"Lite House" Ultralight Monocoque build - 6/25/11

[Thomcat316]

Finally time to build!!

Having dragged my butt through the winter (best building season for composites in S. Florida) and spent a lot of intervening time digesting what Andy and others have said on here, I've finally got my order in for Plascore honeycomb core panels in sizes ranging from 1/4" to 1-1/2" thick and up to 60"x144" WxL.

I've decided to go ahead and build two of these little puppies - 4'x10' & 5'x12' - to absorb some of the fixed costs of shipping and mold tooling.

The A-frame tongue and floor-edge reinforcements will be structural fiberglass extrusions (square and L-angle respectively) which will be bonded directly to the box. The axle will be torsion. The axle will bolt through the edge reinforcement and the floor panel, with the A-frame starting directly in front of the axle mount.

I listened when Andy poked fun at my build plans, and though the plan I'd had initially worked out fine in a full-scale test I've decided to scrap some of the fancy work in favor of build speed now that I've built myself into a tight deadline. So - no roundovers from the sides to the top. It'll look traditional.

I'll still be forming the front and rear curves on a female mold, vacuum bagging down to Formica sheets over MDF ribs, and tabbing together the interior skins before skinning the entire exterior in one shot.

Fastener points will be high density foam plugs inserted in the core, or reinforced epoxy putty for small ones.

Should be quite the fun adventure!

Visit http://tnttt.com/viewtopic.php?t=42048 for previous discussion...

 

[madjack]

...having followed the previous thread, I, and I'm sure many others will be following your build with great interest.............
madjack

 

[Thomcat316]

It starts....

I'll have photos soon (camera is on an airplane from the West Coast as I type...), but the mold for the front curve is finished and the mold for the back curve will be done by Thursday morning.

The extrusions for the tongue and outer lower corner reinforcement will be here tomorrow, as will the fiberglass and dynel. I have the WEST System epoxy resin already, and am waiting on vacuum bag, breather, and peel ply which should be here about the time I get the molds done. I'm also anxiously awaiting the arrival of a large pallet of core material - might be here tomorrow, I'm told.

In case it seems insane that I'm trying to do in 15 days what others have taken years to do, please rest assured that I'm nuts. I also have lower expectations than most - the first trip this trailer will make will be without a real galley, but full of a trade show booth that has to be set up in Norfolk, VA on June 21st. It's not an extended vacation.

I do intend to install the galley bulkhead and the 12v electrics - gotta have a vent fan - before the trip, but little else in the way of amenities.

Photos of Progress(TM) by Thursday!

 

[Thomcat316]

OK, so the core has been delayed... I'm now told it will be here Wednesday 6/8 - with a travel deadline of 6/18. This is gonna be fun!!

I'd promised photos:

The pattern for the two ends of the trailer - I routed around this with a 3/8 pattern bit to create the female mold formers. If I do this again I'm going to do it differently, as it's tedious and annoying to plow a pattern bit through what seems like a half-mile of MDF.

And here's how to make the notches for the crossmembers - jigsaw, square, a couple sanding sticks, and a bit of cutoff crossmember to make sure the notches are the right size and shape.

Here's what the front curve looks like with crossmembers glued in.

And the runout plate - this is where the curve trails off into the roof.

Here's the rear form with crossmembers and runout plate installed.

And the first skin of bending ply being fitted.

Here's the rear curve glued up - the temporary 2x4 clamped on the left is there to keep the mold from bending, the one on the face is to force decent glue contact in the deepest part of the curve. The 43 bazillion clamps and the series of screws and fender washers marching up the centerline are just there for show....

And this is the front curve, also glued up. The moral of the story here, folks, is that if you don't own a bazillion clamps (or have access to same) stick to softer curves. If I didn't insist on having that deep curve in the back of the TD I wouldn't have had to do the gymnastics I did. Note in this photo the extra strips of wood and bunch of bar clamps in the runout area.

Also note the two screws helping to align the unsupported centerline in the runout area.

The secret to only using a few clamps - compression! I'm literally pushing the panel down the curve, which in turn causes it to push out into the concave form.

The proof is in the pudding - pretty literally in this case! Every mold and crossmember has a bead of epoxy like this oozing out at the edges - great contact all the way around!

Next I'll be skinning over the inside of the forms with postform grade matte white formica to get them ready for vacuuming down the core layup!

Stay tuned....

 

[Thomcat316]

This is a little update that belies a lot of coordination and work...

How to apply Formica to concave surfaces.

Required items:
Roller with extension.
6 mil poly film.
Spring clamps to hold poly.
At least four friends who aren't mechanically clueless.

Steps were:
Trim 4x8 ft. sheets of VGP grade matte Formica (chose white, it's simpler to write on) to 4x6 ft.
Make sure forms and 'mica are smooth (mostly) and free of chunks of stuff.
Dry fit 'mica and mark forms with Sharpie so thinking is not required while applying 'mica.
Slather on 1-1/2 gal. of contact cement with a roller - let dry.
Spread 6 mil poly film/visqueen over form to serve as temporary separator between 'mica and forms.
Align 'mica to dry fit lines.
Starting at bottom, lift edge of Formica and slowly pull the poly film up under the 'mica.
Making sure the 'mica is aligned, adhere the bottom edge.
Working with your hands from the center toward the edges, have two friends slowly retract the poly film, one or two others hold the 'mica up away from the surface, and you and another friend use your palms to brush the 'mica down onto the form surface.
If you don't remember to work from the center out in small increments you will develop a bubble in the center (like we did) and will have to cut or break the 'mica, iron it flat (yes, this does work), and sand off the ridges before sealing the cracks with epoxy resin. This is not entertaining.
Sheet no. 2 goes on the same way, using the top edge of sheet no. 1 as an alignment guide.

The more difficult rear form, which we of course did first - and which came out perfectly.

The simpler and easier front form, which requires repair due to excessive hubris. See the big crack in the middle, and the big gap between the Formica sheets?

A better view of what overconfidence can bring you.

Luckily the fix was as simple as sandpaper, epoxy resin and putty, and a few lengths of white vinyl tape. The mold surface is quite airtight.

 

[Thomcat316]

After a couple iterations of "almost right" on the panels for the 4ft. wide trailer, we ended up with two pretty much perfect panels for the 5ft. - not that there's a structural difference, but "perfect is perfect"...



The basic method:
Dry fit panels in form by aligning and clamping the top edge and forcing the curves to lay down. Bear in mind we're using two layers of 1/4" core for flexibility.
Cut the bottom edge so that the panels are in line when in the form - they won't be when they're flat.
Lay the panels out on top of a cardboard sheet, cut the fiberglass, peel ply, and breather to fit and set them aside.
Cut the bag the size of the form (or a little bigger).
Apply seal tape around the form perimeter.
Align the bag and seal the top edge into place - leave the backer on the rest of the seal tape.
Roll up the bag and flip it over the top of the form and out of the way.
Apply epoxy to bottom (outside)sheet of core.
Lay top (inside) sheet of core onto bottom sheet, align very carefully at the top edge.
Lay fiberglass onto dry top sheet of core.
Roll epoxy to saturate the core veil and the layer of fiberglass.
Lay peel ply onto fiberglass - overlap sides by a couple inches wherever you can.
Lay breather onto peel ply. Don't overlap as much with breather - it wants to be removed along with the peel ply, not separately adhered.
Tape the top and bottom edges of the breather around the ends of the stack and onto the bottom layer of core in 3-5 places at each end - it keeps the breather from falling as you bag the stack.

Breathe yourself for a few minutes - if you picked the right resin you now have ca. 30-45 minutes open time to get things under vacuum.

Back to fun!
Put three spring clamps onto the top edge of the stack - these will keep the sheets from shifting against each other as you move the stack into the mold.
With assistance, move the stack. Align the top edge with your witness marks on the mold, and transfer the three clamps to clamp the stack to the mold, through the top edge of the vacuum bag.
Help your assistant to make sure the bottom edge of the mold is aligned with the witness marks and that the top and bottom sheets of core are aligned.
Go to the bottom of the mold, and while your assistant pushes on the bottom edge of the stack to keep it forced into the mold place a few spring clamps to keep it in place.
Seal the vacuum bag down the mold edges, leaving enough bagginess in the middle so you're not stretching the bag too much.
As you seal the bag across the bottom, remove and replace the spring clamps in about the same places.
Pull yourself a nice little vacuum.
Find and fix the leaks.

Go have a nice beverage.

Sleep.

Come back the next morning, pop the vacuuum, remove the bag, and peel off the breather and peel ply.

The core should be stable in the form you've pulled it into, but still a bit flexy - it will stiffen completely when you skin the outside of the trailer.

And now, the pictures!

Pallet o' Plascore! Hint: Build four or five if you're doing this - the pallet weighed twice what the core does. Spread the freight cost among friends...

My photogenic side. Please use the method in the text and ignore what the man in the photo is doing - this was the first panel, which we are glad worked as well as it did.

See? It turned out sorta curvy and "back-of-TD" shaped!

Say "Hello" to my little friend... This is a spendy but VERY versatile vacuum pump, with both regulated and "always on" modes. Down here where it's 85F at night you need a blower running to keep it cool (has a thermal cutout) while it runs overnight for you.

These are the Front and Rear panels for the 5ft. trailer - by this time we were practiced enough to pull down two at once. Note the PVC pipe across the Rear form - it holds the sharp curve into the form during setup and bag placement (and means you only need *one* assistant), and ensures that if you somehow lose vacuum before the epoxy cures you won't have to rebuild the part - the sharp curve will still be there.

And here's what the 4ft. panels look like when they're out of the mold and freestanding.

 

[Thomcat316]

More resin and fiberglass!!

Not too much explanation of technique here, except for the note that large thin flat panels like to have both skins put on and cured at the same time, or else you end up with a slight cupping away from the side that gets the single skin. The side panels are currently curing their second skins under a few sheets of 3/4" MDF - stuff makes a very convenient panel clamp!

Also, I ended up going out and buying a precision jigsaw - the Bosch 1591EVSL saw kit, which includes a bunch of accessories that make it much more than just your average saw. I have to say that you haven't reached tool nerdvana until you've tried a jigsaw with a balanced drive assembly (no vibration), real blade guides (no wandering in 1-1/2" thick plastic stock), and a real constant speed controller so there's no difference in cutting feel no matter how hard you load it. For cutting out the PVC sheet doorway doublers (inside frames for the door openings) I used a precision wood blade, but for cutting the honeycomb I chose to use the Bosch T113A3 which allows you to gracefully split a Sharpie line all the way down a 15 ft. curve. Wow.

And the supporting photos!

Taping the side panels together - I ended up using 3" fiberglass tape on both sides of the butted panels (4 ft panel added to 8 ft. panel) to make 12 ft. long panels for the sides.

Side panel laid out with front & rear curves on it, ready to be traced.

My able assistant and true love helping me test fit the trailer - "This is BIG!" (Twelve feet *is* big when it's more than twice your length....)

I can trace lines!!! I can even trace lines for the doors!

As Paul Hogan once said - "THIS is a knife..."

...and here's where we left our heroes last night, with one skin on each of the side panels.

As I post this, the second skin is on both of the side panels and the first skin is on the roof panel - tonight it all gets assembled into a great huge box resembling a trailer with no wheels.

 

[aggie79-HILO]

Very nice!

Can you provide some additional information about your build method? (If it is in the first post, please just say so.)

What thickness of plascore are you using? Regarding the fiberglass cloth, what type/weight did you use and how many plies? I assume you are using epoxy resin. Is this true?

Thank you,
Tom

 

[Thomcat316]

The curves are two thicknesses of 1/4" epoxied together under vacuum. The inner skin is 3.5 oz. satin weave and the outer skin will be 12 oz. plain weave.

The roof panel and sidewalls are 1/2" clamped flat during cure. The inner is 3.5 oz. and the outer is 9 oz. plain weave.

The floor panel is 1-1/2". The inner skin is 3.5 oz. with a 50" long section of 17 oz. stitched biax across the panel in the way of the axle and galley area. The outer skin is 12 oz. plain weave. I don't think the 3.5 oz. was a good choice for the floor (Dynel was supposed to be added as a top layer, but needs vacuum and a LOT of epoxy, and I decided not to...), but I can always add a layer of 12 oz. on top of it if it seems like a good idea.

Overall, the 3.5 oz cloth isn't worth the weight savings (ok, and cost, too - it was a closeout...), as it's like working with tissue paper - it folds and wrinkles when you look at it. If I were to do this again I wouldn't use anything less than 6 oz. just for the handling.

I'm using WEST System 105/206 for the layups and WEST System 105/205 with thickeners (fumed silica, kitty hair and glass microspheres) for "putty" to join panels and make fillets. I'll be using WEST Six10 epoxy adhesive to adhere the tongue and rails to the trailer box, as well as to assemble the tongue parts. Six10 is a toughened adhesive - not as tough and flexy as G/Flex, but a lot more impact resistant than the 105 resin family.

If you do this sort of build, you'll want to test epoxy consumption - rolling vs. spreading. I'm finding that I can save quite a bit by using a spreader rather than a roller, but YMMV.

 

[Rock-TNT]

Cat hair for real?!? I missed that one in "101 Uses for a Dead Cat"

Eric

 

[Thomcat316]

Cat hair for real?!? I missed that one in "101 Uses for a Dead Cat"

Eric

Kitty hair as a reinforcement is from the compendium volume "1001 Uses for Dead Things (Roadkill Edition)" - #772, right after "Using cat hair to improve the efficacy of your K&N Filter"

Great book - everyone should have one. The recipe section would be especially useful to us TD folks.....

 

[Heifer Boy]

So what's happened with this build? Did it get finished?

 

[Thomcat316]

Alllllmost!

Got to about 90% and had to pack it in for a week or so.

Have a bunch of process photos to show, but no time to post them 'til I get back from the trade show I am off to today.

Neatest feature so far: being able to simply pick up the side of the trailer to install the tires.

Oddest bit: asymmetrical A-Frame tongue.

Anyway, thanks for watching it go together, but I've got o go load a van and drive to Norfolk, VA....

Oh, and we've got a site reserved at the Suwanee Music Park for the July 4th weekend - gotta have the other 10% done by then!

 

[Heifer Boy]

Sorry if my post seemed like a push along. I just noiticed that I was looking at your 'join' date and not the 'post' date and I thought nothing had been done since January. LOL!!! No hurry in that case!!!

 

[synaps3]

How much do you think the finished tear will weigh? The build methods you are using are so unconventional, I'm fascinated. You should post up the pics of the build so far!

 

[Thomcat316]

Our little trailer now has a name!

In keeping with the "freakin' light" theme, it's the "Lite House"

 

[Thomcat316]

After a brief hiatus to go run off to the trade show this trailer was supposed to attend (but didn't), here's more photos!

Here's a photo of gooping together the roof panel and the end curves with epoxy putty. The little round things are fender washers - I'm using thumbscrews & wingnuts to clamp the panels into alignment.

After filleting the joint between the side panel and the roof I pressed fiberglass tape into the wet fillet and epoxied the tape to the roof and side.

Here's what it looks like when it's taped.

Getting ready to fillet and tape the driver's side - the support in the middle is to keep the walls parallel. If you don't keep the walls parallel in this stage you'll end up with funny angles in the joints and odd stresses later.

This is when the upper shell was set down onto the floor. It overhangs the floor on all four sides, and is adhered with putty, fillets, and tape all 'round the inside.

Filleting and taping the rear joint.

It's a big honeycomb box, all ready for an outer skin!

At this point it's light enough to easily move around and turn over by myself. It gets a bit heavier from here.

 

[StandUpGuy]

I bet you got pretty buzzed working with resin inside that "box".

Pretty interesting stuff you have going there.

 

[Thomcat316]

More trailer building fun!!


Here's my pretty lass squeegeeing epoxy into the weave of 12oz. tight-weave cloth. The cloth extends over the side of the trailer by an inch on either side, and past the points of the front and rear curves by about four inches.

These are the "frame" rails. I wanted to spread the forces at the axle support point further under the galley, battery, and cargo loads, so I designed in a 3"x1/4" "L" angle of pultruded fiberglass to be bonded 5 ft. along the floor/sidewall joint. It may be overkill, but I like it. It will also make a convenient hard point to attach wiring runs, etc.

This is the passenger side of the "A" Frame tongue bonded to the floor and the front of the rail. I give full credit to Andrew for pointing me in this direction with his "Superleggera" design - thank you!! Those with sharp eyes may notice a couple screws at the left end of the tongue extrusion - those are 1/4" machine screws tapped into the frame rail and used to "locate" and clamp that end of the tongue section.

While the tongue was being installed, my lass was gooping and clamping hatch doublers. The walls are 1/2" thick, which means that most things made for RV use need backing plates to fit. These are 1/2" plates made of foamed PVC sheet and cut to exactly fit the doors I bought from Vintage Technologies.

Back to the bottom - this is a photo of the tongue bonded in place and the axle sited with the mounting holes drilled.

And the 1/4" aluminum backing plate for the axle. The section the plate sits on is as follows: 6oz. tape, 3.5oz. skin, 17oz. biax, 1-1/2" honeycomb, 12oz. skin, and 1/4" fiberglass angle. I haven't potted the holes with thickened epoxy yet - does anyone think I need to?

With apologies to the Muppet "Sweetums" - "Jack not name, Jack job!"
I guess if I ever have a problem getting the jack to work, all I have to do is unload the galley and....

Well what do you know? The door fits!!

Anyone see any problems with this design? (I really hope not!!) I had two options here - do a complicated 2 into 1 with twice as many joints and no continuity of fiber back from the coupler to the trailer, or this, which only involved one precision bevel and a couple plates of homemade G10 , and gives both a continuous run of fiber and a nice box to run the wiring in.

Almost ready to go camping!!

 

[Thomcat316]

I bet you got pretty buzzed working with resin inside that "box".

Pretty interesting stuff you have going there.

Actually, the epoxy doesn't outgas stuff that makes you high like polyester resin does, so it's a more insidious way of poisoning yourself - I really should be wearing a breather or an organics cartridge filter, but it's too bloody hot. Right now it's raining, too, so I could take some time and update the journal.

Only one more resin session and it's time to install lighting, doors, and fan!