Dented OTA, dust cap removal

[sorrimen]

Hi all 

About a month back my OTA in a large rucksack slipped out my hands. Annoyingly, the useful little knob for moving the scope around sticks out which meant inescapable denting. Writing this now, thank god it wasn’t my focuser… Anyway, the resultant dent is thankfully very little and the knob still works well enough, but I would of course like to fix the dent! 

Currently, I’m thinking pouring boiling water and trying to work the dent out with my hands. Seems for boiling water I would be best off taking off the black plastic and pointing the tube upside down vertical, so that there’s no risk of water getting into the OTA and coming at all close to either mirror. 
Basically looking for thoughts on the boiling water, as well as whether the black plastic simply screws off and on as it looks like it does. Any other ideas greatly appreciated. 

(Last image just shows the black plastic and one of the 6 screws that hold it in place, dent is on the opposite side)

TIA

Ross

p.s. note that there is the knob screw on inside of the OTA, which may interfere with certain techniques. Does seem itself entirely undamaged so maybe best to remove?

Edited September 26, 2022 by sorrimen

[DaveL59]

The black plastic trim should come out OK, personally I'd remove the secondary too so you've space to work with less risk. You might then be able to ease the metal back using that knob but put a large washer on the inside of the OTA to spread the force a bit. You may not get it quite back into shape tho without resorting to panel beating methods in which case for sure remove the primary and perhaps the focuser

[PeterCPC]

Personally I would leave it as is as long as the scope works ok. There is a danger of doing more damage.

[PeterStudz]

I can see how leaving it as is as long as it’s working is good advice. But personally my OCD would mean that I’d do something about it. 

The plastic rim should easily come off once you remove the screws. And if I was doing it I’d remove both the secondary and primary before any work. I’ve taken something similar apart before (a Skywatcher 200p Dob) just to be safe. It’s not as scary as it seems. Then remove the knob. I’d then use panel beating tools to flatten out the dent as much as possible. You can get a basic panel beating kit for £30. Or just use a panel beating hammer plus curved block of wood. The steel on these tubes is quite thin so it won’t take much effort. Be aware that however you try and take out the dent it will probably remove some white paint. If so a little white metal paint will cover it.

When I was young I use to remove the inevitable dents in a similar fashion on my old car, a 2CV. The metal on that was about the same thickness/thinness 😀

[sorrimen]

Thanks for the suggestions. Got the black trim off okay, went boiling water then a combination of pulling knob and pushing other side and hammering as well. With it being right at the end, I don’t think it’s the right type of dent for boiling water method so going to have to panel beat it seems. For the price of the panel beating kit, might just see if a PDR specialist will have a crack at it.

[Cosmic Geoff]

What are you trying to do with the boiling water? This will have no effect whatsoever on steel or aluminum sheet.  As suggested above, once you remove all the breakable stuff, steel sheet can be straightened out by panel beating.   Inevitably this may flake off some paint, and you will not get the shape perfectly restored.  Bending the metal in the opposite direction with that knob might help to straighten it.

Steel will soften if heated red-hot, but there is no need to go to that extreme. 😁

[sorrimen]

36 minutes ago, Cosmic Geoff said:

What are you trying to do with the boiling water? This will have no effect whatsoever on steel or aluminum sheet.  As suggested above, once you remove all the breakable stuff, steel sheet can be straightened out by panel beating.   Inevitably this may flake off some paint, and you will not get the shape perfectly restored.  Bending the metal in the opposite direction with that knob might help to straighten it.

Steel will soften if heated red-hot, but there is no need to go to that extreme. 😁

God knows 😆 Just following things I see online but I did think it strange. Only saw it used on car bodies and panels though, so figured it was worth trying.

Flaking paint isn’t too much of a worry. More worried that I’ve got no experience with panel beating or metal work and may hammer it to ****! 

[Carbon Brush]

A thin steel OTA will respond well to firm fingers, non marking plastic tools, etc.
You have to bear in mind that some steel will have stretched in the damage so it won't look good as new.
Your bending and beating cannot un-stretch it. But can make it worse if you don't think about how you straighten it.
If some paint does flake off, just buy some touch up paint.

If you are unfamiliar with working steel, then practice on some empty baked beans cans or something a bit more robust like an old fuel can, mower grass box, anything.

Definitely remove the plastic trims, the spider, the knob and all the glass.

At the end of the day, it is cosmetic and doesn't affect the view.

HTH, David.

 

 

[RT65CB-SWL]

1 hour ago, sorrimen said:

God knows 😆 Just following things I see online but I did think it strange. Only saw it used on car bodies and panels though, so figured it was worth trying.

Flaking paint isn’t too much of a worry. More worried that I’ve got no experience with panel beating or metal work and may hammer it to ****! 

Instead of the quote: "...hammer it to ****!" method, then what I would do is strip down the OTA of anything and everything, so you have just the tube. If you have a rolling-pin, then roll the rolling-pin parallel with the tube across the dent on a clean, dry and dust free flat surface. One of many crazy ideas/thoughts going through my head as I write. It will come out after a few attempts, so don't rush it. If you decide to beat it out with a hammer... use a wooden hammer/mallet or tent-peg mallet.  

Edited September 27, 2022 by Philip R

[lvan]

As has been mentioned, firm fingers, maybe pliers with some rubber to cushion or a rubber mallet and a curved surface to gently bang against. You might find something around the house to use. You've got this! You can do this!

Edited September 28, 2022 by lvan

[DaveL59]

if you decide on the hammer approach then make a former to lay that section of the OTA in - wood cut to match the original curve - and then gently work it. Bear in mind tho that hammering may well stretch the metal further. I like the rolling pin idea, using that on the inner with the OTA able to roll on a firm flat surface may do the trick. Pliers I'd avoid since you're as likely to add further to the distortion. Just take your time and work it slowly whichever way you decide to go.

I'm wondering if @Stu might have any other suggestions as he's had to fettle an OTA that got blown over by a strong breeze not so long ago IIRC...

[RT65CB-SWL]

3 minutes ago, DaveL59 said:

if you decide on the hammer approach then make a former to lay that section of the OTA in - wood cut to match the original curve - and then gently work it. Bear in mind tho that hammering may well stretch the metal further. I like the rolling pin idea, using that on the inner with the OTA able to roll on a firm flat surface may do the trick. Pliers I'd avoid since you're as likely to add further to the distortion. Just take your time and work it slowly whichever way you decide to go.

I'm wondering if @Stu might have any other suggestions as he's had to fettle an OTA that got blown over by a strong breeze not so long ago IIRC...

Also @Peter Drew as he has built some nice looking 'scopes.

Edited September 27, 2022 by Philip R

[sorrimen]

Thanks all for the suggestions again. Came across the rolling pin method briefly on another post, so seems like the next thing to try. Luckily got a couple days away to take in more advice and get a plan of action. Thanks Ivan for the words of encouragement as well, more motivated than I’ve ever been! 😆 

[Peter_D]

If it were me and I was continuing to transport the OTA in a backpack, I would wait until I had a few dents in the tube before I attempted to remove them. For one ( and the views are ok), I'd leave it for now.

[Peter Drew]

Some good suggestions so far that should prove successful.  If in doubt about the ability to do this I would advise leaving well alone if the OTA is otherwise working well.  Removing the optics, necessary for panel beating could lead to protracted efforts to replace them and perform the collimation.  If it was my OTA, because I can and have some experience in these matters and not least have the facilities, I would cut two wooden formers, a convex and a concave of the correct radius, support the OTA on the concave former and then tap the inner convex former until the dent was removed.  Good luck.    🙂