Construction Notes
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 For you amateur telescope makers that are interested in the construction of Cyclops, please refer to the navigation on the left.

 
Filter Slide •PDF• •Print• •E-mail•

I felt this project was so simple in it's concept that I didn't document it all in pictures, and it's a bit hard to see details in the installed pictures below, but the concept is pretty simple, so here's some notes:

The slide itself is made from 1/8" thick x 3 1/2" wide aluminum ripped from the side of a piece of 4" x 4" square tubing.  A hole saw was used to cut holes in it sized to fit the smaller diameter of Adorama Step-Down Adapter Ring 58mm Lens to 48mm Filter Size SKU: FLD5848 MFR: SDR5848 which were glued to the slide with 30 min. epoxy.  I cut four holes, three for filters, one for no filter.  The one for no filter does not have an adapter ring glued in it.

 

The thing the slide slides on started out as a solid rectangular block of aluminum, which I basically turned into a little table with a recessed top.  I started by cutting the recessed top of the table on the mill.  The bottom of the 'table', with it's legs, I shaped by first roughing out all the material to be removed with the sliding miter saw with the blade depth stop set.  I removed all the material close to the final depth, leaving the table legs.  Next I cut the center hole with a hole saw, I then cleaned up the bottom of the table and the legs on the mill.  Two 1/8" thick pieces of alumiinum were used to capture the slide, the outer edges of the table top drilled and tapped for allen head bolts to hold the slide retainers in place.

 

One edge of the slide has small indentations centered on each filter hole, cut with a dremel cut off wheel and smoothed with a small diameter grind stone.  An indexing pin made from 1/8" diameter delrin rod from McMaster Carr is held with tension against the edge of the slide with a piece of stainless steel feeler gauge.  Maybe it's about .040 thick.  There is a slot milled across the raised edge of the table, under the filter slide retainer, for the pin to slide in.  To install or remove the slide, I pull down on the feeler gauge spring to remove tension (so the pin doesn't go flying out when the slide is removed).  

 

The top of the slide has a 10-24 screw going through as a safety and finger grabber.

 

To install the filter slide assembly in the optical tube, I drilled and tapped the bottom of the legs for 8-32.  I cut four little pieces of 8-32 screw material and sharpened one end of each to a point, and threaded them into the bottom of the legs.  I racked the focuser all the way in, centered the table's central hole over the focuser, and pressed the pointed screws into the side of the optical tube to mark the drill locations.  Then drilled the holes and mounted the slide table inside the tube.

 
 
Right Ascension Disk Edge Details

The right ascension disk's periphery bearings are 1" diameter stainless steel in 1" pillow blocks.  The 'tire' for the r.a. disk is 1/8" thick x 3/4" wide aluminum.  I routered a groove down the middle lengthwise and have a 1/32" cable running down the slot to turnbuckles at the top of the disk to pull it tight.  There are three slightly oversize holes with wire brads nailed through to keep the tire on widthwise.  The brads are of my own construction from 3/32" diameter piano wire.  Initially tried actual wire brads, but they're too soft and bend too easy.

 

The dec. axis pillow blocks are bolted through to a length of aluminum angle beneath, and the large truncated triangle side pieces bolt to the vertical flange of that angle.  The load is therefor carried straight down to the gluelam at the south.

 
Curved Vane Construction

 Secondary mirror curved vane spider:

I used 7475 T761 aluminum sheet, 37 thou. (.037) thick to create the curved vanes.  I used a router compass to cut two disks from 1" thick melamine sourced from a display table I got for free from a store that went out of business, and screwed them together to create a round mold 2" thick.  I had read that 7000 series aluminum is easy to bend and hold a shape at a low temperature, and that it can be done in the oven.  Not even.  It is extremely tough and resilient material.  I cut the material on the band saw with a fence, and drilled a hole in both ends.  I screwed one end to the edge of the mold, and then jammed it against a wall and bent the strip around the mold and screwed it in place at the other end of the strip.  I'm here to tell you it took FULL force to get it to bend.  Thin and light though it seems to be, it is VERY tough material.  I then heated the strip by waving a propane flame over it until quite hot, then quenched it with a spray bottle.  I repeated the process three times before the material would more or less hold the shape.  I made a couple extra vanes, and picked three that were closest in shape.

 

Hans of Destiny Spiders provided the secondary holder and the hexagonal piece of aluminum that the holder mounts to and the spider screws to.  I had originally made some vanes out of carbon fiber, but that did not work, and Hans wanted to support that experiment.  Carbonfiber is a great material for a variety of applications, but in this case, aluminum was better.  I decided to reverse the mirror mounting screw that goes through the center of the hexagonal part the vanes screw to.  Hans had it with the head inside the wood mirror holder, with the thread end stick through the spring and out the top of the hexagonal part.  I wanted to mount the mirror in a box for transportation, so I made a mirror mount from a big chunk of balsa wood, cutting the 45 degree angle with the Makita sliding compound miter saw.  In the middle I drilled a hole large enough for a pair of dew control resistors, and mounted a T-nut inside.  The mounting screw has a large knob I made by using a hole saw to cut a disk, tapping the center of it and threading it on the mounting screw all the way up to the head of the screw and using 5 min. epoxy to hold it in place.  This knob is used to attach the mirror in the transportation box as well as attaching the mirror in the telescope.

 

The secondary mirror is rather heavy though, and the curved vanes, while strong enough to hold the mirror along the telescope tube's axis, they are not strong enough to hold it centered when the tube is tilted over on it's side, so the mirror sags.  To solve this I used the thinnest available piano wire (I might mic. it if I remember, but it's probably about .010, basically the thinnest they had at the hobby store) stretched from the center to the tube's edge at three places.  Each curved vane mounts at the optical tube with two 'bolts'.  One  is a 1/4 20 bolt and the other is a piece of 1/4 20 all thread rod with a hole drilled through one end, through which I passed the end of a length of piano wire and wrapped it around itself once or twice to hold it in place.  The other end of the piano wire I soldered to an electrical ring end connector with the plastic taken off.  The ring connector is screwed to one of the two screws that attach each end of the curved vane to the central hexagonal aluminum piece.  The piece of all thread sticking through the optical tube has a nut, and that is tightened to adjust the mirror until it's supported in the center of the optical tube (well actually offset a little bit of course to accommodate for the shape of the truncated angle of the cone of reflected light).  The three piano wires hold the mirror quite rigidly in place in the center of the light path.

 

Why all this effort?  I'm sure you know, and you can read more detail at Hans' web site, but in short, anything placed in the optical path creates diffraction effects.  A straight piece of metal will create diffraction spikes around bright objects like car headlights in movies and stars in the telescope.  By bending that metal in an arc, the diffraction spikes are still there, but thrown in a fan around the object instead of being four actual bright spikes.  The effect is the spikes are not visible to the eye.  Now I had to compromise that a bit with the piano wire, but they are thread thin, and my expectation is any visual artifacts will be slight.  FOLLOW UP: I can't see any diffraction from the super thin wires.

 


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