All of the resources that I can find say that it should be done with the screw tip pointing up and the hanger below with up to a twenty-degree angle from horizontal.
Contrary to what you might think, the best angle for the screws is slightly upward, meaning the hanger is slightly lower than the teeth in the ice. This counterintuitive method is ...
I will only focus on signs to assess the quality of a placed ice screw. There are many factors that influence the outcome like the location, temperature, ... but they deserve an answer of their own.
The most important thing is, that the screw is placed all the way in solid ice. On the surface you can judge this easily. The deeper parts are assessed by what ...
Addition to ShemSeger's answer, from way back in my mind:
A concave spot in the ice is stronger than a convex spot, given equal ice quality.
The ice should be deeper than the screw is long, so the screw doesn't push the ice away from the rock.
Sounds obvious, but that's the answer, you need to learn how to identify good solid ice for all your screw placements.
The best ice is the thickest ice you can find, so you can place your longest screws; clear and blue will be the most solid, while the worst ice is cloudy or brown, full of bubbles (aerated) and 'crunches' when you poke it, or has ...
For me, I'm fairly experienced at sharpening knives by eye. If you don't have access to a guide, which is not something that immediately comes to mind when you're packing for a hunting or camping expedition, it's a good idea to learn how to do it by eye. For some cases, such as butchery and knife restoration, a guide is essential. Also know that sometimes,...
There exist specialized tools which can assist sharpening. However those generally only work well with a specific brand/type of screw, since the angles of the screw's teeth differ.
(One example is "Lim'Ice" from Petzl, see video https://www.youtube.com/watch?v=BzN7l4JxxpA )
Some shops also have a commercial sharpening service.
If a screw is really dull, ...
Finite Element Analysis
Ice Screw Analysis by John Gregel shows computer models of the stresses applied to an idelaized screw in differing strength ice blocks at three angles:
+15° hanger higher than tip / ‘downwards’ in Charlie Brumbaugh’s answer
-15° hanger lower than tip / ‘upwards’ in Charlie’s answer
It shows the most obvious difference ...
It's easy to tell when your screws need to be sharpened, because they don't cut as well and get increasingly difficult to place, but with proper maintenance your screws should never get to that point.
The best practice is to sharpen your tools and gear after every climb, even if it doesn't really need it. You don't need to go overboard, but the most serious ...
A number of kits have guides for angle. I happen to like the Sypderco but it is not cheap.
Hopefully you can get angle from the manufacturer. 40 degrees is common (20 each side). 30 degrees is also common. Even a combination of 30 degrees followed by a 40 degree micro bevel.
On a stone you could just cut a guide using cardboard. Consistent is more ...
What you want is a guide in a knife sharpening kit that will hold the knife in place and the stones at the correct angle.
Mine looks like this,
you can see the angle marking on the left side of the holder (they are on both sides).
The way it works is like so (pictured without the knife for clarity),
The guide rod keeps the stone at the same angle to the ...