CNC Build: The Bed and Breakfast at 4 years and 40,000 miles

[capnTelescope]

Did the 3/4 inch not want to bend?

It wasn't enthusiastic about bending. As you might have guessed from the photos, I "kerfed" freehand with a utility knife. Score, break, repeat. Quick and easy. I didn't want to use the table saw because of the mess. Also, I didn't think kerfing technique was going to be real critical. (See my remarks on the need for insulation.) I was far more interested in the ply making a good bend than the foam, and I didn't want the ply to have to fight the bend and the foam. Note that I cut the kerfs on the outside of the curve, as opposed to hard-core Foamies who cut many kerfs on the inside to get an impressively smooth curve. If it won't show, Git 'er done!

I am hoping that I can keep the kerfing to a minimum.

With 2 layers, you should be able to get away with the utility knife kerf with minimal loss of insulating effectiveness. I was making 2-3 cuts per panel, and it is easier to do the break on a wider section.

This one time management seminar I went to (They were *always* sending me to time management seminars, it seemed ) made the point that "if it's worth doing, it's worth doing poorly." Ponder that. He had a good point. The parts that show--Important to do well. The parts that don't show--not so much.

Professor Telescope has left the building.

[capnTelescope]

One of the many things rattling around my brain is that one of my Dear Readers asked in their build thread whether pre-coating with poly on a piece of ply that will be bent will affect the bending. I have an answer.

Those of you who have been following my build might remember this picture of me "training" a sheet of ply to skin my hatch with:


Some time after I took this picture, I did a pre-coat of wipe-on poly on the inside side of that sheet. Time passed, the sheet got set aside and forgotten until yesterday, when I got started on skinning my hatch. The ply definitely bends much better the "other" way now. IIRC, I let the sheet be flat while the poly cured.

I'm not sure what the lesson here is. Either the trick is to poly the other side from the bend. or let the poly cure while the ply is bent. Or both.

I'm checking the usual suspects' threads for the original question. {EDIT} You can find the original thread here.

Hope this helps.

[KCStudly]

Hey capnT, I wonder if there is any chance at all that you might have coated the outside of your trained ply by accident. That would simplify the analysis paralysis.

In reality it makes sense that the poly makes it harder to bend. It acts just like a glue binding the fibers of the wood together and making them stiffer. It's just that I would expect it to work the other way. The outer fibers need to stretch and the inner fibers need to compress. If the poly side doesn't want to stretch or compress as easy at raw wood, wouldn't you think that the raw side would be more agreeable to stretch extra, rather than compress extra in compensation for the poly'd side?

Mud?

[noseoil]

Yep, functionally it's added another lamination to the ply. The raw side will swell up around moisture and expand when humidity increases. It will contract if it dries out, works just like a tree. Plywood is great stuff!

[capnTelescope]

Mud.

I wonder if there is any chance at all that you might have coated the outside of your trained ply by accident. That would simplify the analysis paralysis.

Accidents do happen. I'm "pretty sure" I got this one right.

My observation is that ply will bend toward one side easier than the other, given the same grain orientation. Which makes sense, since it is a natural product. And... I did choose that side for appearance reasons. An unscientifically small sample of 1 or 2 sheets seemed to indicate the ply bends away from the "good" side.

... wouldn't you think that the raw side would be more agreeable to stretch extra, rather than compress extra in compensation for the poly'd side?

Yes, that makes more sense than anything else here. We know that wood is weaker in tension than compression. If we pull normal to the grain, wood will split,, but wood will support large static loads in compression. It also makes sense to me that a poly infiltration of the fibers would improve the tension properties.

Now that I've read what I just wrote, I'm going to say "No" to that question. The poly'd layer is stronger in both tension and compression, but the poly'd layer is still weaker in tension, and the raw side is... still raw.

Yep, functionally it's added another lamination to the ply.

That's close. In the present case, it's only infiltrated the fibers, strengthening the poly'd layer. But there's not a thick enough application to qualify as a new layer. A distinction without a difference.

Plywood is great stuff!

I'll go with that statement without qualification.

Mud?

P.S. I never said "Welcome to the thread, Noseoil."

Welcome to the thread, Noseoil.

[KCStudly]

Quite clear.

[capnTelescope]

I'm so happy I could just... The aluminum sheet for this project is jinxed. Totally, completely jinxed. First the 4 x 10 sheets came in as 4 x 8 and no PVC coat. No bueno, Return To Vendor. The 4 x 5 half sheets came in without the PVC coating I ordered, got rained on and managed to corrode beyond repair before I could get my lazy butt going to get them dried off and inside. Then the new 4 x 10s came in correctly. I reordered the 4 x 5s, they called and said they were in, and the guy starts putting it in my truck. No PVC and they look small. They are 40" x 60", s/b 48 x 60. Typo on the sales order. That one's on them. My sales guy comes out to investigate, and Oh! Two 4 x 10 PVC coated sheets are in the rack over there with my name on it. They just need to be sheared to size. Done! They gave me the two 8 x 60" drops from the first mistake.

So comes time to rough cut the right side. Everything's cool until I take the right side out (in?) to the Assembly Department and lay the side up against the right wall and...
(Q) What's wrong with this picture?

(A) The opening for the door is about a foot too far back.

I have a 2-3 theories as to how this happened. There seems to be only one responsible party.

So on Monday, I get to order another 4 x 10 sheet.

[KCStudly]

Ouch.

I hate to say it, but I'm not sure that the CNC machine is your friend. As with any power tool, it is very easy to make a big mistake very quickly.

I sympathize with you, though. I dry fit and screwed my ceiling panel assembly today, and started to train the front curve. All I could think about was, "if you do this too fast and it cracks badly, the recovery is going to be expensive and take a long time".

Look at it this way, you'll have plenty of extra aluminum to cover your tongue box, should you choose to build one.

[tonyj]

Murphy's Constant: Matter will be damaged In direct proportion to its value.

My suggestion to keep that fancy machine from deciding where you want your door is to take the newly cut profile w/o door cutout and hang on the side of the trailer. Use the opening in the side as your cutting template with a handheld router and pattern following bit.

Another Murphy: Smile--tomorrow will be worse.

[capnTelescope]

I'm not sure that the CNC machine is your friend.

... or I'm my own worst enemy. Or both.

Look at it this way, you'll have plenty of extra aluminum to cover your tongue box...

I've had that thought. Maybe enough to armor plate it.

Murphy's Constant: Matter will be damaged In direct proportion to its value.

Murphy's law abounds on this build.

The CNC simplifies the complicated and complicates the simple. Words of wisdom!

Thanks for the sympathy, guys.

[tony.latham]

Double OUCH. I probably woulda stacked two sheets and cut both sides out at the same time...

At least I can stop drooling over your CNC table for three or four days.

Tony

[capnTelescope]

Thanks to the polar vortex, the weather cooled off a bit here. Instead of temperature in the high 90's with 70% humidity, that turned around with temp in the 70's and humidity in the high 90's. It was so humid, water was dripping out of the sky. I'm not talking rain shower here, I think the air was sweating. I certainly was. It actually rained later in the evening, like 3" total.

While I'm waiting for my replacement sheet of Al, I started work on the tongue box. Because the TB will mostly house the propane cylinder and air conditioner unit, I felt a need for "adequate ventilation." I picked up some expanded metal for the TB floor my last time at Metals4U(Me). Framed it in 1" angle iron and set it on the tongue to do some layout.


I marked where I wanted to cut a hole in the front and went to work with skill- and jig-saw.

These were some tense moments, given my uncanny ability to mess things up.

Everything came out just fine. The A/C unit fits in nicely. I love it when things look like the drawing when they're done.

Sweet!

I fired up the a/c unit, expecting to hear buzzes and rattles from the expanded metal, but everything was nice and quiet. Inside the cabin, all I could hear was fan noise. As an extra added bonus, it appears that the a/c responds to the remote if you point it at the left grille. We'll see for sure after I get the front shelf in.

To separate the cold air from the return air, I will duct the cold air to a couple of vents that go on top of the front compartment. So, off to the table saw and CNC to start on the shelf. Measure, saw, spiral rout a 4" hole, and soon you have this:

I'll use 4" dryer vent hose to hook these up. Stain & poly first.

Here's a preview peek at the front compartment with vent laid in place:

A storage compartment will fit between the two vents.

[GuyllFyre]

Very cool.

[rebapuck]

Nice work.

[capnTelescope]

Very cool.

Thank you.

If you think that was "cool," take a look at this!

A/C under test:

Drop cloths for "doors," A/C system plumbing assembled, and loosely hooked up.

The ac unit blows into a piece of 4" PVC pipe with a "window" cut out to fit over the exhaust grille, which feeds cold air to the left & right ducts.

This will be more firmly affixed at final assembly. I still need to get the tongue box bottom welded to the frame and the ac unit firmly attached.

Right duct run:


Left:


Left end of headboard:

Return grille, cold air grille on top.

Ditto, right side:

Return air grille removed for access.

Admittedly, the setup as shown is leaky, not final and doesn't guarantee future results, but it cooled off the cabin nicely!

Thanks for stopping by.