bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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Today was a milestone in the scope project. I bought a new router bit and made a circle jig. To test it out, I made a mirror blank out of a 1/2" sheet of the cheapo home depot birch plywood.
The jig worked well. Its a 1/4" piece of plywood that came in some box or other as cribbing for shipping something else. It was nice and square so I kept it, and now it turned into a nice little jig! I traced the hole pattern on my router's plunge base, drilled and countersunk the holes so the flat head bolts would fit flush with the surface. I used a spade bit to cut the hole for the bit to fit through.
Measuring the radius from the inside of the bit, I marked the spot and drilled a hole. I also marked the center of a 24x24" piece of plywood and drilled a hole there. The pivot point is a #12x1.5" screw. I sunk it all the way into the plywood, but not so tight I couldn't turn the jig. It worked like a charm.
Here is a picture. It was taken after the cut, so that is why the screw is backed up so high.
My only regret is the piece of plywood isn't long enough to cut the radius of my altitude bearings (based on the balance calculations I've been performing, I figure they'll need to be near 40" in diameter), so I'll have to make another, longer, jig when the time comes. The good news is this only took 5 minutes to build.
Thanks to everyone who's been answering my questions as I forge through the design process. This forum is great. I'm sure that I'll have more as I go! I'll try and keep this updated as the project progresses. Hopefully someone will learn something from my work!
-Brian
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Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
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rboe
Reged: 03/16/02
Posts: 45410
Loc: Phx, AZ
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For a very large radius I used two pipe clamps as the arms of the jig. Lazy suzan bearing for the pivot spot (c clamped on - not for for complete circles - so glue some blocks on that jig there for the pipe clamps to grab and use the same center hole and Bob's your uncle) and a separate mount for the router.
The clamps clamped onto the pivot board. Scraps of wood with holes cut into them with knobs captured the other end of the pipe. Fined tuned by tapping the router mount board up and down the pipes.
Once your done you still have pipe clamps to clamp up things like your mirror box. 
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Ron
NS11GPS
Pronto
16" dob
15X70 Obies
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Nathan F
sage
Reged: 10/10/08
Posts: 223
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Thanks for posting! I've been meaning to build myself some sort of spiffy adjustable circle cutting jig, though as you've shown, such a thing is not necessary for good work.
Trying to cut circles on my band saw for my parallelogram mount was utter hell, even with a similarly solid jig. The movement of the blade ensured that every circle was just slightly off, necessitating some serious fixup work at the oscillating spindle sander. It seems the router method is immune to this, though I think the stock I was working with was probably way too thick to use this technique on.
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12 inch f/5 Deep Space Observer Dob
31mm Nagler, 13mm Ethos, 1.6x Antares 2 inch Barlow
Celestron SkyMaster 15x70 Binoculars
Homemade Maple Parallelogram Binocular Mount
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Undermidnight
Pounder of Brass
Reged: 05/25/04
Posts: 2427
Loc: Hilliard, Ohio
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Using a circle cutting jig for a router is one of the best ways to cut circles in plywood. I went ahead and spent the money and bought the jig at Woodcraft. Now I can make accurate circles from 2" all the way up to 36".
Question for you guys:
Do you do multiple passes plunging the router 1/8" every time? That way, the router bit never cuts more than an 1/8" everytime.
Jason
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WO Megrez 90 on EZTouch Mount
WO Zenithstar 66 on Microstar Mount
PST
8" F/4.2 Ball Scope, "Marilyn"
12.5" F/4.3 Ultralight, "Ada II"
11x70 Oberwerks
6" F/6 Polishing
Pans, Orthos, and Naglers
"We who cut mere stones, must always be envisioning cathedrals." - The Quarry Workers Creed
http://www.undermidnight.com
http://undermidnight.blogspot.com
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rboe
Reged: 03/16/02
Posts: 45410
Loc: Phx, AZ
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Rough cutting with a bandsaw is a great idea. Use the router to clean up the edge - a lot easier on you and the router. 
For circles under 30 some inches I use a commercial jig that I picked up a few years ago. No reason you can't use a larger piece of plywood to do the same. To be really accurate you should have some means of tweaking the radius length. With the commercial rig all the holes are pre-drilled and it's right on. But I'm stuck with 1/4" increments.
I do multiple cuts with the router. I try to do a clean up pass that is full depth on the last pass - at which time I also tweek for the correct radius.
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Ron
NS11GPS
Pronto
16" dob
15X70 Obies
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dave b
Post Laureate
Reged: 05/10/05
Posts: 3548
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i do 1/4" per pass with my 3.5 hp router
also, many router bases have two 5/8" or 1/2" holes lengthwise in them so you can use 2 pieces of drill rod to make a jig:
http://www.extremehowto.com/xh/article.asp?article_id=60623
support your work; this guy is not going to have a perfect circle, but you get the idea
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dave bonandrini
30" f/5.2 Dobsonian
President of GCAC
Astromart Moderator
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Houdini
professor emeritus
Reged: 07/13/07
Posts: 525
Loc: Europe
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Here's my router setup using this technique for cutting some upper cage rings (about 45" diameter). The jig uses two long 8 mm threaded rods, some Alu tubing, and a 6 mm bolt as center pin. Works very well!
Robert
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16" f/4.9 motorized alt-az, 25" f/5 Dobson, 43" f/4 alt-az under construction
Mirror Edge Support Calculator
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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Got some more work done. I cut the upper cage rings. I started out by marking a 30"x30" square on a sheet of 3/4" BB. I traced the diagonals to find the exact center, and drilled a pilot hole for the circle jig. Those lines also served to mark the locations the struts will go. I also drew in the lines to mark the relative locations of the truss blocks, for both an 8 truss arrangement and a 6 truss arrangement. I've since decided to go with 8 for other layout reasons, but I marked the lines anyway. Note that the piece of wood is square. The distortion is a neat effect of the ultra wide angle lens I used to take the picture. Makes me look fat to. Notice the wife strategically places at the 'skinny' end of the wide angle effect  (she doesn't need the help though).
I cut the outer diameter (28"). Then reset the jig for the inner diameter (24"). I used several shallow passes to make this cut, and made sure to support both the inner scrap piece and the portion that would become the ring very well so as not to let either fall away from the bit and nick or scar. I also left the little bridges at two places as illustrated in the K&B book. I cut them very carefully after the rest was cut. Worked great.
Finally, I decided to make a jig out of cheap plywood I have laying around. I drew the 30" square again, marked the strut locations and truss locations as before and I cut the OD the same as the ring, 28". As opposed to the K&B method, I'm going to dowel my struts in place so no hardware is visible on the top ring. I'm going to use struts that measure 1.75", so I went ahead and drilled a pattern for the dowel holes.
Now I'll be able to line up the rings, clamp them, and drill the dowel holes so they'll be exactly registered. I can also clamp the struts to the jig and drill them so the spacing will match. Hopefully it works as well as I think it will.
The Moonlight focuser arrived today too! Now I just need to get my secondary holder and spider and I can start gluing.
-Brian
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Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
Lust for something Larger
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Jeff Morgan
Carpal Tunnel
Reged: 09/28/03
Posts: 1987
Loc: Prescott, AZ
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Quote:
Rough cutting with a bandsaw is a great idea. Use the router to clean up the edge - a lot easier on you and the router.
For circles under 30 some inches I use a commercial jig that I picked up a few years ago. No reason you can't use a larger piece of plywood to do the same. To be really accurate you should have some means of tweaking the radius length. With the commercial rig all the holes are pre-drilled and it's right on. But I'm stuck with 1/4" increments.
I do multiple cuts with the router. I try to do a clean up pass that is full depth on the last pass - at which time I also tweek for the correct radius.
I was using my router like a saw, the end result was I was spending more on router bits than wood! A rough cut using a jig saw close to my cut line is much easier and faster. That way I can do one pass with the router. And since I set full depth, the bit wears evenly, instead of the bottom 1/4" being dull while the remainder is essentially virgin.
Ron, on my Jasper circle jigs I noted they are calibrated for a certain size bit. By going with a slightly smaller or larger bit you can achieve arcs between the preset sizes.
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Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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Well tonight some metal dust flew. I'm still waiting on my secondary holder and spider to arrive, so work on the upper cage is on hold for now. I did have a friend plane my uprights - I'll reveal the details on those later.
I found a great local metal shop thanks to the guys at the UNL Physics/Chemistry Instrument shop. I got a better price than I could find online and it was ready same day. I decided on 6061 aluminum for the triangles and bars. 1/4" for the triangles, 1/2" for the bars. Both cut easily with my bandsaw. I punched the location of the apices and pivot points so I can accurately drill them later. I also sanded the edges to smooth them up a bit and take the sharp edges off.
Piece of advice - wear gloves, goggles, and a dust mask when working with this stuff. It gets HOT when cutting and sanding, and metal dust isn't great for your lungs.
-Brian
I'll get some pictures posted later this weekend.
Thanks,
Brian
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Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
Lust for something Larger
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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Finally got some pictures downloaded. I've also gotten a little more work done. I clamped my rings into the jig pictured above
and drilled the dowel holes. I did have one major error here. As I was drilling the ring, the stop collar on my bit slipped and I didn't notice. The last two sets of holes punctured the bottom side of the ring. Oh well, I guess no project occurs without any penalties. I cut a new one and finished it. I used the same jig to drill the dowel holes in the uprights. Here is a picture of the final assembly glued and clamped, waiting to dry.
The uprights are 1.75" hardwood. I had a friend run them through his jointer and planer, and I squared up the ends with my sander. Having put all that work in, clamping things in square was a snap. The wide surface area of the blocks kept everything nice and solid under the clamping pressure.
Next step will be to drill out the holes in the bars and triangles, then on to the tailgate jig!
-Brian
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Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
Lust for something Larger
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Past Lovelies:
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artmustel
super member
Reged: 05/30/07
Posts: 128
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It is looking really nice!
I have a comment regarding UTA uprights made out of wood: I did in my scope and regret it because the unnecessary weight they added to the Uta. Yours look great, however. Congrats!
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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I considered the weight issue. I'm basically trading off the looks for a smaller finder. I have an 80mm finder on my 15", which weighs about 4 pounds, so I may have to go lighter on this one to offset the wood. I ran the calcs based on estimated weights, and the wood only made about an inch difference on the bearing diameter. When you're talking about 40" bearings, going to 41" isnt a deal breaker.
-Brian
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Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
Lust for something Larger
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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Well, after a few weeks of traveling for work, having family visit, and a star party, we got back to work yesterday. We're in the process of assembling the jig for our tailgate. This one will be sure to look crazy to the K&B purists. I've made the cell big enough to reach all four sides of the mirror box. My mirror box, like Fiske's will be little more than a light baffle and a place to stabilize the lower truss clamps. So the theory is that this larger cell will bolt to all four sides and help provide strength to the structure. Its sort of like the many UC scopes that are coming out with no mirror box at all, the tailgate is is the main structure.
I should be able to get some pics up later this week.
-Brian
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Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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Ok, so here is a picture of the tailgate, with the mirror cell rigged up. That's a piece of plexiglas I had laying around. Its not quite as wide as the mirror, but it works for this purpose.
There is a bit of the wide angle effect due to my lens and the close quarters of the garage. It is indeed square. It is also not a K&B design. I've made it the same size as the inside of the mirror box (which I haven't built yet). The idea here is to put as much weight as possible in the back in order to bring the balance point back closer to the mirror. This will ultimately allow me to have smaller bearings. My mirror box will be a fixed height, maybe 8" or so, so balance will be achieved by changing the bearing diameter.
We'll see how it goes!
I got the holes for the mirror cell drilled and tapped. I bought a set of TiN coated taps from McMaster Carr. MUCH easier to work the SS with these taps, than non coated taps, even high quality ones.
I broke my drill press before I got all the other holes drilled though. The friction fit of the chuck to the spindle wore loose. Won't stay on anymore. I've got to go to Harbor Freight tomorrow and see if I can replace the chuck. I've gotten way more than my $50 worth out of this drill press over the years, so a whole new one might just follow me home. We'll see.
-Brian
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Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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Good news. I was able to get the drill press back together. Couple of good raps with a wood block and mini sledge (4lb) and it stayed. Then I found the real problem - my 3/8" bit was shot. When the bit bound and the chuck popped off it must have chipped the leading edge of the bit. I was sailing along, drilling in increasing step sized and everything was fine until I got to the final size. It just wouldn't cut. I thought I'd smoked the final two holes when the chuck popped off and hardened them. But I got a new bit yesterday morning and it went through like butter! Great news.
I learned a few things though.
1. Use TiN coated bits for SS. It makes a huge difference. Same for your taps
2. I have a 1/3hp 660rpm minimum drill press. This is a bit too fast to be ideal for cutting stainless, but it works if you are careful and use lots of cutting fluid. However, the motor was struggling to cut the 3/8" holes even though I stepped up gradually (see #3). If I replace this puppy, I'm going to look for one that has a slower minimum speed and a larger motor.
3. Make lots of steps when drilling out holes. I started with 1/8" bit, and went up 1/32 in steps until 3/8. It was tedious but the less time each of the drills spends in contact with the metal, the less likely you are to overheat and work harden it. I probably could have gotten away with making steps in 1/16ths, but I was also contending with the weak motor on my press. The smaller steps reduced some of the load on the motor and helped that situation. It wasn't an issue until about 5/16ths, but then the motor would bind every now and again.
All is well now. Jig built, holes drilled. Just need to clean them up and get them to the welder. I also need to place an order for laminate so I can finish the upper cage. I think I'm going to user the 'sparkle' series from Formica which others in this forum have reported good luck with. MUCH cheaper than the Wilsonart stuff of the proper finish.
-Brian
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Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
Lust for something Larger
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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FYI I ordered a 4'x10' sheet of Black Faux Marble Formica brand laminate in the 'Sparkle' finish from Lowes. This was the only size they offered. It was $2.05/sqft, which was $1.20 cheaper than home depot or any of the local cabinet shops. $80 for the whole sheet instead of $120. Not bad.
-Brian
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Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
Lust for something Larger
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Past Lovelies:
Oberwerk 20x100 binocs
Meade AR5
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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What a sleepless night. I just woke up at 2:30am from a dream, and can't get back to sleep.
Today we dropped off the tailgate for welding. Some friends of my wife's are doing it in their free time, so I should have it back in about a week. Those guys are awesome!
Also went with Protostar for the secondary. I emailed around to several of the major vendors, and theirs seemed to be the best available in a reasonable time frame. Hopefully that'll show up in a week or two.
-Brian
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Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
Lust for something Larger
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Past Lovelies:
Oberwerk 20x100 binocs
Meade AR5
Meade LX10 8" SCT
All sold to a good home
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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Wow, its been a long time since I updated. Sorry about that. Got some good work done. This one is going to be pic heavy.
Here is the tailgate back from welding, getting painted in our garage.
The guys did a great job. The rectangle pieces we got weren't exactly straight, they were slightly warped, but the jig I bulit held it in place well and they got it welded in. It is nice and square.
Next order of buisiness was to build the upper truss clamps. I went with the same design as on my Astrosystems.
That allowed me to get the upper cage assembled, formica installed and the focuser mounted. It is squared, but I still need to center my spider.
I think the look is coming together nicely. The wood looks good against the marble finish laminate.
The next order of business was to build the mirror box. Its 9" tall.
Next order of business is going to be to build the lower truss clamps. I have a ball mount design in mind that I'm going to save sharing until I know if its feasible or not, lest I look like a fool. 
More soon I hope!
-Brian
--------------------
Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
Lust for something Larger
Lust for something Larger than that
Past Lovelies:
Oberwerk 20x100 binocs
Meade AR5
Meade LX10 8" SCT
All sold to a good home
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bbasiaga
professor emeritus
Reged: 05/10/06
Posts: 724
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Well, I did indeed outsmart myself on the lower truss block design. I had hoped to use a ball socket down there, but I've found that I just can't get enough tension on them to hold the ball in place, even against just the weight of the 7' long truss tubes. I started to get visions of the whole upper cage and truss assembly falling off, and that went bad places. I had ideas on how to hold them in place - a couple of pins would do it, but the design just seemed to get more and more complicated, and what I thought I was doing when I started was making it simple. So I think I'll be changing direction. I'm going to use a grealy simplified split block. Only it won't have a split. It'll just be a hole bored in a piece of hardwood to fit the truss tube. I'll drill another hole in the side of the block perpendicular to the tube axis, sink in a t-nut, and use a small threaded rod with a handle on it to hold the tube in. This will attach to the mirror box with screws. I'll have to put one screw in until I get the tube angles set, then add one or two more to hold it in place, and I may have to shim it 'out' a bit to line up easily with the upper clamps. These are things I was trying to avoid with my ball socket idea, but oh well. It isn't insurmountable.
Some money wasted on materials, some time wasted on putting them together, but I'll chalk it up to R&D expense.
I'll get some pics up once I have a prototype.
-Brian
--------------------
Vixen 80EDSF
Stellarvue 102ED2
Orion Atlas 11 EQ-G
15" Astrosystems Telekit w/ Discovery Optics
Lust for something Larger
Lust for something Larger than that
Past Lovelies:
Oberwerk 20x100 binocs
Meade AR5
Meade LX10 8" SCT
All sold to a good home
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