choosing the material for a small project

[Florin Andrei]

Hi, I'm building a small dobsonian mount for a telescope, the plan is here:

http://stellafane.org/tm/dob/

The whole thing is about waist-high. It doesn't have to support a large weight, the telescope tube is made of aluminum and it's not very heavy.

The recommended material is 1/2" and 3/4" plywood. I could definitely use plywood, it's cheap and easy to work.

But I went today to Home Depot and I noticed there are other materials available. I could use: red oak, poplar, pine (white and other varieties), redwood. Which one should I choose? Price is not really an issue, this is a small project. The requirements are:


The material must be durable. I don't want to keep fixing this mount, or keep making new ones because they break easily.
It should not be very hard or tricky to work. I don't want to use a material that hates newbies like me.


The telescope is going to spend most of its time in the garage. When doing observations, it's going to stay outside during night time - so there's going to be some dew, and possibly cold temperature. Maybe some transitions between warm and cold when I'm taking it outside. It will do some mileage in the trunk of my car once in a while. Also, kids may peek through the telescope, so expect little feet to bump into the turntable at the bottom, occasionally.

I'm going to prime and paint the wood really thoroughly - I will do everything by the book.

So, given all these constraints, which material would you choose?

P.S.: Before I start building the mount, I'll have to make two other smaller devices, much smaller, which are going to serve as practice before the final project:

http://stellafane.org/tm/atm/test/tester-main.html

[Josiah Bartlett]

Florin,
I think you should use plywood- for your telescope you will want the mount to be dimensionally stable and able to resist warpage due to changes in environmental conditions like temperature and humidity. Plywood is great for this. In fact, I would use either baltic birch, sign grade, marine grade, or aircraft grade plywood for this project, depending on what you are willing to spend. I think you will find that the shop grade plywood you can usually find at Home Depot tends to be full of voids and isn't well pressed.

[Tim Livingston]

Your link talks about the grades of plywood to use. Follow that for guidance, if this is something you'll keep for a long time I would use the best you can find but since this is your first project I would recommend going with the cheaper grade materials like the A-B or B-C grades of plywood. You could call this first project your prototype much like Norm used to do on the New Yankee Workshop. You are going to have mistakes so start on the low end and work you way up. After you learn a little about woodworking you could move on to utilizing something like some teak or mahogany.

[Bill Huber]

I am with the others on this, I would go with the plywood, it will be stable and not want to move like the others would. I am sure there is a lumber yard that would sell better plywood then Home Depot, I really don't like there stuff that much, to many gaps and the like.

Remember this will not be kept in a very stable environment so you want it to be stable.

[Joe Angrisani]

Florin.... You definitely want to use a high quality plywood. Do not use board lumber, and do not use "regular" plywood from Home Depot. Use a high quality thin-ply plywood like baltic birch or a marine grade ply.

A telescope mount will see more moisture than you can imagine if you haven't spent time observing. The optical tube will generally get colder than ambient air temp, causing condensation even when other things around you aren't getting covered in dew. While I live in dry Colorado where it isn't too bad, I have used my scope in places where the dew dripped off the optical tube and mount as if it was being misted with a garden sprayer. Your dob mount won't be smooth in it's altitude motion for very long if things start warping, even slightly.

Feel free to contact me off-list if you have any specific astronomy or scope questions.

Clear Skies....
....Joe

[John Coloccia]

I would do plywood, and then cover it with a layer of fiber-glass...and then paint. It will be durable, water resistant and easy to clean.

[Bill Orbine]

You could look into something like Azek sheet goods. Pricey stuff but basically rot resistant and durable. The material is fairly flexible but I think once formed into box like structure it'd be fairly rigid. And no need to paint!. It's fairly heavy stuff and messy to work with as a sheet but once done it's done and light enough. In the end, I think you'd have a really cool piece. You should ask around on the astronomy forums about this idea to be sure if it makes a makes a good and stable mount.

[Tony Bilello]

This will probably and hopefully a one time piece. I would bite the bullet and use marine grade plywood and roll epoxy on all surfaces and also use epoxy for your adhesive. This is called "encapsulating" and is a popular technique in modern wooden boat building. If you decide not to use epoxy, at least use marine plywood. It is stron, stable and waterproff to a certain degree.

[Florin Andrei]

Got it - I'll use one of those high-quality plywoods that everyone is mentioning. Any suggestions for a good source of plywood, or vendor? I'll look for lumber yards nearby, but I was wondering if there are any well-known vendors and such, since Home Depot turned out to be less than ideal.