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Drawtube Slip


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Can anyone suggest a solution to the following problem?

When I attach a QSI camera (which weighs about 3.5 lbs) to my SW Evostar 120 ED Pro (which has a Crayford focuser) the weight of the camera causes the focuser drawtube to slide down even when the focus lock screw is tightened. This results in the camera going out of focus.

I've tried tightening all the screws in the focuser housing but the drawtube continues to slip.

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I had the same problem with my Equinox 120. The issue was the 'flat' contact part of the draw tube. You can dismantle this, hold a straight edge up to it and see that they are not flat at all. Instead of the Crayford roller friction contacting the whole width of the 'flat' draw tube part, it only touches the edges resulting in low grip and slippage under load. Fortunately the solution is simple- take a fine grade, flat (preferably new) honing stone and carefully hand hone the draw tube 'flat' flat. Check constantly the progress with your reference straight edge (engineers steel rule) in both directions (parallel & perpendicular to the tube) and in a few minutes you should have a much flatter contact surface. You will loose the nice glossy finish, but that coating seemingly is the cause of the problem!! Now my scope can hold a pro weight DSLR looking at the zenith with no shift.

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