PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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And a closer view of the machined CF spiders in about the orientation they will be when finished...spacing between the 3/8" raduis in the center should be about 5 inches.
At the inside the spiders are 6 inches high, outside 3 inches and length from inside to outside is 11 inches.
If the metal order arrives today, we will machine the 2 tubes for forming the short 1/2 inch length between the 2 CF plates and the inter tube that will act as the pivot for the collimation...similar to the primary collimation tube.
That's is for today, enjoy. 
Regards,
Preston
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A few I enjoy,
and a few more in the works ;<)
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 6006
Loc: Bremerton Washington
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Preston..great work my friend..I can't wait to see it assembled.
I had a dream last night I was related.........and lived next door........and that was my scope we were working on....
Rob(And then the 5:30 alarm sounded)
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www.goldmtobservingcenter.com
Providing a great place for amateur astronomers, and ATM's to come and enjoy their hobby.
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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Hi Rob, Move next door and that could be a reality...
And there are houses in the neighborhood for sale with acre lots...
But, you would be moving from Paradise to He?? with the humidity in the summer...
Two out of three of our shops are Air Conditioned...ie the wood shop and metal shop...
Could have not done much here after April without Air Conditioning...
Best Regards,
Preston
ps...I'm up to drive my father from Long Branch out on the Key Penosula at the very southern end...to southern Calif in late October and would like to come by for a visit...as my father was born in Bremerton...
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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: 1102
Loc: Fort Worth TX
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Preston,
Here's the analysis for centered and offset spider vanes. I modeled the vanes as 0.1" thick for both cases. As you can see, there is no real impact on the imagery whether the vanes are offset or not. The MTF curves are identical for either case, right out to cutoff frequency. The MTF is affected only by the vane width, not the position of the vane in the pupil.
You should be fine with the spiders you are making now.
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
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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Mike Thanks for the very fine analysis work on the spider vanes...I hope this puts everyones mind to rest...
I note that you included the secondary baffle diameter into the final calculation.
The other thought from the group was to just drill the holes to allow a standard spider assembly to be substituted should this one cause a problem. However due to the design of the offset one currently being built, a standard one raises several problems.
Mounting is differant, spacing between the primary and secondary would likely differ, some form of centering would be required, new baffle attachments/adjusters, amoung a few of the likely problems...not a simple unbolt one and bolt on the new one... 
Thus, with your analysis hopefully this will not be an issue.
Very 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: 817
Loc: Houston,Texas
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So...we machined the 2 aluminum tubes to be the male mandrals for forming the CF tubes to be used in the secondary assembly...the other day.
Yesterday I got the small one of the 2 wrapped with all of the plys and CF, covered and manifolded...the sealed everything and did the vacuum leak test just before noon today...
Ok we are ready to turn on the vacuum and heator...quick check and we are out of mixing cups...
Ok off to the little store to get 2 packs of mixing cups...
Now turn on the vacuum and heator... 
Where's my note book  not in the office, ah it's in the metal shop...
Ok, record everything...it's been 5 minutes, so we should be up to about 140 deg F and rising...I want 170 to start the infusion, as I want the aluminum tube expanded to its max at 185 deg F just after we start the infusion...
This will give us over 200 degrees of temp change for shrinkage in removing the tube after it cures.
 The temp is only 100 F
Next 5 minutes determines that the fan on the little ceramic heater is dead and the control curcuit will not allow the heating element to turn on without the fan...SAFETY
Ok, Walmart will have a heator 
Ya Right, it's the middle of summer in Houston, Texas...just how much demand is there going to be for Heators in the SUMMER
NONE not even Fry's Electronics...so I'll have to wait till tomorrow to see if Graingers has any in stock in town tomorrow morning...
It 3:00 PM...I think I'll just take the rest of the afternoon off
Hope everyone else had a better day,
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: 817
Loc: Houston,Texas
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Ya Right...NOT...
Back in the woodshop at 3:15 had the heater apart and back to working in 15 minutes...
Did the infusion knowing that there would be pleats due to having tried to cheat the system and lay down 8 layers pulled tight with the 3M spray adhesive holding the layeres tight together...
It did release due to taking the curing composite up to 196 F for quite a while...
Upon removing all of the tape, it just slipped of easily...
Tomorrow I'll post the pic's and start over with only 2 layers at at time...thus the next 2 tubes will likely take 4 days each to do 8 layers...
The mold came out clean and without any damage...
Regards,
Preston
Edited by PrestonE (08/10/08 09:09 PM)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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Hi All, We got a good part out today with a wet layup...not nearly as clean, but it worked and when cured at 200+ deg / F for one hour was almost as stiff as the 8 ply that ripples yesterday and this was only a 4 ply...
It is 3.25 inch ID by 3 inches long but 0.040" wall and weighs 28 grams...for not vacuum forming, I'm quite happy.
Doing the 4 inch ID by 9 inch long tomorrow morning the same method and I promise pictures of The Good, The Bad and the Ugly tomorrow...
Then we need 2 more flat plates 8 x 8 inches by 0.080 inches thick and we can start to CNC the plates and bond the pieces into place...Some how I overlooked these other plates...
Just TOO late now to even think about posting pics and getting the wrong sizes...Heaven forbid I upset the Moderators again...
Very 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: 817
Loc: Houston,Texas
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OK, pics
Finished mandrals about 3.25 inch OD for the small mandral and 4.1 inch OD for the larger one.
Note that you must turn the aluminum tubing true to use it as a mandral...otherwise, you will have a very difficult time getting it off of the mandral.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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We will do the small one first so if problems occur as the did, we don't waste more material or time than necessary.
Taped nylon bagging material to the mandral.
Note that the tape is ONLY to the bagging and not the aluminum mandral...we want it to just slip off when finished.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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The bleader, peelply and finally 8 layes of CF that was misted with 3M #77 spray adhesive lightly to hold the CF in place.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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In the cure oven after vacuum test and ready to turn the heator on to warm and cure the epoxy.
The infusion was started once we reached a temperature of 170 deg F on the aluminum tube. You can see the thermometer in the left end of the tube.
The infusion of 248 grams of mixed epoxy took about 45 seconds.
Temp in the oven hit 190+ within 15 minutes and we cured for 1 hour.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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After curing for 1 hour here is the mandral with all of the vacuum bagging still attached.
If you look closely you can see what looks like wrinkles in the bleader material...they are and are in the CF also...
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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Well even with the wrinkles we got to see the effect of curing at 190 F...
The expansion of the aluminum tube was enough that at room temp the contraction was enough for the composite CF tube to just slip off of the mandral.
At least that part worked and the mandral is in perfect condition.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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Sooooooo.....
What do we do now
Was the 8 layers just TOO much? Would 2 or 4 layers work better
If we looked back at the Primary Baffle, it only had 2 layers and we had small wrinkels...let's learn from that and try something else...
Yes, this is not as elegant but it does work.
We will do a wet layup but with a twist.
What's that you say?
We will lay the CF on a sheet of poly as pictured.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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Next we will pour 248 grams of mixed resin onto the carfon fiber. 
I like pouring things but it's usually a glass of wine in the evening
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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Next we will lay another sheet of poly on top of the epoxy and carbon fiber as shown.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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Can you guess what comes next?
Note just how much wider the poly is than the CF.
With a squeege we can now move the epoxy anywhere under the poly sheet without disturbing the carbon fiber in the least.
Once everything is wet out, we will the squeege all of the excess resin down to one end and collect it in our mix cup.
Of the 248 grams of resin we mixed, 135 were squeeged off of the wetted out CF and put back into the cup.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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Now we start the carbin fiber that has the minimum amount of epoxy on the mandral over the peelply. The poly will just peel back as we turn the mandral and the wet cf will roll snuggly round and round for 4 layers.
--------------------
A few I enjoy,
and a few more in the works ;<)
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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Once all of the CF is on the mandral we apply the peelply as we want to be able to get a matte finish for future bonding and be able to smooth the CF without disturbing the fibers.
Here the mandral with peelply is on the hanger ready to go into the cure oven.
--------------------
A few I enjoy,
and a few more in the works ;<)
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