Drawing a Straight & Plumb Line Along 48" Length Tube?

The best idea I can come up with is a plumb bob. I need a straight line along the entire 48" in order to attach a 48" long rail tube to the rocket (see my recent Marvin Martian Jr. thread in High Power Rocketry).

What techniques do you use? Since the three fin roots for this rocket are 12" and are attached so that the top of each fin is at the 24" point on the 48" long tube, I'll also need to draw three parallel & plumb lines to mount the fins.

Tubing is notoriously difficult to work with, as you already know. A "good" straight angle iron would probably be your best bet. Unless you're absolutely positive the ends are square, a plumb bob'd steer you wrong. You could try the 'ol Estes door jamb trick, but most aren't truly straight either.

Ok, It's entirely possible that I'm an idiot. Just looked at the pic and realized it's not tubing. Find a friend that works in the trades an borrow a laser? As in laser level.

A piece of aluminum angle is what I use. Should be able to get from most hardware stores for less than $10

timbucktoo said:

A piece of aluminum angle is what I use. Should be able to get from most hardware stores for less than $10

Click to expand...

Yup, aluminum angle is the sweet spot. I just cut up my personal favorite piece to use for hangers in my printer enclosure build so I'm gonna have to hunt down a new one.

Aluminum angle it will be. The pic I attached is just my 2D layout to get my brain around what I'm about to make. Internally there will be a 4" dia. Blue Tube 48" long which will be the motor/parachute/spine tube of the rocket. Everything gets attached to it.

Ok, you're not trying to get a vertical line on an egg shaped tube then? That makes things WAY easier. Angle iron/aluminum is your friend, or the classic Estes door jamb trick is always an option..Just "eyeball" whatever you decide to use for straightness first. Most things are not as straight as you'd think and 48 inches is a relatively long span..

I tend to use what's in the barn and the tool chest. Anything over the length of my 4 foot carpenters level I would snap a chalk line....

Do you know anyone with a Laser level?

Tony

Wish I did know someone with a laser level, but alas, no. The aluminum angle sounds just fine.

Next bit of fun will be trying to cut the three fins with my jig saw.

Jig saw is an ugly tool. I'd go handsaw personally. Just measure carefully, drill the ends and cut between with a "something".

Door jamb... Nuff said.

jimzcatz said:

Door jamb... Nuff said.

Click to expand...

Only if they’re square to the floor.

timbucktoo said:

Only if they’re square to the floor.

Click to expand...

Most door jambs/ casings are neither plumb nor square, but are very very close to both, a door is installed in such a way as to look like its both but due to various issues with framing and other factors it may be "interesting" but the finished result needs to look plumb and square, and the door has to work correctly. The stop is the part of the door casing is the narrow strip running around the middle of the opening that stops the door trying to swing both ways, it however has to be parallel to the casing its mounted too, hence it makes a good edge to mark tubes on, since it acts just like a piece of angle metal.

jmmome said:

Aluminum angle it will be. The pic I attached is just my 2D layout to get my brain around what I'm about to make. Internally there will be a 4" dia. Blue Tube 48" long which will be the motor/parachute/spine tube of the rocket. Everything gets attached to it.

Click to expand...

What are your plans for the "external" body? Looks pretty cool, yet also not an easy thing to create.

Thanks for the explanation of the "stop".

Outer body will be concentric circles of 1" foam board. 24" dia. will be the widest piece. Already have the measurements of each "step-down" piece. I'll use an electric foam cutter with each square foam piece on a turntable to rotate it (or just run a screw through it to the work surface underneath) as i wire cut it to the proper diameter.

A 4" hole cutting bit is perfect fit for the 4" Blue Tube to slide through. I'll be sanding the concentric 1" circles outside after affixing to the central tube, or using a custom-made foam cutter of the proper profile to bring it to the narrow football shape. I may put the entire assembly on a sort of "spit" to turn it as I sand or foam wire cut.

There will be a central 24" dia. piece of 1/4" plywood to act as a base for the altimeter bay, as well as to attach/support the three fins along their top horizontal portion before they emerge from the body.

Then fiberglass the body, with a door for access to the altimeters and a tiny ejection charge wire-sized hole through the central tube (already successfully used this hole-thru-the body-tube technique on my pyramid-shaped McDonnell Douglas Delta Clipper).

Outstanding, sounds like a solid plan. Anything rotating you can come up with short of a lathe will make your life soooo much better. I'm lucky enough to have a lathe and it's paid for itself many times over. You could even rig something up with a drill or drillpress if you have either..

Not really sure what your intent is, but it would be "best" if you cut the central core after assembly. That is if you can figure out a way to make that happen. Avoids "tolerance stacking", Ya follow?

Wouldn't have a way to cut the central core after assembly. But what you say makes sense.

I'll be posting updates to the build on the High Power board under my "Marvin Martian Jr. Build" post, which I've already started there. Mine will look similar but half-sized to the St. Louis' Kaboom Krewe's 10 foot tall version launched at LDRS 38.

Maybe hole saw w/bit extension(s)?

I'm pretty comfortable that I can sand down the 1" thick pieces after assembly to make a fairly smooth transition between each. The fiberglass skin laid on top should further hide imperfections in my technique. I've even considered locking the foam cutter at a slight angle to get closer to the smaller circumference while fixing it at the larger circumference for each piece to be cut.

I'll be playing around/practicing with different techniques, since the foam board is relatively cheap. I've attached a drawing made by someone else (maybe the Kaboom Krewe?) which shows the stacking of the 1" foam pieces.

No top fins on mine, and my fins will emerge from the body at it's fattest point, so to (hopefully) eliminate the loss of airflow on Kaboom Krewe's fins caused by the shape of the rocket relative to where their fins were placed on the body & speed of the rocket.

What are your plans as far as glue/adhesive? I've never attempted it myself, but have "read" plain 'ol yellow wood glue works?

Haven't got that far- assumed the adhesive would be straightforward and easy to look up on the web. Sounds like i need to buy a few more bottles of wood glue!

Don't take my word for it, just what I've read. Be prepared though for uneven sanding at glue joint hard spots.

Be conscious of the foam board curling up when gluing layers together. Use a thin layer of wood glue and apply lots of weight, but not so much it compresses the foam. Cant wait to see the progress pics.

Oh, and to cut those circles, a jig saw will work fine. Use a fine blade and be sure to leave the line. Then you can sand down to the desired profile once glued up.

Thanks for the advice gluing the foam layers together. I'm going to try an electric foam cutter from Michael's. Yardstick will be used as a compass- screwed through the center of the foam and into a wood board beneath, with a hole drilled through the yardstick at 12" from the screw to give me the 24' dia. piece of foam, and so forth as the segments go to each smaller diameter. We'll see if that actually works.

Probably next week I'll buy the 1/4" Baltic birch plywood for the fins and the central 24" diameter plywood circle. That plywood circle will be the base for the altimeter bay and door. I envision making a 5" square box on the plywood circle in which will sit a 4" dia. body tube, situated horizontally and epoxied to the door, inside which the two altimeters will reside. A couple of port holes through the door and into the altimeter tube will allow the altimeters the barometric sensing they require. Successfully used the same basic construction for the altimeters on my pyramid-shaped "Delta Clipper".

I will also have to make one fin removable so as to get it out of the basement!

bibbster said:

Be conscious of the foam board curling up when gluing layers together. Use a thin layer of wood glue and apply lots of weight, but not so much it compresses the foam. Cant wait to see the progress pics.

Oh, and to cut those circles, a jig saw will work fine. Use a fine blade and be sure to leave the line. Then you can sand down to the desired profile once glued up.

Click to expand...

A spray glue might work better especially one that doesn't cure hard, or since you will be clamping anyways or weighting the stack use Great Stuff Sealant (aerosol can insulating foam) to bond the layers together since it sticks to just about everything and should "machine" about the same hardness as the rigid insulating foamboard used on the body.

jimzcatz said:

Door jamb... Nuff said.

Click to expand...

Tried and true method especially for long things but angle aluminum works too.

jmmome,
I have used the foam disk method many times. I have a few observations:

Always use bare extruded styrene sheets [blue or pink foam], not the white, bead-based foam. Extruded is more rigid and cuts cleaner. Blue is typically 1 inch or 1/2 inch, while pink is usually 1 inch or 2 inch in my area. I used the thickest foam available at the time and no thinner than 1 inch.

Regular glues and epoxies don't really stick and some dissolve the foam [like regular fiberglass resin, regular spray adhesive, some spray paints and body filler].

There is a spray adhesive specifically for styrene that won't dissolve it like regular spray adhesive. Regular spray adhesive can be made to work, especially if you are gluing a paper template to each layer [what I do]. If you only spray regular adhesive on the paper and stick it before all the solvent leaves, it does not dissolve very much and will stick. Epoxy sort of works but does not stick well. I have seen no issues with flat foam 'curling' but I saw rather than hot wire.

I work out the angle of the tangent line for each layer and cut that angle into each disk with the corresponding adjusted diameter. Sanding the seams down until they blend with the middle of each layer works very well. I have a sears 3 wheel bandsaw that works very well, the hot wire cutter could work well if it can set an angle reliably, but the paper template would need to be cut to size.

Slitting the disks to get to the center hole works fine as long as the slits don't all line up.

Sanding with coarse paper on a sanding board [glue a half sheet to a flat board with spray adhesive], using a spiraling motion around the body seems to blend the most uniformly [no sanding horizontally or vertically, always diagonally].

I have skinned rockets in epoxy/fiberglass and have left the foam bare with paint [watch out for dissolving the foam], both have worked fine. Fiberglass tends to look lumpier than bare foam for the same amount of foam prep.

I run a phenolic center tube to mechanically locate all the disks, provide a tube to bond fins, provide a straight structure for an internal launch lug/rail button, and to capture the stack of foam so the inter-layer bonds are not critical.

hope this helps,

Tony

Beautiful work, TonyL!!!!!!!!!!!!!!!!!