16 inch f5 with Nichol Optics.

[fwm891]

Started making up the secondary mirror tilt/collimation assembly. The lower plate in the photos (with the 4 cap head screws) is fixed the upper plate is allowed to tilt/tip it's movement resisted by 3 compression springs and activated via 3 screws. The actual adjustment screws will be 'tool free' the cap heads shown are temporary to let me check the movement. As a guestimate at the moment there appears to be circa ± 7-8 degrees of tip/tilt movement, more than enough to collimate the secondary.

The angled plate still needs some shaping and a few holes drilled/taped to take the secondary elliptical back plate.

Any resemblance to a cuttle fish is purely by chance....

Edited July 24, 2021 by fwm891
Text added

[fwm891]

Working on the 18 point primary mirror support structure. These are the 3 pivot bars and brass domed triangle supports. Waiting on the correct cap head screws which will pass down through the triangles, through the domed pivots and into the support bar.

[fwm891]

The mirrors have just arrived and they look beautiful. All packed away again now while I get myself in gear to complete the rest of the scope.😀😀😀👍

[fwm891]

More metalwork today. Continued and put together the mirror support frame and 18 point supports.

 

[fwm891]

The mirror box has had it's first coat of matt black after routing the corners to take the ali angle acting as a corner reinforcement and the anchor points for the truss poles. The top edge of the mirror box is left as bare wood at present - this will have a hardwood edging added later. The interior will have a further coart of matt black the exterior will have a clear varnish/lacquer top coat to enable easier cleaning after handling.

Photos show an exterior corner and detail of the pole ends. The pole ends will be secured with a knurled circlular ali nut (temp cap head screws used at this stage).

[fwm891]

Little more work on the 18 point mirror floatation assembly.

[fwm891]

I'm working on the upper cage at the moment. Just need to make the captive hand wheels to secure the truss tubes to the upper cage lower ring. Currently having further thoughts on the adjustable spider vane assembly attachment to the upper cage framework...

[Swoop1]

I envy anyone who has the skills to produce this type of work.

I am a bodge it and scarper type of DIYer so couldn't dream of taking on a project like this.

[Piero]

6 hours ago, Swoop1 said:

I envy anyone who has the skills to produce this type of work.

I am a bodge it and scarper type of DIYer so couldn't dream of taking on a project like this.

 

There are different ways to make dobsonian telescopes, but in general, one does not need a lot of skills to make a good one.

My 16" f4 was my first wood / metal project. I literally never drilled before, and my only tools were / are: drill (+gator drill guides), router (both bases), jigsaw, and sander.

The whole project can be successful with: patience, careful research / study, attention to details.

Edited August 19, 2021 by Piero

[fwm891]

Continuing with the upper cage. I've had a great time struggling to get the plywood panels (2) into their slots in the upper and lower cage rings. Never enough clamps or hands for this job. The long elasticated cord wrap helped immensely with this task. Assembled dry first of all then when everything was seated correctly CA glue was spread along all the joint lines where capillary action drew the glue down into the joints. Once dry a further bead of CA glue was added to seal the joints. This will be painted black before adding the secondary spider adjustments.

TBC...

 

Edited August 22, 2021 by fwm891
Text added

[fwm891]

Clamps and ropes removed. Baader SteelTrack focuser and one of the upper truss tube anchors added just to make sure everything fits...

Paint job on this next.

[Piero]

Will you install the spider directly to the thin vertical plywood panel or will you install 4 struts for holding it?

If the latter, it was probably easier to recess the strut base on the rings to lock their alignment and stiffen the structure: two star nuts per strut and bolts passing through the rings.

Then, the thin plywood sheets could be glued or nailed to the internal wall of the two rings.

From the photo, the wood of the top ring seems different from the one in the bottom ring.

 

 

Edited August 24, 2021 by Piero

[fwm891]

@Piero Mine will have aluminium struts between the upper and lower cage rings (see earlier drg's) to take the adjustable secondary spider vanes. The upper (9mm) and lower (12mm) thickness rings are stiffened with the addition of the 3mm plywood panels which are bonded into each via a 3.2mm slot. My focuser panel is fixed with the focuser being adjustable (axially) for centring the focuser over the secondary. Likewise the secondary will also be adjustable axially to position the focal plane at the correct working height for the focuser. Once these positions are found the secondary vanes can be locked in place and tensioned, the focuser centred on the secondary and likewise locked in place. Then the optical system can be collimated in the normal way from the eyepiece position.

My secondary holder is adjustable for tip/tilt only. Axial movement via sliding the whole spider assembly up/down within the upper cage.

Next part of the project is to finish the upper cage/spider assembly then move on to the rocker box and modifying my EQ platform to take the rocker box.

TBC...

[fwm891]

Upper cage with spider vane assembly.

Image 1 shows the cage from the primary mirror side, with central hub and vanes under tension.

Image 2 shows the cage from the sky side.

Image 3 is a detail of the spider vane axial adjustment. There's +/- 20mm axial travel here to position the secondary along the optical axis so the focal plane sits at the correct height for my eyepiece set.

Image 4 shows the spider's central hub. The angled plate carries the secondary mirrors back plate (still to make this). Two of the collimation adjustment springs can be seen the third is inside the hub and adjusted from outside.

Beginning to look more like a telescope rather than just a collection of parts.

Everything will be stripped down for final painting art some stage. Probably after first light (whenever that is....)

TBC

[Alan White]

Looking good Francis,
in fact rather better than good.
 

[fwm891]

20 minutes ago, Alan White said:

Looking good Francis,
in fact rather better than good.
 

Thanks Alan.

[faulksy]

very nice work there francis. looking foward to the next step

[fwm891]

It's finally beginning to look like a Dob OTA. No optics in at present just making sure all the bits go together first. Rocker box in progress.

I'm hoping that later I can install the optics and just let the sky drift past with the assembly as it is pointing straight up...

[Mark at Beaufort]

Francis it looks brilliant. You are clearly very talented. Hopefully will see you Thursday.

[fwm891]

Sort of fist light. Mirrors in an a quick laser collimation. Focus about 5mm inside where I wanted it but eyepieces still focused OK. Started with a lowish power 24mm 68 degree ES ep. First straight up then with the aid of some wooden blocks I tilted it into the Swans neck - so many stars. I now need to finish the rocker box so it can be pointed at a known target.

TBC.

[fwm891]

Sort of second first light!

Clear Outside predicted a few hours of 8% cloud cover tonight. Having now got a working rocker box and a temp ground board it was out on the patio for a quick look at the moon low to the south, very yellow but the terminator detail was superb. I used a 24m ES 68° (x83) to view the whole disk and then slotted in an unknown 9mm (x221) and just eased the scope up and down the terminator. Very crisp even with the moon so low down.

Vega was almost overhead in a bright sky but it was dazling, steady blue/white to my eyes. Then Alberio and the colour between the pair was amazing in and out of focus. As the sky began to darken it was back to Lyra to take a look at M57, I've not seen M57 visually for a very long time and it was better than I remember. Lots of detail in the ring (ES 82° 14mm x142) tried with the 9mm but not as good.

I tried searching for M27 but cloud had come in and ended the session completely. Hung around for half an hour but cloud just thickend so all packed away again now.

Really chuffed with everything whilst it was clear. I was also pleased that having been playing with the set-up in the conservatory when I dismantled and moved everything outside, re asembled and collimation was almost spot on. The red laser was just outside the centre ring marker on the primary and just needed a small twist to one adjuster on the secondary to bring it into line. The primary was fine with the laser returned to its source.

I've found I made an up-cock when calculating the balance point as I need to add some weight to the rear of the mirror box to balance out heavier eyepieces at low altitude.

[fwm891]

Still a bit more paint to apply but I've been having a play when clear and today I've been altering the EQ platform built for my old 10 inch dob. The upper cage light shield has been omitted to show the weight reduction alterations to the cage. The extra weight behind the mirror box can also be seen.The lazy Susan is still too free so that needs some attention. 

Despite the moon Jupiter and Saturn have been awesome over the last few nights. Nudging the scope to follow them has been an incentive to get the EQ platform mods done.

Edited September 20, 2021 by fwm891
Text added

[faulksy]

On 14/09/2021 at 22:16, fwm891 said:

Sort of second first light!

Clear Outside predicted a few hours of 8% cloud cover tonight. Having now got a working rocker box and a temp ground board it was out on the patio for a quick look at the moon low to the south, very yellow but the terminator detail was superb. I used a 24m ES 68° (x83) to view the whole disk and then slotted in an unknown 9mm (x221) and just eased the scope up and down the terminator. Very crisp even with the moon so low down.

Vega was almost overhead in a bright sky but it was dazling, steady blue/white to my eyes. Then Alberio and the colour between the pair was amazing in and out of focus. As the sky began to darken it was back to Lyra to take a look at M57, I've not seen M57 visually for a very long time and it was better than I remember. Lots of detail in the ring (ES 82° 14mm x142) tried with the 9mm but not as good.

I tried searching for M27 but cloud had come in and ended the session completely. Hung around for half an hour but cloud just thickend so all packed away again now.

Really chuffed with everything whilst it was clear. I was also pleased that having been playing with the set-up in the conservatory when I dismantled and moved everything outside, re asembled and collimation was almost spot on. The red laser was just outside the centre ring marker on the primary and just needed a small twist to one adjuster on the secondary to bring it into line. The primary was fine with the laser returned to its source.

I've found I made an up-cock when calculating the balance point as I need to add some weight to the rear of the mirror box to balance out heavier eyepieces at low altitude.

lovely first light report Francis.

you said you had to add some weight, remember it will need a bit more when you add a shroud, especially if its damp as the shroud will absorb moisture

lovely read though and made up for you

mike

[faulksy]

are you leaving your u.t.a.open ?

[fwm891]

3 hours ago, faulksy said:

are you leaving your u.t.a.open ?

@faulksy Mike, yes I am. Reason being I’m having a rear light shield covering 180 degrees made from a waterproof tent material (black) very light weight and opaque. From UK Fabrics, and cheap too!

That will clip on the cage and extend well above and below it.

I may order the same for a shroud if the shield works and doesn’t absorb moisture too much.

Francis