DIY Pan/Tilt tripod head for my AZ-GTi

[fwm891]

I like to tinker and after getting a SW AZ-GTi and trying to get it aligned off a 3-way pan-n-tilt tripod head I decided to try building my own....

This is it so far.

The attached drawing shows its basic layout being built arounf a pair of roller thrust races, the outer halves of each are linked together by three (not 4 as shown in Drg) cap head bolts. The inner halves press against the Azimuth plate which is adjusted by two small knurled hand wheels (see photos) Turn both in the same direction for motion either way, Oppose directions to lock. The silver looking cylinder in a three part hinge which will take the Altitude plate (that and the alt adjustment mechanism is under construction atm).

I'm building this with about ± 5° movement in it's current config. If I change the alt adjustment screw for one of a different length I can change the range but as I will principally be using this in the UK making it 0°-90° was just adding a complication it (I) didn't need.

Photo 1 shows the upper face, 2  & 3 show the under side. The threaded hole centre 2 & 3 is a 3/8 standard tripod thread.

More to follow...

Francis

 

Edited March 23, 2023 by fwm891
Text change

[vlaiv]

2 hours ago, fwm891 said:

The inner halves press against the Azimuth plate which is adjusted by two small knurled hand wheels (see photos) Turn both in the same direction for motion either way, Oppose directions to lock.

Could you provide more detail for this?

How does it operate? As far as I can tell - it's not usual "push against central pin" configuration.

[fwm891]

8 hours ago, vlaiv said:

Could you provide more detail for this?

How does it operate? As far as I can tell - it's not usual "push against central pin" configuration.

@vlaiv I've annotated two of the photographs which I hope will help with the description.

I'm ignoring anything to do with the Altitude part of the head as it's only it's hinge that's shown at this stage of the build.

1,  The Azimuth unit comprises 3 basic parts: a lower disc (fixed to a tripod column or pier and does not rotate), an upper pressure disc (there to provide pressure to the two thrust races and a locator to the azimuth plate) and the Azimuth plate (horizontally adjustable between the upper and lower discs)

2, Both the discs are channelled to take a thrust race (thrust races are 60mm OD x 40mm ID x 5mm Thick) the channels are 60 x 40 x 4.5mm so the thust races sit 0.5mm proud of each disc.

3, The Azimuth plate has a hole 40mm in diameter bored through it (the upper disc locates in this hole to prevent sideways movement) and the link bolts between upper and lower discs pass through this hole. See schematic below.

4, the lower disc has a bracket fixed to it to take the pivot pin. The pivot pin passes through a barrel nut which is threaded at both ends (standard righthand threads 6mm).

5, The Azimuth adjustments are made via two 6mm screws one each side which enter the barrel nut. The barrel nut is threaded to a depth of circa 18mm each side. Each of the adjustment screws are threaded approx 12mm with bare 5mm shafts going out to a pair of knurled knobs.

6, Azimuth adjustment is made by rotating the knurled knobs. Left/Right motion turn the knobs in the same direction (ie one thread tightens one thread slackens) to lock azimuth motion turn knobs in the opposit directions. I'm getting circa ± 10° left/right azimuth rotation which is enough for PA alignment.

I hope this helps

Edited March 24, 2023 by fwm891

[Mr H in Yorkshire]

With the level of precision of adjustment in alt az this will give, what are you going to do about levelling on a pier or tripod?

[fwm891]

@Mr H in YorkshireThere is no need for an absolute level, close will do as I'll be doing a polar alignment via Sharpcap et al once all the kit is mounted on the head. Which is all you're doing with an EQ mount anyway.

When using at home I will keep the tripod legs at a set height and have three holes drilled in the patio stones to place the legs in to each time and only need very minor adjustments (if any) night to night.  If going to a different location then a small bubble level will suffice to level the tripod top plate after eyeballing north.

[vlaiv]

2 hours ago, fwm891 said:

4, the lower disc has a bracket fixed to it to take the pivot pin. The pivot pin passes through a barrel nut which is threaded at both ends (standard righthand threads 6mm).

5, The Azimuth adjustments are made via two 6mm screws one each side which enter the barrel nut. The barrel nut is threaded to a depth of circa 18mm each side. Each of the adjustment screws are threaded approx 12mm with bare 5mm shafts going out to a pair of knurled knobs.

6, Azimuth adjustment is made by rotating the knurled knobs. Left/Right motion turn the knobs in the same direction (ie one thread tightens one thread slackens) to lock azimuth motion turn knobs in the opposit directions. I'm getting circa ± 10° left/right azimuth rotation which is enough for PA alignment.

I hope this helps

Still having trouble understanding, I'm afraid.

I've been thinking about same/similar mechanism and here is what is troubling me:

In above diagram ends of shaft that are used for adjustment don't follow circle with center in the center of the disk.

There should be two constraint degrees of motion for that cylinder - not just one. You have pivot point to let it rotate, but I think that you should also have "vertical" component - or distance from the center of the circle.

Maybe I should draw another similar diagram - but this time, just to make it obvious what I'm saying - I'll reverse what is spinning.

In this case - let the adjustment shaft / knobs be stationary and let central disk rotate instead (opposite from your case where rectangular body is rotating and circular disc is stationary). Diagram would look like this:

So above diagram is exaggerated to make a point. Imagine that adjustment knobs are fixed to threaded rod and there is nut that is attached to rotating disk. When we turn knobs, since threaded rod is stationary - it is the nut that will move left / right and given that it is attached via arm to central disk  - disk will rotate. But we need to have both pivot point and some sort of "telescopic" mechanism in that arm for thing to work properly.

How is above different from your arrangement?

[markse68]

there are slots to allow the pivoting threaded bit to move in and out and stay parallel

Mark

Edited March 24, 2023 by markse68

[fwm891]

As Mark @markse68 has pointed out the side blocks are slotted. Along with the pivot around the centre pin and the slotted side blocks there’s enough constrained  freedom of movement.

It works in the reverse fashion to the normal push on a centre pin with the advantage ( for me) that the adjustment screws never extend outwards, they always maintain their positions.

There are some small washers and compression springs to add yet. These are to maintain side pressure on the threads during adjustment and take out any shifting when locking azimuth adjustments.

[Mr H in Yorkshire]

17 hours ago, fwm891 said:

I like to tinker

I like to tinker too. My current project, which will take about a year, is a binochair incorporating the design principles already developed (see Motorised Binochair design for 100mm binoculars here on SGL), except that this one will have a 6" f/5 BT and the whole caboodle will be trailer mounted. So far I've bought an old trailer (had to dig it out of a field almost) and cut it to a 'chariot' form and I'm working on the azimuth drive base at present. I want a two speed drive this time, as the drive rate of the Mk1 is about 180 seconds per full revolution. This is a compromise which is tolerable for slews but a bit fast for centring and following targets in the binos. I have all the optical parts for the BT, got a pair of Jaegers a decade back. When I have solved the two speed base issue I will start a proper thread for the project.

[fwm891]

Well it's pretty well finished now. Few little bits to finish off and a good clean/grease up. I've loaded it up with the expected loading and had it pointing east/west up/down and many stops between. Without access to sky at present I can't comment further but it feels really solid.

Will post some DSO's once the clouds part but until then heres a few photos of it tonight.

Thanks for looking - Francis