Re: [ATM] Small Dob truss question

[Mike Lockwood <melockwo@uiuc.edu>]

Scott,

Scott Carson wrote:
> I'm assembling a small 8" f6 dob....
> My question... I'm curious why the traditional dob truss has the paired 
> tubes meeting at the top ring (secondary cage bottom ring) verus having 
> the tube pairs (two tubes on same side of mirror box) cross in the 
> middle (form an "X") and attach at the top ring with a geometry 
> comparable to tube arrangement at the mirror box?  

I sort of did this with my 8" F/5.4 travel scope:
http://bi-staff.beckman.uiuc.edu/~melockwo/telescopes/8in_trav/8in_trav.html

The difference is that I used six poles instead of 8, so if the poles 
were to meet at an "X" they would have to bend.  Since my truss is in 
two pieces, the bend is not an issue.  My motivation was to reduce 
tube length.

> Seems the "X" tube configuration would significantly increase the 
> rigidity for a small increase in tube length, and especially if the 
> tubes are physically bolted together where they cross (middle of the 
> "X")?  I've taken a quick look at the geometry I'm evaluating for my 8" 
> (secondary cage 8.5" IN x 11" OD) and didn't see problems with the truss 
> poles crossing into the light cone.

Yes, you're right, the triangles have wider legs so it should be more 
rigid.  There is absolutely no reason you can't do it.  Any problems 
will become evident and get solved as you build your prototype.

Go for it.

Mike Lockwood
http://bi-staff.beckman.uiuc.edu/~melockwo/index.html

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