For anyone who happens to own an Orion ED 80 or 100 you may not know it but the flat on the focuser tube is well..........not flat, but infact slightly cupped inward.
The prob is the round focus rod that runs against this flat is actually only touching the 2 outer edges. Under any weight such as a heavy eyepiece or camera & it wants to slip.
I loosened my 4 focuser screws & pulled out the focuser tube & it was obvious the smooth contact areas were only on the outer edges of the flat spot so I took a honing stone & gently filed(honed) the area flat. I used a flat razer edge to gently pull the finish to a smooth polished surface. There is also 4 BBs that press against the sides of the focuser & they spin a bit rough as they are dry BBs so I placed a single drop of duralube oil on ea BB then re-assembled the focuser.
MAN! It feels sooooooooooooo much smoother now & the focus lock holds fast with much less pressure. So if you own this model of scope remove it & look at the flat its in dire need of a tweak & the BBs needs a tiny dab of oil also.