HandyAndy
professor emeritus
Reged: 01/11/08
Posts: 652
Loc: West Midlands and around
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Hi,
The problem with trusses is the funny angles the tubes join at and to the mirror box and top ring.
I have thought of having a sphere of hard plastic which just fits into the truss tube. The sphere has a hole drilled in for the bolt to the required tolerance. The tube has an oversized hole drilled through at the correct length and roughly in the correct orientation.
When two tubes are bolted together to the mounting point the sphere can revolve to the right orientation.
An alternative to get the centre points of the tubes to meet is to machine off just over half the diameter of the end of each tube so they can be bolted on to each side of the hole in the sphere. I think this would give the stiffest triangle as there is no offset.
The sphere cut be cut in half across the hole with the cut the thickness of a lug attached to the mirror box or top ring. The bolt would then pass through a truss end, one sphere 'half', the lug, the second sphere half and the second truss end. All the connection axes will then be co-centric.
Cheers. Andrew.
--------------------
Monarch 8x42, Zeiss 10x50 WA
10mm F2, Pentax 60mm F5
City: 7" MN78: MK4#2, 10" F6.3: MK4#1, 16" F5 ParaCorr
Country: 8" VISAC: (GP2)
Car: 6" F5 MPCC: SP, 5" 127mm F7.5 (GP2)
TV 55mm, Paragon 40mm, UO Pretoria 28mm
B&L 32 Pl, Clave's 25, 8, 6, 2x
Hyperions 5, 8, 13, 17, 24, 31
Nagler1 9mm, Meade 14mm 4000 UWA
Antares 1.6x, 0.7x, 0.5x
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polaraligned
sage
Reged: 12/26/08
Posts: 233
Loc: P. R. of New Jersey
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Spherical truss ends is a good idea and has been used by a number of commercial manufacturers.
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Don W
Postmaster
Reged: 05/19/03
Posts: 14629
Loc: Wisconsin, USA
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Ayup. Moonlite sells them.
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Don Wyman
Obsession 18" f/4.5 #1166
W/Argo Navis DSC and Torus Primary
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Owen
professor emeritus
Reged: 06/21/07
Posts: 514
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Just a little thought experiment... whilst you are considering the truss connections...
Is a sphere actually necessary to obtain the same level of 'flexibility' in positioning of the truss..?
Owen
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Howie Glatter
Vendor
Reged: 07/04/06
Posts: 196
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>Is a sphere actually necessary . .
Only a segment of a sphere is necessary, but it must be a sphere.
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Owen
professor emeritus
Reged: 06/21/07
Posts: 514
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Hi Howie...
are you really sure that it needs to be a segment..? (thats a clue)
Owen
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HandyAndy
professor emeritus
Reged: 01/11/08
Posts: 652
Loc: West Midlands and around
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Hi,
I was thinking of a sphere which in the simplest option fits inside the truss tube. The bolt goes through an oversized hole in the tube and a fitting hole in the sphere. This is a simple self aligning bearing. I am not thinking of a round knob on the end of a truss tube.
In the second option I have one sphere with two reduced section truss tubes with one hole in so one can be bolted on to each side of the hole in the sphere.
Between the bolt head or nut there needs to be a washer, possibly a short half section of a larger tube with the inside diameter matching the outside diameter of the truss. Or maybe a soft washer to conform to the indent of the larger clearance hole in the truss tube.
Cheers. Andrew.
--------------------
Monarch 8x42, Zeiss 10x50 WA
10mm F2, Pentax 60mm F5
City: 7" MN78: MK4#2, 10" F6.3: MK4#1, 16" F5 ParaCorr
Country: 8" VISAC: (GP2)
Car: 6" F5 MPCC: SP, 5" 127mm F7.5 (GP2)
TV 55mm, Paragon 40mm, UO Pretoria 28mm
B&L 32 Pl, Clave's 25, 8, 6, 2x
Hyperions 5, 8, 13, 17, 24, 31
Nagler1 9mm, Meade 14mm 4000 UWA
Antares 1.6x, 0.7x, 0.5x
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jasonharris
sage
Reged: 09/16/06
Posts: 253
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Doesnt it depend on the design of the telescope? I use the moonlight connectors on my 16" I built following 'the book' and the balls certainly make it easy to put the top on the scope but the purpose isn't to get the angles right is it?
A ball and socket has huge advantages when the trusses have compound angles but most dob scopes only have one angle to contend with and thats mostly important at the connectors down the bottom which I have never seen a ball used there.
At least thats how I see it on most dobs.
JAson
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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This was a small chore to build but it works very well. The rod ends give 17 degrees of movement.
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Roy
MN65
114NT/500
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Owen
professor emeritus
Reged: 06/21/07
Posts: 514
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A simple self aligning bearing, doesnt need to have a 'sphere' at all, thanks to geometry...
Another clue - # The contours and plane sections of the sphere are circles.
This property defines the sphere uniquely.
Owen
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Scott Watson
sage
Reged: 05/26/06
Posts: 282
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Roy has it. Spherical rod-end bearings are the key to a good hexapod truss. I've been told several times by members of this forum that this very idea doesn't work. Sorry, but it does. 3 points define a plane and two planes with 6-degrees of freedom (trusses) are all that is necessary for perfect, no slack, properly contstrained collimation. Here is another tip. If you use rod ends with different thread pitches, but the same handedness, your adjustment will be ohhh-soooo-fine. Heck, maybe Art B. will come back if more than two of us push this idea. For those who are still on board, another tip is to use plastic rod ends. They are MUCH lighter, cheaper, and have nearly the same precision and slop as the stainless variety. Good luck...
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Owen
professor emeritus
Reged: 06/21/07
Posts: 514
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http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3404168/page/0/view/collapsed/sb/5/o/all/fpart/1#Post3404802
Take a look - all the advantages of a spherical bearing, with little of the pain/cost...
Have fun
Owen
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Vincent Becker
super member
Reged: 09/16/08
Posts: 198
Loc: France
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Here are some pictures of spherical bearing trusses (about halfway down the page):
http://sites.google.com/site/dobson2005/dobson400serruriercarbone
Owen's link is very interesting too.
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Vincent Becker
10" dobsonian on EQ platform (home-made by my father)
8" string newtonian as travelscope (home-made by myself )
Orion 80ED and GSO 200/1000 on Atlas EQ-G for astro-imaging
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Owen
professor emeritus
Reged: 06/21/07
Posts: 514
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Those are fabulous...
Owen
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Jim Romanski
scholastic sledgehammer
Reged: 01/02/05
Posts: 844
Loc: Guilford, Connecticut
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Here is the setup that I’m using with the 17.5” Scope.
One of the design principles that I was taught with truss tubes was to have the connection butt together in the horizontal plane so that there’s less movement in the vertical. In other words, I didn't want to stick a bolt in from the side when connecting it to the scope to prevent wear and slop. The bottom uses Moonlite ball connectors. The top has Tie Rod Ends or Heim joints from McMaster Carr permanently bolted into an aluminum angle plate. The 1/4-20 thumb screw is captive and screws into the top ring. By having the connections butt in the horizontal plane the vertical length is maintained overall collimation is better retained. Also, this makes for 4 pairs of struts that are easy to assemble in the dark.
I used studs with 1/4-20 thread on one end and 1/4 -28 on the other for the Heim joints since the ones sold by McMaster Carr are only available as 1/4-28 and the tube inserts are 1/4-20. I prefer to use the tube inserts as this also retains the same connection scheme of butting in the horizontal.
The struts are also adjustable.
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Jim
17.5" Dob "Project"
13.1" Coulter
8” Cave
NP 101 on a CG-5
25x100 binos
Naglers, Ethos, etc.
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Jim Romanski
scholastic sledgehammer
Reged: 01/02/05
Posts: 844
Loc: Guilford, Connecticut
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Top tube connectors.
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Jim
17.5" Dob "Project"
13.1" Coulter
8” Cave
NP 101 on a CG-5
25x100 binos
Naglers, Ethos, etc.
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Jim Romanski
scholastic sledgehammer
Reged: 01/02/05
Posts: 844
Loc: Guilford, Connecticut
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Bottom tube connectors.
--------------------
Jim
17.5" Dob "Project"
13.1" Coulter
8” Cave
NP 101 on a CG-5
25x100 binos
Naglers, Ethos, etc.
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Jim Romanski
scholastic sledgehammer
Reged: 01/02/05
Posts: 844
Loc: Guilford, Connecticut
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Quote:
Heck, maybe Art B. will come back if more than two of us push this idea.
Come back Art! 
--------------------
Jim
17.5" Dob "Project"
13.1" Coulter
8” Cave
NP 101 on a CG-5
25x100 binos
Naglers, Ethos, etc.
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Owen
professor emeritus
Reged: 06/21/07
Posts: 514
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Art is very, very busy at the moment.. but he does pass by now and then
Owen
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MitchAlsup
super member
Reged: 08/31/09
Posts: 186
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Quote:
The problem with trusses is the funny angles the tubes join at and to the mirror box and top ring.
See attached picture. Since the angle only has to be established once, the spherical rod ends are complete overkill. The poles, themselves, were filed to fit the angle brackets and are about 1mm sort on one side compared to the other.
To establish this fittment, assemble the scope with minimal tension in the bolts on the angle bracket to truss tube. Watch how the base of the angle bracket is mismatched to the tube. Find the point of maximum gap and draw this size on the opposite side of the truss tube. Then use a file to remove slivers of the tube until the fit is perfect.
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Kalle
newbie
Reged: 06/29/09
Posts: 2
Loc: Germany
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I remember someone using roll-on deodorant spheres and its counterpart. see pictures below http://www.eifeltwister.de/projektekugelson22.htm
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Kalle
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HandyAndy
professor emeritus
Reged: 01/11/08
Posts: 652
Loc: West Midlands and around
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Hi,
The last post is interesting.
However my point is that the geometry means the apexes of the triangle occur inside the truss poles. And not projected out into empty space.
Someone using wire mounted secondaries said that the wires need to terminate together at the apex other wise they were not very stiff.
Cheers. Andrew.
--------------------
Monarch 8x42, Zeiss 10x50 WA
10mm F2, Pentax 60mm F5
City: 7" MN78: MK4#2, 10" F6.3: MK4#1, 16" F5 ParaCorr
Country: 8" VISAC: (GP2)
Car: 6" F5 MPCC: SP, 5" 127mm F7.5 (GP2)
TV 55mm, Paragon 40mm, UO Pretoria 28mm
B&L 32 Pl, Clave's 25, 8, 6, 2x
Hyperions 5, 8, 13, 17, 24, 31
Nagler1 9mm, Meade 14mm 4000 UWA
Antares 1.6x, 0.7x, 0.5x
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Glig
sage
Reged: 10/02/05
Posts: 370
Loc: Baltimore, MD
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guys these are very good ideas - but why don't people use a six or 8 pole interconnected system? ATMs have been using these for years. Obsession came out with a nifty 6 pole interconnected system for the 15 UC and 18 UC Obsession. Its the best commercial truss system to date.
Now I'm "obsessed" with improving it. See, it has captive screw mounts top and bottom - 6 contact points in all.
If you replace the 6 screws with Moonlite balls and sockets
You get the fastest truss system known to ATMs.  
Now, the only thing I have to do (hopefully with some advice from you guys) is to figure out how to integrate/create hardware for the truss ends to make the magic work. Only the most elegant design will do.
Requirements:
1.The joint at each intersection of 2 trusses must be permanently connected at all times.
2 They must fold and unfold without slop.
3.They must unfold easy - use a bearing or bushing perhaps?
4. a single ball is hard connected with one of the poles at an angle that aims straight up when unfolded. Somewhere between the truss end and the Moonlite ball there must be a way to connect the other pole as I required.
There are 6 of these balls top and bottom of the trusses.
6 socket blocks for contact points.
5. All bolts that tighten the ball ends be captive and made to tighten by hand. No knuckle busters! 
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Richard Caldwell
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grendel
sage
Reged: 04/12/09
Posts: 250
Loc: Canterbury, Kent, UK
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how about usind a wire spring clip with a ring to constrain the ball, this could hinge on the uta / lta and spring under a catch plate. on the uta there could be a recess to take the ball. then all you would need to do is place the truss in place and flick the sprung part round and secure it, then repeat for the next one.
If you want I can produce a drawing, but it will take me an hour or so to CAD it up.
Grendel
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Please do!
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Roy
MN65
114NT/500
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Glig
sage
Reged: 10/02/05
Posts: 370
Loc: Baltimore, MD
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Thanks Grendal - this has been done, though not on a interconnected system. Was it the JMI NGT-12.5 telescope? I like the idea, but not as much as a ball and socket. I don't want to be pulling on a cold piece of metal in the winter. Also, I think the ball and socket is as fast as any.
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Richard Caldwell
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MitchAlsup
super member
Reged: 08/31/09
Posts: 186
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Quote:
guys these are very good ideas - but why don't people use a six or 8 pole interconnected system? ATMs have been using these for years. Obsession came out with a nifty 6 pole interconnected system for the 15 UC and 18 UC Obsession. Its the best commercial truss system to date.
Now I'm "obsessed" with improving it. See, it has captive screw mounts top and bottom - 6 contact points in all.
If you replace the 6 screws with Moonlite balls and sockets
You get the fastest truss system known to ATMs.
<snip>
Only the most elegant design will do.
Requirements:
1.The joint at each intersection of 2 trusses must be permanently connected at all times.
The thing I did was to take the mirror box out of the stiffness equation of the truss. Thus the truss poles attach as seen before at the top of the scope, and attach directly to the triangle that carries the mirror cell at the bottom. See image:
This means the mirror box is mostly just a protection and storage device and you can get rid of most of the weight. The mirro box for my 20"er is made from 3/8ths (¿9mm?)baltic birch ply.
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grendel
sage
Reged: 04/12/09
Posts: 250
Loc: Canterbury, Kent, UK
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ok rough and ready, I havent drawn the full spring clip or catches yet, but the idea is that these fit on the sprung ring to constrain the ball.
Grendel
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grendel
sage
Reged: 04/12/09
Posts: 250
Loc: Canterbury, Kent, UK
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actually it could be a rubber belt with a hole to centre the ball, clipped at one end fixed at the other.
Grendel
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Andrew, Is this what you had in mind?
And as Grendel mentioned it could be held in a number of ways.
Edited by Roy McCoy (10/24/09 12:52 AM)
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Pic 2
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Quote:
1.The joint at each intersection of 2 trusses must be permanently connected at all times.
All the poles remain connected.
Edited by Roy McCoy (10/24/09 01:22 AM)
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Quote:
2 They must fold and unfold without slop.
3.They must unfold easy - use a bearing or bushing perhaps?
4. a single ball is hard connected with one of the poles at an angle that aims straight up when unfolded. Somewhere between the truss end and the Moonlite ball there must be a way to connect the other pole as I required.
There are 6 of these balls top and bottom of the trusses.
6 socket blocks for contact points.
Basically, these do all of this.
Edited by Roy McCoy (10/24/09 01:20 AM)
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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I'm not advocating rod ends one way or another.
I simply wanted to throw out the idea.
These do work great. At the time, my goal was to use my tools and off the shelf hardware.
Using rod ends can be cheaper or more expensive, depending on the design. They can help one achieve their design goals and precision without a lot of specialized equipment. I use them quite a bit in other projects.
Even though I really like the stiffness and function, this truss feels like a solid tube. I would probably use Moonlight the next time just for the convience.
Or if I were to build it again, I would probably build what Jim made.
Unless of coarse, it turned out that the deodorant balls where really strong! That was interesting.
Or maybe Moonlight will make Andrew's idea.
Best Regards,
Roy
Edited by Roy McCoy (10/24/09 01:17 AM)
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HandyAndy
professor emeritus
Reged: 01/11/08
Posts: 652
Loc: West Midlands and around
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Hi,
Thanks for doing the drawing. I have no CAD.
My insight is to have the sphere 'inside' the truss pole with the spheres centre and the truss poles axis aligned.
1. Simple separate pole ends on one bolt.
Take hollow truss poles and find a sphere which is a good fit inside the pole. Drill a hole in the sphere to take the solid shank of a bolt. Drill a slightly oversize hole in the end of the truss pole at an angle to the similar hole at the other end to allow for the expected inclined angle of the pole.
Slip the sphere into the truss pole and pass the bolt through the hole in the truss pole and the inserted sphere and tighten up. To allow the truss pole and sphere to move a semi-circular washer with an inside diameter matching the outside diameter of the truss pole would be ideal.
Any small miss-alignment of the hole in the tube will be taken up by rotation of the sphere in any direction.
A jig can be made so the holes at either end are drilled a consistent distance apart and at the calculated rotational angle.
Can someone supply a suitable formula to calculate the angle for a 6 and 8 pole truss arrangement?
Two poles can be slipped onto one bolt but there will be a small distance between the axis of each truss pole so a proper triangle will not be formed.
If the two truss poles are bolted separately onto a plate again a proper triangle is not formed.
2. Make the apex of the triangle formed by the two truss poles meet within the length of the truss poles.
Machine off just over half the diameter of a few inches from the end of each truss pole. Allowance has to be made for possible miss-alignment of the poles. Again drill a clearance hole in the half section of each truss pole.
The half sections are placed on either side of the sphere with the holes aligned. A bolt can then be passed through and used to attach the poles.
The apex of the triangle formed by the two poles is located mechanically 'within' the truss poles on their axes as constrained by the sphere.
3. Mechanical connection to the OTA/Mirror Cell and top cell.
For the top cell if there is a lug or a flat ring the sphere can be split with a clearance to allow the lug or ring centre line diameter to be aligned with the apex of the triangle.
If the sphere is large enough and the top ring of suitable diameter and thickness then the triangle apex could be on the centre line of the ring in both directions of the cross section with the bolt passing through a hole drilled through the centre of the ring side.
Personally I would use the same bolt to mount the spider vanes to.
A similar argument can be applied to the OTA/Mirror Cell connection.
If the focuser mounting plate is attached to 2 truss pole top ends and a vane from the spider to its bottom then it would be ideally aligned to the spider mount.
Perhaps you could draw up my 3 conjectures.
Thanks. Andrew.
--------------------
Monarch 8x42, Zeiss 10x50 WA
10mm F2, Pentax 60mm F5
City: 7" MN78: MK4#2, 10" F6.3: MK4#1, 16" F5 ParaCorr
Country: 8" VISAC: (GP2)
Car: 6" F5 MPCC: SP, 5" 127mm F7.5 (GP2)
TV 55mm, Paragon 40mm, UO Pretoria 28mm
B&L 32 Pl, Clave's 25, 8, 6, 2x
Hyperions 5, 8, 13, 17, 24, 31
Nagler1 9mm, Meade 14mm 4000 UWA
Antares 1.6x, 0.7x, 0.5x
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HandyAndy
professor emeritus
Reged: 01/11/08
Posts: 652
Loc: West Midlands and around
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Hi,
To make your drawing work the flats which meet for each pole would have to be perfectly offset at an angle to the bottom mounting points which is a 3D angle I believe.
Cheers. Andrew.
--------------------
Monarch 8x42, Zeiss 10x50 WA
10mm F2, Pentax 60mm F5
City: 7" MN78: MK4#2, 10" F6.3: MK4#1, 16" F5 ParaCorr
Country: 8" VISAC: (GP2)
Car: 6" F5 MPCC: SP, 5" 127mm F7.5 (GP2)
TV 55mm, Paragon 40mm, UO Pretoria 28mm
B&L 32 Pl, Clave's 25, 8, 6, 2x
Hyperions 5, 8, 13, 17, 24, 31
Nagler1 9mm, Meade 14mm 4000 UWA
Antares 1.6x, 0.7x, 0.5x
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Quote:
To make your drawing work the flats which meet for each pole would have to be perfectly offset at an angle to the bottom mounting points which is a 3D angle I believe.
Hi Andrew,
I not sure I follow this. In my drawing the two halves can move in any direction and could be used with any number of trusses. They would be self adjusting, you simply clamp them in. The bolt hole in the center is only to bolt the two halves together.
I can't seem to visualize what you are describing in the other post above. Could you sketch it and take a picture?
Best Regards,
Roy
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lightfever
Pooh-Bah
Reged: 09/27/04
Posts: 1281
Loc: Macomb Michigan
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Roy,
This is close to how I am doing mine right now. I wanted good registration to minimize collimation after setup.
Take the left element and rotate 180Deg, then machine a partial sphere into the right end. Then one end will register into the upper cage bracket, the next locks into the first.
I probably made that clear as mud but that's the Idea behind my upper truss connection.
--------------------
Mark
Tasco 15-TE 76mm
Sky Watcher 80mm ED
AT-111 Triplet
XT8i (with Woden re-figured mirror)
Discovery 12.5" f/5 Premium DHQ (PDHQ Split-tube Dobsonian)
12.5" f/6.3 Dob (Underconstruction)
Celestron CG-5GT EQ Mount
Celestron C4 EQ Mount
"Life is not about waiting for the storm to pass, but learning to dance in the rain" unknown
Edited by lightfever (10/24/09 02:28 PM)
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Glig
sage
Reged: 10/02/05
Posts: 370
Loc: Baltimore, MD
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This idea won't work for me as it is because I want the poles to fold up parallel - I suppose it would work if they were angled, though.  Ya know, with some tinkering this thing has real possibilities...  
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Richard Caldwell
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Glig
sage
Reged: 10/02/05
Posts: 370
Loc: Baltimore, MD
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This one doesn't fit the bill as the bolt must be threaded into the cage. All bolts must be captive and require no tools, I should have said. The truss end must SLIP into a cage socket and tightened - not threaded. Too hard to do in the dark or in cold with mittens.
--------------------
Richard Caldwell
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Quote:
This one doesn't fit the bill as the bolt must be threaded into the cage. All bolts must be captive and require no tools, I should have said. The truss end must SLIP into a cage socket and tightened - not threaded. Too hard to do in the dark or in cold with mittens.
No tools are require in the desert, not even gloves.
But if you want bolts in the cage rather than in the poles, then clearly this would not work.
--------------------
Roy
MN65
114NT/500
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Mark,
I think i see. Something similar to this only with two distinct parts. Here i simply flipped the one part around as that is all i have modeled.
--------------------
Roy
MN65
114NT/500
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Quote:
Ya know, with some tinkering this thing has real possibilities...
By tinkering do mean something like this?
It would fold flat nearly, but you would need to install the top fitting 60 degrees off of the bottom fitting for a hex truss and 90 degrees for an 8 pole.
This is essentially what I did with the rod ends.
--------------------
Roy
MN65
114NT/500
Edited by Roy McCoy (10/24/09 04:15 PM)
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Scott Watson
sage
Reged: 05/26/06
Posts: 282
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A shoulder bolt is much much easier.
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Hi Scott,
It would be if the hole was perpendicular to the ring. It is not with the six pole configuration. As Andrew mentioned the hole is a 3d, or in other words it is pitched inward. I'll exaggerate this in the following drawing. The hole in the drawing is only for connecting the two halfs of the fitting together. So if this were a single universal part you would need to clamp the ball to the ring. Universal in the sense that you could use it for any number of trusses.
With 8 poles and rings of the same diameter and exact measurements a shoulder bolt would be easier.
Best Regards,
Roy
Edited by Roy McCoy (10/24/09 07:28 PM)
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Glig
sage
Reged: 10/02/05
Posts: 370
Loc: Baltimore, MD
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Well lets see how the pros do it. Here's Moonlite.
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Richard Caldwell
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Glig
sage
Reged: 10/02/05
Posts: 370
Loc: Baltimore, MD
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here's a clamp from Webster Telescopes.
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Richard Caldwell
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Glig
sage
Reged: 10/02/05
Posts: 370
Loc: Baltimore, MD
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This one is very similar to the Obsession offset bracket - the best design, according to David Kriege. This is the one, along with moonlite, I would like to merge the best features of both.
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Richard Caldwell
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Glig
sage
Reged: 10/02/05
Posts: 370
Loc: Baltimore, MD
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Here's AstroSystems. These are 4 of the best - anyone have more?
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Richard Caldwell
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Glig
sage
Reged: 10/02/05
Posts: 370
Loc: Baltimore, MD
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the single ball and socket by Moonlite.
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Richard Caldwell
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Scott Watson
sage
Reged: 05/26/06
Posts: 282
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Ok, I'll bite. Why wouldn't you put the shoulder bolt perpendicular to the ring? A rod end pivots in both angles. No problem whatsoever. I cannot imagine a mount that is more simple than a single shoulder bolt, or one that is easier to manufacture or more solid, with less play.
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Quote:
Ok, I'll bite. Why wouldn't you put the shoulder bolt perpendicular to the ring? A rod end pivots in both angles. No problem whatsoever. I cannot imagine a mount that is more simple than a single shoulder bolt, or one that is easier to manufacture or more solid, with less play.
Hi Scott,
I'm confused. I thought you were referring the post just prior to your suggestion of a shoulder bolt. In that picture there are no rod ends. These drawings are what I thought (though apparently incorrectly) the OP was describing. Now they have simply been tinkered with.
The reason the drawings don't show the bolt perpendicular to the ring in this case is because they don't have an inner sphere to rotate. It is the outer sphere that serves this function. But the outer sphere must be captured in some way similar to the way a rod end does.
If you are talking about using rod ends, then sure I agree they are solid with less play. The truss poles I made for myself do indeed have a perpendicular bolt (see the earlier pictures in this thread).
I could use a shoulder bolt as you suggest.
I simply chose to use a bolt with two nuts locking each other instead of a shoulder bolt because I wanted the poles to stay together.
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Roy
MN65
114NT/500
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Jim Romanski
scholastic sledgehammer
Reged: 01/02/05
Posts: 844
Loc: Guilford, Connecticut
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Quote:
The truss poles I made for myself do indeed have a perpendicular bolt (see the earlier pictures in this thread).
The point I made in my post is that attaching in this manner as many or most struts do is is inherently prone to developing play in the vertical. This means less consistent collimation. I prefer to attach to the bottom of the ring so that two flat surfaces meet and there's no opportunity for wear and tear to create free play in the attachment.
I'm not saying that all attachments of this sort are sloppy but that they must rely upon very strong materials and very tight tolerances to minimize free play. If they attach in the other plane then they minimize this by design.
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Jim
17.5" Dob "Project"
13.1" Coulter
8” Cave
NP 101 on a CG-5
25x100 binos
Naglers, Ethos, etc.
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MitchAlsup
super member
Reged: 08/31/09
Posts: 186
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Quote:
This one is very similar to the Obsession offset bracket - the best design, according to David Kriege.
You might notice that I use teh same attachments at the mirror box end of my scope. That is, the mirror box, itself, carries no structural loads. The truss tubs are loaded to the upper ring assembly and to the mirror cell directly.
If you want to accomodate the notion of a spherical center on this attachment, you can place a small sphere between the truss tube angle brackets. The holes in my image at 1/4" so a sphere of 3/8'ths or 1/2" would work well.
This sphere will have a hold in it so the stud fits through, the fit must have essentially no slop on the stud. Then the angle bracket will have the surface of this sphere removed from one face concentric with the hole. Finally, a means to hols both ange brackets to the sphere is needed.
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Dick Jacobson
super member
Reged: 12/22/06
Posts: 132
Loc: Plymouth, Minnesota, USA
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Here is the pole upper end attachment I built for my 14" scope. It doesn't have the elegant look of the commercial products, but I believe it solves the problems better and is easy to build. A bolt protruding from the secondary cage drops into the slot at the top and a clamping knob secures it in place. The poles are permanently assembled in pairs. The pole on the right is rigidly attached to the aluminum plate, while the pole on the left pivots. The poles fold together parallel. There is no unnecessary pivoting motion, as there would be if the right pole was attached with a single bolt. You will also notice that both poles point precisely at the bottom of the V-slot where the secondary cage rests, so the poles are in tension or compression; there is no bending force as there would be if the secondary cage bolt was not in line with the tubes. This system has excellent rigidity and is very quick to assemble.
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Equatorial Newtonians, 20" and 14"
"The purpose of life is to be defeated by ever greater things." - Rielke
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Glig
sage
Reged: 10/02/05
Posts: 370
Loc: Baltimore, MD
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Elegant simplicity, Dick. Bravo! 
Do I detect a small bend to compensate for angle?
You know, this V - slot duplicates the "can't miss" action of Moonlite's ball.
Was this inspired by Webster's UTA slot shown here? I think yours works better as part of the truss, though. It simplifies things, as a simple captive thumbscrew can secure it.
Got a pic of the bottom? Perhaps a pic of the telescope?
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Richard Caldwell
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Dick Jacobson
super member
Reged: 12/22/06
Posts: 132
Loc: Plymouth, Minnesota, USA
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Yes, there is a bend in the plate so that the upper part is parallel to the secondary cage. I thought of the V-slot idea myself. It works very well - just fasten the three truss pairs in place, then drop the secondary cage into the slots. You have to line them up one by one since the truss is not rigid until the secondary cage is attached.
There is a picture of the telescope here, about one screen down. I don't have a detail of the bottom right now but may post one later today.
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Equatorial Newtonians, 20" and 14"
"The purpose of life is to be defeated by ever greater things." - Rielke
Edited by Dick Jacobson (10/26/09 08:41 AM)
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Dick Jacobson
super member
Reged: 12/22/06
Posts: 132
Loc: Plymouth, Minnesota, USA
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As promised, here is another picture of my truss upper attachment. This shows the bolt and clamping knob which rest in the V-slot securing the secondary cage to the truss. It also shows how the open tube end makes it easy to run wiring (for anti-dew equipment) inside the tube.
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Equatorial Newtonians, 20" and 14"
"The purpose of life is to be defeated by ever greater things." - Rielke
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Dick Jacobson
super member
Reged: 12/22/06
Posts: 132
Loc: Plymouth, Minnesota, USA
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And here's a photo of the lower truss attachment. Each pole has a hole drilled in its back side (not visible here). The hole fits onto a steel post which is a hex bolt with its head cut off. The T-knob does not "clamp" the tube, it merely holds it in position on the post. A quarter turn of each knob secures two truss tubes.
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Equatorial Newtonians, 20" and 14"
"The purpose of life is to be defeated by ever greater things." - Rielke
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HandyAndy
professor emeritus
Reged: 01/11/08
Posts: 652
Loc: West Midlands and around
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Hi,
Here are 3 pictures of my hand drawing of the proposal.
I have copyrighted and reserved the commercial rights.
The idea is free to use by individuals.
John Wall gave the Crayford for free as he was employed and Mr Poncet regretted not protecting his design.
Cheers. Andrew.
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Monarch 8x42, Zeiss 10x50 WA
10mm F2, Pentax 60mm F5
City: 7" MN78: MK4#2, 10" F6.3: MK4#1, 16" F5 ParaCorr
Country: 8" VISAC: (GP2)
Car: 6" F5 MPCC: SP, 5" 127mm F7.5 (GP2)
TV 55mm, Paragon 40mm, UO Pretoria 28mm
B&L 32 Pl, Clave's 25, 8, 6, 2x
Hyperions 5, 8, 13, 17, 24, 31
Nagler1 9mm, Meade 14mm 4000 UWA
Antares 1.6x, 0.7x, 0.5x
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HandyAndy
professor emeritus
Reged: 01/11/08
Posts: 652
Loc: West Midlands and around
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Picture 2
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Monarch 8x42, Zeiss 10x50 WA
10mm F2, Pentax 60mm F5
City: 7" MN78: MK4#2, 10" F6.3: MK4#1, 16" F5 ParaCorr
Country: 8" VISAC: (GP2)
Car: 6" F5 MPCC: SP, 5" 127mm F7.5 (GP2)
TV 55mm, Paragon 40mm, UO Pretoria 28mm
B&L 32 Pl, Clave's 25, 8, 6, 2x
Hyperions 5, 8, 13, 17, 24, 31
Nagler1 9mm, Meade 14mm 4000 UWA
Antares 1.6x, 0.7x, 0.5x
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HandyAndy
professor emeritus
Reged: 01/11/08
Posts: 652
Loc: West Midlands and around
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Picture 3
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Monarch 8x42, Zeiss 10x50 WA
10mm F2, Pentax 60mm F5
City: 7" MN78: MK4#2, 10" F6.3: MK4#1, 16" F5 ParaCorr
Country: 8" VISAC: (GP2)
Car: 6" F5 MPCC: SP, 5" 127mm F7.5 (GP2)
TV 55mm, Paragon 40mm, UO Pretoria 28mm
B&L 32 Pl, Clave's 25, 8, 6, 2x
Hyperions 5, 8, 13, 17, 24, 31
Nagler1 9mm, Meade 14mm 4000 UWA
Antares 1.6x, 0.7x, 0.5x
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Glig
sage
Reged: 10/02/05
Posts: 370
Loc: Baltimore, MD
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These pics are not clear at all. Pic 2 seems to be 2 separate truss tubes, capable of folding just a tiny bit. (like crushed tubes) Pic 3 seems to be only one truss tube.
 
What is the purpose for the split ball inside of the truss tube?
And if they are 2 separate truss tubes how do you get each half ball inside the tube? And the bolt running through the balls is attached to a thread insert? On the spider? 
What I really want to know is, what design requirements are satisfied with this idea? 
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Richard Caldwell
Edited by Glig (10/27/09 09:20 AM)
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 642
Loc: Glendale, AZ
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Hi Andrew,
I think these pictures are very clear. Thank you for drawing them, as I now understand your idea.
Best Regards,
Roy
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HandyAndy
professor emeritus
Reged: 01/11/08
Posts: 652
Loc: West Midlands and around
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Hi,
I would be interested in your proper CAD drawings taking into account the angles for a real world example for perhaps a 8 pole and a 6 pole example.
I hope you can see now that all the forces will pass down the centre of the truss tubes which gives the stiffest result. The mirror and secondary cages should be designed to pass the forces through the triangle apexes with no residual twisting forces if possible.
For the upper cage one can make a plywood ring to go inside the rolled 6mm ring and like wagon wheels of old heat shrink the rolled metal ring onto the plywood ring. The tension can then match the tension of stressed spider vanes and so cancel them out.
It may be a bit stiffer to make a cut out where the tubes cross and have a bit of the full truss pole at the top to resist the cut out spreading under the tension on the bolts.
I imagine a short length of a larger tube with the same internal diameter as the external diameter of the truss pole can be slipped over and welded or glued on, of sufficient thickness to make the cut out as strong as the full tube.
My main design issue is with repeatability of the length between the upper and lower bolt shanks as I have to allow a clearance hole in the truss pole.
If one can find a suitable solid plastic sphere to match the truss pole inner diameter then the construction is easy.
A jig can be made to drill the truss pole clearance holes.
The bolt clearance hole in the sphere can be machined up with a lathe accurately.
A jig can be made to hold the sphere. Drill a hole the size of the sphere to drop it into. Drill a cross hole to line up with the bolt clearance hole. Push a wooden dowel through the drilled bolt clearance hole to stop it rotating. Cut the sphere in two using a router with a 6mm bit.
Cheers. Andrew.
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Monarch 8x42, Zeiss 10x50 WA
10mm F2, Pentax 60mm F5
City: 7" MN78: MK4#2, 10" F6.3: MK4#1, 16" F5 ParaCorr
Country: 8" VISAC: (GP2)
Car: 6" F5 MPCC: SP, 5" 127mm F7.5 (GP2)
TV 55mm, Paragon 40mm, UO Pretoria 28mm
B&L 32 Pl, Clave's 25, 8, 6, 2x
Hyperions 5, 8, 13, 17, 24, 31
Nagler1 9mm, Meade 14mm 4000 UWA
Antares 1.6x, 0.7x, 0.5x
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