CAD render 3ring construction

Frodo - a 10 inch travel Dobson

10 inch, f/4.8 newtonian


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basic considerations


hogging out
smoothing the curve
foucault tester


mirror cell
wire spider
middle ring
rocker box


travel and assembly





two inch Crayford focuser

The thing is: when you start making everything yourself – you just cannot stop!

Crayford focuser mounted   Crayford focuser without drawtube

The focuser is again a design I found on the net, This one is by Jim Sapp and can be found in the ATM resource site.

I took bearings from old PC fans, used plywood for the body since I didn’t have access to high precision metal working equipment, some parts from an old tape drive like the drive wheel as knob and a 4 mm stainless steel rod from an old Fischer Technik box I used to play with as a boy. This part cost me nothing, but the drawtube and the adapter I had done from a professional on a lathe was quite costly.

The bearings are mounted on an aluminium plate which is mounted with some play to the plywood body to allow for adjustment of the drawtube axis. The plungers that hold the pinion shaft are pressed towards the drawtube by two thumbscrews, thus allowing easy adjustment of the torque necessary to turn the focuser wheel.

All holes into the plywood body were drilled with an electric drill on a stand. The drawtube hole was cut out using a hole saw. Not really accurate, but it works…




   © 2005 by Andreas Derwahl •  contact