Cut it deep

Then shim areas up to the desired depth sort of like putting in foundation piers. If you think that is too hard....try it in Homasote. Foam should be a cakewalk!

I *think* I understand what you're saying

So, you're saying that I should cut (or, more likely, irregularly gouge) in deeper....say an inch or two, then put in any number of shims/inserts until the gatorfoam panel sits in place securely?

Yes

It just took a little adjusting and my warehouse nestled into place pretty quick once the hole was completed. It was an experience I hope to never duplicate but the homosote was the real problem in the "dig". My layout was built with the land forms established first and then the methods of making building sites was figured out as I went along. I like the look of scenery and buildings to mimic real life and so many layouts are just to artificially flat to me so I did this as a self imposed challenge. Lot's of building site construction and reconstruction has kept me very busy,,,,,,,,,,,,

 The warehouse was scratch built and somehow I screwed up the loading dock height, What seemed like a simple problem was complicated by my scratch methods which just didn't allow for adjustments without the probability of major damage.....so the hole was excavated. I always knew that the rising topography at the back of the building was going to be trimmed but the total excavation was not planned for.

Cheat and change the rules.

It would be really easy to cut a piece of your gator foam base big enough for the entire town that fits your plateau.  Then plot where the structures will go, and carefully cut those holes out of the gatorfoam.  Glue the remaining piece of gatorfoam on top of the plateau.  Now you have all your holes, exactly the right size and depth.  And you have bases for all your buildings that exactly fit the holes they’re supposed to go in.  Except it’s 1/2” higher.

Are you sure you don’t want the extra half inch of height?  Can you maybe peal off the top layer of foam and replace it with a thinner layer you could then put the gatorfoam on top of to get the height you want?

Otherwise, you could make a hot wire cutter with the wire fixed to a 1x2 or something that rides on the edges so you get a consistent depth.  I think that’s your best bet for making a clean uniform depth hole in the foam without a following fix up the bottom effort.

One little thing

You don't have to install the piers into the bottom of the hole. Work the other way around and use flat material to stack them on the bottom of your top piece. A little adjusting here and there to the hole or the stack will level it up pretty quick.

Cutting

I have never tried this so no personal experience.

I have seen articles in magazines where they got a foam hot wire cutter and set it to cut a rectangle 1/2 in deep and as wide as the cutter will go. There is some sort of stop to keep the cutter from going more than 1/2" deep.  Then you cut a series of troughs separated by narrow strips (for the hot wire cutter ride on) and come back and cut out the narrow strips.

Or....

If you think about it you really only need a 1/2" or 1" area around the edge to be deep enough for the gator foam, just wide enough to form a lip that the gator foam can sit on..  The middle can be deeper or even cut out completely.  Just cut a narrow section around the edge to 1/2" deep. and then hack out the middle.

Or....

Don't raise the bridge, lower the water.  Cut the footprint out completely through the top layer of foam and the build up layers of foam or gator foam to form a lip the building sits on.  If you cut completely through, put a couple pieces across the bottom of the hole and then add layers of foam to build up to the level you want.  And it doesn't have to be solid, it could just be pieces along the edge, enough to form a lip that the building bases can sit on.

1/2 inch is not very deep

You could probably set a razor knife to cut 1/2 inch deep then cut around the perimeter of the hole then cross ways in a grid, then  starting in the center cut down far enough to turn the knife on it's side and smooth off the bottom working from center of hole to the edges. However I'd think about the town base a bit.Do you really want the whole town at one elevation? If not you could just set the  buildings on top of the foam at different elevations as you work across the foam landscape. Slopes between them ( gradual near level slopes perhaps) could be filled in with plaster or other material.....DaveB

I like a lot of the ideas above.

DaveB with the knife to start would give the depth.  Remove small squares at a time for in the middle.  The opening does not have to be perfectly flat, only has to have support in three spots.  (Three points define a plane.)  A Shureform file would allow for topping the high spots.  if you decide to use adhesive it will stabilize the inserted module.  It can be shimmed also.

I want to know how you did it and see some pictures of the process and results!!!

Good luck and enjoy!

Nick

Dremel tool is your friend...

Try a wire brush or some other attachment on a moto-tool. Experiment with different ones on a scrap piece of foam.  Just keep the shop vac handy and maybe even have it running while you work. On a big area, take frequent breaks!

When I was cutting trenches

When I was cutting trenches in the foam for my roundhouse inspection pits, I trimmed a yogurt cup down to fit over my hot wire cutter to act as a guide to control depth of the cut. That worked reasonably well. I don't know if you could adapt it to cover a larger area, but it didn't cost anything to try.

Router

I needed to excavate an area on my friends layout, in order to set a structure into the scenery.  The structure was built on a piece of Gatorfoam.  So I used a trim router (smaller than a regular plunge router), with a straight bit.  A trim router has a much smaller "footprint", i.e. much smaller base plate, so it needs to be carefully handled when in operation, as it can wobble or tip.

It worked very well, but it is important to have a helper with a shop vac following the router closely, as this method creates a lot of pink (or blue) dust.

Now that I've successfully debuted this method on my friends layout, I wouldn't hesitate to try it on my own layout 

Al Carter

I was looking at Rick Sutton's photo

And I think there's another way to describe Rick's idea. 

Think of patching drywall... shims or blocking cross behind the hole and your gatorfoam drops onto that.  Like a hole in a wall, but rotated to a horizontal plane.   This could be done in a 2" deep cut... cutting fully through may be unnecessary.

(I do like the trim router idea... )

a router

will knock it out fast but much of the foam will end up flying around the room. Hand work will be slower but easier to control the mess. As Rick posted above the bottom of the hole doesn't have to be perfect, just excavate a bit deeper than needed then squirt some foam friendly caulking in there and press down the module to the desired height.....DaveB

Dang!

DaveB

Gonna have to have you come on down the next time any excavating needs to be done. The caulking idea is brilliant!

peter-f

Even though I was explaining what I had done....your explanation is clearer to me than my own. That says something!

@Rick... glad to compare notes!

Your posts are always fun... must say something about you (or me, that I find such amusement in them!)

And-- re a router... cut a hole in a large plastic bowl, add a vacuum hose and cover the machine to confine the shards     (OK, While I like the router idea, it's a bit of amusement... the foam may burn, or worse... overheat and GUM up!)

Thanks for all the great

Thanks for all the great help, everyone. I don't have a router but I sniffed around a bit and a "trim router" doesn't seem that expensive. Y'all have sensitized me to the mess, though. I have already seen quite a mess just using my jigsaw to cut slopes. Maybe I'll take a flyer and try one out.

The "make cross cuts and pull out chunks" also seems doable. I'll try that, too to see if I can get a bottom flat enough so that the gator board doesn't sag under the weight of the diorama - especially dios that have heavy hydrocal components.

Most of all, I hope to plan a little better so that I don't have to do this more in the future. Making the base a little shorter and putting the dioramas on top would certainly be easier, more flexible, and allow for easier below-grade terrain variation between scenes.