Since there has been a lot of discussion about secondary mirror supports, I thought I would try to explain how I built mine for my 10" f6 scope with a tube that had a ID of 12". The design is very adjustable and rigid.
I hope this is clear enough to help.
Erin Handgen (erin@fc.hp.com)
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Material List:
1 3" by 1/4" carriage bolt 1 1/4" nut 1 1/4" washer 1 1/4" tee nut 2 5/16" fender washers 3 1/2" #6 self tapping sheet metal screws 3 3/4" #6 wood screws 8 1/4" #2 bolts 8 #2 nuts 16 #2 lock washers 1 1 1/2" x 3/4" x 2' poplar board. 4 1 1/4" x 6" 0.010 mil semi-hardened stainless steel sheets (You may need to adust the length of these strips to fit tubes that have a ID not equal to 12")
(Estimated Cost: $10 to $15)
Power Tools Required:
1 3/8" Drill
Directions:
Cut two 3" lengths off the poplar board and glue them together to make a 1 1/2" x 1 1/2" x 3" block of wood. (I used wood dowel pins to hold the wood together, but you really don't need them.) Let the glue dry over night.
Drill a 1/4" hold through the edge of the poplar board and cut the board to be 3/4" long. This gives you a 1 1/2" x 3/4" x 3/4" piece of wood with a 1/4" hold down the length of it.
Take your stainless steel strips and lay two of them to the left and two to the right so that the ends overlap by 1 1/8" and clamp them to a board with a C clamp.
Side View:
<- 1 1/8"->
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Top View:
+------------------------------------+--------------------------+
| | | |
| |(overlap)| |
| | | |
+------------------------------------+--------------------------+
Drill four holes for the #2 bolts centered 3/16" in from each corner of the region where the strips overlap. (Even with a sheet metal set, it will be hard to drill the holes without the drill bit walking around on the steel. A little movement is OK since any error in hole placement will be matched by pieces that join together later.) Unclamp the steel strips and use the #2 bolts, nuts and lock washers to join them as follows.
Edge On View:
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|
|
|
| #2 Bolts
#2 Bolts --> || |
/ \ v
/ \
- --------------------
---------------- -
\ /
^ \ /
| || <-- #2 Bolts
#2 Bolts |
|
|
|
|
|
|
It will take a little bending to get everything to fit together. (Thin semi-hardened stainless steel is very similar to spring steel, so it will fight you quite a bit.) When everything is together, make sure that the #2 bolts are as loose as possible and squeeze the 3/4" x 3/4" x 1 1/2" piece of wood into the center. (This is not as hard as it sounds. You may need to sand the wood down a little.) Tighten down all of the #2 bolts so the wood is squeezed between the steel bands and will not move. (You will be amazed at how strong this is.)
Label the two fender washers "A" and "B". The side of the washer that has the label will be called the front and the other side will be called the back. Clamp washers A and B together so that the back of A touches the front of B. Drill six equally spaced holes around the edge of the washers large enough for the #6 self tapping sheet metal screws to tap into. Number the holes from 1 to 6 on each washer. (Make sure holes #1, #2, #3, etc. on washer A match holes #1, #2, #3, etc. on washer B.) Drill out holes #1, #3 and #5 on washer A so the the #6 sheet metal screws can turn freely in the holes. Drill out holes #2, #4 and #6 on washer B so the #6 wood screws can turn freely in the holes.
Once the glue has dried on the 1 1/2" x 1 1/2" x 3" block of wood, cut the block in half with a 45 degree mitre.
Side View:
1/2"
<--->
^ +---+
| | \
| | \
1 1/2" | \
| | \
| | \
V +------------------+
<------- 2" ------->
End View:
^ +-------------+
| | |
| | |
1 1/2" | |
| | |
| | |
v +-------------+
<-- 1 1/2" -->
Center washer B, front facing up, on the end of the wood block and attach with #6 wood screws through holes #2, #4 and #6. (Make sure that the wood is removed below holes #1, #3 and #5 so the ends of the sheet metal screws do not hit anything.) Push the carriage bolt through washer A so that the back of washer A is in contact with the head of the carriage bolt. Sandwich the head of the carriage bolt between washers A and B and use the #6 self tapping sheet metal screws to pass through holes #1, #3 and #5 on washer A and tap into holes #1, #3 and #5 on washer B.
Side View:
+---+
| || \
|\|| \
\\\\\\\\\\\\\\\\\\\| || \
|/|| \
| || \
+------------------+
| |
Washer A ---+ |
Washer B -----+
Set the tee nut into one end of the wood block that is in the center of the vane assembly and thread the carriage bolt into the tee nut and all the way through the vane assembly. Use the 1/4" washer and nut to secure the carriage bolt into the vane assembly.
Use RTV silicon adhesive to glue the secondary mirror on to the 45 degree surface of the mirror holder. Allow 24 hours to dry. Use pillow blocks to mount the vanes to the telescope tube. By turning the carriage bolt, you can adjust the depth of the secondary mirror in the tube and it's angle with the focuser. By using the three sheet metal screws, you can fine tune the collimation of the secondary mirror.