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Custom mount for 40cm cassegrain

This mount was originally constructed by the famous Jac Suurmond after his own design. The mount carries a 40 cm Cassegrain telescope.


The new owner Detlef Koschny wished a modern GoTo drive system on this mount. The original one one only had a simple synchronous motor for the right ascension axis drive and the declination axis was fitted with an tangential arm.




The original system did not have an appropriate construction for installing and adjusting a guidescope.


Avery sturdy bracket construction has been made for the guidescope and two finderscopes. The 15cm guidescope is fitted with a X-Y adjustment device for the searching and locking on the selected guidestar in the field of view.


The X-Y adjustment device of the 15 cm guidescope was revised and modified for a analog readout.




For the modification of the right ascension drive a lot of parts of the original Byers drive system were re-used. The bearing-arrangement of the worm has been improved by using preloaded angular contact bearings, an extra no-backlash reduction gear and a precision worm-wormwheel combination.

The used motor is the well-known SECM steppermotor.



The declination axis drive was more difficult. Because no wormwheel was used in the original system the existing construction had to be modified.

On the pictures you can see the how this modification was done. 


The solution for the new declination axis drive was increasing the inside diameter of the bronze wormwheel so it could be fitted to the declination axis.


The new declination wormwheel must also be driven, so also here a completely new construction had to be designed.

For the worm that drives the wormwheel a special construction has been developed. Important is that the worm-wormwheel combination is completely free of backlash and very stiff. This was reached by pushing the worm with sufficient spring-loaded force into the wormwheel.

It is of utmost importance that the worm does not move in any direction except perpendicular to the wormwheel. To trick is that only one of the six degrees of movement is allowed to move. This has been solved with an elastic hinge construction.

Both axis drives are fully protected against dust and dirt.

See here all pictures and a description of the modification on the website of Detlef.






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