Chemist Abdul Razzak on JB weld metal Motor mount epoxy

[Scott Chase]

I want to secure my motor mount in my project rocket. It has a Radio Frequency transmitter mounted in the cargo bay. I wanted to use the JB Weld original epoxy for the centering rings. The problem I think I'll have is interference from the metal that is in the JB Weld. Is there another epoxy with a long dry time that is strong enough to withstand G motors?

I want to thank everyone for there help in this matter
I decided to do an actual test of the steel impregnated JB Weld. So I went to the source and sent an email to JB Weld customer service. I asked JB Weld how much the epoxy is impregnated with metal. below is the email responses.

Apologies but I do not have that kind of information. I will contact our chemist and see if it is something he will know.
Thank you for your patience.
J-B Weld Support

P.O. Box 483 | Sulphur Springs, TX 75483
Ph: 903.885.7696 | Fx: 903.885.5911

Next the chemist answered the question quickly.

From: Abdul Razzak
Sent: Monday, August 17, 2020 11:53 AM
To: esupport <[email protected]>
Subject: RE: J-B Weld: Customer Service Inquiry

Cured product may have 5 to 6% steel powder
S. Abdul Razzak | J-B Weld Company
Vice President, Technical & Business Development

I tested my rocket with JB Weld Steel inside the air frame
I had a signal 79 % of 100%
Without the JB Weld in the rocket I had a signal strength of 84%,
The lower signal strength with metal JB gets worse the farther away from the rocket i get the signal degrades much more than the signal from the rocket without The JB Weld.

 

[llickteig1]

Pretty much any epoxy will work. JB Weld is overkill. There is far too much analysis paralysis going on around here regarding adhesives.

 

[Funkworks]

JB Weld is popular because it’s sold in every hardware store, and marketed as the strongest epoxy on the shelf. But also, because Aeropack specifies it for its motor mounts.

You could check with a multimeter to see if a JB Weld fillet is actually conductive, but if you insist on using an alternative, Rocketpoxy is another good choice. Very long curing time.

 

[Funkworks]

Double post

 

[dr wogz]

to be "that guy".. [smirk-mode: on]

Aeropack recommend it for their motor retainers. not necessarily motor mounts..


But I do agree, JB weld is expensive, and it does contain some iron particles to give it strength & high temp ratings. But the amount you are using is minimal, and also far below your Tx. Think about it.. Unless you coat the inside of the AVbay tube & bulk heads with JB weld, or you happen to be exactly under the rocket as it ascends (or descends) as it transmits, it's likely not going to cause you too much trouble.

I'm assuming a typical MPR / low end HPR build.. Cardboard & wood build? BSI 30 minute epoxy is plenty. Yellow wood glue even.. No need for exotic glues..


Now, if the BT is carbon fiber...

 

[jqavins]

Aeropack recommend it for their motor retainers. not necessarily motor mounts.

And, on top of that, they recommend it because of its temperature tolerance, not its strength. Strengthwise, any epoxy would do for the retainer (and nearly any glue at all for paper or wood to paper or wood, as others have stated).

But the amount you are using is minimal, and also far below your Tx. Think about it.. Unless you coat the inside of the AVbay tube & bulk heads with JB weld, or you happen to be exactly under the rocket as it ascends (or descends) as it transmits, it's likely not going to cause you too much trouble.

That's what I was going to post, but it's hard to argue with empirical results.

I tested my rocket with JB Weld Steel inside the air frame
I had a signal 79 % of 100%
Without the JB Weld in the rocket I had a signal strength of 84%,
The lower signal strength with metal JB gets worse the farther away from the rocket i get the signal degrades much more than the signal from the rocket without The JB Weld.

Would you explain your experiment in more detail. The test configuration and methods? Because this result is really surprising. Just putting some metal near a transmitter is unlikely to cause any issues. Cell phones send and receive signals just fine even in a pocket full of change.

 

[manixFan]

....<snipped>...Would explain your experiment in more detail. The test configuration and methods? Because this result is really surprising. Just putting some metal near a transmitter is unlikely to cause any issues. Cell phones send and receive signals just fine even in a pocket full of change.

I guess it depends on what you mean by metal near a transmitter. I know that if I mount my transmitter antenna parallel to a piece of metal all-thread it definitely attenuates the signal, depending on the location of the all thread to the receiver. But as others have pointed out, unless you coat the A/V bay in the JB Weld, it should have no effect on the transmitter signal.


Tony

 

[XrayLizard]

It is detuning the Antenna

have measured quite a few with a network analyzer, and have seen the effect from nearby objects including one’s own hand lol
The receivers ability to detect weak signals is much more important.
We have had cell phones in RF shielded rooms, and it takes a really well made and shielded room to have the RX side drop out .
Your piece of all thread might actually cause the antenna to become somewhat directional and increase signal on one side or the other lol
It’s magic

 

[Steve Shannon]

Pretty much any epoxy will work. JB Weld is overkill. There is far too much analysis paralysis going on around here regarding adhesives.

Absolutely! And a lot of other things.

 

[K'Tesh]

I might be wrong, but I got the impression that the OP is coating the interior of the rocket with JB Weld, perhaps for improvements in strength and temp resistance. Since Starlite has been rediscovered, I wonder if a lining of that would handle the temps aspect, and just use a regular epoxy for the strength?