I ordered a triple 24 to BT-70 engine mount for Justin's "Long Rocket" (still needs a proper name) from UMRS thinking we'd be getting three-holed rings. It was my mistake... I didn't read the page well enough. It's a single-holed ring to which you glue the upper end of the engine tubes. I consider that design entirely inadequate.

So who will sell me three-holed centering rings for BT-50 into BT-70? Hopefully for a fair price, of course. I've already wasted $4.25 of Justin's money, so I feel I must pay for the replacement myself.

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NAR # 115523
Once upon a better day... SAM #0076
My site: http://rocketry.gonnerman.org

The problem with making a 3 X 24mm BT70 motor mount is there is almost no wood on the edge of the ring 1/16" at the most and if you use heavy wall 24 mm tubes there is no wood on the ouside of the tube. I have a Hawks Hobby Cherokee 3 D the uses 3 24mm tubes and you must CA the ring to reinforce it But I will probably wrap each tube with a couple wraps of masking tape and epoxie and glue wadding in the gaps (ala Sieron 3) or use hevy wall tube and skip the tape.
Mr. Bob
Starlight Dude
www.starlightrocketry.com

We will send a set today. It is RA-5070X3.

Sorry I did not have it online yet.

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Carl McLawhorn
NAR#4717 L2
semroc.com

The rings I made for my 2x18 Baby Bertha were like that (though I used cardstock rather than plywood or balsa... smaller rocket needs less strength) and the "rings" Justin made for his 3x18 Renegade had no outside material at all. But that wasn't a problem... we just glued the segments to the engine tubes individually. The main thing there was the gas seal.

But with this rocket, it needs a bit of outer support. I really feel that the retention will be done with allthread and a nut, as I said above; Justin did that on the Renegade and it works marvelously. The rings could actually be broken into three pieces and still work. I ordered rings for my 2x18 mount for the New Centurion, and basically I did break them in half to install them.

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NAR # 115523
Once upon a better day... SAM #0076
My site: http://rocketry.gonnerman.org

Carl, you are beyond cool. THANK YOU.

Edit: By the way, the BTH-70 tubes and the cone arrived in perfect condition. I'm really impressed with the stiffness of that tubing. If I'd known you had the rings, I'd have placed the entire order with you.

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NAR # 115523
Once upon a better day... SAM #0076
My site: http://rocketry.gonnerman.org

Bob,

IMO, it's okay if the ring doesn't go all the way around the tubes. I've made up similar motor mounts. The rings basically consisted of 3 pie pieces to plug the three gaps on the outside. The center was plugged by my motor retention. Three pieces requires more work than one, and additional attention to detail is required to ensure the pie pieces are on plane, but it works just fine once they are reinforced with some extra glue.



This motor mount doesn't seal perfectly, but at prep time, I apply a little tape at the gaps, and that seals it up adequately to get the chute out.

These bits were hand made. Having laser cut parts to work with would surely make it even better - the tape could probably be omitted.

Doug

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YORF member #11