From another post TODAY!
Posted by Bttocs:
Want to point out something that doesn't seem to be discussed when debating base bevels.
For a 0.5 deg base bevel, you take 0.0007 inches of steel off the outside edge, and taper it back to 0.0 as you get back to the ptex. This assumes your edge is flat to the ptex and at 0.0 degrees to start (in theory what a base grind does for you) This also assumes that the edge is 2 mm, or 0.80 inches wide. That is an incredibly small amount of material. I am a mechanical engineer, and the only way to do something that precise with a really tight tolerance is with a precision grinding machine using ceramic wheels. The base bevel tools that use hand files are set up for that angle, over a large distance, but the depth of cut from the file comes into play at these small numbers. Just for reference, the thickness of a sheet of paper (from the copy machine at work) is 0.004 inches. So we are talking about something 1/6 th the width of a piece of paper. Doing it by hand will be hard for the bevel not to vary somewhat, and the touch required on the file will be very important. What I am saying is one pass with a heavy touch will remove more than .0007 inches and over bevel your skis.
Atomicman is basically correct about everything he says in this thread concerning base bevels. I just had skis tuned by SkiMD in Framingham, MA and I am amazed at how consistent and accurate he was able to put a 0.7 deg bevel on my skis with his machines. He told me that he couldn't really do a 0.05 bevel, that he has calibrated his machines to a 0.75 bevel and holds that as close as possible. He is saying the difference of 0.25 deg is so small it is at the limit of what ski tuning machines can produce, even with his calibrations and knowledge.He is always trying to hold 0.5 to 1.0 degrees for race tunes. I am guessing the exact number depends on the useage on his grinding stones, new ones produce 0.5 and ready to be taken off are approaching 1.0 deg. He will produce a consistent number on a pair of skis.
After measuring almost 10 pairs of my skis (family skis) the bevels vary from almost 5 deg to slightly less than 1.0, and I mean that on the same pair of skis.
Getting a consistent bevel all along the entire edge is very important. My skis vary a lot, and this causes them to ski very bad on hard conditions. I would guess that having the edge vary by +/- 0.25 deg is pretty standard, even for a good tune.
I am taking my skis to a new local shop to correct them and they can only hold as low as 1.0 deg base bevel with accuracy. They seem to hold it pretty well and the bottoms are flat, so this is good enough for all most all skis, except my race skis. Their prices are reasonable as well, so they are getting my business. I am doing some skis by hand to compare how I can tune versus the new shop's machines.
BTW, I have found a lot of bevel math on the web, which is just plain wrong. SkiVisions site is wrong by a factor of 2 on their base bevel information, in terms of material removed for a given base bevel. I have their tools and now question if the base bevel tool is also wrong by a factor of two. I suspect it is.