PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Hi Guys and Gals...
This will evolve slowly...
We have the optics set...
We have the design...
We are building...
And we have taken pictures...
The group will likely benifit from this thread...
OTA to be completed within a few months...
Pictures coming soon...like tomorrow..of the start...
Best Regards,
Preston 
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Ok...
Everyone has ask me to start this thread...
and now I have...
Tomorrow I'll post pictures of the machining of the bits and pieces...like the tube ends...the tube end capture blocks and the spherical ends in Invar....
You will love the details....I hope...
Best Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Hi guys...
This started as one of my projects....and then lingered...
Far TOO long..
I offered the optic set on Astromart...and it was quickely picked up...We are a team of 5 currently...they will take the OTA and finish the Robotic build somewhere to be determined...and they have looked at Australia...
From there I offered to both design and build the OTA...
That was 2 years ago...
And to day we are seeing the back plate, collimation plate and mid rings being machined....Finally....
I know this sounds like a fairy tail...
But it is the total truth...
Please follow our path...
Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
Edited by PrestonE (05/02/08 07:42 PM)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Ok, some pictures of the start of the tube ends and capture blocks in 6061 T6 aluminum.
All done manually 32 tube ends and 16 capture blocks and capture plates...
Enjoy,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Drawing of the capture block.
You will notice the use of lots of holes for lightening.
We are trying to keep the entire OTA with optics, focuser, filter wheel, and camera under 100 pounds. The optic set weighs in at 53 pounds for the primary and secndary.
The tube ends premachining weighed 170 grams or 6 ounces and after machining weighted 28 grams of 1 ounce for each tube end. Quite a savings and well worth the time.
Each step was completed on all 32 ends and then the next step was machined...in toll 18 hours to machine the 32 ends.
By the end, I was really wishing for a CNC lathe...as one starts to get very bored doing the same thing 32 times with 15 differant machining steps...
Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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One of the 16 Catch Blocks getting the bevel that will hole the ball end that fits into the Tube End.
Thats, enough for now.
Thanks and enjoy,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Ok, well do the ball turning with the 0.500 inch diameter Invar and call it a day.
First pic of machined pieces in two differing stages. Left after first turning and right ready to turn the ball.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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And turning the radius of the ball to 0.375" diameter.
This was the first real test of my Hardinge toolroom lathe since getting it home.
Edited by Don W (06/14/08 10:37 AM)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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A close up of the finished ball ends.
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A few I enjoy,
and a few more in the works ;<)
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The bear
professor emeritus
Reged: 02/11/08
Posts: 699
Loc: rushville, indiana
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this is very nice i love the machine work wish i had one would make some awesome stuff also. i will watch this thread religiously thanks PrestonE for your doing this build. i would hope you will do it from start to finish from this work to the electronics involved with this for the benefit of all especially me...
doc
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Longitude -85.42786 Latitude 39.59153
when all else fails use duct tape "works for me"
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Thanks Bear,
I'll do my best. We fell way behind when a shipping company that I hired to move my new to me CNC mill last April and dumped it over in the truck while changing trailers here in Houston...total loss and I'm still working on trying to rebuild the control system.
But thanks to Kerry aka "The Captain" here on CN, we have contracted someone to do the really large mid rings, upper ring, back plate and collimetion plate...
That should all be here next week and then I can recheck the lenght of pvc tubing being used to simulate the lengths of carbon fiber tubing...before cutting the CF tubing.
The mirror spacing is fairly critical between the primary and secondary in a RC so we will be trying to hit it within .020 inches or plus or minus .010" at least that's the plan.
Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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The bear
professor emeritus
Reged: 02/11/08
Posts: 699
Loc: rushville, indiana
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i would say that is cutting it close for sure but if you are going to do it right that is the way to go. i am learning about RC through several threads here very interesting design for sure. thanks for your work
doc
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Longitude -85.42786 Latitude 39.59153
when all else fails use duct tape "works for me"
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Thanks Doc,
We are trying to get this OTA completed ASAP...within reason...
Here is a shot of the Capture Plate being chamfored for the ball end...
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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And then the capture block and plate being radiused...
fixture and then assembly
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Assembled Capture block ready to machine the radius...
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Ok this was roughed on the mill in a rotary table and then finished on tha lathe in the same fixture...
--------------------
A few I enjoy,
and a few more in the works ;<)
Edited by PrestonE (05/02/08 11:02 AM)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Finished piece after turning on the lathe...
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A few I enjoy,
and a few more in the works ;<)
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Sky Captain
Scope Builder
Reged: 11/07/04
Posts: 5658
Loc: Seattle Washington
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Thats looking great Preston! I'm really happy the machine shop I use will be able to handle your larger project too.
Do you know when they will get the aluminum plates?
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Equipment Overload!
Kerry.
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Thanks Kerry,
The plates are being shipped from 2 locations as we had already purchased the 18.5" diameter x 1.25" thick cast aluminum tooling plate Being machined for the collimation plate. It shipped Wednesday and I'll have to get the tracking number from Speedy Metal. I can say that Speedy Metal was $750 for everything and Jim $1100...so we went with Speedy.
I'll find out and let you know. Thanks again for the introduction to Jim the owner of the machine shop doing the work.
Best Regards
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Ok, next let's take a look at the collimation plate...CAD rendering. I'm working on attaching the Rendering, not like attaching a picture 
It has 3 two point pivots to suspend the mirror, with 1" diameter pads at the ends that sit on ball ends so that there will not be any binding...
Included is the mirror support tube in the center, this goes out the back and is centered in the mirror back plate with a metal o-ring to keep it centered in the back plate when collimating...
Notice the second slots from the ends of the three arms...these have an oilite bronze incert that can rotate slightly during collimation. These will be the tightening cap screws that oppose the push secrews that will push against the back side of the outer 3 holes on the arms...
The diameter at the edge of the arms is 18.5" and the thickness of the cast aluminum tooling plate is 1.25"
This collimation plate will likely be the first to get machined early next week.
Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
Edited by PrestonE (05/02/08 02:27 PM)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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And finally the almost complete OTA...I had to cut and paste various changes from dozens of drawings to just get this far...
Hope you enjoy...
Mirror back plate is 26.5" in diameter and 0.75" thick, lightened with milled holes that do not go through...they were originally hexagons, but we could not get anyone to bid on doing that work.
The spacing between the primary and secondary is 31.5 inches
I've got a little work still on the secondary design, but have taken Mike Jone's recommendation and gone with a tilt/tip a 90 degrees, around a fixed corner ball.
Spiders are Carbon Fiber/Aramid/CF sandwich in the hopes that should the carbon crack, the Kevlar will hold everything in place.
Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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Hi Preston, your mirror cell is quite different from what I am doing, specifically I am trying to make sure that the centre hole never touches the baffle.
I am guessing that this is because your mirror is not a plano back, hence only 6 supports as well?
Thanks ,
Jason
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Hi Jason,
Our mirror is a conical with an outer edge thickness of about 0.75" and a central hole thickness of 2". Hole diameter is 4.5"
The diameter of the flat on the back is about 7 inches and the 6 leveling pads will rest there with the Mirror support tube going through the Mirror's hole and contacting the mirror with a nylon O-ring at the center of gravity of the mirror in cross section.
This will restrain the mirror from any lateral movement and not put any uneven strain on the mounting location.
Not shown in the rendering is the threaded locking ring that will retain the mirror to the collimation plate. The area that will contact the mirror will be cork lined and little if any torque will be applied.
The baffle will adjusted independantly from the Mirror tube.
This should keep collimation very well, as I've used a similar system on my 10" RC "The Unfinished Telescope", by Paul Van Slyke. I learned a lot about what to and not to do from working on that scope.
How is your build coming along?
Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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jasonharris
super member
Reged: 09/16/06
Posts: 137
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That makes sense and is along the lines of what I have seen with conical mirrors - which I wish I had at one point to simplify mine! 
I will machine some of the spider support today and my cell will be cast ready for pickup on wednesday I will update my thread then, dont want to hijack yours.
Your is looking really god btw!
Jason
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The bear
professor emeritus
Reged: 02/11/08
Posts: 699
Loc: rushville, indiana
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Robo Scope indeed i like the simple but effective design of this scope looks very strong.
doc
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Longitude -85.42786 Latitude 39.59153
when all else fails use duct tape "works for me"
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Thanks Jason
Some of the details that are not yet shown include the plate for mounting to the tracking mount.
Most of the OTA's that I've seen using Zero expansion carbon fiber tubes, then break the reason for using the carbon tubing by solidly joining the Rear support to the mid ring with a solid aluminum mounting plate...
With any temperature change, that aluminum mounting plate is pushing and pulling constantly as the temperature varies on the 2 plates that it attaches. It also is putting stress on the truss tubes unevenly and changing the spacing between the primary and secondary...
We will use and aluminum mount that mounts solidly to the rear plate and has a precision linear rail and car that attaches to the mid ring. That way any movement due to temperature changes will cause the rail to move smoothly back and forth in the precision car and not cause any change in mirror spacing.
Doc I sure hope that it's up to the task of staying in collmation over long periods of time...
Originally I was going to build the OTA out of steel 2 inch square tubing...but that would have been much TOO heavy and temp changes would still have been an issue, though less than aluminum...I modeled the fisrt one in balsa and was very impressed with just how stiff it really was.
For a 1/4 scale model a load of 5 pounds on one corner caused a deflection of only .005"
I'm looking forward to doing a similar test to the assembled OTA without the mirrors...don't want to chance damaging them.
Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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The bear
professor emeritus
Reged: 02/11/08
Posts: 699
Loc: rushville, indiana
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i model my stuff always something about holding it in your hands makes it real plus i work out all the build in my head better this way. its nice to have drawings/renderings to get the idea but i like the feel. often times like now i am building things in my head then often when the design is final i just go ahead and build them if they are simple enough.
doc
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Longitude -85.42786 Latitude 39.59153
when all else fails use duct tape "works for me"
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Your right Doc, and this thing gets quite difficult to get some things into place...like moving those darn tubes that are not at 90 degree angles, bout drove me crazy.
I ended up making a full scale model of 2/3 of the OTA to make sure that the tubes stayed out of the light path.
And I'm still going to wait for the big machined pieces to arrive to assemble and again check the tube lengths before cutting up that $800 in Carbon Fiber tubes...
Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 750
Loc: Houston,Texas
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Ok...let's move to the future...
I ask Mike Jones at first to design a focal reducer...which he started...but, the group wanted a field flatner...
If you were building this scope...would you want a focal reducer or field flatner...
and Mike, please explain your views and the proposed designs...
Mike are you out there???
Best Regards,
Preston
--------------------
A few I enjoy,
and a few more in the works ;<)
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Mike I. Jones
Pooh-Bah
Reged: 07/02/06
Posts: 1069
Loc: Fort Worth TX
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Hey Preston!
Yep, I be out here, enjoying your posts. The scope sure looks good - first time I've seen all your CAD work as well. I've only seen the d |
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