Large Scale Central

Hale & Norcross

Modeling Technical Modeling
#41

Yeah, and also not run angles up the corners. It’s a good idea, but I’m trying to accommodate the stresses by [edit] perpendicularly-braced joints at or near each edge of each main wall, with tabbed / welded connections. Thanks for your observations and comments, I really appreciate them all. Almost. (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)[edited to put in a long-lost emoji!]

Here’s a shot of the tabbing, as things stand.

You know how time-consuming this is…

Hence my 2-year estimate. However, I’m trying to get a jump start on it, and maybe things will go more quickly than that.

#42

Cliffy,

Here is a question / observation you may or may not appreciate (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)Do you plan on assembling the walls first, and then putting it on the base? Or do you plan to assemble the walls to the base as you go? Reason I’m asking is, if you plan to do the later, you might be painting yourself into a corner with to many tabs. (ask me how I know). For instance, look at the left transparent wall. You can’t engage tabs on the base, in the horizontal member, and in the interior cross wall all at the same time. Even though your acrylic will flex, might not flex that much.

Anyway, you have fun with that. You are absolutely right, doing that is a LOT of work.

Second obersavtion / idea. Instead of pvc stubs, how about just using the laser and making tabs and slot to connect the sub-structures? You could even make it a hook, to where you slide it in and drop it down to engage the sections. (Now I’m done. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif))

Chris

#43

Hey Chris,

Yep, I agree re. the tabs; and the acrylic sure won’t stretch or compress when cumulative tolerances kick in. In the test building, it was sometimes tough to get them to all fit up. I’ll have to gradually work the pieces together, section by section (the green module has 3 sections) with the aid of a Dremel if need be. Also, walls / braces would usually fitup first, with the base pieces tending to lock them together.

BTW, the cementing would only come after all the parts (for a particular module) are dry-fitted and the whole thing clamped.

I really like your thoughts on the pass-throughs. If it were a simple thick boss or even tabbed tube, welded to and sticking out from a “satellite module,” it could easily stab into a hole in the center module.

For securing, vertically hooking might well work, but the fixed compression distance might not work well with a compressible gasket, so that has to be worked out. Maybe an acrylic wedge or “dog” could secure a penetrating tab and provide the varying tension.

The advantage of screws or bulkhead fittings is that you get that variable compression. So an acrylic feedthrough, 4 truss head screws epoxied from the inside of the small module, and 4 wing nuts on the main module, with a gasket, might be all that’s needed.

Thanks much,

Cliff

#44

Here’s a quick illustration of what I was talking about, but maybe even simpler. No hardware is shown, but you get the idea.

The black gasket fits in the recess of the red wall, which is backed up by a welded-on acrylic piece. The green wall has a reinforcing piece, but that’s probably not needed (if it is, it should be on the red wall backing piece as well). The gasket is slightly thicker than the acrylic, so when the wing nuts are snugged down onto their screws (not shown), the gasket compresses and the walls go almost line-to-line.

The gasket would be cut on the laser, so this would be pretty cheap. However, the bulkhead fitting, with it’s gaskets included, would be a lost less fuss.

#45

You’re going to put a gasket between the sections. That is getting fancy now.

Chris

#46

True, but comparatively free. It’s to keep rain drippage out, and also bugs. Well, limit them at least; the roof won’t be a perfect fit to the walls by any means.

#47

If you seal it too tight, the heat will not be able to escape.

#48

Hi David, I’ll be using the same sort of vent as in the “test” building (louvers under the roof, at the peak, with a hole behind).

#49

He

re’s the current model of the acrylic core, with all the tabs between sheets. Next comes the roof structures.

#50

Cliff Jennings said:

Hi David, I’ll be using the same sort of vent as in the “test” building (louvers under the roof, at the peak, with a hole behind).

Cliff, with a vent up top to let the heat out, you should also have an inlet down low to let cooler air in. Well screened to keep out unwanted residence.

#51

Yep, I agree David. Thanks.

[edit] Thinking it over more… Thanks for your advice, but not sure about the whole vent thing…

#52

Speaking of vents, with this approach I no longer believe there is any reason for them. Here’s why.

  • The roof assemblies are not attached to the structure
  • The roof assemblies have small gaps between their ribs and the structure’s walls
  • I don’t know what sort of pressure buildup the heat might have; but…
  • WAY, I mean WAY before it would break the structural acrylic, it would lift the roof to a minuscule degree, and
  • Bleed off the pressure

For these reasons I’ll probably not bother with either vents, or (because they invite insects) inlets.

If I’m wrong, I’d like to see some evidence with my own eyes. And if I do, I’ll take a drill and make a 1/8" hole under each eave apex. A vent aperture, under these conditions and volumes, should not need to accommodate some massive air flow.

Cliff

[PS] A test might be as follows. Put a spare fish aquarium out the yard, in full sunlight. Put a lid on it, say, a cookie sheet. Tape it down with electrical tape. And after a hot day, see if the aquarium blows up.

#53

The thought of venting is a good ponderance. While I doubt the building will ever build enough presure to blow up, it may pop a weak joint. Your building is of substantiale size, and all the modules are going to have pass thru holes allowing it to act as one. I believe it would take a sustained heatsource to build up enough pressure to do any real damage. Still, I can understand the reason for having it. I can also understand the desire to keep the bugs out. Leaving my roofs loose is not an option, they would simply be gone. Wind speed today is 20-25mph, and that is a good stiff breeze here. Since your building does have cupolas, you could design a safety valve in the roof underneath them, that would open if needed, otherwise remain closed and bug tight.

Chris

#54

Chris, Dave, all this talk about airflow is great. I very much appreciate your thoughts, because they make me think more. And that’s always a good thing. Budding geezer that I am. (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-foot-in-mouth.gif)

I honestly don’t have any eyes-on experience with either of these factors of heat buildup or wind, in regards to a big model building that I’m designing.

However, I’ve stated my case in regards to heat / venting. And again, I’ll state that – in the context of this design ONLY – that the roof will slightly lift and relieve the pressure. Lift, in a microscopic sense, not observable. Over time. As long as I don’t weld the roof to the walls, that very gradual pressure delta will equalize itself just fine.

If someone wants to place a bet, I’m willing to take it. (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-laughing.gif)

But like I said, I’ll drill a relief hole if needed.

Wind, however, is an entirely different subject. Totally different forces. But with the weight of the roof assembly here, I think it will rest well against the structure.

I think it’s at least ok enough to not pay to put into a frickin wind tunnel to prove that I think it’s ok.

Good point on the cupola though Chris. Seriously (no ranting here; just calm and loving), I should just fit it into a hole in the main roof. And make a few spare cupolas, in case I can’t find where it went.

(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-laughing.gif)

C

#55

I wasn’t talking so much about air pressure build up, I was talking about heat build up. We have all gotten into a car on a hot day when the windows were left rolled all the way up, and we felt how much hotter it was inside the car then it was outside. You are building buildings with plastics. How much heat can they stand for how long before the plastic starts to get brittle? If letting cooler air in at the bottom, and hotter air out the top, extends the life of the building a few years, then isn’t it worth it?

#56

Those are good points David.

#57

Chris, BTW, I’m sure looking forward to your big building build. And rest assured,

(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)

#58

There will be 4 roof structures, all lift-off in nature.

Though the larger roofs will be reasonably heavy, there may be wind issues, especially for the smaller ones. If that becomes the case, I plan on drilling holes through end walls and into the rafters behind them, enlarging the outer (wall) hole, and inserting a fastener such as a sheet metal screw. Not elegant though, and the rafter might crack. Maybe just a SS nail poked through would be better. I’m open to suggestions. For the time being though, I’d like to see how well the roofs do over a season, just with gravity.

The legs pointing downward are to allow the assembly to be set on a table for shingling, detailing, etc., or to just be set aside on the layout without damaging the shingles or trim.

BTW, the internal “walls” and “floors” in the core structures are only bracing, and do not correspond with real life features. My objective is to make these structures strong but lightweight. As a point of reference, the main (green) core weighs 19 lbs (without sheathing & detailing), and its roof weighs 8.5 lbs (without shingles & detailing).

As for vents, I’ll probably end up putting holes at peaks, through wall and rafter behind, and gluing on a louver like I did on the test building. Still pondering the inlet, David.

Thanks for the input & ideas guys, and thanks all for viewing.

Cliff

#59

David Maynard said:

I wasn’t talking so much about air pressure build up, I was talking about heat build up. We have all gotten into a car on a hot day when the windows were left rolled all the way up, and we felt how much hotter it was inside the car then it was outside. You are building buildings with plastics. How much heat can they stand for how long before the plastic starts to get brittle? If letting cooler air in at the bottom, and hotter air out the top, extends the life of the building a few years, then isn’t it worth it?

Thanks for your persistence David, I’m appreciating better your argument. So if an inlet is needed, here’s what my thinking is for it. For each module, in at least 1 place:

  • A hole through the wall and also through a small doubler plate or disk behind it
  • Run a 1/2" npt tap thru the hole
  • Screw in this (from the inside):

https://www.mcmaster.com/#9833k11/=182jzx6

Over time the plating will break down, but who cares. The scintered bronze will keep bugs out and let air in (very gradually).

The hole should be high enough to not get rain-splashed mud into it, say 4 or 6". And / or it could be hidden with something, like a stood-off sign.

Thoughts?

#60

Yea, but I was thinking something that would look natural on the building, like an open window, or half opened door.