OOUK VX16 refurbishment

[Nigella Bryant]

Oh dear, that's not good but it'll be great in time. 

[Len1257]

On 10/01/2022 at 13:53, discardedastro said:

The one to fit over the top I'll put some dowels in around the edge to let it just rest on the tube without slipping off which should work OK as a "lens cap"!

To get a good grip you can use clear silicone rubber tube with a screw inside to grip the tube. I used something like that to grip kite line halo reels for a winder I made. Something like a M4 stainless setscrew bolted through the cover and the slicon tube just a good push grip over the protruding screw. Arrange three or four around the periphery. slot the holes to adjust the grip. I think the silicone tube came from an aquarium air tube. I can dig it out of the back of the shed if you want a photo.

[discardedastro]

12 hours ago, Len1257 said:

To get a good grip you can use clear silicone rubber tube with a screw inside to grip the tube. I used something like that to grip kite line halo reels for a winder I made. Something like a M4 stainless setscrew bolted through the cover and the slicon tube just a good push grip over the protruding screw. Arrange three or four around the periphery. slot the holes to adjust the grip. I think the silicone tube came from an aquarium air tube. I can dig it out of the back of the shed if you want a photo.

That's a great shout. I'll have to give that a try. I'll be picking up some ply to make the cover tomorrow.

Made good progress - have been slowly but more aggressively cleaning the mirror (fingertips only) and there's clearly still *some* debris on it, so just trying to get that gone without making things worse. Mixed results so far but it's better for it. My plan is to remount the mirror for now and run it till probably next summer - then I'll ship it off to OOUK to get it measured since it predates their Zygo. If it looks good optically then I'll recoat, if it's iffy might consider a new primary.

The tube now has better steel/rubber trim, a plastic handle for maneuvering, and I've attached both the new finderscope mount and Telrad mount with M4/M3 bolts. The dew heating system is starting to go in, too - I'm just putting cable tie anchors down the length of the tube (avoiding the region where the tube rings will contact the tube) to secure all the cabling. The fan with its damaged wiring is on the workbench to repair, and I'm also going to adjust the barrel jack - the supplied one is clearly not compatible with the mounting plate of older OOUK scopes so will just 3D print a clip to hold it at the edge of the plate instead of passing through.

Tube rings and cradle are both looking better with some smooth Hammerite, which I've also used as a first-pass coating to blacken the ends of the stainless bolts/nuts which are securing everything. Going to take a few more coats to get it all properly sorted but it's already massively improved from where it was - all the exposed metal is now well covered.

[Paz]

On 08/01/2022 at 13:04, discardedastro said:

Well, all the awful weather we've had lately has driven me to take the opportunity to take my VX16 apart rather than wait for summer.

The primary really needed a clean - which was the main trigger for this - but there's a bunch of other problems I want to resolve to make this scope a really reliable "daily driver" for my use, which is purely visual observation with little setup time in quite a humid area. The scope lives outdoors all year round under a cover.

Things I'm going to try and do:

• ...
• Renew all the PTFE bearings on the mount
• ...

 

Will post updates as I go for anyone interested - I'm curious to know if any other OOUK dob owners have noticed the flattened section of tube above or if this is a damage/defect.

 

Are you getting replacement ptfe bits from OOUK? I am wondering about getting spares for my VX14 (although they don't need replacing yet).

My VX14 is a little flatter where the OTA joins but less so than yours. 

[discardedastro]

14 minutes ago, Paz said:

Are you getting replacement ptfe bits from OOUK? I am wondering about getting spares for my VX14 (although they don't need replacing yet).

My VX14 is a little flatter where the OTA joins but less so than yours. 

For the bearings? I've not considered getting new bits from OOUK, but there is a lot of stiction in it - once the mirror's back in the cell/tube I'll have room to pull the azimuth bearing apart fully and see if that's the problem, but the altitude bearing isn't super-smooth either. I do have some PTFE sheet to hand, but it's probably not thick enough to form bearings from.

[Paz]

15 minutes ago, discardedastro said:

For the bearings? I've not considered getting new bits from OOUK, but there is a lot of stiction in it - once the mirror's back in the cell/tube I'll have room to pull the azimuth bearing apart fully and see if that's the problem, but the altitude bearing isn't super-smooth either. I do have some PTFE sheet to hand, but it's probably not thick enough to form bearings from.

Yes, mine work ok (not brilliant, but good enough) and interestingly they have steadily got better over the years with use.

[johninderby]

When I had my 14” OO I glued an EbonyStar ring onto the base and movement became perfect. The ptfe pads that OO use are good and don’t need replacing.

Pity the EbonyStar rings are no longer available from Telescope Express. 😢

Edited February 10, 2022 by johninderby

[faulksy]

have you tried putting a light under your primary mirror and view it from the mirror side. this will show you how thin your coatings are.

john will re coat your primary for around £150. might be worth getting your secondary done as well.

stiction in the azy motion is greatly reduced by applying car polish to the base then polishing by hand. you can do it on the alt bearings as well 😄

[discardedastro]

8 hours ago, faulksy said:

have you tried putting a light under your primary mirror and view it from the mirror side. this will show you how thin your coatings are.

john will re coat your primary for around £150. might be worth getting your secondary done as well.

stiction in the azy motion is greatly reduced by applying car polish to the base then polishing by hand. you can do it on the alt bearings as well 😄

Car polish! Got that for days - is the goal there just to make the opposing surface as smooth as possible? I was thinking of taking a PTFE sheet - I've got a few - and covering the base as far as the pads on the bottom plate go, so the contact is PTFE-on-PTFE there.

Bit harder to do for the az-axis, though.

[johninderby]

Be arefull what car polish you use. You need a pure wax free from additives. The best wax to use is Turtle Wax Original as recommended by Obsession among others.

https://www.amazon.co.uk/Turtle-Wax-50187-Original-Shell/dp/B00068OL1A/ref=sr_1_7?crid=15PT67FD21NT&keywords=turtle+wax+original&qid=1644746912&sprefix=tirtle+wax+ori%2Caps%2C99&sr=8-7

[discardedastro]

Bit of delay on finishing up, but the mirrors are - as-is - back in the tube and remounted. I'd planned to add a dew heater strip but realised on reassembly the mirror clips don't really accommodate anything much between the tube and the mirror, so I've spread it out behind the mirror to see if that can work acceptably. The fan in the mirror cell is in and sorted, at least. All much cleaner than when it started!

Mechanically, all looking OK - I've also added a set of cable tie anchors down the side so I can secure all the cables once it's back in the tube rings and remounted. The Telrad base and new finder base are all bolted in place now, and I've added just the one handle for now for maneuvering. My guess as to the right thumbscrews for the secondary turned out to be incorrect, so I'll need to source some extra long ones for that.

Now the mirror's off the workbench I've stripped the base and rings down and repainted most of the key surfaces. I've got some simple wax car polish to clean up the base and contact surfaces, so hopefully that'll help, but it's looking much tidier with a lick of paint on the damaged surfaces to start. I'm going to tap a few holes for future encoder mounting options and then reassemble so I can crack on with collimation and get it back in use.

I think if this comes apart again it'll be for a full service and recoating with OOUK, but it's in much better shape than it was a year ago! I need to get it out of the garage to make room to make the new tube cover, so that's the last thing I'll do, but that's about all I had left on my todo list - I'll fit the heaters once the scope's back in the tube rings.

[discardedastro]

And we're back in business!

I've not yet sorted out the cable management - waiting on a few bits and pieces - but you can see some of the heaters and the handle on this photo.

All back together, re-collimated, and the views are great (as far as I can tell on a full moon light)!

Very happy with how it's all turned out. The car-polished and PTFE-lubricated bearing surfaces are much easier to move - much less stiction - and the handle is a serious upgrade (!). The Telrad and finder both worked great with some minor realignment, but mechanically are very solid compared to before.

I've fitted the heater controller between the rings and that seems to be working - given it was a light night I just left it all out there for a few hours with the heaters running. The Telrad and finder dewed up with heat on about 20%, the primary and secondary at around 25% were dew-free.

The eyepiece and the finder eyepiece both dewed up, which is a challenge - I might need to add a second dew heater controller and some more heating bands to have this work for long-term observing sessions where we are (which is a very damp area).

I've not done the tapping required to connect any encoders yet. I've not got these on order and it'll be pretty easy to do after the fact.

All in all, I'm going to call this "done" bar some cable ties and a new tube cover, which I'll make now I've got my workshop clear of the scope itself. Definitely worth the faff in my mind and I'm looking forward to some dark skies!