Orion ED80 drawtube modification

One major issue that I found was the focuser could not hold any weight. I put the Canon EOS on the eyepiece adapter, and held the ED80 vertically and watched the focuser tube rapidly slide down, even without the focus knob turning. I tried to adjust the two small allen screws to increase pressure on the axel , but to no prevail. After taking the drawtube out and holding a straight edge against the machined flat surface, I could see the edge was touching only the outsides on some areas and the middle in others. I then used a fat tip black marker to make the flat surface black. Then using a medium grit knife sharpening stone and rubbing it against the surface, high spots became visible. It's important for a Crayford style focuser to have a flat surface across the entire focus axel in order to support weight.
Using a medium grit knife sharpening stone and water, carefully run the stone across the face of the machined surface. It's important to keep the stone square to the surface and prevent the tube from rolling. Don't stay in one area as you'll need to evenly remove material from the entire length of the machined surface. Note the black duct tape over the end to keep out debris.
After 20 minutes of careful wet grinding, the surface is starting to look even. The black marker indicates the low areas.
Keep wet grinding until the surface is even. Don't overdo it. Almost 45 minutes later, the surface is as flat as it will get. After reassembly, the focuser now was able to hold the weight of the Canon EOS when the OTA was held vertical as well as the SBIG ST2000-XM with CFW filter wheel weight of 3 pounds. The feel of the focuser also is much firmer. For the cost of this OTA and the APO performance it delivers this problem is easily fixable.

© 2004-2008 Michael A. Siniscalchi