PST Modification - removing the Gold Tube?

Poita (Peter) · #1 02-09-2011, 09:31 AM

I have everything ready to go with the PST modification to move it all over to a 90mm objective.
The only holdup is removing the gold tube.
I have removed the gold tube with etalon in place, but cannot separate the gold tube from the tuning/etalon mechanism.

I have broken two heavy duty boa-constrictor pipe wrenches in the attempt.

Anyone have any ideas how to get the two parts unscrewed? They are drowned in red threadlock so they are a bugger to get apart.

And I thought the eyepiece holder was hard to remove

Poita (Peter) · #2 02-09-2011, 09:49 AM

Tried it in a padded vice - no go. This thing is in *tight*

Merlin66 (Ken) · #3 02-09-2011, 09:51 AM

Peter,
Sounds like you have one of the early assemblies from Mexico - they went overboard with the loctite!
No easy answer....I had similar problems with a unit and ended up with a couple of HD Boa straps ( I saw a suggestion recently where a piece of car fan belt was clamped using a pair of molegrips to form a strap)
A good sharp pull when everything is set up should/will get it started.
Don't be tempted to use any dissolving type aid....there's a 99% chance it gets into the filter assembly then you're lost.
Unfortunately, according to the supplier you need to heat up the joint above 250 degrees to soften the loctite, so again that's not an option.
Worst case if all else fails you could cut the gold tube and use it as the mounting adaptor to the donor scope.
With a bit of patience and the right gear I haven't found one yet which will not separate - but there's always a first time.

multiweb (Marc) · #4 02-09-2011, 10:01 AM

Red Loctite ... Ouch! Heat is the only solution to break the bond but a goodle search brought this up:

"Methyl-ethyl-ketone (MEK) will dissolve loctite. It will also dissolve your liver, and the insulation on the wires. Better to use heat."

Maybe with a small syringe along the thred, bit at a time?

Merlin66 (Ken) · #5 02-09-2011, 10:02 AM

Seriously, don't even think about it......

Poita (Peter) · #6 02-09-2011, 10:34 AM

It is seriously getting to the cutting the tube stage, it is like the bast age is welded on.

Poita (Peter) · #7 02-09-2011, 11:34 AM

Even the mole grip solution is not working, it seriously won't budge.

Which leaves me with cutting the tube, which I really, really, really didn't want to do as I already had an adapter made.

Am I better to use a pipe cutter to cut the tube, or hacksaw it off?

Poita (Peter) · #8 02-09-2011, 01:38 PM

Broke my 3rd Heavy Duty Boa, drilled a hole through the tube, inserted a long screwdriver, still won't budge.

Have taken the hacksaw to it. Am very disappointed as I hoped to be able to return to a stock config if I wasn't happy with it, so I am now hopeful the 90mm will be enough of an improvement that I won't ever regret it!

multiweb (Marc) · #9 02-09-2011, 01:54 PM

Sounds like you're past the point of no return now. I would still have applied some kind of solvent very locally to the edge of the thread interface with the loctite. All you need is to break the initial bond. You'll never get loctite out otherwise unless you heat it really hard then use brute force and in your case it wasn't an option. Even when heated you'd have to unscrew it real fast while it's hot or it will seize again.

Poita (Peter) · #10 02-09-2011, 02:11 PM

The thread is pretty deep, and there is so much loctite that it is like a hot-glue-gun went at it. I don't think a solvent would have gotten me there.

I figured if this all worked, I'd never want to go back to 40mm anyway.

I've just clamped the PST body to the 90mm for a quick look, and WOW!

It is an astoundingly better picture, looks much more like the photos people post here.

Now I just have to work out how to attach it all now that I have a bit of extra tube out the front that I really wasn't counting on.

multiweb (Marc) · #11 02-09-2011, 02:18 PM

Solvent will impregnate by capillarity. Very small amount goes a long way.

Poita (Peter) · #12 02-09-2011, 03:36 PM

I dunno, it is up against a wall of red

I may try the solvent now that I can see the etalon and can be sure it isn't getting anywhere near it. I would like to be rid of the tube end.

Merlin66 (Ken) · #13 02-09-2011, 03:37 PM

Sounds like you got there in the end.
I have a guy in the UK who cut the tube (left about a 50mm nosepiece) instead of buying an adaptor. He made a sleeve to allow it to fit into the rear of the donor scope. Worked OK. He also had a connection sleeve machined (don't have the details) - must have been <2" inside diameter by roughly 100mm long to allow him to re-use the front of the gold tube with the objective.
I'm not sure, however, if he ever went back to a standard configuration.

Just double check for filings etc inside the tube at the etalon...also all the shaking around may have loosened the front and rear lenses at the etalon. These should obviously be tightened and secure.
I'm sure you'll be impressed with the final results....
Your current efforts will make the Stage II mod (dump the black box) feel like child's play.