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.
I received my aspheric glass lens ! The good news is that it is of good quality and a perfect fit in lieu of the standard C8 glass, the bad new is that it is too far away from the led and so it is not focus at all so its useless… Cant even fit deeper in the C8 since the edges become narrower.
How is the beam, is it worth than stock lens?
Perhaps you can decrease the distance with some aluminium piece underneath the star?
The lens in my aspheric zooming c8 is very thin compared to yours by the looks of it. Mine would only be ~10mm thick at most.
I tried the lens out of my UF-T20 Host once as it is a perfect fit and the light was utterly useless. The emitter needs to be much closer to the lens when they are that thick.
Sorry for the late reply I have forgot about this…
The beam is full of rings & artefacts and I have WAY less lumens than stock reflector. Totally useless.
Its WAY too far away from the LED, playing with the pill screw does absolutely nothing.
Well… I understand nothing about your thread… You don’t specify the lens and where you bought this C8 model, nor pictures. But you say on this thread this a lightmall C8, but where do you get the lens ? It was perfectly at the right heigh in-place of the regular glass ?
I have also seen this convex glass at kaidomain could be better as it is flatter.
Sorry, I have no idea what you are talking about…
I have never mentioned anything about a lightmall C8? The only other post I have made was on the previous page stating that I bought the Zooming C8 host from WALLBUYS and then linked to my build thread for it. I never bought another lens, it came with the aspheric and I did try the thicker aspheric out of my UF-T20 and it didn’t work.