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Pinching Primary Mirror

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#1 patindaytona

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Posted 12 September 2019 - 04:51 PM

Someone here already assured me that i couldn't pinch the primary mirror by over tightening the lock screws...but...I'd like to be RE-assured! I do tighten them with a screw driver. I don't go nuts on them, but they are much tighter than by hand tightening.



#2 havasman

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Posted 12 September 2019 - 05:36 PM

TIGHT is very bad. Leave about the distance between the 2 lines below between the mirror clips and the mirror surface.

 

                                                                 //


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#3 Redbetter

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Posted 12 September 2019 - 06:12 PM

Sounds like you are over tightening them and I would expect degradation of the image.  Other than during transport there is no need to have them that snug (and likely not even then as it hasn't been an issue with our 10").

 

On the 10" we tighten them until they just make contact, then back off a little. 


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#4 Don H

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Posted 12 September 2019 - 06:22 PM

The lock screw tips usually just butt up against the back plate of the mirror cell. This should not be related to how tight the retaining clips are on the front of the primary cell. But as mentioned, those clips should not touch the mirror. 

 

I don't see why you need to crank on the lock screws that much. The idea is that by touching the back of the cell plate, it will not move due to spring sag. You can simply check them each session and see if they have vibrated loose, and just finger tighten them a bit again. If any become loose, double check collimation prior to tightening the lock screws again.


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#5 Bean614

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Posted 12 September 2019 - 06:36 PM

Make a note of who told you that, and remind yourself not to listen to him/her again!


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#6 Kunama

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Posted 12 September 2019 - 06:53 PM

The lock screw tips usually just butt up against the back plate of the mirror cell. This should not be related to how tight the retaining clips are on the front of the primary cell. But as mentioned, those clips should not touch the mirror. 

 

I don't see why you need to crank on the lock screws that much. The idea is that by touching the back of the cell plate, it will not move due to spring sag. You can simply check them each session and see if they have vibrated loose, and just finger tighten them a bit again. If any become loose, double check collimation prior to tightening the lock screws again.

What he said .... waytogo.gif


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#7 Ken Watts

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Posted 12 September 2019 - 08:38 PM

I had a pinched mirror, not by the retaining clips, but from the collimation screws coming too far through the cell.  Just another place to check things out. 


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#8 scotsman328i

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Posted 12 September 2019 - 08:55 PM

Everyone responding here can’t emphasize enough to loosen the clips. Your mirror should be ‘held’ in place...not ‘gripped’ in place. Havasman said it best...the distance between the two lines, approx 1mm.



#9 Kunama

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Posted 12 September 2019 - 09:01 PM

Everyone responding here can’t emphasize enough to loosen the clips. Your mirror should be ‘held’ in place...not ‘gripped’ in place. Havasman said it best...the distance between the two lines, approx 1mm.

I think the OP is talking about the lock screws that lock the cell in place after collimation not the mirror clips... 


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#10 scotsman328i

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Posted 13 September 2019 - 05:10 AM

I think the OP is talking about the lock screws that lock the cell in place after collimation not the mirror clips... 

Oh I see, if this is the case, then I simply will concur on making a slight grip of the mirror cell over any overtightening of the lock screws. 



#11 patindaytona

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Posted 13 September 2019 - 08:39 AM

The lock screw tips usually just butt up against the back plate of the mirror cell. This should not be related to how tight the retaining clips are on the front of the primary cell. But as mentioned, those clips should not touch the mirror. 

 

I don't see why you need to crank on the lock screws that much. The idea is that by touching the back of the cell plate, it will not move due to spring sag. You can simply check them each session and see if they have vibrated loose, and just finger tighten them a bit again. If any become loose, double check collimation prior to tightening the lock screws again.

Makes sense. After reading all these, I'm only finger tightening them from now on. I hope I didnt' permanently do anything to my primary already. I have not done the over tightening except for past week or two at most.

They do have a slot in the locking screws for a screw driver. I wasn't tightening them like a screw in wood! But still......pretty tight.



#12 Vic Menard

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Posted 13 September 2019 - 09:58 AM

Jeez--so much angst!

If I recall correctly, your primary mirror locking screws are adjacent your collimating screws. It's extremely unlikely that you could have tightened them enough to stress the primary mirror (you would have to bend the primary mirror cell).

 

They're locking screws--make them snug enough that they don't unscrew themselves--and don't worry about it.


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#13 patindaytona

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Posted 13 September 2019 - 10:43 AM

Jeez--so much angst!

If I recall correctly, your primary mirror locking screws are adjacent your collimating screws. It's extremely unlikely that you could have tightened them enough to stress the primary mirror (you would have to bend the primary mirror cell).

 

They're locking screws--make them snug enough that they don't unscrew themselves--and don't worry about it.

Yes they are adjacent to the collimating screws. ok




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