFAIK.

Hope it helped 

Although if you set two relays you can turn a light on and off in rapid succession, emulating a strobe effect!!! So you could have a stobe light effect which could be activated from a light beginning either on or off! 

What is the correct scale and how to scale it?

I rotate it 45 degrees, go into transform, click scale, and add 1.060606 to X and Y cos I read it here, but it doesn't fill the gap.

I am basically using a half cylinder to act as a guide for the arch and need it to fit exactly in the space shown in the screenshot below.

http://www.esnips.com/doc/61063d95-e191-4e23-87be-81c76859d544/arches

Anyone? 

try reading