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Equipment Discussions >> ATM, Optics and DIY Forum

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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: Fan baffle material new [Re: Dick Jacobson]
      #5669076 - 02/08/13 01:39 PM

Quote:

but the foam in the core should be dew resistant.







it doesn't hold up well to moisture and bends easily, gatorboard is similar but stiffer and won't bend so easily.


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Jeff Porter
super member
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Reged: 09/03/10

Loc: Utah
Re: Fan baffle material new [Re: Project Galileo]
      #5669701 - 02/08/13 08:12 PM

Great job, looks very professional. Plus it takes care of the need for additional weight.

Jeff P


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azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: Fan baffle material new [Re: Mark Peterman]
      #5669759 - 02/08/13 09:00 PM

Quote:

Mine is made from 3mm thick PVC; rigid enough, yet lightweight. Weatherstrip on the edge seals it around the OTA. No noticeable vibration from the SilenX fan.

The first photo is the baffle for an 80mm fan. The rest of the photos show the 120mm version.










Lol, I was about to say "there's this guy who used black PVC and- " we'll there you go - you responded. And again a very tight finish to your project.'

I sealed off my tube with the rubber end cap PARKS provided with the OTA. Cut a hole, mounted a5" fan and the rubber is a wonderful dampening material. It does NOT look as nice as Marks - but it's perfect for me.

Pete


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Dick Jacobson
scholastic sledgehammer


Reged: 12/22/06

Loc: Plymouth, Minnesota, USA
Re: Fan baffle material [Re: Jeff Porter]
      #5670563 - 02/09/13 11:34 AM

Another good material (though not rigid) is polypropylene, as used in report covers and hanging file folders. You can get larger sizes that are used for art folios.

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Mark Peterman
super member


Reged: 08/07/12

Loc: Texas
Re: Fan baffle material new [Re: Dick Jacobson]
      #5670904 - 02/09/13 03:19 PM

Thanks for the compliment Pete.

Like you, I had actually first looked for an end cap from Orion like the one on the front of my scope but could never find one.


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ZeroID
sage


Reged: 04/21/10

Loc: Auckland, New Zealand
Re: Fan baffle material new [Re: Jeff Porter]
      #5673105 - 02/10/13 09:26 PM

Quote:

..... It seems to me that ATM is a frame of mind, rather than just doing a project.

Jeff




Never a truer word was spoken ...


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Sebastian Quirk
member


Reged: 01/04/12

Re: Fan baffle material new [Re: ZeroID]
      #5688169 - 02/19/13 01:10 AM

Ive used neoprene. Neoprene sheet is a great natural vibration dampener; it's cheap (eBay), cut-able with scissors, but its not rigid. You can glue Velcro to nylon backed neoprene., and zip tie fans to it.....

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derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: Fan baffle material new [Re: careysub]
      #5689033 - 02/19/13 02:50 PM

Quote:

Yes, a large (120 mm) slow fan is best.



Why would this be? I think the two factors are damping, and I understand higher frequencies die quicker than low frequencies, and interaction with the surrounding materials - which would be on a case-by-case basis.


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derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: Fan baffle material new [Re: derangedhermit]
      #5689040 - 02/19/13 02:53 PM

Coroplast (like cardboard box material made out of plastic) would be superior I think to a foam sandwich. I bought a 4'x8' sheet of black at a local signmaker's shop for $20. He said lots of people use it to make guinea pig cages - I'm thinking meat farmers. Didn't mention rabbits, though.

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careysub
Carpal Tunnel
*****

Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Fan baffle material new [Re: derangedhermit]
      #5689360 - 02/19/13 05:41 PM

Quote:

Quote:

Yes, a large (120 mm) slow fan is best.



Why would this be? I think the two factors are damping, and I understand higher frequencies die quicker than low frequencies, and interaction with the surrounding materials - which would be on a case-by-case basis.




Two factors - the presence (or absence) of resonance with the telescope structure, and the amplitude of the exciting source.

What matters most is the natural frequency of the telescope structure - typically in the range of 20-60 Hz. If this frequency is higher then vibrations will die out faster (because the structure flexes faster).

But you want to avoid any exciting source with a frequency close to the resonance frequency, and you want it to have the smallest amplitude possible. If a fan puts out a detectable vibration close to the resonance (that is transmitted to the structure) then the structure will never settle down.

A slow rev 120mm fan spins as slow as 800 RPM, or 13.3 Hz, well below most telescope's resonance frequency.

Then there is the question of who much the fan really vibrates. It seems large slow fans have a much reduced vibration amplitude. With the Scythe 800 to 1000 RPM fans at least I can attest to the fact that you can hold it in your hand without being aware that it is on. It is virtually vibration free.


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