In reply to Heike:
I asked needlesports about this and they replied
"
Our Ice screw sharpening machine was designed and made by Grivel and intended for there screws. If the screw to be sharpened is in good condition but a little dull on the leading edge, the machine will only need to take off a slither of metal. (I would say less than .5mm). So to clarify, the machine sharpens the leading/cutting edge but won't make the teeth longer.
We have found that nearly all modern Ice screw apart from the newer Black Diamond Screw have the same tooth profile/angles.
The latest Black Diamond Ice screws have both longer teeth and the Inside edge of the screw is a little more angled towards the middle of the barrel.
When we sharpen the newer BD screws, we need to take off maybe another .5mm more, so the cutting edge of the screw has a flat face and not two different angels. (the Grivel machine is set at an angle for there screws and can not be altered). This then makes the screw a little more like a Grivel, Petzl, DMM etc. We tend to only sharpen screws that really need to be done and If we think it's not necessary, we will say so. A well treated ice screw can maybe be sharpened 5-7 times as each time the teeth length will get a little shorter.
"
My take on this is that for screws that have been badly blunted (or if you want to maintain the BD as new bite) you are really better hand sharpening them.
Post edited at 10:36