Haig Mount

[jjjnettie (Jeanette)]

Got a quote yesterday for a steel pier.

50x50 3mm box section @1500mm
Cut to 26.7 degrees (gotta check that) on the top
A 60x100mm plate welded on the top
Section of whitworth bolt fixed into the top plate
Total Cost approx $25

Am digging the hole today while the ground is wet. How deep should I go?

[bojan]

Like for planting a tree: ~40-50cm deep, I would say, ~30-40cm in dia or square should be more than enough for your purpose.
You may need 2 or 3 packs of premixed concrete (Bunnings).
Do not drop the steel pipe all the way, allow ~15 cm of concrete on the bottom. All depends on how much of pier you want to have above the ground.
I think this will be useful for something bigger in the future too :-)
Good luck,
Bojan

[Dennis]

Hi JJJ

I know it may be a little rich, a city boy telling a country girl what to do, but try to get the altitude and azimuth aligned as accurately as you can. I assume the top plate is not adjustable, so you can always insert shims between the top plate and tracker base to touch up the alignment.

Somewhere, I once read (for heavy supports) have approx 1/3 of the post below ground.

Nice to have some wet soil to dig into eh.

Cheers

Dennis

[jjjnettie (Jeanette)]

I'll be very careful with the alignment, there's no allowances for error at all. I guess I'll have to sort out some framework to support it, unless I want to hang on to it until the concrete dries.
That first 15cm of concrete, should it be put in a few hours before to make it firmer for support, but mushy enough to push through it a bit? (know what I mean?)

[bojan]

Yes I guess that will be fine...
You can even drop in some chunks of old concrete in it, or bricks or stones if you can find them to support the pier (and so you will need less fresh mixture for the rest of the job). The concrete sold in packs at Bunnings to be used for fencing etc could be very fast-setting (couple of minutes only, you just put the mix in your hole, then the pier goes in then you you pour water and thats it, after 5-10 minutes it is set enough so you can remove the support. Of course, the full grip will be achieved after couple of days and couple of buckets of water. Wet soil will also help a lot.
It may be a good idea also to weld couple of bits of steel rods and to drill couple of holes on the part of the pier that goes in the concrete, so that concrete grabs the whole structure more firmly.

[Dennis]

I've never done what you are doing JJJ, but I do recall seeing on Backyard Blitz that the guys compacted some gravel (approx 10cms) at the bottom of the post hole to allow for water drainage, and then they poured the cement mix all at once, after having nailed some support struts to the post after first getting it nice and vertical.

I think they drove some wooden pegs into the ground to fix the support struts to, which were at right angles so the post was vertical in both planes.

They also used the rapid setting stuff as they had to do the job over 2 days.

Where the post exits the concrete above ground, they also sloped the concrete away from the posts, so water would not pool on top of the concrete (if it were level or flat).

Cheers

Dennis

[jjjnettie (Jeanette)]

We've got the quick set post hole mix.
Pouring the concrete will be the easy bit, it's getting the prep correct so it stays polar aligned that concerns me most.
Fun project though.

[bojan]

Waiting for pictures taken with the new setup :-)

[jjjnettie (Jeanette)]

You must have blinked and missed them Mr Bojan.
I've posted some test shots on the first page of this thread. Taken with the Canon Powershot using 12x zoom.
One of Canopus and one of Orion. 15 seconds each, without tracking and then with tracking.

[bojan]

Oh OK :-)
But what I meant was pics from the new pier :-)

[bojan]

Double arm drive is here:
http://www.astunit.com/tonkinsastro/...cts/scotch.htm


But, there is no need for double arm... if the tracking speed is variable (see below)
http://www.keteu.org/~haunma/proj/barndoor/

[erick (Eric)]

I was going to build an isosceles design - seemed pretty simple to allow a nut to swivel and the drive point will automatically swivel. Glad to see the error of that is substantialy less than that of the tangential drive. But that's on hold until I try out my second-hand RA-driven Meade mount.

[bojan]

If you bend the threaded rod, the error is even smaller.
http://www.tucsonastronomy.org/barndoor.html

The wheel can be driven with the stepper motor, of course.

[bojan]

Threaded rod M10x1.5, bend to radius 342.834 mm will require rate of 1 turn /min.
If it is driven by stepper of 200 steps/rev, the rate will be 3.3333 steps/sec, quite reasonable speed.
This can be increased by additional gear reduction.

[jjjnettie (Jeanette)]

I've countersunk a hole in the top board for the head of my drive to slot into so it doesnt' move. This should allow me to shoot for at least 20 min before any errors start to happen.
Come winter time, 20min is a long time to sit perfectly still and carefully turn a handle. Brrrrr

[bojan]

That is what stepper motors are for :-)

[jjjnettie (Jeanette)]

LOL
If I motorised, it might as well be with a little ED80 on an EQ. Sweet.

[bojan]

Well... Not so long ago the wall clocks powered from mains were popular.
The axis that drives the minute arm is just what you need here... There was enough torque available to move the Haig mount timing wheel, if everythig was smooth enough.
Also, sync motors from washing machine programmators (or mechanical timers) were suitable for the purpose ( I was using such motor for this purpose a long time ago - it had output speed exactly 1rev per minute.... unfortunately it was lost during some unfortunate events in the past).
The output speed of those timer motors with gearboxes of course depends on the model... but then, if you have such a motor, you can always adjust the rest of the design of the Haig mount :-)
If I find something suitable I will let you know.
To start thinking about it have a look at the link:
http://www.globalspec.com/FeaturedPr...g_Motors/201/0

The amateur astronomy is supposed to be a pleasure, and not torture.....

[bojan]

I found this on ebay..
http://cgi.ebay.com/5-Small-AC-Timin...QQcmdZViewItem
They are designed for 60 Hz, so the speed here in Australia would be 20% lower. But it only means that the Haig mount arm must be 20% shorter.
120V AC power supply voltage is easily dealt with by 5kOhm, 2W resistor in series with the motor.
B

[jjjnettie (Jeanette)]

I downloaded some formulas to use for this.
One fellow made his mount small enough to slip into his camera bag!