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Jeff Porter
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Reged: 09/03/10

Loc: Utah
Fan baffle material
      #5666725 - 02/07/13 09:51 AM

I am looking to add a fan to my 12" dob, but I want to add a baffle as well to close out the back of the tube.

I have looked at both Kydex and ABS plastic, and a range of thicknesses up to 1/4". I want the baffle to be rigid, but I am not sure how thick of material I will need. Also please let me know if there is any benefit of using Kydex vs. ABS plastic.

Thanks,

Jeff P


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Pinbout
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Reged: 02/22/10

Loc: nj
Re: Fan baffle material new [Re: Jeff Porter]
      #5666847 - 02/07/13 10:57 AM

kydex is a pvc and abs mix.

you could use 1/8" thick black sintra [foam pvc], draw up what you need and have a sign shop cnc it. sign shop use sintra all the time not kydex or abs.

but on my 9.5 tube I have.028 kydex that is loosely velcroed to the inside, very loosely.


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careysub
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Fan baffle material new [Re: Jeff Porter]
      #5666886 - 02/07/13 11:15 AM

Are you cutting a hole in it for the fan? Will it carry any load? How will it be attached/supported it? Is the actual weight of any importance? Will it be exposed to handling, or will it be shielded inside the tube?

All of these have some effect on the best choices.

Stiffness goes up with the cube of thickness, which has the effect of creating an apparent threshold of thickness where you start regarding the material as "stiff".

You might look at Coroplast - the corrugated polypropylene used for signs, either by itself of a with a sheet of thin opaque plastic glued to it. It is 4mm thick, very rigid and light and cheap.

Thin plywood is also good 1/8" (3mm) is quite stiff and light (its density is about half that of the plastics and is twice as stiff). Actually somewhat thinner plywood would be stiff enough, but is not generally available. This would be over spec'd for the application really, it would be able to handle practically any method of attachment, load of a fan (if needed) and wear exposure fine

The Kydex and ABS are rather flexible (ie not very stiff) and a fairly thick sheet would be necessary, compared to some other materials. I have some 0.7mm Kydex it is quite flexible. I would guess that 1/8" (3mm) if you have a source would be stiff enough.


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Jeff Porter
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Reged: 09/03/10

Loc: Utah
Re: Fan baffle material new [Re: careysub]
      #5666976 - 02/07/13 12:06 PM

My thoughts were to attach the fan to the baffle material, and then suspend the baffle from the tube using some sort of elastic since I wanted to keep vibrations to a minimum.

I have a fan that I got with the scope that I can use, but I was also thinking of getting a larger fan with lower RPMs while maintaining the CFM rating. I have heard that he lower RPMs help with vibration. By suspending the baffle I figured that I would need something more rigid, especially if I use a larger fan.

Jeff P


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Dick Jacobson
scholastic sledgehammer


Reged: 12/22/06

Loc: Plymouth, Minnesota, USA
Re: Fan baffle material new [Re: Jeff Porter]
      #5667116 - 02/07/13 01:40 PM

I used a plastic coffee can lid on a scope that I'm currently building. I don't think the material makes much difference, as long as it can support the fan and doesn't let the air flow through. What's really important is that you isolate fan vibration from the scope. I've found that small, weak compression springs seem to work best.

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Mark Peterman
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Reged: 08/07/12

Loc: Texas
Re: Fan baffle material new [Re: Jeff Porter]
      #5667208 - 02/07/13 02:36 PM

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.







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Scanning4Comets
Markus
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Reged: 12/26/04

Re: Fan baffle material new [Re: Mark Peterman]
      #5667234 - 02/07/13 02:51 PM

I am in the midst of experimenting using both methods. I used a thick cardboard baffle for about a year and now I am trying the elastic bands thing.

Only reason for the change is that when your batteries die and you are out in the field, the next best thing is cold air getting to the mirror rather than having the baffle without the fan working. In the latter scenario, your mirror is covered with nothing getting at it.

Cheers,


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Jeff Porter
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Reged: 09/03/10

Loc: Utah
Re: Fan baffle material new [Re: Scanning4Comets]
      #5667358 - 02/07/13 03:57 PM

Thanks to all for your responses so far.

Mark,

Thanks for the pictures. It looks like you use the weather stripping for sealing the end of the tube and for vibration suppression. I also like the use of Velcro to attach for access. Simplicity and elegance.

Jeff


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Tom and Beth
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Reged: 01/08/07

Loc: Tucson, AZ
Re: Fan baffle material new [Re: Jeff Porter]
      #5667569 - 02/07/13 05:57 PM

Guess I'm old school. I used plywood with rubber washers for the fan.

Have an old wet suit lying around? You'd be able to make your baffle AND isolate it. Failing that, Walmart and the like have rubber sheets in small squares for a few bucks.


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Jeff Porter
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Reged: 09/03/10

Loc: Utah
Re: Fan baffle material new [Re: Scanning4Comets]
      #5667619 - 02/07/13 06:25 PM

I do like the idea of being able to remove the baffle in the field. That is why using elastic bands or Velcro has great appeal.

Typically here in the high desert the temperature will drop 30-40 degrees in the summer over the first few hours after sunset. After that things settle a bit and so the fan is not as necessary.

Jeff P


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careysub
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Fan baffle material new [Re: Jeff Porter]
      #5667726 - 02/07/13 07:38 PM

Quote:



I have a fan that I got with the scope that I can use, but I was also thinking of getting a larger fan with lower RPMs while maintaining the CFM rating. I have heard that he lower RPMs help with vibration. By suspending the baffle I figured that I would need something more rigid, especially if I use a larger fan.






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

You might consider this one:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835124023
(A Kingston 120mm, 950 RPM, 40 CFM, $5)

I prefer Scythe 120mm fans, the best on the market, dead silent, energy efficient (0.1 amp), vibration free and rated for 10 years of continuous use(!). I use them in all my computer builds, and have used them for other equipment cooling applications.

Unfortunately they just closed their U.S. office which has disrupted their supply. I have just emailed their central office in Taiwan to see if they can be ordered directly from there. (Fortunately I laid in my own supply for scope use.)

BTW a CD makes the perfect template for cutting a 120 mm fan hole.

Although a 120mm fan does add a load to the baffle, it also stiffens it since the fan body is rigid.


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Jeff Porter
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Reged: 09/03/10

Loc: Utah
Re: Fan baffle material new [Re: careysub]
      #5668071 - 02/07/13 11:10 PM

Thanks for the recommendation on the fan. I want something quiet and durable there.

Jeff P


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David Castillo
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Reged: 09/09/06

Loc: Carmel Valley, Ca
Re: Fan baffle material new [Re: Jeff Porter]
      #5668206 - 02/08/13 12:46 AM

I just re-purposed an old plastic "For Sale" sign, painted it ultra-flat black to keep the comments down, and it's held up for 10 years now. Kydex -Really ?
----
Dave


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tnranger
super member


Reged: 01/14/12

Re: Fan baffle material new [Re: David Castillo]
      #5668371 - 02/08/13 06:19 AM

What's wrong with 1/4 inch plywood?

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Dick Jacobson
scholastic sledgehammer


Reged: 12/22/06

Loc: Plymouth, Minnesota, USA
Re: Fan baffle material new [Re: tnranger]
      #5668462 - 02/08/13 08:23 AM

I've also used foam-core poster board. Very light and stiff and easy to cut.

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Pinbout
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Reged: 02/22/10

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Re: Fan baffle material new [Re: David Castillo]
      #5668473 - 02/08/13 08:36 AM

Quote:

I just re-purposed an old plastic "For Sale" sign,




is that the corragated plastic sheet, coroplast? cut it up and layer it and you can make a very good baffle to create a laminar flow.


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Jeff Porter
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Reged: 09/03/10

Loc: Utah
Re: Fan baffle material new [Re: Pinbout]
      #5668487 - 02/08/13 08:47 AM

All of the suggestions are appreciated.

Since I have not done much ATM myself, I don't pick up on the day to day stuff that could be used like you folks. I read a lot of the suggestions and wonder why I didn't think of it. It seems to me that ATM is a frame of mind, rather than just doing a project.

Jeff


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careysub
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Fan baffle material new [Re: Dick Jacobson]
      #5668555 - 02/08/13 09:20 AM

Quote:

I've also used foam-core poster board. Very light and stiff and easy to cut.




I had thought about recommending that - it is certainly stiff and strong enough -but was concerned about its durability, especially the fact that is covered with paper which would suffer from the humidity of dew-laden air.

Giving it a good coating of spray paint might give it adequate moisture resistance though.

What is your experience?


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Project Galileo
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Reged: 11/14/07

Loc: Jefferson County, Colorado
Re: Fan baffle material new [Re: careysub]
      #5668690 - 02/08/13 10:50 AM

LB16s need a lot of counter weight in their butts especially if you use a paracorr, large eps, and a finder scope. That is why I used 1/8" steel. After cutting, grinding, and punching I had a 7.5 lb baffle. It was powder coated and a neoprene gasket was made to seal it up. The final result balances like a dream and I believe is elegant.



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Dick Jacobson
scholastic sledgehammer


Reged: 12/22/06

Loc: Plymouth, Minnesota, USA
Re: Fan baffle material new [Re: careysub]
      #5669054 - 02/08/13 01:34 PM

Quote:

Quote:

I've also used foam-core poster board. Very light and stiff and easy to cut.




I had thought about recommending that - it is certainly stiff and strong enough -but was concerned about its durability, especially the fact that is covered with paper which would suffer from the humidity of dew-laden air.

Giving it a good coating of spray paint might give it adequate moisture resistance though.

What is your experience?



I have to admit, I'm still building the scope so there is no experience. It occurred to me that dew could be a problem, but the foam in the core should be dew resistant.


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Pinbout
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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
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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
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Reged: 01/17/09

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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 new [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
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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
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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
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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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