I have been looking around for disc options for my frame which has 110mm spacing. I haven't been able to find anything other than 120. In Osaka the LBS told me I could use an axel conversion kit but it would only cut the difference down by 5 or 6mm or so. I don't want to stretch my frame even if it is only 5mm. I haven't been able to find anything via search, just 110 hub discussions and a lot of stem discussions.
why don't you want to stretch the frame? if it's 110 spacing i'm assuming it steel, correct. you don't need to cold set the frame, just pull apart slightly when you put the wheel on.
when shimano came out with 8 speed in '89 or '90, the dropout spacing went from 126 to 130 mm for the extra cog. their early hubs had a tapered nut on one end to make it slide in more easily on older frames since 126 was still the standard dropout spacing.
Even older disc wheels (in the days of 120-126 spacing) were not 110.
What kind of frame do you have that has 110 OLD spacing that would take a disc wheel?
My dedicated path bike has 110mm rear but i just find it better to run a lightweight tubular wheelset than to mix in a new looking disc. (although I have a 126mm disc for my TT bike)
With a steel frame, I think it's completely safe to do what you can with spacers then stretch the rest of the way. It's only gonna be a couple of millimeters. Wouldn't do it with a carbon fame, but I wouldn't worry about it with a steel bike.
Personally depending on the wheel u might not need to change the axle but change the spacers. I would change the axle as the lbs told you, the extra axle coming out can be fixed usng extra washers (will look like crapppp) or just cut it. Using a dremel will take like 10 minutes or less. Done.