ATM Altitude Trunions - how to make

[Jmkasunich@ra.rockwell.com]

Keith Wichman <kwichman@draper.com> wrote:

>Can you suggest a robust way to build and mount the
>trunions directly to my sonotube?  I have good wood-
>working skills and equipment.
and Ran <ran@netgate.net> replied

>The ones that Orion sells are described as "machined
>wood".  I imagine that they just cut a thick disk,
>then mill one side to the right radius (he said,
>blithely.  Milling to that kind of radius is not
>something *I'd* want to attempt).

IF you have a table saw AND the radius you want to mill
is the same as or smaller than the radius of your saw
blade, this isn't difficult.  I made wood side plates
for my 4" f/4 RFT this way (6" PVC tube).  Here's a short
description - if you are interested, mail me privately
for the details.

Be very careful!! - this trick isn't particularly risky,
but you do have to run your saw with the guard removed.
During most of the cut, the blade is under the workpiece,
but you want to be very sure of where it will come back
out, and use a push stick or block.

The basic method involves moving the wood block over
the blade sideways or at an angle to cut a curved
"valley" on the underside of the wood.  You have to
start with a square or rectangular board, so you
have a straight edge to run against a temporary fence
clamped to the saw table.  If you want round blocks
(for trunions), start with square or rectangular
pieces, make the valley first, then cut out circles
with a router or bandsaw.  For instance, if you want
6 inch diameter trunnions, start with a 6.5 wide by
13 inch long board, make the valley lengthwise, then
cut it in half and convert each 6.5 inch square into
a 6.0 inch circle.

I hate ACSII art, but a picture is worth 1024 words.
This is an end view of a board, perhaps 6 inches
wide and 3/4 inch thick, as it moves into the
screen and over the blade.

                                             _______
                                            |       |
      _____________________________________ |       |
     |                                     || Fence |
     |     Workpiece                       ||       |
     |                                     ||       |
     |        _____----------_____         ||       |
     |_____---                    ---______||_______|
--------------------------------------------------------
     Saw Table

If your saw blade is the same size as your tube, you
can simply run the piece straight across the table.
Otherwise, you will have to move the piece at an angle
to get the right radius.  Calculating the correct angle
isn't too hard, but it takes some trig and a calculator.
If you want to do it, let me know.  It is harder to
explain than to do.

Once you know the right angle, clamp a fence (2x4?)to
your table behind the blade.  Use the miter guage to set
the angle.  Lower the blade so only 1/16 inch or less
sticks up, and SLOWLY run the board across the spinning
blade.  Use a push block to hold it down and against the
fence.  The blade will help push it against the fence.
If the fence is angled, make sure you feed against the
rotation of the blade.  After each pass, raise the blade
a little bit (no more than 1/16 inch) and make another
pass, until you have the correct depth.

If this is not perfectly clear, then DON'T DO IT.  Some
things are really tough to describe in text.  I don't
want to be responsible for somebody losing a finger.
Let me know if you are interested and I will walk you
through it.

John Kasunich