building Luceal
Luceal is a 16-inch F4.5 telescope I'm building(formerly a Meade Starfinder).
The OTA will be flexible with respect to different mounts it may be used with.
The first mount is a simple ball, the ball will eventually be driven with a trackball mount.
Dobsonian and equatorial mounts are also planned.

The 26 lbs mirror is housed in a 22 lbs, 25" polyethylene ball hence the name.
Everything below the center of the ball will be heavy everything above the center will be light
The rough idea here is that the center of gravity of the mirror,cell etc. can sit at most maybe 7" below the center of the ball.
The focal length means the center of gravity of the upper cage will be maybe 56" above the center of the ball.
For an approximate 8:1 ratio. so every pound in the secondary cage area will need about 8 lbs in the primary cell area.
secondary mirror, spider, focuser, 2" eyepieces, paracor, telrad ... (public friendly construction) are all fairly non negotiable design points.
The primary mirror will balance out about 3 lbs, the hole in the ball a few ounces... (the rest of the ball is balance neutral)
Whatever else is needed to shift the center of balance needs to be made up by adding weight as low as I can.
Instead of just adding dead weight after the fact I am going to build a very heavy duty mirror cell and mirror box to see how much of the difference that takes up,
if I over do it it is far easier to add a few ounces to the upper secondary cage or drill some weight out of the mirror cell.
Construction began with the not quite round ball (spheorizing it).
a sphereometer is a tool for measuring the radius of curvature of a surface.
a router shaves material off.
by combining the two you can shave off material that protrudes from a sphere of a given diameter.(pick your router depth carefully)
An 18 point flotation cell is a little much for a 16" 1.6" thick mirror so... why not.
Where the 18 points of the mirror cell need to be are calculated with 'PLOP'.
A trip to the junk yard decided the cell supports were 1" stainless steel
and a piece of aluminum that, after cutting 3 flanges off of, looks like it was made
to hold my mirror will be what everything bolts on to.

After considering tie rod ends etc I settled on sandwiching the support triangles over
turned balls on the ends of the of pivot bars.
The pivot supports are also the made from the same 1" stainless steel rod.
Since stainless on stainless does not form a happy bearing surface I made brass bushings that are bearing surfaces on both inside and outside so thermal changes won't matter as much.
The sandwiches are also brass. using the sandwich ties and pivot bar to prevent the support triangles from spinning was a happy side effect that fell out of the design.

Getting the mirror as low in the ball as possible means the the outside of the bottom of the cell need to be as close to touching the inside of the ball as can be.
so the bolts that hold the pivot supports are countersunk and filed to fit the curve of the ball

Another trip to the junk yard decided the poles would be attach to the cell with 1 3/8" 6 t.p.i. stainless all-thread and that the poles would be 2" .050" wall aluminum irrigation pipe.
three or four ... three or four ...poles I keep vacillating. I'll make parts for four, and see if three can work (starting to worry if it is not too heavy). three works fine, except the chord around the outside of the poles cuts across the light path. I'll live with it.

make some 4" long 2" diameter aluminum nuts with a flat on one side to bolt to the mirror box. a foot or less of the 1+3/8 threaded rod sticking up.

likewise 4" by 1.9+" nylon inserts are threaded and pressed into one end of the 2" aluminum tubes
the tubes cam then be screwed onto the the 1+3/8" all-thread.
this arrangement means the distance from the primary to the secondary can be adjusted several inches
(no more running out of focus travel [with motors this could BE the focuser])
it also means collmination is archived by twisting the poles. (can't wait to see if this works) it does work but only if the secondary can translate in 2D parallel to the mirror.
that is: twisting the poles performs the task of tilting the secondary (so the secondary needs no other tilt adjustment) since the primary can't tilt, the secondary has to be able to translate to where the primary does point. having the mechanical axis close to the optical axis helps.

the upper cage and how it attaches to the poles is still in flux.
I don't like that any fastener that allows each pole to twist about its axis must also allow the secondary cage to twist about the optical axis with flexure in the poles... only solution I have now is using a string truss, but am hoping for something simpler (or that it is not actually a problem in practice)

August 2007
I have had the scope out a few times and adjusting it to the comfortable eye height for each kid is priceless.
It is a little top heavy so when looking low on the horizon I have to hold it to keep it from creeping down.
Until I make a lighter top end I am just glomming a counterweight under the mirror cell
I am also trying out some wire cable trusses with turnbuckles between the poles, they do add stiffness,
but more importantly they translate the secondary cage for prime focus collmination.
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