Pier hub mounting advice.

[Adam J]

I am currently making my first observatory. 

I have a pier mounting hub for my HEQ5pro and am wondering about the number of threaded rods I should be mounting within the concrete pier. 

It currently has 6 x 8 mm holes drilled into the hub. However, I have found myself wondering if I would not be better off drilling three of the holes out to 10mm and using only three 10mm threaded rods for mounting. My reasoning being that it will be simpler to adjust for level and easier to get under the plate with a spanner to tighten the mount down onto the hub. 

Does anyone have any thoughts / recommendations?

Cheers,

Adam

 

 

[Gina]

I used four lengths of M14 studding of but three would have been better.  Any more and there's a possibility of bending the plate or unduly stressing the studding - getting the adjustment exactly right was a problem with four.  With three this problem doesn't arise.  Just get the plate reasonably level and the PA adjustment will take care of everything - exact levelling isn't necessary.

[Adam J]

1 hour ago, Gina said:

I used four lengths of M14 studding of but three would have been better.  Any more and there's a possibility of bending the plate or unduly stressing the studding - getting the adjustment exactly right was a problem with four.  With three this problem doesn't arise.  Just get the plate reasonably level and the PA adjustment will take care of everything - exact levelling isn't necessary.

Yes thats what i thought so ill go with three, not sure if I can make M14 work though maybe M12. 

I thought that when out of level RA Dec errors could translate into each other and result in the guiding constantly chasing itself as a correction in one plane results in an error in the other?

At any rate just so long as it holds it all firmly and without vibrations.  

[tooth_dr]

I used four, three is defintiely better as Gina says.

[Gina]

M12 is probably sufficient, particularly with an HEQ5 mount though bear in mind you might want to upgrade later.  I built mine for an NEQ6 and have upgraded to EQ8 - it's as solid as a rock    We tend to over-engineer these things

[SW130p]

I used brake disks for my mount and 4 M16 rods and bolts as well as scaffold poles bolted in between to make it very solid unit.

[Adam J]

1 hour ago, SW130p said:

I used brake disks for my mount and 4 M16 rods and bolts as well as scaffold poles bolted in between to make it very solid unit.

Very nice, but I am going to try and keep the rods quite short as this in itself will minimize movement over longer rods. Is there a design reason for the large standoff you have used?

[Skipper Billy]

This is the point where many really substantial piers can go wrong. I have seen massive concrete blocks with really substantial piers then a rat box on top with long spindly M8 bolts.

I would suggest using M14 studs and use 6 of them. use three 120º apart to level the plate (although that isnt strictly neccesary but looks better) then just nip up the other three for support and strength to alleviate any flexure. Keep the studs/bolts as short as possible.

Have a look at the bottom of this page https://sites.google.com/view/astro-imaging/equipment?authuser=0  for some ideas.

I 

[sloz1664]

Another issue that is sometimes overlooked is the thickness of the top plate. I used 10mm stainless plate, anchored with 4 x 14mm stainless bolts. That scopes moving nowhere unless I command it  

Steve

[SW130p]

2 hours ago, Adam J said:

Very nice, but I am going to try and keep the rods quite short as this in itself will minimize movement over longer rods. Is there a design reason for the large standoff you have used?

It was Short when I first built it but as I used the scope more I needed to get it up higher to see over the obsy walls.

[Adam J]

When drilling the holes in the mounting plate should i drill them to the same diameter as the rods or should i make them slightly bigger to allow tilt / reduce stress during adjustment?

[SW130p]

8 hours ago, Adam J said:

When drilling the holes in the mounting plate should i drill them to the same diameter as the rods or should i make them slightly bigger to allow tilt / reduce stress during adjustment?

I had to use a bit the same size as the rod. Bought a 16mm bit same as the rod, as you drill its gets slightly bigger anyway, just enough for it without being tight.

[spillage]

I am planning to do away with steel bars altogether. I will be bolting two brake discs together with no gap between them and then use a shaped wooden block to bolt to the bottom plate wide enough to gain access to the middle of the disc.

My pier is a 6" plastic pipe filled with concrete (I may also got hold of some steel ducting to place around the pipe but only to half height to make it more stable) and at the top will cut out a section to allow the wooden block to sit in.

Once the block is unbolted from the botton disc it can then be removed from the pier leaving me a owls nest to access the bottom.

This is a little bit more to it as you also need to fit a steel rod to the block to assist in its removal.

In theory you could fit the botton disc in place and then when removed use a disc cutter to do the same but I think this would be harder work.

[ollypenrice]

23 hours ago, Adam J said:

 

I thought that when out of level RA Dec errors could translate into each other and result in the guiding constantly chasing itself as a correction in one plane results in an error in the other?

 

No, that's not what happens. A non-level mount can be 100% perfectly polar aligned. You are aligning the RA axis of your mount to the celestial pole, not your pier to the centre of the Earth. What you are thinking of is that the drift alignment method (which is surely the best in a fixed observatory?) involves doing an Azimuth adjustment in the south and an altitude adjustment in the East or West. If the mount is not level an adjustment in one of these will affect the other slightly, so you'd go back to do a second iteration of each. In fact this effect is very slight and an approximation of level is all you need to make it negligible. Once polar aligned there is no interaction at all between RA and Dec.

I'd also go for three strong bolts, short. If you have more than three I'd have thought that you would risk distorting the plane of the top plate. We have four four-point piers in our robotic shed. The trick when levelling them is to work in diagonals, so get one diagonal level with no pressure on the other diagonal, then get the second one level.

Olly

[Adam J]

I guess it would in fact lead to you being not perfectly polar aligned in a non permanent setup when using a polar scope as you would fail to place Polaris in the correct position when setting the zero hour angle. At least in the procedure I follow at any rate. However, I was thinking of drift alignment now I think of it, it is something i researched recently as I will be doing it once i have the mount setup in the obsy, just a couple more weekends of work to go and ill be away.

I am going to go for 3 x M14 studs  with 3 inches of standoff concreted into the pillar anything bigger will leave the holes in the hub too close to the outer edge and may result in cracks forming. 

[laser_jock99]

My advice is do away with the 'wobbly bolts' altogether and get a pier head puck machined to drop directly into the steel tube.

[Adam J]

1 hour ago, laser_jock99 said:

My advice is do away with the 'wobbly bolts' altogether and get a pier head puck machined to drop directly into the steel tube.

Its a concrete pillar

[laser_jock99]

7 hours ago, Adam J said:

Its a concrete pillar

Make a proper one from steel :-)

 

[ollypenrice]

7 hours ago, Adam J said:

Its a concrete pillar

I'm inclined to agree with you about doing away with the levelling bolts altogether provided you can bolt the mount down. We really need to persuade mount manufacturers to stop the foolish practice of using a design which needs access from beneath. It is a royal pain when it comes to making piers. They are catching on and making their products top-fixing, thank goodness. My next pier will have no facility for levelling, though I'll get it reasonably level to start with.

Olly

[spillage]

I had tried to draw up my plans for my concrete pier. Sorry I am defiantly not a draftsman. 

I have counter sunk a nut in the wood to bolt the wooden block to the disc and will also do a similar thing on the horizontal to help extract the block from the pier.

[smudgeball]

Hi

I was fortunate to already have a pillar mount

So I popped it down to my local blacksmith (minus legs) and it's currently getting fabricated into a pier.

Seemed daft to layout for another mount plate and pier when I effectively had one.

Parts and welding will be approx £80 compared to paying for new.

 

Neil

 

 

[Jkulin]

On 11/05/2017 at 07:56, ollypenrice said:

I'm inclined to agree with you about doing away with the levelling bolts altogether provided you can bolt the mount down. We really need to persuade mount manufacturers to stop the foolish practice of using a design which needs access from beneath. It is a royal pain when it comes to making piers. They are catching on and making their products top-fixing, thank goodness. My next pier will have no facility for levelling, though I'll get it reasonably level to start with.

Olly

Olly, are you saying that there is absolutely no need to get the pier perfectly level? For me I use a QHY Polemaster, which I find perfect, but I believe it does require to be level?

In addition in my case I will have to remove the mount at the end of the night as there is no way I could get away with an observatory in the middle of the garden, so how else could you release the mount if there is no access underneath?

[spillage]

I do not think that the mount has to be level when using a polemaster as this is just a digital form of alignment. Having the mount as level as possible makes it easier to make adjustments when polar aligning but I am sure that is all it will do.

I am not sure if I have seen anyone attach a plate on the bottom of the mount that has a wider diameter with elongated holes to attach a mount from above?

[ollypenrice]

7 hours ago, Jkulin said:

Olly, are you saying that there is absolutely no need to get the pier perfectly level? For me I use a QHY Polemaster, which I find perfect, but I believe it does require to be level?

In addition in my case I will have to remove the mount at the end of the night as there is no way I could get away with an observatory in the middle of the garden, so how else could you release the mount if there is no access underneath?

From memory the Polemaster sits on the RA housing pointing along the RA axis. What it does is measure the extent to which the RA axis is at variance with the Earth's polar axis by recording star positions as the RA is rotated.. This is exclusively to do with polar alignment and PA does not require a level mount. (Imagine having a magic steel shaft in perfect polar alignment and immovable, passing snugly through your mount's RA axis. You mount is now perfectly aligned. Raise your tripod legs so they are a foot clear of the ground and let the magic shaft support the mount. Now you can loosen your mount's PA adjusters and tilt the tripod anywhere you like, but the mount will remain perfectly aligned.) When drift aligning, a non-level mount will see interactions between adjustments in altitude and azimuth, meaning more iterations, but on a 'reasonably' level mount they will be trivial. I don't advocate a wildly tilted top plate, I merely mean that my next pier for equatorial use will not have a fine tuning function because it isn't necessary and introduces weakness.

The need for access from beneath has been eliminated on many mount designs. Right now we have here an Avalon, three Mesus and three 10 Microns (mostly not mine!!!) which are top-fixing. The makers supply a pier-top plate whcih is fixed to the pier and then a mount which sits on top of that and is bolted down onto it from above. So simple, and a godsend for pier makers.

Ironically, since saying that my next pier wouldn't have a levelling function I was obliged to give it one anyway - but that's because it is carrying an Alt Az fork mount rather than an equatorial. And I needed access from beneath since Meade are amongst those sinners who make it obligatory!

 

Concrete or steel? This pier has proved to be a great success and both easy and cheap to make. I'm a concrete convert!

Olly

 

[Jkulin]

Thanks Olly for taking the time to reply, I fully understand what you are saying and would love to be able to have a permanent Observatory in my garden where I never had to worry about removing the mount after each session or indeed worry about the UK rainfall eroding the soil and with two clumsy boxer dogs barging into things, it might be wise even if never needed to have the ability to re-level.

I'd love to have a mount such as the Mesu 200, however having just acquired an AZ-EQ6-GT I need access underneath for nightly removal and refitting (I just when I say nightly as our clear nights have been atrocious of late so more like yearly :-) ).