Removing a cemented focuser-adapter from CF tube?

[GTom]

The Crayford on my 105mm f7 generic APO gave up terribly and needs a proper replacement. 2" would be straightforward but I want to upgrade to a 2.5" RAP in order to accommodate larger format reducers/cover a FF sensor.

 

Any idea how to replace the thread adapter that appears to be cemented on the tube? So far tried turning by hand, didn't budge at all. Last resort would be to cut it off and screw a new, larger adapter on.

[Albir phil]

Hi sometimes if you turn it to tighten it then allows it to unscrew,not always but as worked for me in the past.Another way is to warm it , tighten it then unscrew I would suggest hot water on a rag so as not to get water into the scope you may need to repeat this more than once. Hope you sort it

 

[Stargazer33]

If the adapter screws INTO the 'scope, then I would cool the adapter. You want it to shrink away from the 'scope tube; not expand into it. If it screws ONTO the tube then indeed heat it to expand it away from the tube. The trick is keeping the other side of the joint at a temperature opposite to the piece you are affecting directly. So heat one side and cool the other. 

[GTom]

Many thanks, I think it is screwed (hopefully) on the outside, will try to warm it with a hair drier this evening.

crazy idea in case it doesn't want to come off: the black adapter piece with the thumbscrews has an ID of approx 72mm. Will try to get someone with a lathe and produce a 72 OD adapter to whatever the focuser needs. My current focuser is long, a shorter SC focuser could work.

Edited September 9, 2023 by GTom

[John]

That looks very similar to the Stellarvue Raptor 105 F/7 or is it a clone ?

[Rusted]

When there is no room for a Prussic loop, I use a car, oil filter, removal strap.
Avoid anything sharp or metal or it might damage the parts. Preferably just plastic and rubber for friction.
A friction design is far more desirable than crushing power.
If these straps can overcome the PST's red locking cement then it might work on your adapter.

Use two straps in opposition to each other. Choose your tools wisely to avoid damage.
There are countless oil filter removal designs on the market. Some destroy the old filter so take care in your choice.

Wrapping the parts in grippy net-like, silicone cooking mats and using hand power might work.
Two people will double the torque applied.  These mats provide superb friction when most needed.
Supermarkets have them sometimes if you search.

 

[Peter Drew]

A pair of "Marigolds" will give you a good manual grip.  PST components can be freed easier after the careful application of some hairdryer heat.     🙂

[GTom]

On 09/09/2023 at 11:27, John said:

That looks very similar to the Stellarvue Raptor 105 F/7 or is it a clone ?

I believe it is an early Synta prototype. The guy I bought it from was in business relationship with them that time. Took it apart, absolutely no writing or marking on the cell, 105/735, lens in cell weighs 1535g.

16 hours ago, Rusted said:

When there is no room for a Prussic loop, I use a car, oil filter, removal strap.
Avoid anything sharp or metal or it might damage the parts. Preferably just plastic and rubber for friction.
A friction design is far more desirable than crushing power.
If these straps can overcome the PST's red locking cement then it might work on your adapter.

Use two straps in opposition to each other. Choose your tools wisely to avoid damage.
There are countless oil filter removal designs on the market. Some destroy the old filter so take care in your choice.

Wrapping the parts in grippy net-like, silicone cooking mats and using hand power might work.
Two people will double the torque applied.  These mats provide superb friction when most needed.
Supermarkets have them sometimes if you search.

 

 

12 hours ago, Peter Drew said:

A pair of "Marigolds" will give you a good manual grip.  PST components can be freed easier after the careful application of some hairdryer heat.     🙂

Thank you both for the good advice! In the meantime I'll look if I can get away with a 2" focuser with a short drawtube.