Telescope Reviews: Is Kydex Still King?

Aircraft Spruce delivered the 1/16" mahogany plywood promptly and it is being prepared now. I think this will be a good material for ATM use. Firstly, it looks GREAT. Aircraft Spruce calls it African Mahogany. I was not aware of this so I suspected another species such as Luan. Close inspection against Honduran Mahogany I have on hand shows no obvious differences. When cut and sanded, it has the typical smell of real mahogany. If it is not the real deal, it's pretty darn close.

The center ply apparently is poplar. The face plies are extremely thin. I gave it a light sanding with 400 sand paper and some artifacts (from the core?) became visible. Further finishing has covered this, but it probably could have went straight to finish w/out sanding. I am preparing it as I would with regular mahogany:

1) Apply grain filler and stain 2:1 mix;
2) Four coats of Sam Maloof oil/polyurethane; and
3) Two coats of Sam Maloof oil/wax.

It is taking the finishes very well. It looks like a million bucks. But there are a few issues with it:

1) On a 24 x 48 sheet the grain runs the long direction. Since the circumference of my upper cage is 42", it means that if I use one continuous piece, the wood grain will be oriented 90 degrees to the wood in the rest of the scope. For matching grain orientation I had to cut the sheet in half, so my light shield will have a seam opposite the focuser.

2) The flexibility is less than Kydex or ABS. For a 12.5" scope it is workable. For a smaller scope, one may need to immerse the piece in water and then form it into the required cylinder.

3) It will not be the lightest material available. I don't have a specific density for this. However, using a figure from Mel Bartels ATM site for denser Baltic Birch, the 5.8 square feet I am using should weigh no more than 1.15 pounds. (Having used carbon fiber epoxy in my last scope I am a bit spoiled in this regard.) Of course, the inside surface will still need a blackening treatment which will add a bit more weight. My new design is a double-truss, so it is much less sensitive to upper end weight than the Obsession style Dob.

Attached is a photo of two panels, raw and stained/filled. No oil applied in this photo. I have cropped it down and selected a low JPEG quality to make the CN file size limitations, hopefully the grain detail still shows.

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Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making