TRF Tips and Techniques Comments Thread.

[cwbullet]

If you have a favorite tip or technique on the forum or online, please share a link here or by PM. I could use your help this week.

 

[Huxter]

Have you talked about the paint trick where after you tape off the base color, and getting ready to paint second color, you spray a coat of base color to fill any seepage under the tape? So if it leaks onto the base color, you cannot see it! Great tip - this works really well.

 

[John Kemker]

If you have a favorite tip or technique on the forum or online, please share a link here or by PM. I could use your help this week.

"Pointy end up."

That is all.

 

[neil_w]

When sanding the end of a cut body tube on a sanding block, keep rotating the tube as you sand. This will help you avoid inadvertently sanding a bevel onto the end of the tube. This advice applies in general to whenever you're hand-holding an object to be sanded... keep changing its orientation in your hand to even out the natural bias in your sanding motions.

 

[Tech 68]

"Five Minute" epoxy can be used to bond/encapsulate wiring that needs to be secured against vibration and "gee" forces. Careful use of a heat gun allows the epoxy to be broken down so repairs can be made. Obviously the underlying surface needs to be capable of surviving the heat.
How we bonded/secured wiring harnesses in developmental Sidewinder seekers. Integration into the guidance system was sometimes brutal... reversed feedback loops, etc.

 

[OverTheTop]

CA glue is good for tacking down wires at intervals. It is fairly permanent.

Hot-melt glue works well for wires too and can usually be sheared off when changes are needed. Heat with a heat gun also works but is a little more messy.

 

[Sandy H.]

1: If you have more tools than space, look into flip-top designs and build one or more. The attachment is an example of one I did and still use. Sander and scroll saw on one side, small wood lathe on the other. Some tools are more logical than other tools, but I've even seen examples with a miter saw on one side and a mini-drill press, so look at examples that have tools you also have/want to get.

2: If you build a flip-top tool bench, don't randomly place other items on the random flat surfaces. It takes longer to clean-up before flipping to the next tool. . . #DoAsISayNotAsIDo. . .

Sandy.

 

[John Kemker]

When soldering wires, remember that a good mechanical connection is just as important as a good solder joint. Heat the joint and let the solder flow into it.

 

[prfesser]

You've inserted the shock cord and chute, and you're trying to insert the payload section's coupler, but it just doesn't want to get started (especially with smaller tubes). To make it a little easier, sand a very slight bevel on the edge of the coupler and on the inside edge of the booster airframe. 180-220 grit paper is good for thicker-walled mid- and high-power airframes/couplers. For thinner-walled model tubes, 320-400 grit. Wrap the paper around a smaller tube or a finger to do the booster, rotate the tube as you sand, and sand only on the "pull stroke" to avoid a ridge on the inside. Don't press hard, the bevels don't need to be huge. If you use CA on the edges of the tube/coupler, sand after the CA has done its job.

 

[SolarYellow]

You've inserted the shock cord and chute, and you're trying to insert the payload section's coupler, but it just doesn't want to get started (especially with smaller tubes). To make it a little easier, sand a very slight bevel on the edge of the coupler and on the inside edge of the booster airframe. 180-220 grit paper is good for thicker-walled mid- and high-power airframes/couplers. For thinner-walled model tubes, 320-400 grit. Wrap the paper around a smaller tube or a finger to do the booster, rotate the tube as you sand, and sand only on the "pull stroke" to avoid a ridge on the inside. Don't press hard, the bevels don't need to be huge. If you use CA on the edges of the tube/coupler, sand after the CA has done its job.

I start off by burnishing the cutting ridge outward/flat, first with a fingernail, then with a hard, round, smooth instrument like a socket, using the work bench or some other clean, flat surface as a backer. Knock it down as flat and as smooth as you can get it before sanding. Then use the sandpaper to fully true and clean it, then the CA. That minimizes the amount of sanding of cured CA/cardboard composite you have to do at the end, while maximizing the density of cardboard and minimizing material loss at the end of the tube.

CA on the ends of tubes and couplers prevents the ends from getting burred up during handling rocket prep. The burrs create an artificial and variable but very short tight fit, so they are bad.

 

[Sandy H.]

A zip tie + a cheap clamp opens up the functionality of a pegboard storage system. You don't really want holes in welding gloves (or plenty of other things), but a zip tie and clamp now gives it a sturdy, easily accessed home.

 

[cwbullet]

Have you talked about the paint trick where after you tape off the base color, and getting ready to paint second color, you spray a coat of base color to fill any seepage under the tape? So if it leaks onto the base color, you cannot see it! Great tip - this works really well.

No, can you explain this further?

 

[Sandy H.]

No, can you explain this further?

Paint base color, mask and then spray the same color. Whatever leaks under is the same color, but the tape is then sealed. Spray the next color and it won't leak under. Clear can work too, if you want a less thick paint line, if you're airbrushing etc.

 

[Huxter]

Yeah, what Sandy said! Thanks Sandy. I picked up this tip on TRF, and it works great! Nice sharp lines.

 

[cwbullet]

When sanding the end of a cut body tube on a sanding block, keep rotating the tube as you sand. This will help you avoid inadvertently sanding a bevel onto the end of the tube. This advice applies in general to whenever you're hand-holding an object to be sanded... keep changing its orientation in your hand to even out the natural bias in your sanding motions.

Thanks - added to the list.

 

[Sandy H.]

Yeah, what Sandy said! Thanks Sandy. I picked up this tip on TRF, and it works great! Nice sharp lines.

I learned that tip either here or on Rocketry Planet and it totally changed the world of painting for me.

Another nuance I learned specifically with using clear vs base color with an airbrush was to use clear lacquer (Krylon rattle can etc.) over water based airbrush paint. If you totally butcher the work you're trying to do (i.e. fades etc.) then just clean the airbrush, use some Windex (or similar) to wipe off the paint and try again. The lacquer seals in the previous layer, so all you're removing is what you just screwed up. Maybe I should lacquer myself everyday before getting out of bed. . . 2nd chances make things easy.

 

[cwbullet]

Have you talked about the paint trick where after you tape off the base color, and getting ready to paint second color, you spray a coat of base color to fill any seepage under the tape? So if it leaks onto the base color, you cannot see it! Great tip - this works really well.

Thanks added. I added some verbiage from both you and @Sandy H.

 

[caveduck]

Bondo (2-part polyester resin based body filler, not spot putty!) tips here. I used to hate the stuff - ultra short working time, loaded up sandpaper badly, sometimes would never cure etc. After a few years I've gotten past all that and finally feel like it's useful.

• Brands: The actual Bondo brand is owned by 3M these days and is OK. Stay away from cheap off-brands. The next step up is 3M Professional Body Filler, which spreads and feathers better but only comes in big expensive 3 liter cans. Evercoat is also good but 25% more expensive.
• Hardener ratio: 2% by weight. If you are making smaller batches (say 20-25 grams), weigh the catalyst on a 0.1 gram scale since you are shooting for ~0.5gm of catalyst, which is pretty hard to do by eyeball. Avoid under-catalyzing or the filler will be really awful to sand. Slight over-catalyzing is preferable to being short. You can buy extra catalyst if you need it.
• Don't try to mix batches smaller than ~15-20 grams; you won't be able to control the amount of catalyst well enough even with a scale.
• Sanding: SandNet ceramic mesh #120 to #220 is fantastic. It never loads up and lasts several times longer than even the best sandpaper. If you have to use sandpaper, the 3M pro paper (the purple stuff) is pretty good but nowhere near the equal of SandNet. Most import sandpaper is trash.
• Machine sand if you can. A 5" orbital, an oscillator like the Dremel Multi-Max, or a small mouse sander are all good.
• Mix and apply with flexible non-metallic spreaders. The plastic putty knives you can get from HD etc. are OK for many things. You can also get purpose-made spreaders that are a little softer. The putty knife can be used for mixing as well as application.
• Mix as rapidly as you can for about 45 seconds and then get to applying it. Assume you have about 3 minutes. As soon as it gets even slightly stiff, you are done - do not try to push it on working time. It goes from fully spreadable to impossible in a matter of seconds.
• A flexible plastic mixing sheet is great - you can bend it and the residue from the last batch pops right off.
• Don't use Bondo on balsa, foam, or other very soft materials. The filler is much harder than balsa and you won't be able to sand it down without destroying the balsa. It will attack foam. Appropriate uses are for plywood, basswood, fiberglass, and metal. It works fine over epoxy.
• You can apply almost any kind of paint over the body filler.
• It's pretty whiffy so open the garage door and use a VOC cartridge mask. Do not use in the house if you wish to remain un-murdered.
• Wear nitrile gloves. Spreading it around with a gloved finger is surprisingly effective.

 

[Donnager]

When soldering wires, remember that a good mechanical connection is just as important as a good solder joint. Heat the joint and let the solder flow into it.

Need to read that in an Emperor Palpatine voice as you do it.

"I do"

 

[jqavins]

Gee, I was thinking spice, not force.

 

[cwbullet]

CA glue is good for tacking down wires at intervals. It is fairly permanent.

Hot-melt glue works well for wires too and can usually be sheared off when changes are needed. Heat with a heat gun also works but is a little more messy.

Thanks - used today

 

[John Kemker]

When using epoxy, pull out two paper towels and fold them up and put one under each bottle. After you measure out the resin, wipe the tip with the one under the resin bottle, then discard that towel. Measure out the hardener and use the towel under that bottle, then discard the towel. That way, you avoid cross-contaminating the resin and the hardener.

Also, when measuring 1:1 epoxy by weight, figure out which part flows slower out of the bottle. Measure that one last, as you can get closer to the right ratio as you're weighing it.

If you're measuring a high ratio epoxy, such as Aeropoxy PR2032, which is 100:27, measure the smaller component first, then calculate how much of the larger component you need and measure that.

 

[cwbullet]

1: If you have more tools than space, look into flip-top designs and build one or more. The attachment is an example of one I did and still use. Sander and scroll saw on one side, small wood lathe on the other. Some tools are more logical than other tools, but I've even seen examples with a miter saw on one side and a mini-drill press, so look at examples that have tools you also have/want to get.

2: If you build a flip-top tool bench, don't randomly place other items on the random flat surfaces. It takes longer to clean-up before flipping to the next tool. . . #DoAsISayNotAsIDo. . .

Sandy.

Added for yesterday.

 

[cwbullet]

You've inserted the shock cord and chute, and you're trying to insert the payload section's coupler, but it just doesn't want to get started (especially with smaller tubes). To make it a little easier, sand a very slight bevel on the edge of the coupler and on the inside edge of the booster airframe. 180-220 grit paper is good for thicker-walled mid- and high-power airframes/couplers. For thinner-walled model tubes, 320-400 grit. Wrap the paper around a smaller tube or a finger to do the booster, rotate the tube as you sand, and sand only on the "pull stroke" to avoid a ridge on the inside. Don't press hard, the bevels don't need to be huge. If you use CA on the edges of the tube/coupler, sand after the CA has done its job.

Added today - thanks.

 

[Huxter]

I, personally, would love to hear someone talk about leaving the rear centering ring off to do internal fillets and such.

Can someone say how they glue in the motor mount without that ring? Do you just dry fir the ring on for mounting, then remove after all dries? Any tips or tricks? Thanks.

 

[neil_w]

Can someone say how they glue in the motor mount without that ring? Do you just dry fir the ring on for mounting, then remove after all dries?

Yes

 

[prfesser]

I, personally, would love to hear someone talk about leaving the rear centering ring off to do internal fillets and such.

Can someone say how they glue in the motor mount without that ring? Do you just dry fir the ring on for mounting, then remove after all dries? Any tips or tricks? Thanks.

Essentially, yes.

• Sand the MMT where the centering rings and fin roots will go.
• Glue the forward centering ring on the MMT.
• Wrap a couple of long strips of scotch tape around the aft centering ring as handles, so you can pull it out later. Or you can use t-nuts that have been installed in the aft ring.
• Slide the aft ring onto the MMT, but don't glue it yet.
• Apply glue to the inside of the airframe where the forward ring will land. Be careful not to get glue where the aft ring will sit (yet).
• Slide the assembly in place and allow the glue to dry/cure.
• Remove the aft centering ring. Glue the fin roots to the MMT. Apply your fillets, foam, whatever.
• Remove the tape and glue in the aft centering ring.

 

[KenECoyote]

Can someone say how they glue in the motor mount without that ring? Do you just dry fit the ring on for mounting, then remove after all dries? Any tips or tricks? Thanks.

Yes, dry fit and have screws in the aft cr to be able to pull it out to do internal fillets.

 

[ep29030]

This used to be the standard technique for PML kits. Put two pieces of tape on the forward side of the centering ring. Don't glue the ring on the motor tube (duh!). Once the whole unit is in place in the airframe, glue the forward side of the first (forward) centering ring to set it in place. Also, tack your TTW fins down on the motor tube. Now, remove that aft centering ring by pulling on the tape tabs and you have access to your TTW fin tabs and the aft side of the forward centering ring.

 

[ep29030]

Cardboard Airframes: IF you want to install motor retention clips in a rocket with balsa or thin plywood centering rings, try using those plastic drywall screw expanders to improve the screw's grip. I've used them successfully in the past on LOC kits where I added homemade motor clips after the kit was built. And if you want to replace them, they come right out again.