JB Weld Amendments

[Mad Rocketeer]

Can JB Weld be amended like epoxy? Fillers? Hardeners/Strengtheners? Balloons? Can it be rendered more sandable, lighter, less brittle, more heat resistant, etc.?

 

[Stymye]

it's already most of those things as is...

It's designed to dry rock hard so it can be machined,drilled ,tapped...ect

it's alot like working with aluminum.

 

[llickteig1]

In addition to what stymye said, there's no purpose for using it in any application where you'd need to change it's properties; something else would be better.

JBWeld is JBWeld. Period. It's great at its intended use, nothing else.

HTH, --Lance.

 

[DynaSoar]

Originally posted by Mad Rocketeer
Can JB Weld be amended like epoxy? Fillers? Hardeners/Strengtheners? Balloons? Can it be rendered more sandable, lighter, less brittle, more heat resistant, etc.?

How would you know if you made it stronger?

Tensile Strength: 3960 psi
Adhesion: 1800 psi
Flex Strength: 7320 psi
Tensile Lap Shear: 1040 psi

The stuff is liquid steel. It's been used to patch the cracked block of a tractor. It's far stronger than anything you'd be using it on, and if not, you should be welding instead.

It's not for finishing and probably couldn't be made so without ruining its best properties, so why not use something that IS finishable?

If it could be made take more heat, they'd make it that way. I wouldn't risk my rocket experimenting with something that's obviously a critical component to begin with.


For that matter, anyone have real numbers on how much stronger that other stuff makes other epoxy?

 

[Mad Rocketeer]

My thought was to possibly use JB Weld for my LOC Graduator's fin-tab-to-MMT and CR-to-MMT joints and fillets, since these locations are likely to get pretty hot. My understanding from other posts here is that epoxy will or may weaken over time under such exposure. I think Aeropoxy makes a high temperature resistance (~500 F) epoxy, but I doubt I could justify the cost.

I'd use Bob Smith 30-minute epoxy for the fin-tab-to-CR, CR-to-body-tube, and internal and external fin-to-body-tube joints and fillets.

For the external fillets, I'd make the initial fillet hard and strong but relatively small. Then I'd go over the top of it, before it cured completely, with the same epoxy with microballoons added. Alternatively, this outer fillet could be done with Fill-N-Finish.

Will JB Weld be good for this application? Is it necessary? Will it be too heavy? Too thick?

 

[DynaSoar]

Originally posted by Mad Rocketeer
My thought was to possibly use JB Weld for my LOC Graduator's fin-tab-to-MMT and CR-to-MMT joints and fillets, since these locations are likely to get pretty hot. My understanding from other posts here is that epoxy will or may weaken over time under such exposure. I think Aeropoxy makes a high temperature resistance (~500 F) epoxy, but I doubt I could justify the cost.

I'd use Bob Smith 30-minute epoxy for the fin-tab-to-CR, CR-to-body-tube, and internal and external fin-to-body-tube joints and fillets.

For the external fillets, I'd make the initial fillet hard and strong but relatively small. Then I'd go over the top of it, before it cured completely, with the same epoxy with microballoons added. Alternatively, this outer fillet could be done with Fill-N-Finish.

Will JB Weld be good for this application? Is it necessary? Will it be too heavy? Too thick?

JB Weld for the heat exposure, definitely. That's what it's for. I'm sorry I didn't use it in all such places on mine. I do now. The savings in lost fins justifies the small difference in weight. And rather than try to use different epoxies between the body and motor tubes, I just use it on all parts that have even some contact with the motor tube.

If you got into some major glassing, bulk Aeropoxy is cheaper and you'd have some left for other uses.

For your external, cosmetic layer fillets, consider using epoxy putty after laying down your strength joints. Very easy to work with and easy to finish.

 

[Mad Rocketeer]

I'm not concerned if I add a little bit of weigt to the Graduator, as I've recently re-read some of the rocket reviews that say it's scary on a D motor anyway. If I fly it strictly on E through H, a little extra weight ought to be OK, as long as it's not much. The downside is that I may have to add a bit more in the nose to keep it stable.

Does anyone have a RockSim evaluation of the location of the CP for an LOC Graduator?

 

[Stymye]

here you go

 

[Mad Rocketeer]

Thanks! What does that amount to in inches from the tip of the nose?

Looks like the CP is just barely aft of the front of the fin attachment. So, if I read it right, and depending on the level of stability in the stock design, adding weight in the fin attachment area will pull the CG aft by a little bit, but any weight near the nose will have a much longer moment arm and therefore a small amount of nose weight will suffice to bring it back into stability.

Epoxy clay/putty looks good, but isn't it fairly heavy? I'd have to play with it to see how the trade-off works for me.

 

[Stymye]

if it balances(flight ready) 3" ahead of the fins it's plenty stable
I have never lost a fin joint to heat,Imoh that is rare with epoxy.

large fillets are for looks more than strength and degrade performance(increase interference drag)

you can glue the rocket together with minimal amounts of plain ole epoxy and no nose weight .anything beyond that is just weight and cosmetics and more effort ,but results in a pretty rocket

no need to over-analyse it MR, winter is coming. just grab that glue bottle and start building.

 

[Mad Rocketeer]

Originally posted by stymye
I have never lost a fin joint to heat,Imoh that is rare with epoxy.

That's good to know. I found a page on Rocketry Online!'s Info Central site on "epoxy and heat" that likes West Systems for hot locations, preferably with fiberglass or similar over the fin joints, but doesn't like the hobby store stuff like the Bob Smith I have.

Originally posted by stymye
large fillets are for looks more than strength and degrade performance(increase interference drag)

I don't really want big fillets, just smooth pretty aerodynamic ones. When I think about layering them, I'm thinking about thin layers, built into relatively small fillets.

Originally posted by stymye
you can glue the rocket together with minimal amounts of plain ole epoxy and no nose weight .anything beyond that is just weight and cosmetics and more effort ,but results in a pretty rocket

no need to over-analyse it MR, winter is coming. just grab that glue bottle and start building.

You got my number there. I do tend to overanalyze and achieve paralysis through analysis. It's fun to explore techniques and pick experienced and thoughtful people's brains though. The brainstorming and exploration are part of the fun.

In Central Texas, it rarely gets cold enough to be a problem flying. It might get rainy or too windy, but rarely all that cold, and hardly ever snowy, etc.

How is winter in Nashville? I used to live in East Ridge, near Chattanooga and in Ringgold, Georgia, just over the state line. Nice state.