Strock concept for larger diameters

For telescope builders who do not own thin 250mm diameter mirror as the original strock-250, you will find here a parametric form to make the modifications. These
adaptations have often been requested for the focal length variations and also bigger mirrors. The strock250 drawings conversion to other diameters is difficult
because many parameters check are necessary :

• primary mirror size : diameter, thickness, focal length, mass.
• secondary mirror size : diameter, thickness, mass.
• plywood thickness : box and unbox configuration have to work, so thicknesses have to be frozen in the drawings.

We consider 250-325mm diameter range is easily available without big modifications, higher diameters involve shape pieces modifications not only size.

• Whatever the diameter, it is imperative to stay on fairly short focal lengths (less than 1500mm), and mirror masses quite low (less than 4.5kg), otherwise balancing becomes very difficult, adding masses or elastics on the primary cage .
• it is best to stay on a 1.25 inch focuser. 2" Eyepieces and a heavier focuser will disturb the telescope balance.

Parameteric drawings

You can download HERE explanations and parametric drawings to size the structure according your elements. Optical parameters and structure compositions can be checked
on this excel calculation form. download Here .

If the mirror mass exceeds 4.5kg or if the focal length is longer than 1,3mm, it will probably be necessary to make plywood thicknesses changes not available in the drawings.

CAUTION: Not all possible configurations can be verified, therefore changes must be re-checked ...

Industrial facilities are now Available in Fablabs: Laser Cutting, Numerical Control ...

In recent years, FabLabs have opened in our cities and sometimes offer laser cutting or digital milling. These facilities make possible cutting professional accuracy with
easy assemblies by tenons / mortises joints realization. Compared to the original strock concept, we can do without nails to perform a simple gluing, without risk of bursting
the plywood with a nail!

Below you will find the DXF strock drawings for laser cutting with "standard" optical characteristics and plywood thicknesses that can be easily cut (5 and 10 mm).
Thicknesses greater than 10mm are obtained by gluing parts in 5 and 10mm.