OO/Helmerichs 200mm Final Assembly

[Captain Scarlet]

Over the last few weeks I've been gradually morphing an Orion Optics VX8 1/10 from the sorry state of affairs it was when I bought it, to a state of loveliness, in both form and function. To look at, the original VX8 scope was fine: newish, clean, no scuffs etc. It was only on close inspection that some serious problems became apparent, to the extent that it was essentially uncollimatable, and therefore horrid to look through. These problems were no fault of the SGL member who sold it to me, though it may well have been some of the reason he sold it. The as-sold OO VX8 has design flaws and in the case of this copy, production flaws too. I've tried to fix all these.

I've transformed it into what it should be, and some. It's now a beauty to look at and, I hope, to look through. Though I haven't yet had a chance aside from doing the collimation. But I have checked that my design work worked: I reached focus just where I hoped it would be, 70mm from the outside of the tube. Phew!

The main problems I fixed were:

- The centre-spot on the primary was 3mm (!!) from the true centre of the mirror. It was this that made it virtually impossible to collimate or get a decent view. I removed the old spot and installed a new one, properly centred. Now the 1/10-wave spec can do its thing.

- A new Klaus Helmerichs carbon tube. The original VX8 tube is Aluminium and thin, therefore not rigid. Any significant eyepiece-train load would cause "droop" and collimation-shift. The new tube is extremely stiff, I can't shift collimation with even a hard pull on an eyepiece.

- The VX8 has end-rings to try to keep the tube round at each end. To keep them stiff, these rings wrap over across and into the open end of the tube, leaving a resulting clear aperture at the front of the tube of exactly 200mm, i.e. the same as the primary mirror 871mm away. This means that only the precisely on-axis spot receives the full 200mm. Anything off-axis gets vignetted by the end-ring. The new tube has no such "wrap-over".

- The OO cell is actually a lovely mirror cell, and I would certainly buy one new. But in the factory during assembly all its moving parts and more besides get slathered in gobs of silicone glue. Why on earth? The whole point of the cell is exactly its moving parts. Anyway, I removed all that nasty stuff, plus the sticky-tape untidily wrapped around the edge of the primary, so the cell can now support the mirror in the way it's designed to.

The first image below shows everything neatly arranged, ready for assembly. Easy final step, right? Wrong. The extra 6mm tube-thickness presented me with a good few difficulties, some anticipated but some not. Luckily I did find ways around the unanticipated ones.

Neat and Tidy and ready for assembly:

 

The extra tube thickness meant that the spider wasn't quite wide enough. Luckily I had enough M4 nuts lying around that I could insert between the boss and the spider-arms, giving some crucial extra width:

 

The lovely rear cell:

 

Some pictures of general loveliness:

 

And finally, it joins its bigger sibling (a 300mm OO 1/10 mirror with Helmerichs tube):

 

Thanks for drooling,

Magnus

Edited April 23, 2022 by Captain Scarlet

[JeremyS]

Cracking job Magnus 👍🏻👍🏻👍🏻

[Roy Challen]

Yeah, great job, looks fantastic. I'm sure the views will be as good too.

[Greymouser]

Excellent job. Yes I am jealous of the lovely scopes, your skill, but most importantly that view from your window!

[Mr Spock]

Nicely done 👍

[cajen2]

Beautiful, Magnus, both of them. Looking forward to hearing your first light with the new one.

[Captain Scarlet]

3 hours ago, Greymouser said:

Excellent job. Yes I am jealous of the lovely scopes, your skill, but most importantly that view from your window!

Thank you. The view is much of the reason we moved here. The other is the darkness. By coincidence after a long dry spell (in sunset terms) this vista presented itself just this evening...

 

[Roy Challen]

Err, you will be getting some proper tube rings for this won't you?😀

[Captain Scarlet]

56 minutes ago, Roy Challen said:

Err, you will be getting some proper tube rings for this won't you?😀

Haha I was wondering if anybody would notice that bodge! Well spotted. One of the unanticipated difficulties from the extra ota tube thickness. I’ll probably use the existing OO rings and add the required distance with some slightly longer hinges from the local hardware store … it’s all pretty crudely put together as it is.

Edited April 24, 2022 by Captain Scarlet

[Greymouser]

20 hours ago, Captain Scarlet said:

Thank you. The view is much of the reason we moved here. The other is the darkness. By coincidence after a long dry spell (in sunset terms) this vista presented itself just this evening...

 

I am afraid with a view like that out my window, I doubt I would ever get much else done, other than looking outside.

[ONIKKINEN]

Nice and shiny tube, looks very nice!

Curious as to what this bit is though, ventilation hole for the fan on the cell to pull air from in front of the mirror or just some placeholder thing?

[Captain Scarlet]

1 hour ago, ONIKKINEN said:

Nice and shiny tube, looks very nice!

Curious as to what this bit is though, ventilation hole for the fan on the cell to pull air from in front of the mirror or just some placeholder thing?

Haha that was the other thing I thought I'd wait until someone else noticed before talking about it! You suggest it might be "ventilation hole for the fan on the cell to pull air from in front of the mirror". Well, yes it is, er, sort of, by default though.

There are two explanations:

1. I'd designed the whole thing to the nth degree, worked out where I needed all the holes etc etc. I measured and measured and checked and checked before drilling all the small holes: spider-holder holes, mirror-cell attachment holes, finder-bracket holes, and the single pilot hole to act as a guide for my 80mm hole-cutter for the big focus-tube hole. I have to say, I drill very nice holes with great accuracy, working up from 1mm hand-held spotting-indentation, drilling then all the way up to the required size. Very careful. Finally I got my 80mm hole-cutter, run backwards of course for easier cutting without catching, lovely smooth and also a good job. Lovely lovely. 10 seconds later I realized that I'd used one of the spider-holes as my pilot hole, not the focus-hole pilot hole.  ........................................... Oh God. Oh my God. You can imagine the stream and volume of swear-words as I strode around the house holding my head in my hands. How could I be so BLOODY STUPID!

2. In the design phase, I had given a lot of thought to the thermal management of closed Newtonian tubes, especially extremely well-insulated ones like this with its epoxy-carbonfibre skin and 5mm hardfoam inner liner. I had genuinely been mulling about creating a focsuer-sized ventilation hole near the primary mirror. But in the end I decided to "go conventional" to begin with , and decide later.

This stupid mistake made my decision for me. Once I'd calmed down, I realized I could simply turn the tube back to front and start again. Which I did, being very careful second time to use the correct pilot hole! Hence the makeshift "hatch-cover". If you look carefully at the images, you'll see various random "unused" holes and bits of tape covering holes, the collateral damage of my idiocy.

 

You also say "nice shiny tube". It is, of course, it's beautiful, but more to the point it's extremely stiff, more so than I was expecting. Exerting some serious force to the laser when in the focus tube, I could not get the spot to move. Very pleased and well worth the wait for Klaus Helmerich.

Edited April 24, 2022 by Captain Scarlet

[markse68]

Was going to ask about that flap too- looks a bit like my fullerscope Magnus- handy for removing cobwebs too  I can totally imagine how you felt when you realised what you’d done 😳 was going to ask if you had to drill the holes yourself or if they did them for you. Good you’ve managed to turn it into a positive feature.  Lovely looking scopes- hope they bring you much satisfaction and many great sights. Are you planning to trim down the mirror clips on the OO cell? The previous owner of mine had chopped them off really short so they only catch the bevel which works fine if you adjust the nylon grub screws so the mirror can’t move sideways and clear them.

Mark

[ONIKKINEN]

2 hours ago, Captain Scarlet said:

Haha that was the other thing I thought I'd wait until someone else noticed before talking about it! You suggest it might be "ventilation hole for the fan on the cell to pull air from in front of the mirror". Well, yes it is, er, sort of, by default though.

There are two explanations:

1. I'd designed the whole thing to the nth degree, worked out where I needed all the holes etc etc. I measured and measured and checked and checked before drilling all the small holes: spider-holder holes, mirror-cell attachment holes, finder-bracket holes, and the single pilot hole to act as a guide for my 80mm hole-cutter for the big focus-tube hole. I have to say, I drill very nice holes with great accuracy, working up from 1mm hand-held spotting-indentation, drilling then all the way up to the required size. Very careful. Finally I got my 80mm hole-cutter, run backwards of course for easier cutting without catching, lovely smooth and also a good job. Lovely lovely. 10 seconds later I realized that I'd used one of the spider-holes as my pilot hole, not the focus-hole pilot hole.  ........................................... Oh God. Oh my God. You can imagine the stream and volume of swear-words as I strode around the house holding my head in my hands. How could I be so BLOODY STUPID!

2. In the design phase, I had given a lot of thought to the thermal management of closed Newtonian tubes, especially extremely well-insulated ones like this with its epoxy-carbonfibre skin and 5mm hardfoam inner liner. I had genuinely been mulling about creating a focsuer-sized ventilation hole near the primary mirror. But in the end I decided to "go conventional" to begin with , and decide later.

This stupid mistake made my decision for me. Once I'd calmed down, I realized I could simply turn the tube back to front and start again. Which I did, being very careful second time to use the correct pilot hole! Hence the makeshift "hatch-cover". If you look carefully at the images, you'll see various random "unused" holes and bits of tape covering holes, the collateral damage of my idiocy.

 

You also say "nice shiny tube". It is, of course, it's beautiful, but more to the point it's extremely stiff, more so than I was expecting. Exerting some serious force to the laser when in the focus tube, I could not get the spot to move. Very pleased and well worth the wait for Klaus Helmerich.

Oh my, i can imagine my heart skipping a few beats after a fumble like that, especially since these tubes are not easily replaceable. I think it shows the tube is plenty strong enough if it handles an extra hole like that and still shows no flexure, so you could call it an improvised stability test. 😉

Looks like a useful hole for ventilation and maybe some light mirror dusting though, so not a disaster i hope!

[Captain Scarlet]

I went to the hardware shop today and got some hinges. @Roy Challen. A little drilling of a few extra holes later, my rings work as they should, no bungees in sight! A little black paint tomorrow and nobody would be any the wiser!

Ready for First Light, whenever that may be…

Edited April 25, 2022 by Captain Scarlet

[Captain Scarlet]

On 24/04/2022 at 22:39, markse68 said:

… Are you planning to trim down the mirror clips on the OO cell? The previous owner of mine had chopped them off really short so they only catch the bevel which works fine if you adjust the nylon grub screws so the mirror can’t move sideways and clear them.

Mark

Yes I have a number of things I still want to do. One of them is just what you say: to grind off the excessive diffraction-contributing overhang of the mirror-clips and replace them with the minimum necessary to stop the mirror from falling forward when inverted.

Also the secondary is bigger than I want. 63mm, i.e. 31.5% CO. I’m strictly visual so I’ll be getting a 50mm secondary at some point.

M