How can I remove this rear flange? (carbon tube refractor, metal flange)

[pipnina]

Sadly this rear flange is *probably* not threaded, as it attaches to both the inside and outside of the carbon tube snugly and it probably isn't held in by any fasteners as it feels completely smooth on the outside and everywhere on the inside too...

If it's held in by adhesive, is there a way to break it down without damaging the tube? This flange *has* to come out so I can machine it to have a relevant thread for a focuser replacement & upgrade, as the 2" crayford installed paired with the odd mounting mechanism for it are nothing but trouble, and ruin what seems otherwise a very nice quality scope...

 

Any help appreciated!

[AstroKeith]

They are almost bound to have used a similar resin to bond on the end piece, as was used for the basic carbon fibre tube. Some form of epoxy.

Normally epoxy can be removed with heat (about 200C) but in this case that is not an option.

I think it won't come off!

[pipnina]

4 minutes ago, AstroKeith said:

They are almost bound to have used a similar resin to bond on the end piece, as was used for the basic carbon fibre tube. Some form of epoxy.

Normally epoxy can be removed with heat (about 200C) but in this case that is not an option.

I think it won't come off!

Rats

This focuser has to be changed for the scope to be useful to me, so one way or another it's either got to come off, or somehow be machined while still attached to the scope! The latter would be extremely challenging and risk damaging the telescope even more than other options!

Sadly my options here basically boil down to:

Able to remove flange to machine and re-fit: Ideal
Unable to remove flange and:

• Has to be machined in place (not possible most likely, or expensive if it is!)
• Has to be scrapped and I buy a new scope for the third time this year (Dear god no)
• I use a reciprocating saw and simply cut it off, then blowtorch the flange to remove the carbon fiber, making it machinable... I don't like this idea either but if it comes down to it, it's cheaper than buying a new telescope...

[david_taurus83]

If you have access to an engineering shop for machine work could you not come up with an adapter to fit the flange left on the scope and with the thread for the focuser of choice?

[david_taurus83]

Is that a dovetail flange for the focuser?

[pipnina]

7 minutes ago, david_taurus83 said:

If you have access to an engineering shop for machine work could you not come up with an adapter to fit the flange left on the scope and with the thread for the focuser of choice?

Sadly not if I want to increase the focuser barrel size, the opening of the current flange is only 66mm which is too tight even for a 2.5" focuser : /

7 minutes ago, david_taurus83 said:

Is that a dovetail flange for the focuser?

Seems so:

[AstroKeith]

If you are desperate and still determined - there is a possibility.

Heat the metal piece with a blow torch, keeping the direct heat well away from the carbon fibre tube. Eventually, at about 200C the epoxy will give way allowing you to pull the flange off.

Then clean up the end of the tube.

Do this outside in a well ventilated area. The fumes from burning epoxy are unpleasant at least if not toxic.

I take no responsibility for the result! (but if it was mine I would try it)

Edited October 15, 2022 by AstroKeith

[david_taurus83]

What focuser are you trying to fit? 2" not big enough? 

[Carl Au]

Good luck with it, sounds terrifying 

[Tomatobro]

My approach would be to get a drill, the ones used for wood that have a square cutting face and a small pilot centre spike.

I would do some measuring to find out where the limits are of the tube depth and then drill in from the side going gently a bit at a time to expose the layers beneath the flange. If it goes down and a thread is exposed or an epoxy joint at least you would know what you are dealing with.

The small drilled recess can be dealt with after the modification has been done

[Peter Drew]

If it was my telescope I would cut it off.  You would only lose a few millimetres of tube length.  You could then be more aggressive with removal of the remaining material.    🙂

[Astrobits]

I think that I would saw the tube flush with the flange. When onto the lathe work, cut out the remains on the tube, do the necessary mods that you want and perhaps make a small extender to account for a now shortened tube.

Peter posted as I was writing this🙂

Nigel

Edited October 15, 2022 by Astrobits

[wookie1965]

On 14/10/2022 at 15:04, pipnina said:

Rats

This focuser has to be changed for the scope to be useful to me, so one way or another it's either got to come off, or somehow be machined while still attached to the scope! The latter would be extremely challenging and risk damaging the telescope even more than other options!

Sadly my options here basically boil down to:

Able to remove flange to machine and re-fit: Ideal
Unable to remove flange and:

• Has to be machined in place (not possible most likely, or expensive if it is!)
• Has to be scrapped and I buy a new scope for the third time this year (Dear god no)
• I use a reciprocating saw and simply cut it off, then blowtorch the flange to remove the carbon fiber, making it machinable... I don't like this idea either but if it comes down to it, it's cheaper than buying a new telescope...

Phone Mark at Moonraker telescopes he made a flange for me to fit a Skywatcher dual focuser to a Meade 127" . If anything he maybe able to machine in place.

[pipnina]

3 hours ago, david_taurus83 said:

What focuser are you trying to fit? 2" not big enough? 

I'm looking to use the APM riccardi flattener/reducer with it, which means I need at least 2.5" clear barrel, and I figure getting a 3" focuser will prevent any vignetting. At the moment there is a fair bit of vignetting on my APS-C sensor, and I'd like it to be as camera-upgradable as possible. Since the focuser must be changed anyway due to being defective, I may as well do a full-blown upgrade in size while I'm at it!

I was looking at either the feathertouch R&P 3" (M109 x 1mm thread), or the TS 3" R&P (M117 x 1mm thread).

I am going to go into work on monday and see if they'll let me machine it in there (they are often quite relaxed about these things so it may be possible). If that is the case, I just need to decide definitively on which of those focusers I want, cut the flange off (sawing seems to be the most popular method in this thread so far) and hopefully by that point it just becomes a matter of machining and fitting that focuser, and gluing the flange back on...

If it works, hurrah! If it goes wrong, I will have to reconcile a lot of emotions regarding a lost £2000 haha.😬

[david_taurus83]

I can't see how you can machine that out and still use it after. What's the ID of the tube? TS do various adapters to fit different OTA's. I'd be inclined like others to chop the tube and find or create an adapter to suit that. My concern with this approach though would be how much dust is going to end up on the lens from cutting..

[Rusted]

Remove the focuser and stuff the tail end baffle with tissue or a soft cloth to stop dust entry into the OTA.
Tape a thick roll of paper or masking tape to guide the saw blade and protect the CF tube from cosmetic damage if you slip.
Use a fine toothed hacksaw and work slowly steadily.

Ideally you want a B&D style workbench.
With the jaws opened just enough to act as a well padded cradle to suit the diameter of the OTA.
NOT WITH THE OTA TIGHTENED BETWEEN THE JAWS!

Once the tail end has parted from the CF tube you can rub the cut end on sandpaper to true and smooth it.
I'd glue the sandpaper to a scrap of plywood or metal to keep it flat.



 

[900SL]

If you cut it make sure it is square to the tube axis, or you will be off axis with the focuser. I'd ask a good machinist how best to do it

[pipnina]

1 hour ago, david_taurus83 said:

I can't see how you can machine that out and still use it after. What's the ID of the tube? TS do various adapters to fit different OTA's. I'd be inclined like others to chop the tube and find or create an adapter to suit that. My concern with this approach though would be how much dust is going to end up on the lens from cutting..

The best ID I can give is "SET Optics 130mm f6.6 APO triplet". Apparently the company went bust according to the previous owner, and even they had it second hand so I am the third owner!

 

[Rusted]

1 hour ago, 900SL said:

If you cut it make sure it is square to the tube axis, or you will be off axis with the focuser. I'd ask a good machinist how best to do it

Wrapping the tube with straight tape or paper to provide a guide ensures close proximity to squareness to the axis.
I've used the technique for decades. With tubes up to 18" Ø.

[Peter Drew]

I would expect that the flange unit will be a decent fit to the main tube once the sawn off material is removed.  If the flange is to be glued back on you can adjust the squareness by placing a well collimated laser unit into the  eyepiece holder and making sure that the beam exits through the centre of the objective.  Don't use superglue or any other instant variety!    🙂

[pipnina]

Just now, Peter Drew said:

I would expect that the flange unit will be a decent fit to the main tube once the sawn off material is removed.  If the flange is to be glued back on you can adjust the squareness by placing a well collimated laser unit into the  eyepiece holder and making sure that the beam exits through the centre of the objective.  Don't use superglue or any other instant variety!    🙂

I know that the TS 3" R&P has an accessory you can buy separately to adjust focuser squareness, looks like a tilt adapter for cameras that sits between the scope and focuser. I'd probably buy that with the TS if I go for that option to make things simpler.

[pipnina]

Update: seems like someone at work can help me machine the flange. I have an M117x1 focuser tilt adapter now to use to help us form the thread on the scope side to fit. Now I just need to cut the scope flange off.

On 15/10/2022 at 22:08, Peter Drew said:

I would expect that the flange unit will be a decent fit to the main tube once the sawn off material is removed.  If the flange is to be glued back on you can adjust the squareness by placing a well collimated laser unit into the  eyepiece holder and making sure that the beam exits through the centre of the objective.  Don't use superglue or any other instant variety!    🙂

Regarding re-gluing: What glue would you recommend? Should I find a proper tube of epoxy and hardener mix or are other glues appropriate here?

 

Cheers all!

[Rusted]

On 15/10/2022 at 23:17, pipnina said:

I know that the TS 3" R&P has an accessory you can buy separately to adjust focuser squareness, looks like a tilt adapter for cameras that sits between the scope and focuser. I'd probably buy that with the TS if I go for that option to make things simpler.

The square TS bases have tilt adjustment. Here is my FT2.5x3.5:

https://fullerscopes.blogspot.com/2020/10/16102020-starlight-instruments-feather.html

[Astrobits]

Epoxy would be the best. Go for the normal and not the quick set to give you more time to align the flange. Just a thought, check the position of the internal part of the flange before cutting. It is possible that it is longer than the outside might suggest. A longer interior could help to assemble and align  the components at the original manufacturing stage.

Nigel

[billhinge]

On 15/10/2022 at 17:09, pipnina said:

I'm looking to use the APM riccardi flattener/reducer with it, which means I need at least 2.5" clear barrel, and I figure getting a 3" focuser will prevent any vignetting. At the moment there is a fair bit of vignetting on my APS-C sensor, and I'd like it to be as camera-upgradable as possible. Since the focuser must be changed anyway due to being defective, I may as well do a full-blown upgrade in size while I'm at it!

I was looking at either the feathertouch R&P 3" (M109 x 1mm thread), or the TS 3" R&P (M117 x 1mm thread).

I am going to go into work on monday and see if they'll let me machine it in there (they are often quite relaxed about these things so it may be possible). If that is the case, I just need to decide definitively on which of those focusers I want, cut the flange off (sawing seems to be the most popular method in this thread so far) and hopefully by that point it just becomes a matter of machining and fitting that focuser, and gluing the flange back on...

If it works, hurrah! If it goes wrong, I will have to reconcile a lot of emotions regarding a lost £2000 haha.😬

Why didn't you say. That's what I'm doing with my TMB 115, fortunately only screws to deal with. If you are going to use the Riccardi reducer it will change the back focus so chopping the tube is beneficial to obtaining focus.  Theoretically it could change the internal baffle spacing/size 

It had a  native 2" feathertouch but wanted to use the Riccardi's.  I wanted the 3" or 3.5"  feathertouch but they are hard to find  due to issues at the company and if you can then they are very expensive. You also need the adapter to fit the focuser to the tube. If your tube is non standard diameter getting the adapter is a challenge. (I drew my own and 3d printed one). Rather than getting the feathertouch I bought the APM 3.75". Its half the price and the feathertouch really isn't worth twice the price