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  #41  
Old 12-16-2008, 09:22 PM
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Royatl Royatl is offline
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Quote:
Originally Posted by ScaleNut
ok I have lurked quite a while now but I have to put a rant down on this one.


I have painted nearly all of my rockets with an airbrush and have none of the issues mentioned.

I have read post after post on many forums over the years about problems with painting rockets.
I can say that for me airbrushing has eliminated 99% of them



You don't have to convince me.

You just have to show me how you do it, because it just doesn't happen for me.

What is your equipment?


(Note that I have much the same problem with soldering, which is why I am not an electronics do-it-yourselfer as I would've like to have been. About the best I did there was thirty years ago when I took an Estes Big Foot and built a solid state launcher using a power transistor. My soldering job was still crap, but apparently a cold joint didn't make any difference there!)
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  #42  
Old 12-17-2008, 08:27 AM
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Solomoriah Solomoriah is offline
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My #1 question is: What PSI do you run your airbrush at? The instructions with mine say 20-30 PSI, but I've seen others claim to run theirs at 40 PSI. I haven't wanted to experiment that much (I can just see it exploding and blowing paint all over me).
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  #43  
Old 12-17-2008, 08:39 AM
micromeister micromeister is offline
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I generally run mine between 30 and 40psi depending on what needle I'm using. #5 needle wide open requires a bit more pressure to get good even coverage. smaller needles, finer detail...less pressure.
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  #44  
Old 12-18-2008, 10:15 AM
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luke strawwalker luke strawwalker is offline
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Quote:
Originally Posted by Royatl
You don't have to convince me.

You just have to show me how you do it, because it just doesn't happen for me.

What is your equipment?


(Note that I have much the same problem with soldering, which is why I am not an electronics do-it-yourselfer as I would've like to have been. About the best I did there was thirty years ago when I took an Estes Big Foot and built a solid state launcher using a power transistor. My soldering job was still crap, but apparently a cold joint didn't make any difference there!)


Well, just for a pointer there Roy, the soldering just takes some practice... and also, give the joint time to heat up... make sure you run a little sandpaper over your iron tip before you plug it in to get the funk off, let it heat up good, and then be sure you "tin" the tip of the iron by melting some solder on it. Keep a wet paper towel handy to periodically wipe your iron tip to keep the funk off, as rosin flux tends to make it pretty nasty after awhile. A good wipedown will keep her shiny. I usually melt a drop of solder onto the tip and then hold the iron to the wire or joint, as the solder is much better at conducting heat into the joint than the bare tip. When the solder sucks up into the wires or joint, you know it's hot enough, and THEN push the tip of the solder roll to the joint-- it should melt virtually instantly and suck right down into the wires or joint. Once you have the amount you want on there, pull the roll away and then the iron away and let it cool a few seconds before moving the joint.

Most soldering problems come from just not waiting long enough for the joint to heat, in my experience. Rarely do you see too much heat applied and things starting to melt or delaminate... a finished solder joint will be shiny and smooth-- if it's lumpy or dull, the joint is too cold-- give it another 10-20 seconds to heat up and the results will be much better...

Good luck! OL JR
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  #45  
Old 12-18-2008, 10:55 AM
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Quote:
Originally Posted by luke strawwalker

Most soldering problems come from just not waiting long enough for the joint to heat, in my experience. Rarely do you see too much heat applied and things starting to melt or delaminate... a finished solder joint will be shiny and smooth-- if it's lumpy or dull, the joint is too cold-- give it another 10-20 seconds to heat up and the results will be much better...

Good luck! OL JR


Thanks for the tips, but been there, and done all that. I have been nervous about getting the joint (and therefore the component that I'm soldering) too hot. Maybe I should just throw caution to the wind and see how that does. Maybe after Christmas I'll go over to Fry's and get one of those little project kits. I have a CVS camera that I want to hack, and all I really need to do is solder on a USB connector, but I don't want to screw it up.
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  #46  
Old 12-18-2008, 12:15 PM
Jeff Walther Jeff Walther is offline
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Quote:
Originally Posted by Royatl
Thanks for the tips, but been there, and done all that. I have been nervous about getting the joint (and therefore the component that I'm soldering) too hot. Maybe I should just throw caution to the wind and see how that does. Maybe after Christmas I'll go over to Fry's and get one of those little project kits. I have a CVS camera that I want to hack, and all I really need to do is solder on a USB connector, but I don't want to screw it up.


Soldering is definitely an art. One difficulty which is not apparent on a casual examination is that the heat just doesn't conduct well over a simple soldering pencil to conductor interface. It helps *a lot* for there to be some kind of liquid between the two, filling up the interstices and letting the heat flow.

An analogy would be the use of heat sink grease between CPUs and heat sinks in computers. You put the stuff in there, because even though the two surfaces *look* smooth, from a heat transfer point of view they aren't all that smooth and the heat sink grease fills up the gaps.

So folks apply the pencil or iron, and wait for the target to get hot enough to melt solder, just like it says in the instructions and it doesn't, and it doesn't, etc. And they sort of- kind of- get the solder to melt on there, but the target never really gets hot enough, and they end up with a cold joint and often a joint where the solder blob never really coated the target surface and could be picked off with a fingernail.

This is one reason why whetting the tip of the pencil with solder before soldering is important, but often that is not enough. In particular, once the flux/rosin is burned off (most electronics solder has a core of rosin), the solder starts to oxidize and it becomes less and less good at acting as a heat conducting fluid.

Sooo.... Having a little bottle of soldering flux is nearly a necessity. If you want to do any fine surface mount work it is without question a necessity. You can get a squeeze bottle (about like a small white glue bottle) with a needle tip, or a screw top glass bottle with a brush on the inside of the screw-top. Coating the thing you're going to solder with a bit of flux will usually help it heat much better. I'm not sure if this is because the flux conducts heat, or if it is that the extra flux keeps the coating on the pencil tip from oxidizing longer and so the solder conducts better, but whatever the reason, flux helps a lot.

Similarly, if you are doing any circuit board soldering and desoldering, get the Chemtronics brand of desoldering braid. That brand is well impregnated with flux. The other brands aren't and you can spend all day with the braid applied to the target, and the soldering pencil on the other side of the braid, and you sitting there thinking, "is the solder under there *ever* going to melt?" And it won't. Or you can use most any brand of braid and apply flux liberally before desoldering.

If you need tips on desoldering and resoldering largish (<= 208 pins) surface mount packages let me know. It's amazing what you can do with a couple of Radio Shack pencils and a Milwaukee adjustable heat gun and modeling clay... and, of course, a bottle of flux.

P.S. Electronics soldering flux is not the same as plumbers soldering flux. It serves the same purpose but the formulation is different for good reasons.

P.P.S. After liberal application of flux, it is important to clean up. A can of flux remover is good, but 91% isopropyl alcohol will do the trick.
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