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  #1  
Old 02-03-2012, 10:36 PM
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Question Semroc BT-4, BT/ST-5 fit

If anybody has some pieces of Semroc's BT-4 and BT-5 (ST-5) body tubes, could you slip the BT-4 inside the other and post a picture of it here? Or maybe describe how it "fits" into the other?

I mainly want to know how much "play" (or looseness) there is between the two.


I did the math on a piece of paper yesterday, but left it down in the basement.


Thanks in advance for your help!


Cheers,
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Old 02-03-2012, 11:31 PM
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If want want to center a BT-4 in a BT-5, you will need some centering rings. The picture shows an Apogee AT-10.5 (BT-4) inside of an Apogee AT-13 (BT-5). The two tubes are close enough in size that you would need a good vernier caliper to tell the difference the Apogee and Semroc tubes.
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  #3  
Old 02-03-2012, 11:44 PM
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Quote:
Originally Posted by CenturiGuy
...BT-4/BT-5...I mainly want to know how much "play" (or looseness) there is between the two...


Quite a bit of gap, Jay. The total gap is .067, which is more than the thickness of a laser-cut centering ring (at 0.05"). Half this (wall thickness dimension) would be .0335"...

One method you could try would be several layers of 1/4" wide sticky-back label paper strips, wrapped around the BT-4 in strategic locations. I do this a lot when I'm centering ST-9 into ST-10.
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Old 02-04-2012, 12:21 AM
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Quote:
Originally Posted by CPMcGraw
Quite a bit of gap, Jay. The total gap is .067, which is more than the thickness of a laser-cut centering ring (at 0.05"). Half this (wall thickness dimension) would be .0335"...

One method you could try would be several layers of 1/4" wide sticky-back label paper strips, wrapped around the BT-4 in strategic locations. I do this a lot when I'm centering ST-9 into ST-10.
I'm with Craig - use some paper wraps to build up the BT-4 until it fits in the BT-5.

Besides sticky-back paper, you could cut some grocery sack / kraft paper into 1/2" wide strips, and keep adding wraps until it fits to your satisfaction. Kraft paper should be about 0.007" thick, so it should take 4 or 5 wraps to fit the BT-4 in the BT-5.

Doug

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Old 02-04-2012, 07:45 AM
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Or, take a short section of BT-4 and cut lengthwise once. This sleeve can be slipped over the smaller tube and provide a concentric fit.
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Old 02-04-2012, 08:52 AM
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Quote:
Originally Posted by jharding58
Or, take a short section of BT-4 and cut lengthwise once. This sleeve can be slipped over the smaller tube and provide a concentric fit.
Good idea.

Doug

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Old 02-04-2012, 09:14 AM
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I am sure I stole it.
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  #8  
Old 02-04-2012, 11:33 PM
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Quote:
Originally Posted by mwtoelle
If want want to center a BT-4 in a BT-5, you will need some centering rings. The picture shows an Apogee AT-10.5 (BT-4) inside of an Apogee AT-13 (BT-5).
Quote:
Originally Posted by CPMcGraw
Quite a bit of gap, Jay. The total gap is .067, which is more than the thickness of a laser-cut centering ring (at 0.05"). Half this (wall thickness dimension) would be .0335"...
Quote:
Originally Posted by jharding58
Or, take a short section of BT-4 and cut lengthwise once. This sleeve can be slipped over the smaller tube and provide a concentric fit.
Gentlemen, thank you for your timely responses!

Mike, it wasn't so much a matter of centering, but thanks so much for the A/B comparison photo.

Craig, I'm trying to reinforce the ST-5 body tube on my 18mm Prometheus. I was wondering, as jharding58 (John, IIRC) suggested, if I just slit a 3.5" long piece of BT-4 lengthwise, had the builder slather some glue inside the ST-5, and then shoved the BT-4 into the ST-5 (after the BR-510 had been glued in and allowed to dry), if that would do the trick.

I asked you guys because you're smart.


Quote:
Originally Posted by CPMcGraw
One method you could try would be several layers of 1/4" wide sticky-back label paper strips, wrapped around the BT-4 in strategic locations. I do this a lot when I'm centering ST-9 into ST-10.
Really? Because I just barely managed to shove an ST-9 into an ST-10 earlier this week. The difference between 1.000" I.D. and 0.998" O.D. is 0.002".

Unless there's some kind of highly advanced technology that you're not mentioning. An interociter, perhaps? (sly look)

Cheers,
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Jay Goemmer
"Centuri Guy"/"Tau Zero"
YORF Member 28
Semroc SAM #0029
NAR 86131


"I think about organizing things all the time. Never seems to happen. I find something that piques my interest and I'm off on a quest. Or a Centuri. "

--Bill Eichelberger, 02/22/2022


“Centuri fret buzz in an updated form.”
Bill “Wallyum” Eichelberger re: Estes Flutter-By
03 Sept 2014
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  #9  
Old 02-05-2012, 02:52 PM
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Quote:
Originally Posted by CenturiGuy
...I just barely managed to shove an ST-9 into an ST-10 earlier this week. The difference between 1.000" I.D. and 0.998" O.D. is 0.002".

Unless there's some kind of highly advanced technology that you're not mentioning. An interociter, perhaps? (sly look)

Cheers,


OK, so, maybe not several layers...

As such...

More or less...
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  #10  
Old 02-05-2012, 07:25 PM
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If you are looking for a stiffer BT-5/ST-5 tube, how about using some Quest T-15 instead? A ST-5 should be able to have a telescoping fit with the T-15. You should also note that the T-15 has a wall thickness of 0.020" instead of 0.013". The main drawback of the MRI/MPC/AVI/Quest tubing is the lack of nose cones and transitions available for it.
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