EQ8 - Pier/Stability

[mercier57]

Hey

I've a question for all DIY guys out there I recently made a concrete pier (diameter 20cm) for an EQ6. But now I want to upgrade my mount to use my two telescopes together in a side by side configuration on an Skywatcher EQ8. It's a DIY SC (30kg) and a APO (9kg). So together with some accessories like camera, finder scope etc. my setup will weight around <45kg.  All together with the counterweights and the EQ8 mount head the whole setup will weight around 115kg.

Now this leads to my question, if my pier is stable enough to deal with this heavy load or not. I think I made the base stable enough that it wont fall/move in any direction but my concern is that the pier - mount adapter plate connection isn't strong enough. I used 4 M16 threaded bar about 50cm in hight. (check my picture) 

 

My concern is now that my concrete pier may "bend" or break under my heavy payload of 115kg right 50 cm under the top of the pier where the threaded bar ends in the rest of the concrete pier

What are your opinions about my concern and/or what are experiences with your own piers?

Andy

[trazor]

If it was me, I would make another disc about 20 mm thick and the same diameter as the existing disc, with 4 matching holes.

I would then slide it down the threads until it touched the concrete, then use 16 mm nuts to fix it down.

This I believe, would prevent flexing of the bolts where they enter the concrete.

You would need the holes to be as tight a fit as possible.

You could always weld the new disc to the tower, and to the bolts if you preferred, for even greater strength.

[ollypenrice]

Yes, I'd be inclined to lose the threaded bolts. They don't serve any purpose because mounts don't need to be level anyway. Couldn't you just lower the top plate and shorten the threaded bars? I have a Mesu on the standard portable pier and that has carried a 14 inch ODK plus parallel 7 inch Russian Maksutov and cameras etc. I'm sure your concrete pier will laugh at this task.

Olly

[r3i]

If it was me, I would make another disc about 20 mm thick and the same diameter as the existing disc, with 4 matching holes.

I would then slide it down the threads until it touched the concrete, then use 16 mm nuts to fix it down.

This I believe, would prevent flexing of the bolts where they enter the concrete.

You would need the holes to be as tight a fit as possible.

You could always weld the new disc to the tower, and to the bolts if you preferred, for even greater strength.

Sounds like a good idea.  At the very least I would reduce the protruding length of the threaded studs a fair bit.

[Peter Drew]

If the complete rig is well balanced then the weight will be bourne vertically by the pier. Concrete is pretty good in compression. 

[mercier57]

Thanks for replies and ideas! 

 

Indeed i could shorten the threaded bars. I made them so long that I have enough space under the final adapter plate to be able to deal with the center screw to the mount. I have an additional disc like trazor mentioned but only 6mm thick, but I still have the old EQ6 adapter plate which I could mount in between.

 

But I think it would make more sense just to shorten the bars.

 

@ Peter, thanks thats what I thought too, but thus I'm not an civil engineer I have/had the concern that under the heavy load the top part, the 36 cm(50cm) of the pier together with the concrete (0.1^2*pi*0.36m^3*2400kg/m^3 = 27kg) may break from the rest well anchored pier at the ground (around 1 t ) But yeah there shouldn't be any lateral forces only a vertical one at the center....

[ollypenrice]

Thanks for replies and ideas! 

Indeed i could shorten the threaded bars. I made them so long that I have enough space under the final adapter plate to be able to deal with the center screw to the mount. I have an additional disc like trazor mentioned but only 6mm thick, but I still have the old EQ6 adapter plate which I could mount in between.

eq8mounted.png

But I think it would make more sense just to shorten the bars.

@ Peter, thanks thats what I thought too, but thus I'm not an civil engineer I have/had the concern that under the heavy load the top part, the 36 cm(50cm) of the pier together with the concrete (0.1^2*pi*0.36m^3*2400kg/m^3 = 27kg) may break from the rest well anchored pier at the ground (around 1 t ) But yeah there shouldn't be any lateral forces only a vertical one at the center....

What about some steel straps from top top bottom on the pier to bring tensile strength in the case of an accidental lateral shock? It might put your mind at rest. Concrete in compression and steel in tension is a classic combination in construction.

Olly