An obvious pier question

[AlistairW]

Hello - I am building a pier for my HEQ5 pro mount. The central bar that the alt\az bolts 'lock' on to should point North. Simply put when I set all this in concrete, I presume it is good enough that it simply points roughly North, and there is enough scope for ajustment to align precisely.

Thanks

Alistair.

[Pompey Monkey]

Hello - I am building a pier for my HEQ5 pro mount. The central bar that the alt\az bolts 'lock' on to should point North. Simply put when I set all this in concrete, I presume it is good enough that it simply points roughly North, and there is enough scope for ajustment to align precisely.

Thanks

Alistair.

"good enough" or as good as you can?

Measure twice, cut once... Perfect planning prevents... etc.

But yes, as long as the error in positioning of the dog is within the azimuth adjustment range, it will work.

[1parsec]

As Pompey says. 

Also if you can make a reference line on the ground or similar to Polaris on a clear night it will help a lot when pouring the concrete and setting the top plate.

Dave.

[ollypenrice]

I have to say that I'd be a bit careful here! Two people I know got the pin wrong enough to need some re-drilling. The range of azimuth adjustment is not huge so I'd find your current local magnetic deviation and factor that in to your compass reading. I'd also be sure that the compass were not being affected by any nearby metal, as well it might be. Or, best of all, you coud do a polaris sighting. Cut a piece of ply into a triangle with your latitude as the angle from the horizontal and sight along it to Polaris.

Olly

[Bizibilder]

Most mounts claim +- 10° azimuth adjustment - and this is less then you might think!!  Well worth "sighting" north and carefully marking out so you set within +-2° or better.  it's easy to get that degree of accuracy if you are careful.

[D4N]

Be careful applying magnetic variation to the compass reading, on a normal compass this is fine but on devices like the iPhone it will already be applied unless you set it to display magnetic North.

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[Gina]

I used the sun, using a nail and piece of card as a sundial, I marked the shadow of the nail at several times either side of noon.  Then interpolated the readings to give north.  You need to factor your longitude in unless you live on the meridian.  Note also that noon is not precisely at 1pm (summertime) but can be several minutes out though with the tolerance of the azimuth adjustment this should be negligible.  I had the card sundial attached to my pier head.

[AlistairW]

Thanks for the answers - glad I asked the question now

[D4N]

The shortest shadow will be the one when it was noon local time if you use the sundial trick. This shadow is the one that points North.

This is meridian passage of the sun and used to be used by ships to determine latitude as the altitude of the sun at this point is closely tied to your latitude but not longitude (which was harder to work out as for a long time they didn't have clocks that worked on ships).

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[kirkster501]

Will use my walking compass when I do mine.  Do not want to have to redrill! 

[Gina]

Will use my walking compass when I do mine.  Do not want to have to redrill! 

Don't forget that iron in your pier adapter (or pier) will completey upset a magnetic compass.  But one way to use a compas if you can see your pier from a distance to the north is to move until your compass finds your pier due south and then put a stake in the ground where the compass is.  Then if you align centre and mark the angle of the stake you will have magnetic north.  Correct for magnetic deviation and there you go   This method could also be modified to work from other directions.

[Dave Lloyd]

Surely something as simple as placing a mobile phone with google maps open on top of the pier will suffice to determine north.

[D4N]

Surely something as simple as placing a mobile phone with google maps open on top of the pier will suffice to determine north.

Not really, the flux gate compass in the phone relies on the Earths magnetic field to determine North, the magnetic field will be deviated by the steel in the pier giving a false reading.

Unless you have a concrete pier, then you will be ok

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[Gina]

Rebar is iron though

[Dave Lloyd]

Showing my ignorance again.:-)

[DougAtDallington]

I built a concrete pier for my obsy around a steel RSJ and had similar concerns over the use of a compass to find true North.

In the end I set the M10 threaded 'legs' attached to the modified Skoda brake drum used for the mount base in the wet concrete and aligned it the best I could.

Then, when the concrete had gone off I removed the brake drum plate and had the fixing holes elongated into slots so I could rotate the mount a little to compensate for any misalignment. It worked!

[laser_jock99]

Alternatively- have a steel tube pier and drop-in puck machined up that is fully 360 degree adjustable!

Should be future proof for the Earth's entire 26,000 year wobble........

[AlistairW]

Ok, so I have put some Lat\Long details in to a website I found, and it tells me the following ..... (see pic)

So does this mean I only have to worry about 1 degree (ish) of variation .... so if I simply set my pier to point magnetic north, as long as the mount can handle a few degrees of correction then I should be ok ?

Thanks

Alistair

[Earl]

I liek the way my compass swings to the mount as it get near it... auto aligning LOL I wish

[D4N]

Be aware that the data they have for the Earths magnetic field will not take account of local magnetic anomalies. High iron content in the rocks, nearby metal or power cables can cause further deviation preventing the compass from pointing to magnetic North.

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