Dovetail bar help

[bojan]

Fair enough.. and you gave me a good idea: I will drill a half-way-through holes where the craters are formed.. so the screws will sit nicely into depressions.. so there will be no way for this to fall off :-)
So no risk at all.

On image is Rubinar 10/1000, mounted as discussed earlier.
Solid as a rock.

[BC]

Hi,

Just picking this thread up again now that I have acquired an EQ6. I was going to pose the same questions but most are answered here.

One concern is that 6mm bolts seem so small to be holding a 10” newt and possibly a camera etc. Surely bigger bolts would be the go? Do any of you drill out to a bigger size and tap the hole?

I imagined that the block on the tube ring would sit inside the channel, not sit bridged over it. It doesn’t seem quite so secure where the bolt isn’t holding metal to metal.

Bruce

[bojan]

Originally Posted by BC

I imagined that the block on the tube ring would sit inside the channel, not sit bridged over it. It doesn’t seem quite so secure where the bolt isn’t holding metal to metal.

Bruce

This is my concern as well.. so I still use my 10" newtonian (13kg) on dobson mount.
Some people modified EQ6 head to be like Losmandy's.. I am not sure about that either.
Anyway I will not risk it with current and supplied dovetail bar, it looks too flimsy to me, like OK for up to 5kg but not much more that that.

[bmitchell82 (Brendan)]

Like the old saying is Bigger doesn't mean better.! For instance have you ever looked at fishing line (i know not astronomy related) Dacron (aka fireline/wire) is really fine yet extremely strong as compared to a similar monofiliment ... look at 100 lb fishing line. you could mistake it for rope!

As for your 6mm bolts look or ask for the manufactures specs on what shear strength the bolt has and that can tell you if your bolts are worthy of the effort.! 10 - 20kgs is light talking newtons 20 kg would be close to 200 N and consdering that engineers usually talk kN... not N to give you a grasp on the magnitude of things. some may or may not agree but without looking into it too much ide say your bolts will be sufficient!

[bojan]

Well, it not about how much the screw can take before it bends or breaks.
It is about (elastic) bending and, consequently, vibration or swinging or mechanical/positional stability and resistance to wind gushes etc.
Bigger is always better (in astronomy, that is..)

[bmitchell82 (Brendan)]

that is right elastic deformation depends on the material mainly. Have you ever heard of the term... "Damm these butter screws". you can have the same screw the same size one will just mash itself to bits the second you put a load into the head, the other will torque down so hard its not funny.

Yes it may be experiencing elastic deformation but it will only be in the axial movement not in the lateral so much this is where your bolt will fail due to shear stress and often will lead to a "catastrophic failure (material fractures compleately)" not just "fail(fall into the plastic deformation)".

If you wish to stop your gear from swaying in the breeze then increase the moment of inertia of your matierials or as you said make it bigger but at what cost? Heavier, Bulky, akward cheap or Light, Slim, and costs more! Aluminium is light but not so strong, Aluminum Alloy is a whole different ball game. as you then move to the atomic level and put in place defects to stop the slip of atoms from happening.

Bigger is only better when it comes to aperature! Slim small light is what is needed everywhere else!