Increasing height of a rocker box - advice needed

Hi -

I need to move my altitude bearings on my Meade Dob due to balance
problems, but this will then cause the tube to hit the rocker box, so
I'll need to also increase the height of the box.

I'm trying to figure out if that means I need to start from scratch and
build a new box, or if it's possible to add pieces of wood between the
base and the side/front panels to increase the height - essentially to
shim it up a few inches.

Will this make the vertical panels too unstable or compromise
stiffness? What kind of wood and joint would be best in this case?

If I do need to rebuild, what kinds of wood would get me necessary
stiffness with minimum weight?

Thanks for your help!
Michael

wrote:
Hi -

I need to move my altitude bearings on my Meade Dob due to balance
problems, but this will then cause the tube to hit the rocker box, so
I'll need to also increase the height of the box.

I'm trying to figure out if that means I need to start from scratch and
build a new box, or if it's possible to add pieces of wood between the
base and the side/front panels to increase the height - essentially to
shim it up a few inches.

Will this make the vertical panels too unstable or compromise
stiffness? What kind of wood and joint would be best in this case?


You can probably get away with gluing and screwing another board onto
the top of each upright, as long as you rough up the surfaces well
before gluing. You're gonna have to extend the bearings outward enough
to sit in the new saddle, though. I gotta say, though, if the telescope
is heavy (say, bigger than an 8") I don't think the jury-rig will be
strong enough to last.

You might also try using a screen-door spring to provide the extra
balance. This works well and is simpler/cheaper to do. Simply anchor one
end of the spring with a round-headed screw along the outside of the
upright, attach a cable to the other end of the spring, and then use
another screw with a spacer or something around it to act as a pivot
for the cable. Attach with another round headed screw the other end of
the cable to the rear-end-of-the-telescope side of the bearing. If you
follow what I'm saying, as the telescope is pointed downward to the
horizon, the spring will grow increasingly tense, helping it to maintain
balance.

It's a neat trick. Here's a picture of how one guy did it:

http://www.efalk.org/Miatascope/Flavio/spring.jpg


If I do need to rebuild, what kinds of wood would get me necessary
stiffness with minimum weight?

If you have to rebuild, use very good plywood. I personally like baltic
birch ply, but there are other kinds out there. You probably won't find
the good stuff at home depot and will have to call a real lumberyard
that caters to furniture makers. The Woodworkers Store and Woodcrafters
both carry it as well but they charge way too much, IMHO.

Good luck - Chris

Been there.

I finally chose to add 5 pounds directly under the mirror to compensate for
balancing a lighterweight, open mirror cell. While that didn't decrease the
overall weight of the OTA, it also didn't change the weight of the OTA as
purchased.


wrote in message
oups.com...
Hi -

I need to move my altitude bearings on my Meade Dob due to balance
problems, but this will then cause the tube to hit the rocker box, so
I'll need to also increase the height of the box.

I'm trying to figure out if that means I need to start from scratch and
build a new box, or if it's possible to add pieces of wood between the
base and the side/front panels to increase the height - essentially to
shim it up a few inches.

Will this make the vertical panels too unstable or compromise
stiffness? What kind of wood and joint would be best in this case?

If I do need to rebuild, what kinds of wood would get me necessary
stiffness with minimum weight?

Thanks for your help!
Michael