The horror of cheap T-Rings

[RussellH]

So as you do when starting a new hobby, I tried to minimise startup gear costs where I could. One of these corner cutting measures was purchasing a cheap T-ring from eBay. The one I got came with a 2” adaptor, which was hard find, as everyone else only had 1.25” adaptors.

When I went to mount my DSLR for the first time last night, the camera connection was fine, but screwing the adaptor to the ring took multiple attempts as it kept sticking in spots as I screwed it in, and the last half of the thread to seat the adaptor flush with the ring took considerable force.

But it was together and working, so i gave it no more thought, until this morning. In my last 5 minutes before heading out to work, I decided to check the mounting of my Ba’ader MPCC Coma Corrector, the last piece of my imaging train to install.

So I removed the T-adaptor from the T-ring, and started to screw in the coma corrector. It started getting tight at the half way point again, so I unscrewed it until it came off, at which point I realise that I had not removed the corrector from the ring, I had unscrewed the thread adaptor of the corrector, and it was now stuck in the thread of the t-ring!!!

With no way to grip the now stuck thread adaptor, panic started to set in. Cutting the rest of the story short, I did finally manage to get it back out again, no harm done (I think). I’m now stuck in with a dodgy t-ring, and wondering how much I have to spend to find a decent replacement, as prices weekly wildly different with no way to tell you high ones are decent quality. I am also stuck without being able to use the Ba’ader until I find a replacement.

So, while I probably would play eBay bingo again if I had to do it all over again, sometimes there’s just no avoiding coughing up the big bucks for the right gear. Any suggestions on a good supplier that doesn’t charge the earth?

Thanks. Russell.

[billdan]

If you want to buy locally within Aust', Bintel has a kit of T-Rings for $49.00, that may be suitable for you.

https://www.bintel.com.au/product/bintel-t-thread-spacer-ring-set-2/?v=6cc98ba2045f

[Joshua Bunn]

Hi Russell.


I make custom adapters for the good people here on IIS. check out my forum post in the equipment discussion section 🙂


Regards
Josh

[RussellH]

I’d actually love to get a low profile one for a bit more focus travel and to pull the focuser out of the tube a bit more, even if only a couple mm. Will check your post when I get home Josh.

[RussellH]

I just had an epiphany. When using the MPCC, I can’t use a low-profile T-ring as the MPCC requires 55mm back focus, so I need the standard 11mm T-ring still. The MPCC is not supposed to change the focus position when in use is it, so it will have no effect on my Camera focus position?

I’m wondering if it’s a bad idea to consider lubricating my existing T-ring to see if it’ll free up the binding. i certainly don’t want fluids flowing down into my camera body, or back into the scope, but is a gentle wipe with a lubricant infused piece of cloth still a bad idea? If it’s just bad threading, it’s not going to help, but if it’s rough threading, it might.

Thanks. Russell.

[doppler]

I've come across this before, some Chinese scope adapters and filters etc have the right sized thread but it's at a different pitch. I would tread with caution here it's pretty easy to destroy alloy threads.

[bojan]

Careful lubrication with right lubricant (syntetic grease for example) always helps, especially preventing stucking...

BTW, focusing threads of all lenses are full of lubricant, and there are no ill effects.

[RussellH]

Very odd when they supplied both piece though and they still don’t mate. The listing said m42 x 0.75

As for lubricant, any specific recommendations then? Any particular silicon grease?

[bojan]

Silicone grease (Dow Corning vacuum grease for example) is not good lubricant for metal (Aluminium), it is actually worse than nothing.
I use Litium grease (green stuff - and very little of it).
Also, vaseline (petroleum jelly) is good

[doppler]

"Very odd when they supplied both piece though and they still don’t mate. The listing said m42 x 0.75"


You unscrewed the nose piece from the t adapter, so those parts were fitting ok? but then had trouble screwing in the comma corrector? I was thinking that the corrector and t mount threads were not compatible. Find out which has the bad thread and get a replacement, a lot of places don't even want the old one sent back.

[RussellH]

The ebay item I purchased was a combined T-ring and a 2" t-adaptor. They were supplied in a single box, but unassembled. When I first screwed them together, it was rough and jammed in the middle, but with some insistent pressure, I eventually got the adaptor bedded to the t-ring.

I then unscrewed the t-adaptor to try and put the coma corrector on the t-ring. Given it should have had a similar thread and also jammed, I assume it it the t-ring itself that is bad. I only managed to get a $5 rebate from the supplier, as they wanted me to post it back to china for a full refund, which of course it would have cost a fortune to send back. It's still usable if I don't want to use the coma corrector but use the 2" adaptor, so I'm OK with that, but obviously useless for my primary purpose at this stage, unless some lubrication helps, which I will try with some PJ and the cheap adaptor to see if it actually makes any difference or not, before proceeding further.

[RussellH]

I tried some petroleum jelly on the t-adaptor and it now screws into the t’ring quite nicely, although with one or two spots it does get a little tighter, but nothing like it was. I also have a cheap barlow lens with a t-thread. It screws into the t-ring nicely as well.

The MPCC still binds about 2-3mm short of mating with the t-ring. So now I’m wondering if it might be the MPCC? Hard to believe a $300 item would be worse than a $20 item though. I guess my only option left is to try a replacement t-ring and hope it’s a better fit. i found a low profile one and a spacer, so at least it’ll give me some extra flexibility for future use. Just hope the MPCC will fit, or I’ll be throwing good money after bad.

Russell.

[bojan]

Maybe the thread was damaged ?
You can try to inspect it with magnifyer or microscope if you have one.

[RussellH]

Hmm maybe. I assumed the t-ring was the issue and didn’t think to check the mpcc. I’m at work now. Will check when I get home tonight.

[Merlin66]

Russell,
For the past twenty years I've advocated using boot polish to prevent jammed threaded components.
Just a light smear on the threads is all it takes.
No outgassing, heat melting migration etc.
Works very well.

[Wavytone]

Another possible lubricant is beeswax or even candle wax. Stays put and no marks.

[RussellH]

Oh I have heaps of beeswax. I have my own beehives.

[RussellH]

The conclusion to this saga is that my new low profile t-ring plus 10mm spacer arrived from Sirius Optics yesterday, and I’m happy to report that the MPCC screwed in smooth as silk, I just hope the spacing is correct. Shame the weather is rubbish, so I wasn’t able to go check it out.

[LewisM]

I bought one of those Bintel sets once - every single one of them jammed to the point I had to cut spanner slots on the edges to unscrew them (which is NO fun over a CCD cover glass after it jams in solid!!!). The pitch is cut incorrectly, and there is ample roughness in the grooves and peaks. I always lube my threads with museum-grade micro-crystalline wax, and it still had binding issues, especially with Starlight Xpress and SBIG threads (enough screeching to make my cat go into attack mode!!!).

I solved my issue by having Stefan Buda make me a properly spaced adaptor - those threads are like teflon...

[Imme]

I have a little trick that really helps on those dodgy binding threads.
Apply some mild heat (oven at 75'C) then pull them out, wrap a couple big red elastic bands around each piece and twist.
The heats seems to weaken threads a little to allow them to unbind and the rubber bands give a heap more grip.


Has worked for me a few times

[LewisM]

It does, but I wouldn't be putting coma correctors or, in my case, CCD cameras in the oven to get the offending t-thread ring off :eyepop:

[The_bluester]

The heat will just be expanding the aluminium a little. In theory given the female thread should be larger diameter than the male thread it should open up the clearances just a touch. I feel the pain on this one, I have two adapters that I have been using together and they are always ridiculously difficult to get apart again. You screw them together with two fingers and it is just about a hammer and cold chisel job to separate them again. I had to resort to pressing them between two pieces of hard'ish rubber and twisting in opposite directions to get them apart. And that is with a delrin spacer between them.

The biggest cause of the issue IMO is production tolerances. I recently got a part modded by Joshua (Getting a filter thread turned into an adapter he previously made for me to fit a reducer/corrector to my ED72, something I should have thought of the first time) and ended up having to send the actual filter I wanted to use, measuring everything up showed that while I had a handful of 2" "Filter thread" (M48) parts from various manufacturers, no two of them were actually the same size and it was by big enough margins that the part nearest the average diameter was what had to go with it as the template.

[Merlin66]

While designing and manufacturing the Spectra-L200 spectrograph I needed to incorporate T thread attachment for various accessories.
There is NO recognised working standard for an astronomical M42 x0.75mm T thread!

I ended up using a Baader T thread spacer as a "master" after having numerous complaints about "your T thread doesn't fit my xxxx"

A real PITA!!!

[bojan]

Hmmm..

M42x0.75 should be standard ISO metric thread.
https://en.wikipedia.org/wiki/T-mount

[Merlin66]

Bojan,
Yes....but I don't think any/ many of the manufacturers of threaded adaptors use an ISO gauge to verify their thread.
It's a bit like the wild west when it comes to astronomical adaptors!!!

[The_bluester]

A big example is Skywatcher parts. I had a little ST80 at one point, bought secondhand on a whim and eventually sold to someone who wanted a guider. The fit of the Skywatcher supplied compression fitting adapter in the focuser drawtube was astonishingly loose. Then I bought the Evostar 72mm this year to use with my ASI294 and the supplied compression adapter was just as bad, you had to be really careful in fitting it as it was absurly easy to cross thread. If I made threaded parts which were that poor a fit in year 8 metalwork (Which included some fitting and turning type stuff) I would have been sent back to the lathe to do it again!

Joshua now has dimensions for an adapter that fits my ED72 drawtube really nicely but my worry is if someone else was to get him to make one, it might fit as nicely as the one he made me, or it might not!

[bojan]

Yes...

It all boils down to quality control (or lack of it).

[Sunfish]

Baader, on their website, publish a discussion about thread sizes for filters and suggest that all standard thread sizes manufactured are not exactly the same and a pretty loose standard exists. As we know , 0.75 tpi does not often measure at that exactly. So they have created their own standard which roughly matches all the known brands so the filters will fit every manufacturer except perhaps the worst. I have a set of three t2 celestron identical new OAG adaptors and one will fit a chinese t2 / m48 adaptor and the others will not go past a few squeaky threads.


I wish I was game to try the boot polish but knowing me I will have boot black every where. Perhaps a different colour and then I could see if it was escaping the thread.

[Sunfish]

Another point I wonder about is the thickness of the anodising coating. Anodising coating must come many different thickness and applied after many different chemical processes , very much like the different grades in window coatings from just a few microns to 20 or more microns. Does that make a difference ..?

[The_bluester]

Not if they are designing and manufacturing things properly. They should know that the final finish will add “A” thickness per surface and design the machining of the part to be “Ax2” undersized before coating it. With a small tolerance for variations in machining and final thickness of the coating.

Joshua on here is more or less needing to work the out part by part for bespoke bits, but when they turn them out in batches hundreds strong!