Obsy Qs??

[Gina]

I made my pier base a truncated pyramid too as this seemed a good idea

[laser_jock99]

There's more snake-oil in there than good advice. He's dressing words up to sound pseudo-scientific...what exactly is torgueage? Rotational shear vibration? It sounds impressive to someone that knows very little, but in reality it's made-up guff.

His comments about the welds? Absolute rubbish.

And the slots making the base plate less rigid? Rubbish. There's a million steel-framed buildings held up and loads of them have slotted end-plates (I used to be involved in engineering and steel-framing). Those base plates look like 12mm steel.

The main message is to avoid the 'wobbly bolts'.

Go for something like this- a machined 'puck' that drops straight into your steel pier:

The EQ6 main retaining bolt can be accesed through the 'owl holes' in the pier tube:

[Gina]

Or the puck could be a nice close fit and retained by bolts into tapped holes - this is how the NEQ6 pier extension is arranged. Then you don't need owl holes.

[ollypenrice]

Imaging on a tripod? Nah...it's rubbish

Ask Olly. I'm sure that loads of his customers rock and roll up with tripods and produce stunning images.

I made my base 3' x 3' for that reason. I have the shed up and will be chopping the roof off to make it slide. At some point I'll sort a pier out. Until then, the tripod is going to sit on the base.

Here's the pier base poking through the shed base

Indeed! Yves' 14 inch ODK with 2.4 metres of FL stands, unattached, on a concrete floor and knocks out thirty minute Ha subs like clockwork. The pier is just the propietory Mesu with three adjustable feet. Personally I think some of the American inspired concrete pouring is a bit of internet madness that has taken on a life its own. You can't have too much concrete but you can have a hell of a lot more than you need.

Here's what Yve's freestanding setup has to say on the matter;

The big plus with a pier is that you get longer before the flip and, frankly, that's about it. Oh, you don't fall over them either! Pier for preference but reality check on the concrete would be my take.

Olly

[Gina]

Why does what the mount's supported by make a difference in the time before a flip? I don't understand that.

[Gina]

I'm doing wide-field OIII imaging of the Cygnus Loop ATM and on finding the guiding not working very well I checked and I was past the meridian so I slewed to flip and then re-started PHD to re-calibrate.

[ollypenrice]

Why does what the mount's supported by make a difference in the time before a flip? I don't understand that.

SImply because longer OTAs collide with the spread out legs of a tripod before they collide with the slender pier. Mounts way past the Meridian often go off a bit on guiding, proably due to balance, but many carry on regardless. Try adding a bit of weight to the east if you are losing guiding accuracy when you are weights high. ANything is better than doing a horrible flip!!! (Except using a fork and wedge, he added hastily... )

Olly

[Chris]

This was the adapter that I had made by a local machine shop.... £80

Malc, this is still the prettiest adaptor I've seen to date:D

[Zakalwe]

The main message is to avoid the 'wobbly bolts'.

Go for something like this- a machined 'puck' that drops straight into your steel pier:

The EQ6 main retaining bolt can be accesed through the 'owl holes' in the pier tube:

That's a very nice way of doing it. When I get to do mine I intend to use a 150x150 square box section with a flat plate welded to the top. The central mounting bolt will be accessed through a hole cut in the side. This, for me, is the simplest solution. No machining, no tight tolerances and easy to fab up.

I don't subscribe to the whole "wobbly bolt" thing though. I have done the calculations on the bending moment required to deflect a 16mm bolt, and it is a lot (IIRC, something like a 50Kg end load at 90 degrees to the axis of a mild steel bar 125mm long deflects the bar by half the width of a human hair). 4 x 16mm bolts are not going to go anywhere, especially if they are in tension, like Gina's setup.

[ollypenrice]

Yes, the steel box Owl's Nest does seem like a good idea.

I also agree that the bolts will be fine. My real point on this was to note the irony of some setups in which monumental volumes of concrete go into the bottom but three bolts are all that's needed at the top. That can't be consistent.

It's interesting to look at the design of the highly regarded Astro Physics portable pier. There's one here at the moment. It consists of a wide diameter but thin guage pier which attaches to three long outward pointing feet, in effect a flattened tripod. The neat bit is that the mid height of the pier is connected to the outer ends of the feet by slim steel tensioners, another 'special case' of a tripod. These carry AP1200s and big, long FL instruments. I suspect they have the best stiffness to weight ratio in the business.

Olly

[Zakalwe]

I am toying with the idea of a standard Skywatcher pillar (cost £200). Replace the feet with chemfixers bolted to the pier base. If it needs more rigidity, then a length of 3mm steel cable running from the end of the pillar legs up to about .5 m below the pillar top plate. These would be tensioned with standard turnbuckles. Doing this would put the whole pillar in tension and make it extremley rigid. No fabrication required, all off the shelf components and would only require a couple of holes drilling into the Skywatcher pillar.

[Zakalwe]

This is the sort of thing that I mean. One of these:

(take the wheels off and replace the screw-down feet with suitable threaded studding. Drill suiltable holes into the pier base and drop in some chemical fixers that will bond the studding into the concrete. A nut can then be used to secure the pier to the studding)

made to resemble one of these:

(Astro Physics portable pier)

By using some of this:

and three of these:

Three holes drilled into the pillar at a suitable height allow the hook of the turnbuckle to hook into the pier.

[Zakalwe]

Back to the ridiculous YouTube video of that guy confusing everyone with chewed grass*

Karl Teuwen must be fuming as the slots in his base are obviously wrecking his images.....

*bullshoot, if you know what I mean.

[Paulus17]

MMMMMmmmm,more to think about??

Thanks everyone some great info and images that i'd be more than happy with.

But just to make it a little clearer for me,do you think what i would be doing would be suitable,which would be the 10" ducting for the pier,filled with concrete,a pair of suitable brake discs bolted together with the gap between to bolt the mount to,and a suitable concrete plinth to hold the pier??

[fwm891]

If you're going for a concrete plinth to take the pier, why not just sink your ducting down into the plinth (base slab) with some re-bar running from the slab into your pier and concrete the whole thing in one go. Your pier and base slab become one item! You can then fix your brake disc into the top of the pier when you cast the pier.

[ollypenrice]

I cant's see that concrete is the right thing to put in the pier. I doubt you need anything at all but something with damping properties would be a better idea, I think. Sand and old motor oil comes up as a suggestion. Concrete, being hard, will not stop resonances.

By the way, Karel's setup has grown a bit since then!! (It's not far from me.)

Olly

[Paulus17]

If you're going for a concrete plinth to take the pier, why not just sink your ducting down into the plinth (base slab) with some re-bar running from the slab into your pier and concrete the whole thing in one go. Your pier and base slab become one item! You can then fix your brake disc into the top of the pier when you cast the pier.

That is what i was intending on doing,but setting the ducting in first,making sure its plumb,let that set and then fill with concrete.

then the lower brake disc would have long threaded bar going through it to go into the wet mix and set to hold.

Then the top disc with the 60mm recess,and pin welded to it would take the mount and fix from underneath so i can remove if neccessary.

Would this be ok though before i go ahead wih it all?

[Paulus17]

Yes Olly the sand and oil would be good,i have that in my lathe bench.

[Paulus17]

Would it be ok to put concrete in the bottom of the tube,then a sand/oil mix,packed in, and then cap that off with several inches of concrete to set the brake disc in??

How high does the pier need to be any specific height??

[Gina]

I don't think so - you want concrete all the way for rigidity. The pier wants to be high enough that the scope can see over the obsy walls but not so high that the scope catches the roof.

[fwm891]

I cant's see that concrete is the right thing to put in the pier. I doubt you need anything at all but something with damping properties would be a better idea, I think. Sand and old motor oil comes up as a suggestion. Concrete, being hard, will not stop resonances.

By the way, Karel's setup has grown a bit since then!! (It's not far from me.)

Olly

Olly I have to agree but - As its ventilation duct being used there is very little (if any) rigidity in it at all so it will need filling with something to give it enough strength to hold the mount and scope assembly. Concrete is probably the easiest material to work with in this instance. I've just added an 8-inch steel pier to my concrete slab and if I tap it it rings like a bell so that will be filled with sand before the mount is fixed in position.

Another option for the vent ducting is to have a second smaller duct (6-inch) inside the 10-inch. Fill the 6 inch with sand and then put concrete as a filler between the two tubes - get the rigidity of a 10-inch tube with sand damping.

[malc-c]

This thread seems to be getting very technical. I opted for the "traditional" plastic pipe filled with concrete and rebar. The 3m 160mm pipe cost me around £18. It gets a bit more expensive when going up in sizes, but you can get 200mm, 250mm and 310mm ridged pipe in 3m lengths which would do the job.

http://www.plastics-..._Socket_P-DL195

In normal use I've found my pier solid enough, I mean you don't normally go round hitting it with hammers etc to make it vibrate !! - I opted for the 160mm diameter pipe. a 250mm diameter would have less tendencies to resonate

[ollypenrice]

Sorry, I hadn't realized that the steel was very thin guage.

Oly

[Zakalwe]

Another option for the vent ducting is to have a second smaller duct (6-inch) inside the 10-inch. Fill the 6 inch with sand and then put concrete as a filler between the two tubes - get the rigidity of a 10-inch tube with sand damping.

This would be a bad idea IMHO. You would end up with a 2" thick "skin" of concrete that would be very fragile and susceptible to cracking.

Would it be ok to put concrete in the bottom of the tube,then a sand/oil mix,packed in, and then cap that off with several inches of concrete to set the brake disc in??

How high does the pier need to be any specific height??

Also a bad idea. You would end up with a concrete floating on a bed of sand.

Either make a solid concrete pier, or make a solid base with a steel pier. As for steel "ringing", then don't go round hitting it with a hammer when imaging. There's hundreds of imagers getting outstanding images when using mounts on steel tripods. All of those steel tripods will ring if they are hit.

Personally, I think that there is a lot of mythology building up around piers. Tubes within tubes, tonnes of concrete, oil and sand etc etc. Just build the thing, make it reasonably solid and don't whack it with a hammer when you're imaging. It''l be reet!

[Zakalwe]

As for height? The way that I will do mine (assuming I extract my digit and get the roof sliding!) will be to put the tripod in, see what height will suit both my 80mm and C11 (shielding it from the neighbour's lights while still getting a decent view of the sky) and then get the pier made to suit.