Introduction: Adjustable Equatorial Wedge (Telescope Tripod Meade ETX60/70)
While In the middle of building a Solar scope...
I Finished making a telescope to tripod adapter, hooked the telescope on, and realized it was simply too unstable. I wouldn't be able to mount a 40mm fan to it, without destroying the seeing through vibration. and I want to do imaging that requires a very stable mount.
A little searching and I ran across this build http://robroy.dyndns.info/astropics/ETX-wedge/
For this you will need;
The sacrificial tripod. Camera tripods can work if they have a removable head but don't skimp the point is to find the most stable thing you are willing to use. I am using an old telescope tripod, with the German equatorial mount removed (its way too small for anything modern) Astro optics EQ1 I picked up from the local thrift store for 15$
3/4" structural plywood cut to the at least the width of your telescope base mount. Mine is 6". Use multi ply preferably 5+ don't be cheap on this the more layers the stiffer, the stiffer the better to do photography with.
Piano hinge/continuous hinge at least the width mentioned (you can cut it to size)
2 turn buckles the size will depend on your telescope and latitude. assume about 1/2 the telescope base +1" clearance * sine of latitude. for a 6" mount at 45 degrees (4*.7)=2.8 means 3" turnbuckle is about right
1/4x20 bolts longer than the tripod base thickness+ 1.5" (2 layers of plywood) mine ended up at 2.5 inch because of washers and lock nuts.
3 Wood t nuts (cleats) to fit 1/4x20
1 largest T nut you can find 3/8-1/2 seems to be the biggest common and a 2" bolt+fender washer
3 automotive fender flare auto body push pins aka plastic push rivets Make sure to get the solid dome head rather than the shell dome type. The push rivets are bearing surfaces and the shell type will not have the clearance required.
This project is 2 basic parts the Tripod mount and the Telescope mount. Hopefully this allows easy ish alignment for equatorial/polar The telescope plate can rotate on the tripod mount or be locked in place by tightening the main nut.
The concept should work for most field tripods and most tabletop telescopes, Goto functionality will depend on the computers ability to understand polar/equatorial alignments. Meade 494/497 handsets are all capable of polar alignment,
Step 1: Prep the Tripod and Measure
My tripod had a small raised retaining ring, I wanted to get rid of. Larger and flatter is going to work better.
Using a jigsaw I cut 2 rough circles about the diameter of the hinges of the tripod. Drilled a center pilot hole to use for all compass measurements.
The bottom circle needed some clearance for the tripod legs so I cut relief probably too aggressively but it works with the 7 ply
Once the bolts fit I used the bottom as a template for drilling and adding cleats to the top.
I Drilled a pilot hole, drilled the cleat size hole 1/2 deep, then drilled the bolt hole through the last 1/4" from the opposite side.
I then used that diameter for the Plastic rivet holes. These turned out to be a little too long so I had to trim the tips off to make them fit.
Using the Pilot hole in the center I drilled on the other side the bore for the large cleat, and then finished with the bolt size as before.
Cleats get set in place with a hammer, then the push rivets get put in.
The push rivets are bearing surfaces for the the telescope mount.
Step 2: Build the Telescope Mount and Assemble
The top plate is the base of the telescope width + about an inch 6x8 for me but the extra space is just that and will be used for level and incline checking.
The bottom plate is another inch longer at this size 6x9. its actually 6+radius of mount. I fudged a little over.
Mark and Drill a hole for the bolt in the bottom plate on the long center line 1 radius of the tripod mount plate from an edge. I cut some 1" wide strips about 2" long and mounted them to the base, with 2 screws and some glue.
screw the base plates together with the large bolt and a metal washer. The tightness of this determines wheter you can rotate the telescope or not.
Drill holes in the telescope plate for your telescopes mount. For me on an ETX-70 this was 2 holes 4" apart 1/4" diameter on the long center. Home position and other models may need different mount holes.
Mount the piano hinge to the underside of the Telescope plate. There are tips
Using the mounted piano hinge and a square Mount the hing as close to the big bolt as you can while still allowing the hing to open to ~90 degrees.
You can try and fight with the protractor or you can just mount it like I did to get a rough incline measurement.
I glued the protractor on and gently routed out a zip tie for my plumb indicator.
Unscrew your turnbuckle 1/2" or so you just want to be able to do fine adjustments later, and screw it into the outside of a bottom block on the base plate.
make sure the base plate is level.
Using the turnbuckle determine where to place the other block to mount it too. the closer the turnbuckle is to vertical the better. The incline reading you are aiming for is your latitude -90 for me that's 45 degrees Your placement doesn't have to be perfect the turnbuckles are adjustable, but it should be close within a few degrees.
Mount the blocks on the telescope plate verify you are in the right inclination, screw the turnbuckle on and once its all in the right range glue and screw the blocks in place like before.
Repeat this for the other turnbuckle.
The turnbuckles can produce enough force you can warp the wood and rip out screws so do not loosen/tighten them with out switching back and forth every full rotation or so.
Aligning a telescope is its own instructable, but a spirit level a magnetic compass and an real angle meter would be really helpful for this unit.