Any specs on these lenses ?
Specifically the BFL, or Back Focal Length is of particular importance.
The best way that I have found is to use a conventional bench-top grinder, resting the lens flat side down on the provided support in front of the wheel,with a piece of thin cardboard under the lens to prevent scratching. I bring the lens against the wheel and rotate it horizontally as methodically as I can to try to maintain a circular shape. A fairly slow process but not too bad; nonetheless,I hope someone has a better way.
ChicagoX, thefirst one (Jaegers 41diam./35FL) has a back FL of 30mm, 15mm center thickness,3mm edge thickness. For the second (Pyrex 44diam.,30 FL ) no back FL given,14 mm center thickness, 2.5 mm edge thickness. The last one, the DCX, again no back FL given, 17 mm center thickness, 3 mm edge thickness. All this from their website, again, I don't yet have any of them. Given the $5.00 flat rate shipping I may order all three for 20.50 rather than one for about 10.00. Spend money to save money.
Wow, if a lens can stand that, then dremelling radially (that's what I had in mind) should be plenty safe.
I found dremelling to be very very slow, but I think it would have worked if I was more patient. The grinding wheel does create excessive heat if the lens isn't kept moving or "backed off" periodically.
I don’t have a bench grinder or a Dremel tool but for a while I had access to a friends bench grinder and I did it exactly as mentioned above.
It does get hot so you have to back off every now and then and you need to constantly get turning it. It’s not hard to do however.
I think it would be hard to do with a Dremel with the smaller head size but it’s worth a try.
It helps to know that one doesn't have to be too concerned about cracking the lens or chipping its edges.
I thought it was a very delicate job.
I have had good luck covering the entire lens with a thick layer of masking tape, then cutting out the areas to be ground with a hobby knife.
I have only used a dremel, albeit with smaller lenses than the one discussed here. The grinder sounds like a much faster method.
I had no previous experience either. It turns out that glass is fairly soft so no issues with cracking or chipping.
My main concern was (as is) to wear a mask and to use the grinder where you can clean up the area easily. Keep the area around it clear so that powered glass dust don’t get on things.
I had no previous experience either. It turns out that glass is fairly soft so no issues with cracking or chipping.
My main concern was (as is) to wear a mask and to use the grinder where you can clean up the area easily. Keep the area around it clear so that powered glass dust doesn’t get all over everything. I wouldn’t want this dust in my lungs either!
I use a hand grinder with thick disk usually. I place the lens to a vice bench between two pieces of thick rubber.
I just say, it cuts just knife trough butter, you can make it very fast. I use safety glasses
and protective gloves of course.
So nothing is a perfect fit? kinda sucks.
I pull this back from the grave…
Was somebody successful with a aspheric c8?
I have a xml c8 laying around and thought of putting a lens on it.
i got four from surplus shed awhile back. every thing that was close in diameter and focal length, none were a drop in. needed extensive work to lens or housing. will post part numbers that didn’t work if you like.
How was the result? Much smaller hotspot?
Still no replies since 2011… 
I have found a 40mm convex glass and I bought it : http://www.ebay.com/itm/1pc-High-Power-LED-40mm-convex-lens-optical-glass-led-lens-/180916494907?pt=LH_DefaultDomain_0&hash=item2a1f76a23b
Just the same diameter as the reflector of the C8. I tried with a cheap 30mm convex plastic from another light and the result was not so bad but hardly brighter.
The new XML-2 LED pattern make it way better for aspheric.
Dedome is better for an aspheric thrower ?
Give it a try and find out. :)
I bought the aspheric zooming C8 host from Wallbuys a little while ago. I put a de-domed XP-G2 1A in it. Very tight beam and throws pretty well but the optic isn’t very good quality so I didn’t do anything more with it.
Here is my build thread… Zooming C8
Like we say : You are not better served than by yourself. 
Even if this don’t work it can also be used as a magnifying glass.
The problem isn’t the shape of the aspheric lens, it’s the reflector. You need a special reflector to focus the beam to a point behind an aspheric lens. The light that gets straightened by a normal reflector is already being focused straight ahead and adding an aspheric lens will only bend it in unwanted directions.
