preping angle iron

Hi all,

I'm looking at mounting the gear rack on some angle iron or on the web
of a channel.

The surface is very rough and I am wonding if I should d any work on
it, or just bolt up to to it.

Ditto for the linear rails.

I know there is a trick on dies to use paper to get a better seating.

I have angled washers for the web of the channel, and I don't have a
machine that could cut a flat on it over the 8 foot lenght.

Dave