The Poet Creek Express - Foamie Hybrid

[KCStudly]

I had another 'life-got-in-the-way' gotcha. On Wednesday I had made arrangements to have new tires put on the Jeep (again), so after work I was driving the few blocks over to the tire place. Along the way I had to stab the brakes a little more than moderately… though not a panic stop, and felt the Jeep pull left quite a bit (hmm, that’s not normal). Let’s see, at the next stop lets slow down early and put a little pressure on the pedal (hmm, pedal seems to be creeping down). Seems we have a problem, maybe a rusted brake line or blown out wheel cylinder. Next stop, straight to the floor and I’m grabbing the hand brake, but I already knew something was up, and this isn’t my first rodeo, so I was using the gears and leaving plenty of room. Mind you this is urban traffic at rush hour, so not much speed was involved. Conveniently my next stop was to pull into the repair place and park. Sure enough, brake fluid pouring out of the right rear brake drum. So the Jeep had to spend the night at the shop and I never made it out to Mecca that night.

Last night, Thursday, after picking up the Jeep, I made it out to have a look at those foam and PL test pieces. The first test was a shear strength test by putting the edge of one piece down on the bench and pushing my weight down on the other piece trying to shift them parallel to the joint; didn’t budge.


Tried to pull them apart and they held up to quite a bit of effort. Next I cut thru the coupon with the steak knife. There was a relatively large area at the joint that was void. Despite having scuffed the faces with 100 grit prior to gluing, I did not sand the whole surface flat. The foam has minor dips and depressions from the manufacturing process, such as where the printed labelling is applied, and I think this void was one of those areas. Since I spread the adhesive thinly, this area didn’t get filled.


One piece of this coupon was larger than the other so the flap gave me a hand hold to pop the joint apart (only about 8 square inches now). You can see the light blue fuzz in the glue and the open pore fuzziness on the piece where the glue broke away.


At this point the glue skin was relatively easy to peel up in sections, but you can see how it lifted the printed media and more foam as it came up, suggesting that it is the foam that is the failing point, not the adhesive bond.


Next up was the test between foam and the epoxy/glass reinforced area on the front curve of the cabin. The edge near the top hadn’t fully bonded to the glass because the 1-1/2 inch thk foam didn’t conform to the curve, but I could still not break it away by hand. In fact, with the cabin up on moving dollies, I had to brace the cabin with my shin to keep it from moving around while I tried to pull the foam off. So to break the bond I ended up running a wedged shim up under the edges. It took a lot to get the piece to pop off.






I used a small paint scraper to get most of the PL up off of the epoxy, but was also able to peel up a pretty good piece relatively easily. You can see how the adhesive keyed into the unfilled yet saturated weave of the glass cloth.


I’m struggling a bit to understand how the glued up pieces can be so hard to separate manually, but once done the glue itself seems to come up relatively easily (maybe giving past testers the impression of a weak bond). I think the difference has to do with the composite nature of the joints. With the pieces held close together the joint is stiff, but once that lateral support is busted, the uniformity of the bond is lost, maybe? In other words, the sum of the parts and the stability of the way the loads are dispersed from piece to piece is a lot different when trying to wrest two pieces apart, than it is when you peel the glue away from the surface at a starting point. Kind of like a zipper; try to pull the fabric apart and the zipper is strong, but grab the zipper by the tab and it zips right apart. Maybe something like that. Bottom line, I think the PL will be a great way to bond the foam to the hardened glass/epoxy, but I have still not ruled out thickened epoxy. Other than the slight edge in filling capability, the foam to wood joints I did with TB2 seem to be just as strong, so I might “stick” with that for the raw wood areas.

Back to finessing the hatch bumper. I made an improved dog setup to get the clamps further out of the way and to create a more sturdy and reliable hold. Rather than surrounding the end of the bumper with separate blocks all clamped to the bench, I notched a scrap piece of 1x6 and offset the clamps to one side.



The drop from the previous angle rip made a nice support to hold the surface to be worked level.


The street side of the hatch flares out from the edge of the wall just a little bit more than the curb side, and I wanted to carry that line down into the bumper to avoid a sudden transition that would jump at your eye, even if the gap ends up being a little wider there (which may change again when I work the edge of the walls again). Here you can see a dry fit where the gap between the wall and skin starts out at 1/16 inch above the orange bar clamp, widens to about 1/8 inch at the blue tape which carries into the front edge of the bumper, then goes back to 1/16 inch at the change in angle between the bumper and rear edge of the floor.


You can see here (despite the bunched up blue tape on the corner round over of the lower hatch spar) how the rear of the bumper is just about fully flush with the rear of the spar. Also, that the bumper is still at rough length and extends out a bit for now.


The orange bar clamp in the above pic is being used to simulate the draw latch; the tip of the jaw has a little toe hold in the recess for the side running light just out of the picture to the left.

Compare the curb side to the pic of the street side and you can see how the gap is much more uniform (the little light slivers of oak shim are 1/16 inch thk). It’s a little hard to judge because the bumper is long and I had to put a little angle in the shot to get the flash right.


So the trick to get the spar to fit both ends simultaneously involved planing on a slight taper; one end more than the other. To do this I made marks on the side of the piece every 6 inches and transferred the mark to the top. Then I started planing at the first mark working toward the heavy end in one stroke. Then backed up 6 inches and stroked to the end again. Repeat. By doing it this way the heavy end got 10 strokes of the plane for every 1 at the shallow end, and each station along the stick got a proportional number of strokes accordingly, in a nice gradual transition. Once I had the line at the back parallel, I switched to the powered hand plane and made a couple more full passes until the rear of the bumper was flush to the rear of the lower hatch spar.

Tomorrow I plan to finish fitting the bumper and temporarily install the draw latches. Probably will remove the hatch again to do the glue up and final fairing. Maybe get back to the poly under the hatch before continuing.

[dales133]

Nice work kc, interesting about the foam.
I've trialed different glues on different substrates alot in my work with tiling and carpentry and 9x out of ten it will do as you described..Won't break the glue joint but just shy of it yet the glue often scrapes off quite easy.
That bumpers taking shape too!
Love the way you deal with things that aren't quiet perfect but make them look so with some fine tuning.

[GPW]

I would think tearing and scraping are much different then what the foam would normally feel attached to a trailer cabin .... Tearing is actually putting pressure/ separation on a tiny area at a time , so the weakest element fails first... the foam , much as expected. (It’s like tearing a telephone book in half , one page at a time) Scraping is the same thing , great pressure on a very small area ...
And practically speaking , a good tight covering eventually shrinks a little more and provides a great “sock” effect to hold everything together , making a tight ,strong, light structure ... lessening the worry of the adhesive bond holding the foam to the wood ....
note: You must actually see this shrinking effect to appreciate how well it works ... and then there is the "self-healing properties" , as experienced after a particularly heavy hail storm ... That alone was pretty amazing ... JMHO, I believe the long term benefits of foam and fabric camper trailers is yet to be fully realized...
What , four years now and counting ...

[KCStudly]

Dale, thanks for the positive feedback. Fixing the details is where all of the time goes.

GPW, Yes, absolutely! I agree with everything you just said there. Like I said, I think the PL is a fine solution, despite the ease with which it peeled up; when applied sparingly it cured and held exceptionally well (at least on these smaller scale tests).

One thing I forgot to add is that the PL is rated to work down to 40 or 45 deg F, at least 10 deg lower than the TB2; so that will be a factor that comes into play as this weather continues to turn into winter.

[KCStudly]

As noted previously, the lower hatch spar has a dip in the middle and is higher up on each end by about 3/16 inch. This is locked in now by the hatch skin. Believe it or not, I am able to pull the bumper in to compliance with clamps, but to mitigate that a tad I planed the top of the bumper a bit. Used the same graduated technique by placing tic marks every 6 inches, but this time I started by planing the middle 6 inches first; then took a second stroke on the middle 18 inches, and so forth. I didn’t try to match the joint perfectly, just took some so that there would be a bit less strain and the ends would pull up a little easier. Another pile of shavings.


Now that I was pretty happy with the fit of the bumper it was time to round over the corner at the bottom where the lower edge meets the lower edge of the floor. This is the last place where the canvas will wrap up onto the front face of the bumper.



Next I removed the hatch from the cabin again and blocked it up on the bench high enough to get clamps under the rear of the lower spar. This made it easier to remove a portion of the masking and do the final fitting of the bumper without having to lie on the floor. It will also make the glue up easier.


After pilot drilling and screwing down thru the spar, I traced the rounded ends onto the bumper for the final trimming to length. Curb side then street side.



After cutting the ends to length square, I marked the tangent points of the round over marks to act as a visual guide. Rather than trying to blend the round overs together using the big 3/4 inch bit, I just used the Surform rasp to rough it in.



After a little more work with the grater, I switched to 100 grit paper on the small block.


And then 220 grit. Probably a waste of time at this point as I will have to do a final fairing to match the lower spar, but I like the results.


Doing the other end I think I got better pictures showing the work flow.






So now the bumper could be glued onto the lower spar, but I figure that any weight that I can take off of it will lessen the strain on the actuators and hinge by a factor of at least 7 if not 10 or more (didn’t measure arc lengths). In fact I now wish that I had thought to put lightening holes in the lower spar before it was glued in. Anyway, I set the bumper on Karl’s little digital scale and it weighed 4 lbs.


Next I laid out reference lines on the top surface of the bumper to show where to stop and start short of the screw holes. Then I centered the router using the included guide fence attachment and a 3/4 inch straight cutter. Plunged down 1/16 inch at a time and made multiple passes. Here is a pic after the first few passes. The slots will be hidden against the lower hatch spar, so nothing will show once it is glued up.


And the router set up.


A little deeper now after some more passes.


Very time consuming. I think I can comfortably go down to about 1-1/4 inches deep, but with such a big cutter it goes slow due to the shallow cuts. Before quitting for the night I got down to 7/8 inch deep and had taken over half a pound off.


Doesn’t sound like much but to the hinge that could be 5+ pounds. Besides, I have to make up for the heavy SS hatch handle that I plan on using.

[bonnie]

That's a wonderful looking bumper. Your progress is so fun to watch.

[KCStudly]

Thank you Bonnie. I'm happy to hear you say that!

[Wobbly Wheels]

Heya KC, just caught up on the last few pages of your build this morning - your eye for detail certainly shows. Those maple rib braces really pop against the stain.
Sorry to hear that Chunkin was canceled though - I know that's a big event on your calendar.

As to your question about gluing foam to epoxy: weren't you playing with some 30NF a while back after talking to Grant ?
I've got a couple spots where I want to use foam and latex cement, so I'm curious as to why that didn't make it into your testing process.

Lookin good !

[KCStudly]

Thanks WW. I think it was linuxmanxxx that encouraged me to try the 30NF (3M green). I used it for the foam to ply bonding in my floor, bulkhead and, I think, one of my walls (IIRC). Based on linuxman's recomendation I used wood glue for the wood to wood, which involved tedious masking to get the adhesive down while leaving raw areas for the wood glue. Linux said he didn't bother with that and just combined the two different products. He also hinted at some issues, without getting too specific, but swore by the product.

Well, when I hole sawed the opening in the bulkhead for the small vent fan I found that the stuff had not bonded well at all (I suspect that it wanted more point loading to bond, such as from a heavy roller like for flooring or counter tops)... and at the time it was running about $100 a gallon. So despite other people's reports that TB2 wouldn't dry when gluing foam, I decide to do my own tests. What I found was that the wood would only absorb a certain amount of moisture from the glue before it sealed up, so the trick is to use the glue sparingly, spreading or rolling it thinly and evenly. When done that way it cures and bonds very well, and it only costs $18/gal.

Now on the foam to hardened glass reinforced epoxy, I figured I would need something with a little more of a thickened consistency, and honestly, never even considered using the 30NF... I do have a little left over, but haven't looked at it for some time. Based on my testing I plan to use the PL premium for the front radius and some other spots; and TB2 most everywhere else. Maybe some GS at the edges at the spars if I need a little gap filling.

Today I made a few more passes in the lightening slots of the bumper, getting down to 1 inch deep. At a 3/4 lb. reduction I decided that I had had enough of that.


Next I took a closer look at the bumper fit to the lower spar and decided to plane the top center down some more. Also, I had managed to plane a little twist into it so the ends didn’t pull up evenly leaving some gaps that were a little more than what the clamps or screws would close, and a little more than I felt comfortable letting the PL fill. So I spent the rest of the session planing and dry fitting; marking high spots and gaps, and fitting some more.

I knew when I designed it that the bumper was going to be a critical item bringing all of the transitions together in one piece, so it figures that it would take extra time and attention.

After taking quite a bit off and still only getting the ends somewhat close, I decided that I had better check it against the galley again to make sure I wasn’t going too far in a wrong direction, or if I should continue. Here you can see the curb side.


A closer shot shows the gap below the pencil line. The bottom of the bumper is still a little lower than the floor, so I could go a little more if I wanted to.


Looking down from above you can see the work I need to do to sand the bumper fair to the lower spar at the round over and a little on the end for length.


On the street side the gap at the end is a little bigger and even from front to rear, and the bottom is nice and flush to the bottom of the floor.


And the street side from the top.


So I’m at that point with the fit between the bumper and lower spar where I ask myself, am I going to do more harm than good? Do I want to spend more time on this task and is it worth it to get it perfect? On one hand the joint will never be seen and it’s just a few inches at either end (most of it has come in really nicely over the middle section of the length), but on the other hand it needs to be a secure joint and I don’t want trouble with it splitting apart under the canvas. Maybe this is the place to try some of that thickened epoxy I’ve been threatening to use? That would provide a strong bond while still filling the small voids at the ends.

[KCStudly]

Monday evening I mixed up a small batch (almost too small) of thickened epoxy and installed the bumper to the bottom of the hatch permanently.

Got the ratio right this time; 30 g resin, 6 g hardener and 3 moderately heaping tablespoons of micro fibers. Pushing the recommended temperature window at 57 deg F in the loft (forecast was a low of 38).

Street side.


Underside showing masked off portion of lower spar.


Curb side.


Some sanding work to do, and I can put that task behind me (bah-dump-bump! pun).

[S. Heisley]

I got nervous about weight as I got closer to the end, too! Every ounce adds up! Your weight elimination cuts look a lot better than some that I made!

[KCStudly]

Thanks for your input, Sharon. It's not that I am nervous about the overall weight. In fact I may be over confident at this point in the build.

I have tried to build moderately throughout, and, with the exception of the rugged suspension, some trim details and the hatch actuators, I feel that I'm doing okay... perhaps better than the average traditional style build of this size (he said fairly confidently ).

Really, on the hatch, it is a leverage thing. A little bit of weight at the end of the hatch feels like a lot more to the actuator pivot point and hinge due to the offset teeter-totter leverage effect (put the fat kid on the long end and the skinny kid on the short end and you have a problem; put the skinny kid at the long end and the fat kid at the short end and the two can play nice together).

I suppose a true foamie would be much lighter, and I'm sure I could have pushed the envelope further in all areas, but this is the vision that I have for TPCE and it seems to be working out to the plan.

[Mary C]

Like the glue expirement you did and always. I am wowed!

Mary C.

[KCStudly]

Thanks Mary! How's the weather doing down your way? Have you had any frost yet?

[KCStudly]

I am happy to report that the hatch bumper is now complete!

This “simple” piece of wood is a really good example of how much work is going into TPCE. I glued the blank up for it on Feb. 20. I must be crazy.

Granted, it sat for a long while before I worked on it again, but it sort of developed a little mini reality all of its own. I’ve said it so many times before; every part you touch takes planning, sourcing, blanking, fitting, assembly, finishing, etc., etc. Will it ever end?

Anyway, I took another bite tonight.

I used a combination of the small Stanley palm sized plane, the small Surform grater, the course sanding block, and the small hand block… and my respirator. Here’s the street side of the hatch looking down at the lower spar and bumper, followed by the curb side, then a long shot looking along the back.




Karl gave me a hand flipping the hatch over onto its back so that I could scrape the front side of the bumper (where the hatch seal will go) and pluck the masking tape off of the underside of the lower spar. Actually, I had better luck using the wide chisel, laying it flat against the underside of the spar and pushing it behind the tape down into the little bead of epoxy. Then repeat with the chisel against the bumper taking the little bead with embedded tape away.


Cleaned up nicely.


In preparation for poly, I laid masking tape down on the bumper to preserve the raw wood where the canvas will wrap and be glued later.


So here’s a question for you; should I pull the stainless steel screws out from the bottoms of the ribs before poly or just poly right over them?

Other than that little detail, and doing a good cleanup of the loft to get rid of excess sawdust, I’m back to a good place to lay down the poly under the hatch (Karl suggested bringing it down the stairs and spraying it in the main shop).