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Equipment Discussions >> ATM, Optics and DIY Forum

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mfoose
member


Reged: 05/18/13

PLOP help
      #5943557 - 06/27/13 06:12 PM

I am building a 8" f/5 truss dobsonian. My goal is to be able to make it as transportable as possible. After looking at many possible designs I am building my scope from the inside out. Starting with the mirror cell and expanding outwards. Currently, I am using the PLOP cell designer to determine how many supports and such to build. Unfortunately, I have no idea what any of the numbers mean. Can someone help me understand what they mean?

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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: PLOP help new [Re: mfoose]
      #5943755 - 06/27/13 08:19 PM

Sounds like fun a 10 f5 could fit in a 10inch tube a 3ft long would a truss be needed ? If your mirror is not very thin a 3 point will be fine. Post how you plan to build it .

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Tom and Beth
Post Laureate


Reged: 01/08/07

Loc: Tucson, AZ
Re: PLOP help new [Re: mfoose]
      #5943850 - 06/27/13 09:38 PM

Hmm, this site does a better explanation of the values (and their meanings) critical to designing your mirror support cell

Plop Page

As well as provide a "cut to the chase" grouping. I'm not really sure which of the "numbers" you mean, and thus which you need help with, although I would suspect it may be the properties of your mirror substrate (Modulus of Elasticity) as well as "what is good enough"

Edited by Tom and Beth (06/27/13 09:40 PM)


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StarDusty
sage


Reged: 10/02/07

Loc: Parsippany, NJ
Re: PLOP help new [Re: Tom and Beth]
      #5943887 - 06/27/13 10:07 PM

Cells for small mirrors can be very simple.

These articles show a simple plywood cell that has worked for me:

http://www.clearskyobserver.com/index.php/20-telescopemaking/18-6-f-5-6-newto...

or here:

http://www.clearskyobserver.com/index.php/20-telescopemaking/20-6-f-12-newtonian

I used three generous blobs of silicone caulk to fix the mirrors to the finished cells.


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mfoose
member


Reged: 05/18/13

Re: PLOP help new [Re: StarDusty]
      #5943910 - 06/27/13 10:22 PM

I did read that a 3 point should be fine. My plan is just for the minimal. I plan to use 1/2" plywood for pretty much everything. I don't know which type of wood still looking. But I plan to build a mirror box to hold the cell about 9.5" or 10" with a fan or two. I then want use 2 8" half circles as my pivots and aluminum tubes for the trusses.

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mfoose
member


Reged: 05/18/13

Re: PLOP help new [Re: mfoose]
      #5943913 - 06/27/13 10:23 PM

How do you take of the mirror for cleaning with silicone on it?

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cpr1
professor emeritus
*****

Reged: 03/24/12

Loc: Louisiana
Re: PLOP help new [Re: mfoose]
      #5943971 - 06/27/13 11:04 PM

If your are building a truss tube telescope for the first time I would suggest picking up books "The Dobsonian Telescope" and or "Portable Newtonian Telescopes" These books will help you out with the basic principals to design your scope. Especially being a truss telescope. Good luck by the way.

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cpr1
professor emeritus
*****

Reged: 03/24/12

Loc: Louisiana
Re: PLOP help new [Re: cpr1]
      #5943979 - 06/27/13 11:09 PM

As far as taking the mirror out for cleaning. If you are building a traditional truss with a open cell, most make the cell with the ability to tailgate down. From there you can remove the mirror easily for cleaning and transport if you choose.

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StarDusty
sage


Reged: 10/02/07

Loc: Parsippany, NJ
Re: PLOP help new [Re: mfoose]
      #5944003 - 06/27/13 11:27 PM

As you can see, the whole cell with mirror attached drops out the back of the OTA with a few stainless steel screws. Once out it can be rinsed with water to get the grit off, then lightly washed with soapy water and cotton balls, then rinsed again. All this is done without detaching the mirror. All wood parts are coated with polyurethane, so they have fairly good resistance to damp conditions.

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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: PLOP help new [Re: mfoose]
      #5944344 - 06/28/13 08:00 AM

Quote:

I am building a 8" f/5 truss dobsonian. My goal is to be able to make it as transportable as possible.




so you don't have to glue it, you can sit it on bubble wrap as your float support, just cut a central hole about 2.5" in dia. [our friend Reiner [mr. lowrider] has this on his travel dob]

you can use a top plate of the mirror box as a edge support.

you can "hang" the mirror cell from that same top plate so you'd have front collimation bolts - they are priceless.

then you can use swing away clips for transporting.

on an 8" you can make your own truss clamps. just make sure the thumb part of the thumb screw faces the mirror side on the mirror box, opposite the vid.


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cpr1
professor emeritus
*****

Reged: 03/24/12

Loc: Louisiana
Re: PLOP help new [Re: Pinbout]
      #5945779 - 06/28/13 11:04 PM

Hi mfoose, did you figure out your plop design for your 8 inch? Like the others have said I don't think much more than a 3 point is needed. But, if you just want the experience than go for it. Good luck with your build and post your progress.

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mfoose
member


Reged: 05/18/13

Re: PLOP help new [Re: cpr1]
      #5945914 - 06/29/13 01:58 AM

I did do a Plop but i am confused with the results. I will definitely post progress when I work on it. What wood would you recommend for a build like this? I am looking for some light 1/2inch plywood but not too light that I sacrifice strength.

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starman345
Wait, I'm Thinking
*****

Reged: 07/06/10

Loc: New Brunswick, Canada
Re: PLOP help new [Re: mfoose]
      #5946084 - 06/29/13 07:59 AM

Have a look here It helped me understand some of the numbers.

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