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XT10 Plus fan mounting

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#1 bazookaman

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Posted 04 December 2020 - 02:13 PM

I bought a fan for my Orion XT10 but the screws that came with the fan aren't the right threads. There is also not enough room between the bottom and the mirror to fit a zip tie between it and bend into the hole. So, does anyone happen to know what screw thread type I need?


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#2 ram812

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Posted 04 December 2020 - 07:30 PM

  Hello!

 Our light bucket XT10's use M4x.7 thread. I used them to mount a Mag-Lev fan on mine. Nice, quiet vibration free, I've had frost on the OTA from the mirror cell to the first tube ring when using this in the cold and not a bit of dew on the primary. I have my fan positioned so it's pulling air down the tube which appears to also help keep dew from forming on the secondary mirror. Some folks like to blow air up the tube, and I guess it works for them. I seal the mirror cell itself to help keep stray light from bouncing back into the tube (Using thick, circular cutout cardboard painted black and Velcro tabs every few inches around it) and in doing so found out the fan and the area around it needs a yearly cleaning, if anything just for the dust and pollen that tends to collect there. 

  Hope this helps, and welcome to Cloudy Nights, your one stop information hotspot for our Amateur Astronomy needs!grin.gif Ralphgrin.gif


Edited by ram812, 04 December 2020 - 07:31 PM.

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#3 bazookaman

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Posted 04 December 2020 - 08:21 PM

Excellent, thanks... would it be useful to put some sort of air filter on the outer surface of your cardboard seal to keep particles from entering the tube if you were sucking air from underneath (which you are not).


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#4 ram812

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Posted 04 December 2020 - 09:53 PM

Hello, again!

  Yep, I bought my XT about 6 or 7 years ago and right away knew that light and dust would be migrating into the OTA. So when I did the cutout I brought it all the way to the outer edge of the cell. That first year I must have dusted it out 3 or 4 times (I have 60' and 70'+ pines and old white oaks on my landtongue2.gif) and resorted to using a closed cell foam along the outer edges of the fan cell and perimeter of the tube itself. Pollen is hard on mirrors but since I did this I have yet to clean the mirror itself, choosing to go on a 10 year (Or so) mirror cleaning cycle. The foam gets pulled once a year too, just to dust and clean the foam itself and check to see if the blades need to be Q-tipped with rubbing alcohol, as dust can create an imbalance in the blades causing small vibrations to appear. "Preventative Maintenance" is what I call it. Next time I have it out I'll take pictures of the rear cell and post them.

  I take what I'd call "Anal Care" of my kit as it is an investment I wanted to have for the rest of my life. The venerable XT10 and CGEM has provided my family and friends with a ton of great times, never letting me down. But as I age (Nearing 60) I purchased a Starizona pier adapter kit and am slowly adding supplies so maybe in this next spring and summer the whole unit will be permanently mounted in a ROR, taking a staircase out of the equationlaugh.gif. Have some fun and clear skies to ya! Ralph   


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#5 SteveG

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Posted 04 December 2020 - 11:34 PM

All of the super-quiet 80 mm fans I've purchased have come with rubber mounting spikes included. No screws at all, you just push the rubber spike through the fan and hole on your cell. I agree that a rear seal helps cool the mirror, and will allow that air to come up through the tube. I ended up putting a circular ring just above my primary mirror, that forces the air across the face of the mirror. I did smoke tests to see the difference, and it works very well.

 

There was a lot of discussion over the years about which direction the fan should blow, and the consensus (both here and ATM forums) was that the fan should blow against the back of the mirror.

 

Here are the vibration free rubber spikes, as seen from the top of the mirror cell.

 

LB Cell.jpg

 

 


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#6 MellonLake

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Posted 05 December 2020 - 10:10 AM

I made my baffle out of poster board and have it tight to the back of the telescope.  I use the collimation lock screws to hold it tight to the bottom face of the telescope, this drives more air up the tube.  My fan is a 5B USB fan from Amazon.  I use a 10,000 mAh USB power bank to power the fan (No wires leaving the tube).  It works well, no vibrations visible at 240X (Mars' tiny polar ice cap is clearly visible in good seeing).  All tolled it cost $25.  If you leave the front cover on and remove the focuser cap, you can really feel the airflow coming up through the tube.

 

Using a baffle helps break up air currents in the tube that lead to "seeing" issues while the mirror and tube are cooling.  The baffle will also help drive air up the tube to keep the mirrors warm later in the night.  If the mirrors cool too much (loose heat due to radiation to space) the mirrors will drop below the air temperature and can fog.  Keeping the fan running all night will help to keep the mirrors warm and dew free later in the night.    

 

 

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  • fan.jpg

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#7 bazookaman

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Posted 05 December 2020 - 11:25 AM

I made my baffle out of poster board and have it tight to the back of the telescope.  I use the collimation lock screws to hold it tight to the bottom face of the telescope, this drives more air up the tube.  My fan is a 5B USB fan from Amazon.  I use a 10,000 mAh USB power bank to power the fan (No wires leaving the tube).  It works well, no vibrations visible at 240X (Mars' tiny polar ice cap is clearly visible in good seeing).  All tolled it cost $25.  If you leave the front cover on and remove the focuser cap, you can really feel the airflow coming up through the tube.

 

Using a baffle helps break up air currents in the tube that lead to "seeing" issues while the mirror and tube are cooling.  The baffle will also help drive air up the tube to keep the mirrors warm later in the night.  If the mirrors cool too much (loose heat due to radiation to space) the mirrors will drop below the air temperature and can fog.  Keeping the fan running all night will help to keep the mirrors warm and dew free later in the night.    

Great idea on the charge pack Mellon, I just added one to the cart. I assume you velcro it to something?

 

It looks like you screwed the fan to the poster board, or do the screws go into the bracket with the fan holes?

 

 

All of the super-quiet 80 mm fans I've purchased have come with rubber mounting spikes included. No screws at all, you just push the rubber spike through the fan and hole on your cell. I agree that a rear seal helps cool the mirror, and will allow that air to come up through the tube. I ended up putting a circular ring just above my primary mirror, that forces the air across the face of the mirror. I did smoke tests to see the difference, and it works very well.

 

There was a lot of discussion over the years about which direction the fan should blow, and the consensus (both here and ATM forums) was that the fan should blow against the back of the mirror.

 

Here are the vibration free rubber spikes, as seen from the top of the mirror cell.

 

attachicon.gifLB Cell.jpg

 

I don't think mine came with spikes. I might have some lying around, but I couldn't get them in without taking apart the ota, and I'd like to avoid that if possible.



#8 MellonLake

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Posted 05 December 2020 - 11:36 AM

My fan is not Velcroed.  I simply attached the fan to the poster board baffle with screws and nuts which I bought at a hardware store.  The fans have very good bearings and usually don't Vibrate.  If you have a slight vibration in your fan you could use Velcro to attach it.  I used tape to cover the edges of the poster board so that the paper would not delaminate over time.  It is now about 2 years old and going well.  I have tested if there are vibrations by looking at planets at 240X with and without the fan going and cannot see a difference.  

 

I now (more recently than the picture) do not use the primary mirror lock screws, I have found they actually don't do anything.   So I have used some screws with spacers to push the baffle tight against the rear of the tube so more air goes up the tube (you could also use shorter screws).  

 

Yes the power bank is Velcroed to the baffle.  If the power bank has bright LEDS you might need to cover them with black tape.  


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#9 bazookaman

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Posted 05 December 2020 - 12:47 PM

Ok, I think this looks like an easy solution, and it allows me to use a larger fan. I think the 80mm seems quite small for a 10" mirror. I originally bought a 120mm so I have that one ready to go.

 

 

So I have used some screws with spacers to push the baffle tight against the rear of the tube so more air goes up the tube (you could also use shorter screws).  

I'm not clear what this means. What are the screws going into, the poster board? Pushing against the mirror cell?



#10 MellonLake

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Posted 05 December 2020 - 12:57 PM

I took the lock screws out and put the screws and spacers in the image below in.  This way if I stand the tube up on its end, the tube rests on the screws rather than the fan.  Also, the spacer compress the baffle so it is tight against the bottom of the tube and does not let the fan air leak out the bottom of the tube.

 

FYI - I tested the collimation, with and without the lock screws, and the use of the lock screws make no difference regardless of the angle of the tube.  So they are redundant.  After using these new screws and spacers, in place of the original lock screws, for the baffle, there is no locking mechanism now.

 

Lock screw mod small.jpg


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#11 bazookaman

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Posted 05 December 2020 - 01:05 PM

Gotcha. I think I'm going to just velcro the whole assembly to the rim and cut out notches for the col screws. We'll see how it goes.


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#12 SteveG

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Posted 05 December 2020 - 03:57 PM

Great idea on the charge pack Mellon, I just added one to the cart. I assume you velcro it to something?

 

It looks like you screwed the fan to the poster board, or do the screws go into the bracket with the fan holes?

 

 

 

I don't think mine came with spikes. I might have some lying around, but I couldn't get them in without taking apart the ota, and I'd like to avoid that if possible.

Here's one I purchased. You would need to remove the primary though:

https://www.quietpcu...80mm-AFDP-8025B



#13 SteveG

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Posted 05 December 2020 - 04:00 PM

Ok, I think this looks like an easy solution, and it allows me to use a larger fan. I think the 80mm seems quite small for a 10" mirror. I originally bought a 120mm so I have that one ready to go.

 

 

I'm not clear what this means. What are the screws going into, the poster board? Pushing against the mirror cell?

At 10", 15-25 cfm is all you need. You can get that from 80 mm:

 

https://www.fpi-prot...r/fanselect.htm



#14 SteveG

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Posted 05 December 2020 - 04:03 PM

 

 

FYI - I tested the collimation, with and without the lock screws, and the use of the lock screws make no difference regardless of the angle of the tube.  So they are redundant.  After using these new screws and spacers, in place of the original lock screws, for the baffle, there is no locking mechanism now.

 

attachicon.gifLock screw mod small.jpg

Provided the primary springs are strong enough, I agree. I've had to replace the springs on most of my Chinese dob's. YMMV


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#15 bazookaman

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Posted 05 December 2020 - 06:10 PM

At 10", 15-25 cfm is all you need. You can get that from 80 mm:

 

https://www.fpi-prot...r/fanselect.htm

Thanks for the link, that's good info. I'll probably do the large fan and just leave it on low speed. I already have the baffle cut, but I need to get some small machine screws tomorrow to attach the fan to the baffle.


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#16 bazookaman

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Posted 06 December 2020 - 04:06 PM

fanback.jpg

 

fanfront.jpg

 

 


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#17 bazookaman

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Posted 06 December 2020 - 04:06 PM

Just waiting on the battery pack to get here.

 

fanassembled.jpg


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#18 MellonLake

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Posted 06 December 2020 - 04:12 PM

It will move a lot of air!  Let us know how it works!  Is the baffle held in place by Velcro?

 

Also, you may want to add a cage to the fan at some point.  I kept putting my fingers into the fan when I was collimating (Doh!).  Does not really hurt but scares you a bit.  


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#19 bazookaman

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Posted 06 December 2020 - 04:24 PM

It will move a lot of air!  Let us know how it works!  Is the baffle held in place by Velcro?

 

Also, you may want to add a cage to the fan at some point.  I kept putting my fingers into the fan when I was collimating (Doh!).  Does not really hurt but scares you a bit.  

3 velcro strips. If it gets loose, I'll add 3 more. But even without the velcro it's tight enough to hold it in place so I think it's good.

 

I have the cage, I just forgot to put it back on.


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#20 ram812

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Posted 07 December 2020 - 11:01 AM

Excellent, thanks... would it be useful to put some sort of air filter on the outer surface of your cardboard seal to keep particles from entering the tube if you were sucking air from underneath (which you are not).

 One thing I also do is when I'm pre-cooling for an evening out is put a "Pie Plate" cover over the end of the tube (Secondary end!) and just barely pull the cap from the focuser so a draft is created. It causes vacuum in the tube itself which can be seen as the pie plate cover "Rises" pushing air out of the focuser and cooling the secondary. I ran the fan both ways and found my primary doesn't collect as much dust from forced outside air coming in. And even though the mag-lev fan is smooth as silk I still switch it off when viewing or taking a quick ID pick of my target. Contrary? Maybe, but as I stated earlier it works for me. I'd really like fans around the circumference ahead of the primary blowing air across it, but I'm leery about boring holes in "Old Bessy'.laugh.gif Ralph

  PS. I have 5 reflectors from 76mm to 254mm and every one has been modified in this manner, Using PC mini fans works!


Edited by ram812, 07 December 2020 - 11:04 AM.

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