I have plans for a handful of the early Centuri models that require a proper ST-7 body tube of 10" or more. I am willing to pay good money (or an interesting trade) for ST-7s made by Semroc, eRockets, or even the original Centuri. O.D. 0.759", thickness 0.022"

Just the real thing, though. My last few orders from eRockets (for these early Centuri models actually) included several pieces of BT-20 - they took them back in return but by then it was too late, out of stock. I do not want the Estes spec approximation.

I can detail my plans (1963 catalog models), but I've probably talked or asked about those enough before. The longer tube models though include the Arcon and the Payloader.

Thanks in advance!

The Odd'l Rockets heavy wall BT-20 tubes are the equivalent to the Centuri ST-7 tubes.
The ST-7 Centuri tubes had the same interior diameter as the Estes, but had an extra wrap of Kraft paper.
These BT-20H tubes are available from Jonrocket.com:
https://jonrocket.com/shop/index.ph...roducts_id=1686

__________________
Hans "Chris" Michielssen
Old/New NAR # 19086 SR

www.oddlrockets.com
www.modelrocketbuilding.blogspot.com
http://www.nar.org/educational-reso...ing-techniques/
Your results may vary
"Nose cones roll, be careful with that."
Every spaceman needs a ray gun.
Look out - I'm the Meister Shyster!

Thank you, I will take a look at those.

I believe this assertion to be in error.

The Centuri ST-7, and Semroc reproduction, had an interior diameter of 0.715".

Estes BT-20 has an inside diameter of 0.710".

https://www.erockets.biz/semroc-bod...ng-sem-st-7180/
https://www.ninfinger.org/rockets/body_tubes.html

The difference is noticeable when inserting a motor - much easier with the ST-7. I replace all BT-20 motor mount tubes with ST-7 for that reason.

__________________
-Wolfram v. Kiparski
NAR 28643 - TRA 15520
MTMA Section #606 President

Probably like you, I find the BT-20 (and BT-50) tubes to be too thin.
It wasn't my initial intent to copy the inside and outside diameters of the Centuri ST-7 tubes.
I asked Paramount for the BT-20 interior diameter, but add another layer of Kraft paper to bring it up to the wall thicknesses seen in the Estes BT-55.

I've just compared the size and fit of the ST-7 (pictures on the left sides are a 2009 Semroc Javelin in red) to my Odd'l Rockets BT-20H tubes (on the right).
There doesn't seem to be a difference in nose cone or engine slide fit.

The last picture is an Estes BT-20 (left) and the Odd'l Rockets BT-20H (right side) You can see the difference in the wall thickness.

The BT and ST tube diameters and wall thickness were probably sized using a micrometer. In the 1960s and 1970s, there weren't digital micrometers available. I don't own one myself.
.005" of an inch difference doesn't seem like much.

EDIT: I did just find a bare ST-7 tube in my stash and there is a very slight difference when sliding in an engine. But it is so slight a difference.
This ST-7 tube seems to have a little looser fit when sliding in a 18mm engine.

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__________________
Hans "Chris" Michielssen
Old/New NAR # 19086 SR

www.oddlrockets.com
www.modelrocketbuilding.blogspot.com
http://www.nar.org/educational-reso...ing-techniques/
Your results may vary
"Nose cones roll, be careful with that."
Every spaceman needs a ray gun.
Look out - I'm the Meister Shyster!

From my own experience in dealing with motor fit between BT-20, ST-7, and BT-30 tubes.

BT-20: Tends to be very close with little wiggle room.
ST-7: A little loose. Needs more tape for friction fit than the BT-20.
BT-30: Really loose compared to the previous two tubes. Needs more tape than the ST-7.

YMMV.

__________________
'Til next time,

Mike Toelle

NAR 31692 L1

SAM 0373

Just to add to the confusion a bit.

One of the guys at ERockets told me I'd have to wait patiently until later this year before they got in some ST-7 in longer lengths - greater than 9 inches.

I do check the website periodically and found recently that a large number (642) of 9" ST-7s had come into inventory, but at specs different from traditional (Centuri) dimensions.
O.D. 0.75" (not 0.759")
I.D. 0.715"
Thickness 0.018" (not 0.022")

I guess it could just be a data entry error - the thickness doesn't seem to square with the diameters.

I don't know why anyone would make ST-7 that isn't ST-7, but of course it makes me a little nervous about our future supply of this important Centuri tube.

Al,

Please check your PMs.

Cheers,

Jay

__________________
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

Hi Jay,
I am so sorry to have been away from YORF (and model rocket priorities) for some time now. I was locked out of my account, yes, but mainly just distracted by other things for an extended period. I do appreciate when other rocketeers chime in and help me with projects, and again I apologize for not checking in sooner.

Al,

Not a problem. I just wanted you to know that I hadn't forgotten you.

Cheers and blessings,

__________________
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