Dougie
member
Reged: 07/02/08
Posts: 11
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If I had the tools available to me I could do just about every part you've done. In highschool I did a lot of CNC work and what not and even some after highschool. But now where I live I don't have access to any of that.
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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Ok, we got 3 hours in this afternoon. Roughed the outer part of the Collimation Tube down to just over the ID of the Collimation plate and then did finish passes.
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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Another couple of thou...and Yes, it fits 
Now to reduce the diameter in front of the Collimation Plate so the Primary Mirror will not touch the tube, second reduction to 4.100 for the O-ring to seat 1/2 it's diameter against the 4.10 shoulder and the remainer of which will get threaded to 20 TPI.
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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Here's a wide shot showing all of the swarf that came off of just that turning operation...and It's nasty stuff, at about 1/16" x 1/32" thickness, it was comming off in ribbons that if they caught you could really do some damage to one's body parts.
Pile was about 3 feet high when finished with the pic after this and turning the other 3 shoulders.
Thus, I stayed out of the way 
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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Here's the last pass on the final diameter at 3.90 inches OD. This is what will stick out in front of the face of the primary to attach the Baffold Tube.
The first shoulder in from the end will get turned to 4.10 inch OD in the morning when it's cold and then turned at 20 TPI to fit the Nut we made yesterday.
Then we will turn it around again and turn the short section that fits into the Back Plate with the O-ring for centering.
Until tomorrow.
Regards,
Preston
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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: 5596
Loc: Seattle Washington
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Very impressive so far Preston!
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Equipment Overload!
http://scopebuilder.webs.com/
Kerry.
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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Here is a rough not to scale drawing showing the general idea of the Collimation Tube in blue, the Back Plate at the bottom with the O-ring to keep it centered.
Then the Collimation Plate in the middle fixed solidly to the Collimation Tube. The Rockers and Pads are not shown for clarity sake.
Then the Mirror that actually has a small flat area around the Collimation Tube about 8 inches in diameter onto which the Pads that are on the Rockers rest to support the back of the mirror.
The O-ring holding the mirror centered on the Collimation Tube in reality is positioned at the mirrors center of gravity if viewed from the side position...
Again, nothing in the drawing is to scale except the Collimation Tube.
Hope this helps visualize what we are doing.
Regards,
Preston
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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So, back to finish turning the 4.10 OD on the cool Collimation Tube for threading. Note, we have now put the plug in the end and brought the tail stock up to support the outer end while turning this to exact size and then for the threading.
Pic of roughing pass, taking off 0.010"
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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After the roughing pass we are 0.001 over so a light finish pass and then we will be on to threading...
Sorry, but no threading pics...each of the passes removed 0.002" and last only 10 seconds...I did not have the nerve to try to take a pic and disengage the threading and back out the x axis in 10 seconds ...Sorry 
Pic of finishing pass close up.
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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Threading check with Nut. Removed the tailstock and plug and could just get the nut to start...
Likely about 3-6 more passes removing 0.0005" per pass and checking between each pass.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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So four passes at 0.0005" per pass and the nut is a smooth fit all along the threaded lenght.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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So this end is finished. Time to turn it back around and turn the reduced area for the O-ring to slide up the the shoulder for the Back Plate fitting.
Finish pass at 4.350" OD
And the Collimation tube is finished functionally...but, it came in at 3.6 pounds 
We may have to look at lightening and reducing some of the cross section as there is a lot of metal to radiate heat.
But for now it's onward and upward. Likely to the secondary structure 
Remaining things for the Collimation Assembly are the Adjusting Knobs, Springs and maybe turning knife edges on the ID of the Collimation Tube.
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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Well, I just had to see what it looks like assembled with the lower truss section.
Looks nice, but then I think I'm a bit partial... 
And am really looking forward to finishing this beast.
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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Finally a low angle shot so you can see where the Collimation Tube extends down into the Back Plate where that last turned shoulder would hold the O-ring that centers the Collimation Tube in the Back Plate.
The Collimation Nut is adjusted just about where it will be with the Mirror in place.
I'll make the Primary Conical Baffold before doing any more work on the Collimation Tube...waiting for Mikes latest revision using the 7" secondary diameter.
Happy 4th of July Everyone,
Play safely and Best Regards,
Preston
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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: 1051
Loc: Fort Worth TX
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And here's your optimized baffle tube design, with dimensions.
I assumed a 2" diameter image. If you want it bigger, let me know, it's easy to do now with the new optimizing code. Increasing the field diameter will increase the pupil obstruction somewhat as the secondary baffle has to grow longer and larger.
The rear of the primary baffle is 0.75" from the primary vertex to allow convection to flow through.
Just as a check, 3.39 + 12.67 + 14.69 + 0.75 = 31.5", the mirror separation.
The conical taper on the primary baffle is bounded by the 14.69" cone length, the 4.56" front diameter and 7.07" back diameter. The cone must be this length, and front diameter must be the value specified. The rear diameter should not exceed the value given. You can choose to taper the whole tube as plotted, or taper back halfway and go cylindrical from there to the rear end, or any other shape you like, as long as you stay inside the outer cone shown.
With the conical shape and your ultra-black paint, I don't think internal baffles are necessary. If stray light is visible, interior baffles can always be installed.
Mike
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56 mirrors, lenses, 16" f/6 Newt, 6" f/10 refractor, TOA-130S, Tinsley 5" f/15 Mak, 6" f/4 RFT, Coronado PST. Still to build: 24" f/10 Modified Dall-Kirkham, 10" f/26 Mak, 8" f/12 apo, spectrohelioscope, Herrig, Schupmann, and a new design you'll like.
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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Fantastic Mike
Now that is a Nice 4th of July Present 
I'll start working on the mold plug tomorrow after incorporating your dimensions into my CAD drawings...
Very Best Regards My Friend,
Preston
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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: 1051
Loc: Fort Worth TX
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You are most welcome.
Ready to start thinking about an economical field flattener next? I already have a couple done I can start posting that only use N-BK7 glass, so they should be reasonably priced to have made.
Mike
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56 mirrors, lenses, 16" f/6 Newt, 6" f/10 refractor, TOA-130S, Tinsley 5" f/15 Mak, 6" f/4 RFT, Coronado PST. Still to build: 24" f/10 Modified Dall-Kirkham, 10" f/26 Mak, 8" f/12 apo, spectrohelioscope, Herrig, Schupmann, and a new design you'll like.
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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Mike, are either of the BK7 designs with all spherical surfaces? Then perhaps I could try may hand at making them and a buddy here in Houston has set up a vacuum coating rig that would handle up to 4" objectives...so we could coat them ourselves also...
Either way, let's look at the field flatner designs when you have a chance to post them.
Tomorrow I will post the pics of the VARTM work that I did today for the support for the Secondary Mirrors back mount.
5 layers of 5 oz Carbon Fiber alternating 90-45-90-45-90 degrees...dry fiber weighted in a 71 grams so it will be interesting to see what the total weight comes out with the finished composite.
Until tomorrow...this evening we party , as we took it easy last night...
Regards,
Preston
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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So, finally we discuss what I have been talking about for a while now VARTM or Vacuum Assisted Resin Transfer Molding.
Let's discuss briefly just what one needs to do this type of composite work.
1.) First a Vacuum pump or source of vacuum to evacuate the air and excess resin in the mold.
2.) A bagging material. This can be as simple as the plastic sheet material you can get at Home Depot or top of the line Nylon Bagging material the will streach up to 500%, like what I'm using.
This provides an air tight container for the vacuum to be sealed into.
3.) A Flow Material, or something that helps provide a channel for the resin to flow other than the actual fiber material you are using for the composite. They sell an expensive polyethylene random oriented fiber material, but I have found for many applications that a plastic window screen works very well and is priced cheaply.
4.) A peel ply material. This is typically a nylon or dacron material that does not bond to the resin. It is placed just below and on top of the fibers to be infused with the mixed resin...so that after everything has cured, you can just easily peel it off of the cured composite surface.
5.) Finally a low viscosity epoxy resin designed for composites. The low viscosity/thin liquid helps the wet out of the part happen quickly allowing the mixed resin to move to all parts of the composite.
Other things needed are something to seal the edges of the bagging material. We typically use blue painters tape.
Tubing to connect the manifolds to the vacuum source and the resin source.
Plastic Tee's, spyral plastic tubing and springs to keep the spyral tubing from collapsing under the vacuun and heat.
A mixed resin trap, so as not to allow the mixed resin to be sucked into your vacuum source and a heat source if you are wanting to speed the process up and or lower even further the mixed resins viscosity.
So this pic shows my vacuum pump, resin trap, aluminum molding sheet, and insulation below the aluminum sheet for containing the heat.
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A few I enjoy,
and a few more in the works ;<)
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PrestonE
professor emeritus
Reged: 04/29/05
Posts: 681
Loc: Houston,Texas
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The sequence we use goes as follows.
To the mold first apply Bagging material or paste wax and a release agent....here since the mold is for a flat part we are using bagging material under the fiber bundle.
Next the Flow Material or plastic window screen in this case.
Followed by the Nylon Peel Ply.
You can see that we hold the Bagging material flat by taping the corners.
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A few I enjoy,
and a few more in the works ;<)
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