If keeping the top flat while glueing is the objective, I would not put the joint at a support. I would have the joints between supports so that slight differences in thickness will naturally distribute or could be shimmed/accomodated.
I would put a sheet of waxed paper or plastic wrap over the joint, then a "splice plate" of at least 12" wide plywood or particle board. Then on each side of the joint put a 1x4 under the foam and clamp the edges to the splicte plate enough to keep the foam tight to the splice plate. I would use a foam adhesive in a tube or Gorilla Glue or something that fills voids since foam cuts can have gaps. I would als use dowels or skewers in the ends of the foam sheets to mechanically reinforce the joint. After the glue sets/dries, remove the splice plate and 1x's.
Dave H. Painted side goes up. My website : wnbranch.com
gregc rrebell I became a big fan of my choise when a freind of mine (300+lb) put his full weight on the edge of my last layout. just need to support track on foam
rrebell I became a big fan of my choise when a freind of mine (300+lb) put his full weight on the edge of my last layout.
just need to support track on foam
maxmanI would also check the thickness of the ends of the panels. I read somewhere that the edges tend to be a little thinner due to the way they are made.
I think it is how it is stacked and/or stored along the way. A forklift driver can compress the ends by not squaring up before lowering or raising a pallet. I don't know how some of those guys keep their jobs. They would not last five minutes at the airport around aircraft.
Brent
"All of the world's problems are the result of the difference between how we think and how the world works."
I would want to know the cause of the mis-height. I know that two different sheets of plywood can be slightly different in thickness.
If the two sheets of foam are slightly different (from being produced in two different batches?), the bottom flatness will now be compromised when you make the top perfectly flat.
How would you support that gap along the bottom of the thinner sheet?
If the two sheets are exactly the same, then your benchwork needs adjustment.
But I'm with Brent, I would just make sure all of the foam is properly supported from underneath, then adjust the top to make it flat where it needs to be flat and scenic over everything else.
I've also used cardstock to build up the top of the shorter seem when the heights of the subroadbed material couldn't be shaved.
- Douglas
gregcof course they'll be glued. the question is about keeping the top surface aligned (i.e. flat) while the glue sets
How smooth is the floor in front of the peninsula you want to build?
I think if I were in this situation I'd first lay some protective sheet (waxed paper even) where each glue joint will be. Then lay the foam upside-down over the paper.
Lay out your foam sections ready to glue. I'd want "splice plates" of say 5mm lauan plywood which is strong but light weight. Make them about six inches wide to give three inches of gluing surface on each foam panel.
Glue up the entire lenght while laying flat on the floor. Weight the wood splicers with gallon paint cans, bricks, old phone books, whatever, until set, at least 24-36 hr. (foam contact seems to take longer for the glues to set since they are non absorbent).
I'd also brace one end so that you could apply some "squeezing" pressure, not enough to buckle anything but enough to squeeze the joints together and some way (more weights?) to hold some longitudinal pressure on the whole assembly while it sets.
Then with a helper carefully raise the entire 24-30 foot piece, place it on your pre-assembled supports (benchwork) and flip it right-side-up and the joints should be aligned well enough for track laying. Probably need minimal sanding with a Surform, maybe not.
Good Luck, Ed
greg - Philadelphia & Reading / Reading
wjstixI'm not clear why you can't glue the panels together?
gregc seems obvious that the seam should be resting on a cross brace. i'll need to join at least 2 panels (24'). i'm planning lightweight L-girder-ish benchwork (see no need for heavier benchwork to support track on foam). but i worry about unintended bumping against the layout, causing it to shift. (allowing some give may prevent damage). shelves against the walls obviously don't have this problem it seems that long fascia panels that are better attached to one another (i.e. sideways bridge) can make the entire pennisula stiffer. (maybe even just glass fiber packing tape) while this wouldn't prevent it from being moved, it would hopefully prevent it from bending (assume many of you are cringing)
seems obvious that the seam should be resting on a cross brace.
i'll need to join at least 2 panels (24'). i'm planning lightweight L-girder-ish benchwork (see no need for heavier benchwork to support track on foam).
but i worry about unintended bumping against the layout, causing it to shift. (allowing some give may prevent damage). shelves against the walls obviously don't have this problem
it seems that long fascia panels that are better attached to one another (i.e. sideways bridge) can make the entire pennisula stiffer. (maybe even just glass fiber packing tape) while this wouldn't prevent it from being moved, it would hopefully prevent it from bending
(assume many of you are cringing)
I'm not clear why you can't glue the panels together? I've used Woodland Scenics Foam Tack Glue to hold pieces of their foam sheets together or hold risers in place. I can't see why it wouldn't work for similar foam sheets?
https://woodlandscenics.woodlandscenics.com/show/item/ST1444
gregcseems obvious that the seam should be resting on a cross brace.
Depends on what the attachment method is.
If you are using a a 'splice plate under the layout, then a joint should not be on a cross brace. If you are using "tongue and groove" or skewers/dowels then it could be on a crossbrace.
Depends of course on how consistant the thickness of the sheets are and if you want any deviation on the top or the bottom.
If you want the tops 100% flush, then any deviation needs to be on the bottom, so the joint should not be on crossbrace (or at least doesn't matter). If you want the bottoms to be absolutely flush, then they can be on a cross brace.
If the difference in thickness between sheets is negligible or you don't care then it's just matter of your preference. If you coat the ends of the sheets with glue and use dowels or alignment fixtures, then it probably won't matter if it's on a crossbrace.
I would use a 1"x2" or 1"x4" board and and two giant clamps. Place the 1x2 or 1"x4" down the seam, and a clamp on each end. I would also put a small amount of caulk between them. You could them crawl under the table and see if the seam is aligned. If it's aligned on the bottom, it's aligned on top. You could also put stacked books on top of the 1x2 instead of using clamps provided there is adequate support beneath the seam.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
Ideally, set the butt joints atop risers or ledges supported by risers.
If that can't be done easily or practically, use a lapped underlying plate of thin cabinet quailty plywood. It needs to be good stuff to be stiff. I would glue it with PL300 which, unfortunately, can take some time to set up, but once it does it's like epoxy almost. I wouldn't rely on this type of joint for much strength, maybe 30 pounds, but if you could inset another plate on the top so that the grade isn't disrupted, same adhesive, it would be a lot stronger. Obviously, the best thing is the butt joint atop a support.
What is the support structure?
If the panels are glued down they should be in pretty close vertical alignment.
I would also check the thickness of the ends of the panels. I read somewhere that the edges tend to be a little thinner due to the way they are made.
ROBERT PETRICK Toothpicks.
Toothpicks.
There are Extruded foam Panels with lap joints built-in, however, barring that I would use PL300 on the ends weighted with a flat surface on either side until dry.
I have used a sea of foam and in a couple of spots where the alignment wasn't great, I just took a rasp and made it flat where the track went. Just like real-world geography even a flat surface needs some adjustment for a rail line. My small ups and downs or errant gouges are just left and incorporated as part of the landscape.
LINK to SNSR Blog
I always used benchwork 32" is a lot of distance for unsuported foam. That being said I have seen bamboo skewers or heavy wire by others for jutt outs.
i'm planning on building a 30' x 32" pennisula using foam panels. wondering how to keep the ends butted together aligned vertically
if it were wood, i'd use biscuts. could try using a hot wire to cut "rabbets" and glue the ends together