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Rolling and swinging - easy and safe way to fix a dented dewshield

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#1 LukaszLu

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Posted 27 March 2021 - 07:37 PM

Since the topic of fixing a bent dewshield came back many times, and the proposed methods seemed to me quite invasive and risky, I would like to share my own way of dealing with this problem. In my opinion, it is relatively safe and does not require any special tools.

 

The dewshield of the Towa 60/900 refractor was bent quite badly in several places. I used the method of manually pushing out the flattened fragments from the inside and pressing too sharp arches from the outside. I covered the pressed surfaces with 3 layers of masking tape. It is worth marking on it with a pencil the center of the distortion that we want to remove. Then, with a piece of wood on the outside and an old metal pump on the inside, I was compressing the area around the center of distortion using a rolling or swinging motion.

 

In case of pressure from the inside, I placed the dew shield on the edge of the table. The degree of its extension and the angle at which the tube is held allow quite a precise regulation of the pressure effects. What you cannot see in the photos is the other hand that I was holding the phone with. While working, I tried to use it to squeeze the dewshield so as to counter, in a sense, the side forces pushing the tube sideways.

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Edited by LukaszLu, 27 March 2021 - 07:53 PM.

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#2 LukaszLu

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Posted 27 March 2021 - 07:39 PM

As you can see in the case of the 60 mm aluminum dewshield, the method turned out to be very simple and quite effective. It is a pity that the previous owner was impatient and tried to fix the edge with pliers, cutting the paintwork and causing even more damage. But even these small and sharp bends I managed to smooth out to the certain extend with the "rolling and swinging" method.

 

Perhaps the method is not as precise as some of the other ideas, but the effect of course depends on patience, which is not my virtue as well :-) The most important thing - it is a method of small steps, so there is no fear that with one reckless hit we will cause even more damage, like aluminum cracking.

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Edited by LukaszLu, 27 March 2021 - 07:48 PM.

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#3 DouglasPaul

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Posted 27 March 2021 - 08:10 PM

Very nice, thank you for posting this. I just picked up a Tasco 17T that's been fairly well used/abused with a bent dewshield along with plenty of other cosmetic "challenges". But I managed to put it on the moon sans finder scope and I was pretty impressed. It looks like it will be my first restore project.



#4 Kasmos

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Posted 27 March 2021 - 08:11 PM

Good work and way to do it!

 

I've done it a couple of times and 4 years ago did a thread about it and tube dent removal. My second dew shield repair is at post#17. You might take a look just for the heck of it.

 

https://www.cloudyni...t-removal-tips/


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#5 TOMDEY

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Posted 27 March 2021 - 08:37 PM

Well --- that came out good! The material must be malleable / ductile aluminum, right? I guess the guys in an auto body shop would also have the tools and skills to address telescope parts like that... for those loath to tackle their own stuff.    Tom



#6 Kokatha man

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Posted 27 March 2021 - 08:48 PM

An oldie but goldie Luke waytogo.gif  - the only other comment I'd make is that a couple of different diameter "rollers" helps, with a larger one for the finishing touches...that & wooden "rolling pins" are a bit more protective of internal threads sometimes. wink.gif



#7 LukaszLu

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Posted 28 March 2021 - 07:06 AM

Very nice, thank you for posting this. I just picked up a Tasco 17T that's been fairly well used/abused with a bent dewshield along with plenty of other cosmetic "challenges". But I managed to put it on the moon sans finder scope and I was pretty impressed. It looks like it will be my first restore project.

Thanks! My Towa is also in bad shape, but it was a shame not to try to save it. I'm not even sure what the model it is - probably ET2? If I can restore it, I will be happy to show the restore story. I'd love to see a report from your project!

 

20210324_223635.jpg

 

 

An oldie but goldie Luke waytogo.gif  - the only other comment I'd make is that a couple of different diameter "rollers" helps, with a larger one for the finishing touches...that & wooden "rolling pins" are a bit more protective of internal threads sometimes. wink.gif

Thank you! You're right, it gets more complicated with the internal thread, especially if it's aluminum. Then we usually have a very thick problem, because straightening the thread is not the same as straightening the edge aesthetically. I am struggling with this problem because the cell was badly hit from the side at the height of the thread and dented, as was the thread on the tube. I have no idea how to deal with it yet ...

 

20210328_000954.jpg


 

Good work and way to do it!

 

I've done it a couple of times and 4 years ago did a thread about it and tube dent removal. My second dew shield repair is at post#17. You might take a look just for the heck of it.

 

https://www.cloudyni...t-removal-tips/

 
Thanks! I have studied your excellent thread already. I have to admit that it was an inspiration for me. Your advice to simply use hand pressure made me think that by using the same force you could try to distribute the pressure with a wooden block...


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#8 Garyth64

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Posted 28 March 2021 - 07:53 AM

I briefly looked for a post of mine, and another person, where we used wood to eliminate the dents.  I used Oak.

 

One section of wood fits the ID of the tube, the other section fits the OD.  A clamp is used to tighten the two pieces of wood with the tube in-between.

 

I was able to eliminate the dent on the threaded end of a Swift tube, and the lens cell screwed right on.  Only thing I had to do was to place shims in curved wood to apply a little more pressure to the dent.  The ID of the curve was shimmed to form a slight bump in the middle.  The OD section was shimmed to form two bumps on either side of the dent.

 

A two piece lens cell on another scope of mine was just slightly dented, and the one section would not screw into the other. It was about a half mm out of round, I just couldn't seem to get it perfect.  That lens cell is pretty stout.

 

For what I can see in your picture, I think the two sections of wood with a clamp might work.  I also might make the two sections out of aluminum.

 

dent tool.jpg


Edited by Garyth64, 28 March 2021 - 08:00 AM.

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#9 LukaszLu

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Posted 28 March 2021 - 08:21 AM

Brilliant idea! Do I understand correctly that your experience with shims shows that the diameter of the internal element should be slightly smaller than the internal diameter of the pipe?



#10 starman876

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Posted 28 March 2021 - 09:26 AM

 Very nice work.  Congrats.



#11 Garyth64

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Posted 28 March 2021 - 09:44 AM

Brilliant idea! Do I understand correctly that your experience with shims shows that the diameter of the internal element should be slightly smaller than the internal diameter of the pipe?

In the photo, you can see the three places where I used the shims.  In this photo, they are just a few layers of masking tape.  Real thin sections of sheet metal will work too.  The idea is to push up on the dent from the inside, and down on either side of the dent on the outside.  You have to push the dent just a hair further than it's ideal spot, and then let it flex back.   It's trial and error.

 

Here's a picture of the tube I fixed:

 

dent.jpg

 

After the fix, the lens cell screwed easily onto the tube.

This is the tube that I had powder coated.  While the guy was glass-beading the tube, the air pressure blew the tube off his bench, causing the dent.  He was also glass-beading the inside of the tube.  I asked him why.  They were going to powder coat the inside of the tube the same color as the outside.  Aaaah!  I told him the inside has to remain flat black.  They did paint the inside of the tube flat black.


Edited by Garyth64, 28 March 2021 - 09:54 AM.

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#12 LukaszLu

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Posted 28 March 2021 - 05:32 PM

Thanks a lot! Glass-beading inside the tube... Well, you never know when you will learn something new :-)



#13 Garyth64

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Posted 28 March 2021 - 06:59 PM

Thanks a lot! Glass-beading inside the tube... Well, you never know when you will learn something new :-)

They were glass-beading the outside of the tube to powder coat it.  They were only to glass-bead the outside. They started on the inside of the tube when it got blown off and hit the floor.  They were not suppose to glass-bead the inside of the tube.  Maybe I didn't clarify that.


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#14 Kokatha man

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Posted 28 March 2021 - 07:30 PM

They were glass-beading the outside of the tube to powder coat it.  They were only to glass-bead the outside. They started on the inside of the tube when it got blown off and hit the floor.  They were not suppose to glass-bead the inside of the tube.  Maybe I didn't clarify that.

I groan when someone does something like that - especially when you've been very explicit with your instructions...although whether they're passed on if someone else at the factory gets the actual job is another issue! frown.gif


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#15 LukaszLu

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Posted 29 March 2021 - 05:12 AM

Or maybe that's not a bad concept at all? Maybe such a surface painted then matt would help minimize glare?




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