Re: [ATM] Square over Round Truss Tube

["Arjan te Marvelde" <arjan.te.marvelde@hetnet.nl>]

> From: "Lee Chin Huat" <lee@nakano-const.com> wrote:
...
> Why do people prefer round truss tube over square truss tube ? Is it not
easier to use square tube to connect to the mirror box and the secondary
cage ?

Stiffness is determined by tube diameter in bending direction.
Round tubes are lighter than square, with equal wall thickness.
You can also choose U or I profiles, which are even lighter.
Weight ratio is approximately (thin wall)  4 : PI : 3.

In truss structures, the tubes are usually overdimensioned, but the extra
stiffness and weight decreases vibrations.

I used 10mm cross section U profiles on my 250mm F6.3 scope, carrying a
500gr secondary cage. Plenty stiff when clamped tightly, and they fold
together as a compact package inside a PVC pipe for transportation.

/Arjan

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