Mission Almost Impossible! 2.2m dome meets OO VX14

[SnakeyJ]

Probably not impossible, but certainly optimisitc and stretching the bounds of my limited engineering genius to attempt to shoehorn Johninderby's 'Big Blue Orion Optics VX14'  into my modest 2.2m Pulsar Dome.

Here's Big Blue, against the current incumbent, my 10" F4.8 VX                       and, here's the objective, my currently underutilised dome

                     

The VX14 is 1540mm long by 375mm diameter and weighs in around 20kg, but will need to be substantially ballasted to move the COG forward sufficiently (marginally less than 60:40) to swing this inside the dome.   The OTA will be mounted on a Celestron CGE mount so some margin for additional weight for it's intended purpose, which is planetary, comets and short exposure (globs and small brighter DSO's).

I had to do a little prep to make the workshop operation, fitting my new drill press and compounding table, so I could drill and tap the OO radius blocks to fit my ADM 15" imperial losmandy dovetails.     Tapped and drilled as M6, because I don't possess 1/4" UNC taps     I will fit the second dovetail on top to keep things rigid.

 

Now for some secret magic ingredient to balance and adjust the CoG..........

 

 

I will need to mount this forward of the focuser for maximum effect, which will probably create quite a pendulous effect and I expect the scope will take some time to settle after slews, but hoping this will all work out and be reasonable..

 

[Helen]

? Way to Go Jake! ?

(Just don't get in its way when it is slewing!!)

Helen

PS say Hi to Big Blue for me ? 

[SnakeyJ]

19 minutes ago, Helen said:

? Way to Go Jake! ?

(Just don't get in its way when it is slewing!!)

Helen

PS say Hi to Big Blue for me ? 

 

Thanks Helen - I'm hoping I shall be safely out of the way (and the cold), running this remotely from indoors.    It certainly won't be fully automated, but hopefully I can open up and power things on and then return at the end of the evening to shut it all down (at least that's the longer term plan).  Worst case I can crawl around the pier to poke and prod as required.

[tooth_dr]

Never thought of that. My 12” hits my obsy wall at some angles because of how much it sits forward in the rings. If my mount can cope this seems like a good idea of shifting the CoG. 

[SnakeyJ]

I fitted the cradle last night and conducted a quick and dirty test balance using a short piece of 12mm bar as the fulcrum beneath the centre of the losmandy bar.      Placing the full 7kg roll of lead flashing at the focuser end of the ota, I was able to achieve a balance point (CoG) at 830mm/710mm (or roughly 54:46%) giving some margin of comfort on the 60:40% target.      I will probably lose some of the flashing to cut in around the focuser and access for the spider bolts, and it's mass will also be acting approx 75mm in (half of sheet width), but I have some margin and will also add close to another kilo for the optical train. 

The flashing is a 3m roll of 150mm x 1.3mm and the circumference of the OTA is a little short of 1200mm, so approx 2.5 wraps and 4mm at it's thickest.    I'm not planning to bond this to the ota, but hoping I can achieve a good friction fit by tight winding it on, accurate cut in around the focuser and wrapping with a few rolls of blue PAT (trying to stay close to the colour scheme).

At least the calcs look good - now to test theory against the optics of reality

[Dr_Ju_ju]

To avoid scratching the paintwork, wrap some felt \ sticky back flocking around the tube first...

[SnakeyJ]

5 hours ago, Dr_Ju_ju said:

To avoid scratching the paintwork, wrap some felt \ sticky back flocking around the tube first...

Sound advice - thanks

[SnakeyJ]

It always ends up taking a little longer than originally envisaged, but managed to get a fair crack on with this over the weekend.   I ended up removing the optics, stripping the OTA down and spent a couple of hours re-sticking the edges of protostar flocking down.   Note to self, don't use highly volatile PVC glue, in a confined space (like a 15" wide tube).

A rather poor image of the newly reflocked interior...

 

Cosidering Julian'a advice, I decided to mount the lead flashing on double sided tape around the OTA and countinued along the overlapped lead flashing.  This helped to keep it all tightly fixed and, with luck will stop it slipping in future.   I now have the ballast/radiation shielding in place....

 

And then wrapped the whole lot in white tape, having forgotten to bring any blue home from the office.     Once it was wrapped I carfully cut out the rebate for the crayford focuser and drilled the holes for the spider bolts.

 

Not too bad cosmetically and I don't think it's going to move around once I get a few more fixings bolted through it.

 

I'll give the optics a careful wash to remove the 10+ years of dirt, then rebuild, collimate and see if I can find a strong friend to help get this mounted - I figure it will weigh in around 27kg, but it will be difficult to slide this up in to the losmandy saddle on my own.

 

 

 

[Stub Mandrel]

No cosmic ray artefacts on your pictures ?

[SnakeyJ]

There was a stubborn and almost milky film of muck over the primary and secondary mirrors, that took a bit more soaking and soap than I was expecting (almost enough to remove the stickers).    Won through in the end and hope this will last another 10 years - I will definitely make up some better end caps for the OTA (the OO thermal plastic ones are rubbish).

Before - it still works (like trying to shave in a steamy bathroom mirror)

After - much improved (nerves calmed once it was sercurely mounted back in it's cell)

OO stickers (serial number, date of manufacture, inspector?, diameter and focal length in mm) - Has anyone ever asked OO to provide a copy of Zygo report?

Now to find out how well the optics will work 'sans cataracts'

 

[SnakeyJ]

Nice to get a same response back from John Pemberton at Orion Optics. It seems the can reissue the test certificate, but they needed the serial number engraved on the back of the primary.

 

Not too easy to see this, but best effort..

 

[Stub Mandrel]

Rub it with a soft pencil then wipe off the excess?

[SnakeyJ]

6 minutes ago, Stub Mandrel said:

Rub it with a soft pencil then wipe off the excess?

An excellent and practical engineers solution - I messed about in photoshop for 15 minutes and managed to get:

     F4.6 1/10  

     080805PR01 (or possibly RR01).

 

No entirely certain on this, but it appears the reference is date/project reference so hopefully this will be enough for OO to retrieve the certificate/results.

[Stub Mandrel]

1 hour ago, SnakeyJ said:

080805PR01 (or possibly RR01).

 

No entirely certain on this, but it appears the reference is date/project reference so hopefully this will be enough for OO to retrieve the certificate/results.

Let's just hope the 'R' doesn't stand for 'reject' (only joking!)

[Alan White]

On 29/08/2018 at 20:18, Stub Mandrel said:

Let's just hope the 'R' doesn't stand for 'reject' (only joking!)

or R for Ropey perhaps ?