Centering tube for 29mm to BT-56/S

The Rocketry Forum

Help Support The Rocketry Forum:

Tramper Al

Well-Known Member
Joined
Dec 31, 2013
Messages
334
Reaction score
1
Hi,

I am having a heck of a time finding this centering ring, to seat a 29mm motor tube within a BT-56 body tube. It is not much of a difference in diameter, so this is thin centering tube.

I'm searched Semroc, Sunward, and the usual suspects. Actually, the only place I know I can buy it is as part of the Estes small part TARC collection. But I don't want to keep buying all those parts just to get the one.

Uses for 29mm in a BT-56:
1) Delta-II or other BT-56 Astrocam vehicle, for 29mm BP motor
2) Enerjet Egg Crate*
3) Enerjet 1340 Payload rocket

*The Enerjet Egg Crate is actually the only set of rocket plans I know of that shows how to mount a 29mm motor tube into the slightly larger ST-13 body tube. It is Centuri part EEM-13 in the Enerjet catalog.

Estes sells a lot of 29mm kits and a lot of BT-56 kits, but not the motor tube ring I seek (outside of the TARC) kit. If anyone knows of a source, I'd appreciate learning it.

https://www.ninfinger.org/rockets/catalogs/enerjet72/72ejet20.html

Thank you.
 
Last edited:

dhbarr

Amateur Professional
Joined
Jan 30, 2016
Messages
7,497
Reaction score
1,929
Isn't this just a bt56 coupler, red IIRC? Maybe I'm misremembering.
 

Rocketjunkie

Addicted to APCP
Joined
Jan 19, 2009
Messages
4,543
Reaction score
704
Use the narrowest masking tape you can find - 1/4" is plenty wide. Wrap a couple rings around the motor tube until it fits the BT-56, then glue it in. If you have paper box sealing tape, it works even better - just cut it into narrow strips.
 

Tramper Al

Well-Known Member
Joined
Dec 31, 2013
Messages
334
Reaction score
1
Thanks, I will try the coupler for size. Certainly they are available in a few different versions, but I will start with the Estes.

Yes, it is thin enough to build up with tape, but I am hoping for a more traditional, formal solution.
 

Tramper Al

Well-Known Member
Joined
Dec 31, 2013
Messages
334
Reaction score
1
OK, I just tried out both the Estes BT-56 coupler (red) and the Sunward BT-56 coupler (brown) both are a good fit for the body tube and thus fine for coupling) but both are very loose (wobbling) around the 29mm motor tube. So either would require substantial build up with tape to form a stable mount.

In contrast the Estes 29mm/BT-56 centering tube (green, from the TARC kit), being that much thicker, is a nice snug fit on both the body tube and motor tube. They are not very long, so ideally you'd want to use two for a longish E-G 29mm tube. I just can't figure out how to acquire more without buying so many parts kits. In that kit, they are listed as "2--29 mm to BT 56 Centering Rings".
 
Last edited:

Woody's Workshop

Well-Known Member
TRF Supporter
Joined
Aug 3, 2011
Messages
4,407
Reaction score
253
Location
Reed City, Michigan (Lower)
A BT-56 Estes Coupler will fit loosely over a 29mm EM, for the one's I have.
There is all different thicknesses out there.
I believe the one I have is from Sunward, which is usually pretty stout.
Use Epoxy instead of wood glue, that will fill up the gap easy.
Make sure you give it several twists to even out the epoxy all the way around.
You can cut the BT-56 couple into 1/4" wide bands for multiple CR's.
Other couplers may be thicker than Estes', like the one's from Uncle Mikes Rocket Shack or Sunward.
Good Luck.
 

Tramper Al

Well-Known Member
Joined
Dec 31, 2013
Messages
334
Reaction score
1
Other couplers may be thicker than Estes', like the one's from Uncle Mikes Rocket Shack or Sunward.
Good Luck.
Thanks. The Sunward ones I have seem if anything even thinner than the Estes. I will try a couple of other sources.
 

dhbarr

Amateur Professional
Joined
Jan 30, 2016
Messages
7,497
Reaction score
1,929
I think my 29mm MMT must be thicker, then. I can barely get the three to nest, and would use laminating epoxy to make them permanent.
 

Rex R

LV2
Joined
Apr 21, 2010
Messages
6,103
Reaction score
150
don't use tape, instead try a wrap or two of cardstock which, after you find the right amount, should be glued to the motor tube.
Rex
 

mwtoelle

Flying since 1977
Joined
Oct 14, 2010
Messages
721
Reaction score
5
Location
Middle Tennessee
I would try using a BT-56/ST-13 coupler for the centering ring. Note that the old LT-125 from Centuri/Semroc would telescope with the LT-115 motor tube (29mm motor tube). The LT-125 tube has an inside diameter of 1.125" and an outside diameter of 1.340". Semroc LT-115 telescopes into a BT-56 coupler; however, the 29mm tube that Estes uses will need a little shimming to work. I would use the paper packing/sealing tape to build up the motor tube before gluing it in the coupler.
 
Top