Meru's Pier Build

[Meru]

Hi all! I've finally decided to get my pier done :DI am sick of having to set up from scratch, balancing, PA, setting up cables and packing down. Actual weight of what I currently use is ~40kg, but will use 60kg as a conservative ceiling. My friend is a metal worker and he will be doing the build for me. He comes highly recommended by me to anyone else who may need a contact for any custom fabrication :thumbsup:

To my disposal is either a Square Hollow Section (SHS) measuring 150mm with a wall thickness of 6mm, or another measuring 120mm with a wall thickness of 9mm. As outlined by Troy (http://www.iceinspace.com.au/forum/showthread.php?t=114370) and from my own calcs, the 150mm has better torsional stiffness and less likely to bend. Thus this will be the pier column :) The base plate and top plate will be 300mm square with a thickness of 15mm. After talking to rally I was advised I would need a large concrete slab since my soil is clay, ideally deeply rooted so aiming for 1m^3 of concrete.

I am confident I will be able to pour it almost perfectly level thus am not concerned by an uneven footing. My current dilemma is whether or not to go for the 'rat cage' setup :shrug:Without stirring up another heated debate I do believe that the bolts would be the weakest link and unnecessary. I am debating between the following three options, listed in preference:

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1. Base plate of Pier bolted directly to slab. The top plate is welded directly to pier and the EQ6 goes onto it. This allows for maximum rigidity :D However I have no idea how to access the M12 bolt to secure the EQ6 to the top plate, since that would be within the pier column. Am thinking about cutting out a 100mm square hole on the side of the pier column to grant access to the bolt but concerned about losing structural strength. Is this the best way? :question:

2. Base plate of Pier bolted directly to slab. A rat cage is created by welding atleast 3 solid bars of steel between the top & adapter plate, with the distance between plates minimised to ~100mm. This way I can reach the M12 without cutting into the pier nor using bolts.

3. Base plate of Pier bolted directly to slab with a standard rat cage arrangement using bolts. The bolts would be *atleast* M20 high tensile steel bolts which are threaded throughout the shaft, with the distance between the adapter & top plate at ~100mm. One end of the bolts would be welded to the top plate so nuts are only required on the adapter plate.

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So what do you guys think? I'd prefer option 1 and if not, then option 2. The only thing stopping me is how to get access to the M12 bolt for the NEQ6 with option 1 :question: I am not sure if cutting a section on the side is a smart idea. Can anyone please provide their opinion on this? How do people without the rat-cage arrangement secure their mounts?

Thank you for reading :hi:

[Meru]

Article shortened, no one has ideas?

[JZ]

Hi Meru,
I'm going along a similar path. I had a pier made up out of 150mm square with a 12mm top plate. I'm regretting not going for 15mm as the welding did cause a slight bowing of the top plate. On your rat cage dilemma, a friend turned up some spacers for me out of 50mm round steel. Four pieces all identical with 13mm hole down the middle. I use these with my 12mm thick mounting plate and 12mm bolts when I go to Heathcote and they make a very solid mounting! If you can get a set like that made up they should serve you very well. Go for about 75mm length. Mine are 50mm and it's a bit of a squeeze to get to the centre bolt.

Cheers,
Ross...

[Meru]

Hi Ross,

Thanks for the input! I didn't think about the bowing from welding, I thought 15mm would be overkill but now feel better about it :) That's a very good idea with the spacers + bolts, I was thinking in the future if I ever needed to change the top plate for a different mount then it would be easier to go for the rat cage approach.

Can you post a pic of it's layout? I'd probably go atleast 70mm as you mentioned, probably 100mm

[JZ]

Hi Meru,

Sorry, I don't have a picture as yet. Next time I go to Heathcote I'll take one. My pier is not installed as yet. Hopefully soon!

As for the welding, it really depends on the way it's done. Unfortunately I didn't think of it when I ordered mine from the fabricator and he just did a standard continuous weld which causes shrinkage on the weld side bowing the steel plate. It's only a milimetre or so but when you put a straight edge across it it's very obvious, thus making it a little tricky to get it level. So I'm stuck with a rat cage whether I want it or not. That doesn't worry me as I was going that way anyway.

Cheers,
Ross...

[alistairsam]

Hi,

That's right about the bowing. I'm told its to do with the heat, that's why they have small welds spaced out.

Meru, one other thing you need to consider is that although the FL you're imaging at is fairly long, you are using an OAG which will see any flexure, be it on the mount or pier and correct.

Moreover, seeing and turbulent air will cause your star to jump around a lot more than the stepper or load inertia would make it jump. just zoom into to the guide star and keep exposures at 100ms and you'll see the star jumping around, but that's just seeing.

So I wouldn't over Engineer, rather make practical compromises if required but ensuring you stay within your target parameters.

As for the rat cage, yep with numbers its not ideal, but in practise, i'd be interested to see flex caused by the 4 x M12 or M16 bolts for a load of the EQ6 and an RC8.
It helps to have a levelled base for the mount to start with, so handy to be able to adjust.

Cheers
Alistair

[I.C.D]

G"Day Meru,
I used two top plate's one (12mm) welded to the pier and the other bolted.Doing it this way it allows you to adjust the top plate level if the bottom one becomes warp from welding .
I also have a hole in the plate welded to the pier to put sand in to help lessen the vibration ,if you want a picture let know
Ian C :thumbsup:

[Meru]

Hi Ross,
I see what you mean, I will talk to my friend and make sure to avoid that as much as possible. And so your pier will be installed in heathcote? Very jealous!

Hey Alistair,
I know what you are saying, but if I'd be going to all this effort for the pier (which I will keep for many years) then I'd rather just make sure I get the sturdiest and well-engineered design as I possibly can. Obviously it doesnt not compare to having a huge mount with a CDK on it but every bit counts! Realistically it won't make much difference, and I'd be interested too to see how much a difference bolts can make, but if I have the option to avoid it then why not. I'm really not that fussed about the ability to level the plate

Ian,
That's a good idea, I've got 30kgs of sand lying around so I might do that. I suppose a second plate would overcome the warping which is nifty. Pics would always be appreciated :)

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So far the best option I can see is to go for a rat cage, with one end of the bolt welded on the top plate. This would allow for me to change the adapter plate in the future if I ever change the mount, take into account any warping with the bolts steady in place. I also quite like Ross's idea of steel spacers around the bolts, that would definitely help. I may weld the spacers in place so if I dont really need the bolts to level, I can tighten the adapter plate onto the spacers. I will get some drawings up this weekend and see where it takes me!

Thanks for all your help thus far :D

[I.C.D]

G Day Meru,
If you want a picture of my mount can you send me your email address please as I don't how to sent it via this site
Ian C

[johnnyjetski]

Hi Meru,

Just a quick pick of when I installed my commercially made pier that a guy threw into the deal when I purchased his 8inch Meade LX-90. (I was so happy).

I used 4 foot lengths of threaded rod, all held in place by plate steel, then concrete poured with the last 4 inches protruding to bolt the pier onto.

There is just enough room to get your hand in between top plate and adaptor plate to change equatorial heads/wedge. I use it with an EQ5 head and 150mm refractor.

Hope it gives you some ideas

[I.C.D]

G'Day Meru,
I think I have work out to send you the pictures of my pier .

[Meru]

Thanks for pics guys! Yup the images came through Ian. John you got quite lucky getting the pier for free, and you must have had a hard time keeping all those rods straight during the pour! Definitely a nifty idea, I don't think I'd be game to do that. I'll just stick with Dyna-Bolting for now :P

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After looking around and having a good chat to my friend, we both settled on a design for which I have drawing up a quick spec sheet on my whiteboard. Please ignore the childish handwriting and lack of major technical drawing experience :rofl:The design is a rat cage but a modified approach; thick spacers separate the two plates, with the bottom of the spacers welded to the top plate. On the adapter plate I will drill out holes for M16 bolts which will then be tapped into the spacer. This will give better stiffness and stability (wider contact area) compared to using just bolts, without losing the ability to have a removable adapter plate. I have accepted that this design will not allow any adjustments to be made for leveling purposes. The lateral spacing and height of the spacers came from measuring the dimensions of my fist so I know I can get in comfortably :thumbsup: Note that I have not really included any details on the exact receptacle required for the mount to sit on. I just couldn't be bothered drawing that detail :P

It will be secured to the concrete slab via 8xM16 dynabolts (4 on the corners and 4 on the midpoint of each side) and atleast 125mm deep. I was thinking about going bigger but M16 is largest drill bit I have for this work and I'm sure 8 bolts will keep it planted firmly :D The concrete will have reo mesh in it as well. The overall height of the pier will be ~900mm which places my telescope just about as high as I feel comfortable securing and removing by myself ;)

My friend will start working on it this week; lets see where this goes! In the mean time I need to start looking up places to galvanise/powdercoat. Anyone have any recommendations or ideas on pricing?

[johnnyjetski]

Drawings look good Meru, however I think the 110mm between top and adaptor plate is a bit much. My pier has that dimension at 50mm. Just enough needed to get your hand in as you said.

Also think about using the 4 foot lengths of threaded rod in the footings. The rods are held in place by plate steel every 18 inches or so. so you have a sort of box kite frame that the concrete is poured around.

Good idea to orientate to true north as well.

http://aa.usno.navy.mil/data/docs/AltAz.php

This site helped to get the suns azimuth at any given time, so using the shadow cast on the adaptor plate of a centered pencil, reasonably accurate true north orientation is quickly achieved.

John

[Meru]

Hey John,

That's a nice looking refractor there ;) I have no idea how you fit your hand in just 50mm! I asked my friend to reduce it to 90mm as 110mm was too much, but I'm happy to leave it at that height. I probably will wish in the future I went lower but eh, compromise is everything in this hobby!

That's a good approach with the bolts, I might have a think about going down that path. I already have some M16 190mm Dynabolts, so I suppose the question becomes would it realistically make a difference between the two options? I just dont like the idea of the bolts sticking out and the effort required to get such a footing in the concrete.

Thanks for the link, that's exactly the approach I was going to take :)

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In other news, my pier is coming along now :D The base plate has been drilled and machined, the SHS cut to length (chose 770mm in the end) and the spacers cut to 90mm. Wish time would hurry up!

[johnnyjetski]

Progress sounds good Meru. Looking forward to hearing more.

Ian, That pier setup looks great. :)

Regards, John

[Meru]

Thanks John,

The build is going well so far, I have some pics from the workshop. I also asked to make the spacers 80mm, figured 90mm would be too much. Not looking forward to the dig in my backyard now :P

[johnnyjetski]

Looks very good Meru....Those 8 dynabolts definately look as if they are up to the job.

Start digging Meru. I was lucky because my backyard is very sandy it was easy digging, however I came across a large pipe 3 foot down. Had to move slightly to avoid it.
Just have to be careful.

John

[JZ]

Hi Meru,

I was up at Heathcote on the weekend and had my setup on one of the ASV piers. The wide spacers make it solid as a rock but as they are a bit short I put a big nut on top of each so I can get the spanner in more easily.

Looks like you are making better progress than I am with my pier.
I hope to put it in in the next few weeks.

Cheers,
Ross...

[Meru]

John,
Thanks :) Yes I suspect I may have a sewerage pipe running under where I want to dig... best to double check me thinks ;) Good thing you found your pipes.

Ross,
Good god those are thick spacers! Looks like it's going nowhere fast hehe. I'm pretty you're going faster than me, I have yet to get the adapter plate re below

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Progress on my pier, the bulk of it is done! Last thing left is to make up the adapter to fit the NEQ6. Just waiting to get the NEQ6 measured up and then it's done :D I really should start the dig, I've been very lazy with it :(

[alistairsam]

Meru
wouldn't you need gussets on the sides, I'd think those would be the weakest links in the chain, rather than the rat cage...

Alistair

[johnnyjetski]

Meru, That looks excellent.

Alistair could be right with the gussets. The heavy duty spacers are a great idea too.

Well Done!

John

[Meru]

Thanks John, yes I think in hindsight I'm glad I went with the spacers rather than just bolts.

I'm curious to know why gussets would be a bad idea Alistair? I don't see how it could affect the rigidity in any negative way? I haven't added them yet

[alistairsam]

Hi Meru

I meant not adding them would be a bad idea.
If you are adding them then it's fine

alistair

[MattT]

Hi Meru,
Re powder coating your pier. I tried in vain a month or so back to even get a quote from powder coaters out in Eastern Melbourne. The only one who did reply was Mark Smith from multi coat. Minimum charge is $82.50. I wanted a 1.5 metre aluminium tube for a refractor I was building done. He replied too late for me as I painted it myself. I rang emailed several places….at least he replied, but he took nearly two weeks.
Good luck
Matt

[Meru]

*Slaps forehead* sorry Alistair I read your post wrong, yup I'll be adding some. However with 16mm thick steel and the SHS pier column almost as wide as the mount's diameter, I don't think they would really make any difference. I suppose it's the same as the rat cage idea, theoretically yes but practically no. But I'd rather overkill :D

Thanks for that Matthew, damn that's bad news. I still haven't looked into it yet but with that long of a wait time and difficulty reaching anyone I best start soon. I suspect with December shutdown approaching I might have to wait till next year. Do you think painting it would be sufficient? Or go for a coat?

[Steffen]

I think neither adding gussets nor avoiding "rat cages" have much to do with the load bearing ability of the pier, or its resistance to bending under load. Rather, they improve its dynamic properties, like its propensity for resonant oscillation – sometimes called "pier-induced bad seeing" ;)

Cheers
Steffen.

[Meru]

Hi all,

Hope everyone has had a very good break and christmas :) That's a good point Steffen, never thought about it like that. I suppose I was too fixated on the structural strength rather than it's dynamic properties. My friend has added two gussets to each face on the base plate (I think it's 100mm on the base plate and 150mm on the pier column). I dont have any pics unfortunately yet but I will soon!

In the mean time I finally started the dig. I managed (LxWxD) 600x600x400 in about an hour and a bit before I gave up :screwy: I plan to make it 700x700x500 before commencing the pour :thumbsup: Took some pics but honestly so many you can take before it just... looks the same :P Got the usual "So who you planning to bury?" from everyone :rofl:thanks for reading!

[Meru]

Buzzing in with an update,

Pier is almost done! Should be home by the end of the week. Attached are some pics of the adapter plate being made up and other misc items. Can't wait for it. I have also found a place from a colleague who gets her car parts treated, seems like it shouldnt be too expensive to get the pier coated. I will wait for the pier before I get a quote and take it from there.

[Meru]

Hi guys,

It's been ages but another update yet! The pier was finished a few weeks ago and man was that thing is huge!! It was very much oversized for my needs, very happy and impressed with the workmanship and quality :D All up it costed me $220 which is dirt cheap :eyepop: I will take some pics of it soon. It still needs to be coated or galvanised, a colleague at work recommended coburg plating as she gets all of her car parts done there and said its pretty good. I might take it there this week.

In the mean time I have decided to concrete the entire area surrounding the pier so dug up the ground to suit. All up it's about ~0.25m^3 which equals roughly 25 bags of 20kg premix concrete :lol: I rang up a few places and their minimum was 0.4m^3 delivered for $230, if I did it myself it would run about $150. So might just do it myself :thumbsup:

[johnnyjetski]

Well done Meru....That is dirt cheap $220. No such thing as being oversized for your needs Meru. Bigger the better.... : )

Look forward to the pics.

Regards, John

[Meru]

Hi guys!

Thanks John, yes for the price it really was cheap :) Another update now! It's all done! I widened my slab so it's now 0.4m^3 and I found Vicmix to have a very good price, it was ~$160 for the concrete. I also decided to pour the bolts in too rather than drilling. I made a template of the pier's holes on wood & some metal sheet and used them to keep the bolts aligned during the pour. I rested them on the rebar and used wooden blocks to level the rebar/bolts.

I know that the wooden blocks and metal sheet may disintegrate over time and leave cavities but I think the slab will hold up fine :) now time to paint the pier and start imaging!

[Meru]

Hi everyone,

Very excited to *finally* chime in again. I painted my pier with cold gal (yes, I'm lazy) and last week got around to installing it and using it. Getting the bolts in the concrete to match up was a bit difficult, in the end resorted to gently using a hammer to move them into position. Hardly scientific I know :P I also purchased a heavy duty BBQ cover from bunnings as a cover.


Having a pier is by far the best thing anyone can ever get in this hobby, if you're into astrophotography :D First night I used Alignmaster to get to within an arc minute or two and got 2min unguided easily. I imaged two targets over three nights, and spent another two nights faffíng about with the pier and automating my capturing. Over those nights the pier held PA well and was able to pack up & it was great being able to go from zero to imaging in 20min, and vice versa.

Most useful feature is that the top plate separates from the pier. So during period of known rain and/or overcast I can simply remove the top plate with the mount attached. This way when I put it back on, the mount is very close to good PA and needs minimal adjustments.

[strongmanmike]

That looks great Meru! Solid looking pier. Much better than having to setup and polar align every night! Happy imaging!

Mike

[Meru]

Thanks Michael! Yes it makes such a big difference, just need more clear nights now :D

[traveller]

Looking great Meru,
I thought you are living in the city? Can't resist the "dark" skies of the burbs heh? :P
Bo