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Equipment Discussions >> ATM, Optics and DIY Forum

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296835 - 06/30/12 07:28 PM Attachment (52 downloads)

I swear, one of these days I'm going to make a tube out of masking tape!!

I decided to check and make sure it would roll up all the way before I put any glue in the seams:


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296840 - 06/30/12 07:29 PM Attachment (44 downloads)

And it's a darn good thing I did, because I was able to realize that the forms are too big (or the tube is too small):

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296845 - 06/30/12 07:35 PM Attachment (45 downloads)

Here it is in detail. the forms are 9 3/4" ID, like the lazy susan rings and standard Parks fiberglass tubes. And the tube sides are exactly 1 1/5" wide like the polygon calculator said they should be to get my desired OD. But the tube is about 9 5/8" OD, so it's sloppy in the forms. ID is about 9", so I'm only going to have a half inch outside the light path to the mirror. Good thing I didn't plan baffles!

All isn't lost, though. I figure if I cut a 3/4" gap in the forms, instead of the saw kerf width (about 1/8"), I can clamp it and it'll tighten all the way around the tube okay without breaking the forms. Another thing I could do, I suppose, is rip another slat, really narrow, to bring the tube diameter up to the desired OD. I don't have any more cherry, though. I might be able to find a strip of birch to use, but it'll be bright.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296914 - 06/30/12 08:30 PM Attachment (50 downloads)

I don't know how I manage, but I do! Here I have it all laid out for gluing. Now, that bottle of titebond III is only about 1/4 full. That's got to be enough, right? WRONG! I had to grab another bottle of titebond II I had laying around but couldn't get the top off, and in the middle of gluing up the slats, cut the top off the second bottle and used all of THAT glue too! Got 'er done, though! And then some. Natch, the glue ran out all over the inside of the tube once it was rolled up. I might scrape the worst of it off, but it might also be a good light-deadener with the black paint and all.

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296916 - 06/30/12 08:31 PM Attachment (44 downloads)

Here it is rolled up and clamped in the forms:

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296920 - 06/30/12 08:33 PM Attachment (38 downloads)

Notice the gaggle of Harbor Freight clamps on the truck bed. Those are brand new clamps that DON'T WORK. I had to run around looking for clamps that did work!

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296921 - 06/30/12 08:34 PM Attachment (38 downloads)

Glue running out on the inside. At least there must have been enough after all!

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5297135 - 06/30/12 11:43 PM Attachment (46 downloads)

Turned out pretty round!

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5297137 - 06/30/12 11:43 PM Attachment (48 downloads)

And straight!

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5297140 - 06/30/12 11:45 PM

And while I do like the look, cutting 20 sides, beveling them, and applying all that tape and glue really took a long time - maybe 4 hours?

Now, I've got to get myself rested up for another drive to Utah tomorrow. Guess I'd better check the craigslist ads between here and there, in case I need to make a stop or two along the way!


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herrointment
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5297330 - 07/01/12 04:52 AM

A big glue up is stressful enough without the nightmare of poor clamps adding to it. Titebond III and its longer open time has saved my butt many a time.

That method of ripping strips off a plank produces wood with a rift sawn or quarter sawn figure. This makes for a much more stable product verses plain sawn lumber and it will look three times better to boot!

Four hours? You work fast!!!!!!


Edited by herrointment (07/01/12 05:23 AM)


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Paul Drufva
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Re: Delmarvascopics 8" f/9 OTA build new [Re: herrointment]
      #5297338 - 07/01/12 05:15 AM

Nice work Tim! I tried my hand at this with a 12 sided 12" o.d. tube without using forms. some of the strips moved a little, which required much sanding to correct. Next time I will use your method. That will look awesome when you are done! Keep us posted.

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JoeM101
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5297342 - 07/01/12 05:31 AM

coolest thing i've ever seen! you really gotta love it don't ya?

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: herrointment]
      #5297842 - 07/01/12 12:46 PM

Quote:

A big glue up is stressful enough without the nightmare of poor clamps adding to it. Titebond III and its longer open time has saved my butt many a time.

That method of ripping strips off a plank produces wood with a rift sawn or quarter sawn figure. This makes for a much more stable product verses plain sawn lumber and it will look three times better to boot!

Four hours? You work fast!!!!!!





Actually, it's mostly face-grain. What I tried to do was make the cuts so that the grain would transition from one slat to the next. I started out trying to resaw the whole 6 1/2" plank on my bandsaw, but even with a carbide-toothed blade, the work wanted to wander off the line. I don't have a tall resaw fence, so was just using the stock fence (Rikon 18" saw), which can be set to accomodate the wander somewhat. But without going through a lot of good scrap wood trying to find the perfect setting angle for the fence, I had to guess, and my guess just didn't quite work out.

But since I was going to make such narrow slats anyway, I sliced the planks into 1 1/2" wide boards on the table saw, then resawed each board on the bandsaw - which prevented the wander since it wasn't such a thick stick to have to deal with. The bandsaw also saved wood, since the kerf is only about 1/16" wide, whereas the table saw "thin" blade takes out about 1/8" or so.

Anyway, if you were looking at the 2x6 from the end, I tried to number the slats in such a way that they were ordered from left to right, then zigging back the other way (and turning them on the second row to bookmatch them as much as possible), then zagging at the other end, an so on. I got 5 rows of slats that way out of the 2x6. Structurally, quarter sawing them would have been better, of course. And maybe I could have done that all on the bandsaw and saved stock.

Turns out, though, that I goofed in my numbering in a couple of places and beveled some slats in the wrong direction, so they were upside down with respect to the slats to either side. Oh well! It's still purdy!

After I took the tape off, I lowered a lazy susan bearing over the tube to make sure it fit without binding. And it not only does, but it's also just big enough not to. So the finished scope should look nice and "planned". The rings for my 10" f/6 are quite a bit larger than the tube (I wasn't aware that there were other sizes, and the next size down *might* have worked for the 10"). And I still haven't quite worked out all the little annoying points of flexure in them. The ones for the 8" will be easier to make good and stiff, I'm thinking.

Next weekend!

-Tim.


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Wes James
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5299002 - 07/02/12 08:04 AM

I can only imagine trying to do a glue-up like that!!
Wes


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MKV
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Reged: 01/20/11

Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5299182 - 07/02/12 10:47 AM

Tim, how much does this tube WEIGH?!

Mladen

Edited by MKV (07/02/12 10:48 AM)


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: MKV]
      #5299248 - 07/02/12 11:42 AM

Hi Mladen:

I'm guessing, but I'd say about 1/3 the weight of a fiberglass tube, and a fair amount stiffer, too. Of course, I don't have any finish on it yet!

-Tim.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5299261 - 07/02/12 11:47 AM

Hi wes:

To save time, I simply poured the glue onto the slats and used a wood paddle to spread it around and into the grooves. Turns out I had too much applied that way, but after it squeezed out during the rollup, I was okay. Better than not enough by a lot, too!

The masking tape works really well for this kind of rollup, because it pulls the two sides together quite well, and there's enough tape that it doesn't come apart under the tension. The bonus is that the tape helps keep glue from oozing out onto the outside of the tube and drying there. The tightbond 3 is waterproof, so it can't be washed off - has to be sanded off. I wasn't worried about it on this tube because the cherry is a closed grain wood. On mahogany it would have been a disaster. As it was, the glue on my 10" f/6 took a lot of scrubbing to get out of the grain where it wound up on the outside of the tube (but that was tightbond II).

-Tim.


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Wes James
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5299301 - 07/02/12 03:30 PM

Tim-
I'm a big fan of masking tape in general in woodworking when it comes to glue-up's... Whenever I'm gluing a joint, I always mask it on both pieces, leaving only the glued surfaces exposed... I don't have to worry too much about applying excessive glue. Then, after I get it glued/clamped up, I wipe the excess glue squeeze-out off the tape thoroughly, then pull the tape- presto, a clean joint with no squeeze-out to worry about. Nice for natural finishes, necessary when staining!
Wes


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Wes James]
      #5299449 - 07/02/12 04:49 PM

That's a GREAT idea for getting the excess off the inside of the tube!

I'm going to try that next time I make one of these.

-Tim.


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