Pier design - seeking opinions on the rat box

[niko]

Hi,

this video

https://www.youtube.com/watch?v=AOeLnecOMeg

suggests that the "rat box" set up is a weakness in the pier yet it seems to be almost universally adopted by do-it-yourself'ers.

The video suggests a solid structure with a cutout to access the underside mounting bolt. This obviously adds cost to the build.

I wonder what people's thoughts are...?

Many thanks

niko

[RobF]

Its probably not a good idea at all if the screws are small, the distance between the plates is long, and the mount and scope are large and heavy. For most chinese mounts with reasonably large PE I'd be curious to see proof from anyone showing how undamped vibrations cause problems that are significant versus PE and tracking.

For those putting big RCs on PMEs, I suspect I'd be coughing up more to have a custom mount without the "rats nest".

[Joshua Bunn]

For a permanent setup, all that's needed is an adapter plate bolted directly to the top of your pier plate, then the mount bolted to the adapter plate. Its as solid as a rock and does not involve a mount sitting atop of 4 leveling bolts. Its not necessary to level the bass of the mount to achieve polar alignment.

[traveller]

Hi Joshua,
Can you secure the mount on to the pier from top? AFAIK, EQ6 mounts need to be secured from the bottom, hence the rat cage approach. Also, how do you make AZ adjustments once the mount is securely bolted onto the pier?
Thanks
Bo

[Merlin66]

Bo,
I have a pier with a M12 x1.75 (I think) bolt in the top.
I also have the 200mm NEQ6 extension piece.
This screws securely onto the bolt - tight!
And you still have the Az adjustments on the EQ head etc.
Seems to work very well..

[Joshua Bunn]

HI Bo,
In my case, I can secure it from the top, I guess that doesn't help you :question:
Another option is to make an adapter plate, and bolt your mount to it with a bolt from the underside up (without it being on the pier yet). Then bolt the adapter plate down directly to the pier. You would need to get the Azimuth orientation somewhat right before permanent bolting down, but from my understanding, there is room for azimuth adjustment on the mount head as well.

Alternatively, you can do what you see in my picture, but cut a hole for your hand, so you can put a bolt in from the underside, on a pier with a big enough diameter, this is not going to significantly compromise its structural strength.

Josh

[traveller]

Thanks Ken and Joshua for your input.
My plan is to bolt the adapter to the mount head first and then bolt the entire assembly to the pier.
As the adapter and mount effectively becomes one unit, I am looking at cutting slots to the top plate of the pier, which allows for some az movement. I hope that makes sense. I will do some drawings and post it up later to gauge further opinions.
If this approach does not work, I will look into the pier extension which allows for az adjustment as ken mentioned below, and allows for under mounting of the head.
Thanks
Bo

[niko]

Bo,

more and more I'm leaning towards a concrete pier though I am speaking to a bollard place in Melbourne about getting a 220mm bollard from them.

Will probably get the pier extension from Bintel in order to use the adapter plate.

Sadly my local metal fabricators just can't deal with any of the big stuff needed for a decent mount/plate.

cheers

niko

[Merlin66]

niko,
It would be much easier to incorporate the standard extension (200mm) into the pier design.
Just needs a M12 x 1.75 bolt, about 30-50mm thread length in the top centre of the "base" unit.

[niko]

thanks Ken - that's my thinking too

[OICURMT]

:rolleyes: :screwy:

[el_draco]

So you build a big heavy walled steel pier, fill it with some anti-vibration material then hang a big super sensitive moving mass off four long, thin bolts.... :screwy:

ZERO benefit, massive cost!

[ZeroID]

My pier is a 250mm concrete pipe for the first 900mm or so. I may one day fill it with sand or cement but it certainly lacks any resonance when I hit it. For some reason concrete does not ring when struck. I'll eventually extend it with a cast head when I feel the urge and run out of other projects.

[jenchris]

Ok I have a mount thus:
The pipe is plastic filled with concrete/steel and there are only three bolts on the ratbox.
I can grab hold of the focuser knob and twiddle it with the bahtinov showing on APT on the screen at x10 liveview and the image moves less than 1/20 of the screen width About 3.6 seconds of arc. There is no vibration when I let it go.
So I guess the three bolts do not interfere with my rigidity or strength much.