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post #1 of 13 Old 10-31-2018, 09:11 PM Thread Starter
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Lightweight cabinets

Hi, thid is my first post. Im hoping to get some input regarding an idea i had to lighten plywood cabinet frames for a mobile rv build im doing. I was going to use 3/4 inch plywood for the sides of the cabinet boxes but I was thinking of cutting a lattice into the plywood to maybe lighten it by 25 percent or so. I would cut maybe 6 square holes in the sides of each cabinet which would leave a support lattice or web. Will this significantly weaken then cabinet? It seems like it wouldnt...just curious what others think?
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post #2 of 13 Old 10-31-2018, 09:25 PM
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I wouldn't do that

Just use 1/2" or even 3/8" thick especially if they are attached side by side. A double thickness of 3/8" plywood is incredibly strong. You just need to make the corner attachment of the panels reinforced with either wood corner blocks or 1/8" aluminum angles. Finger joints would be ideal, but a lot of extra work.

On an overhead cabinet, the weight of the interior contents is pulling down and out away from the back wall. The attachment can be reinforced across the top with an extra layer of plywood to prevent pullout. Large fender washers can be used to distribute the load over a larger area than just a screw head.

If you were to make a mock up of your cabinet from 1/2" foam core or Celotex, you'd get an idea of where the weak points are. Hot glue and some tape will hold the seams together until the glue cools. We always made mock up in Industrial Design class for our new projects and we learned a lot from them. Creasing and folding makes strong corners as opposed to cutting and gluing.

Get creative with the joining methods and you'll be surprised how strong you can make something from thin material.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 10-31-2018 at 09:32 PM.
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post #3 of 13 Old 10-31-2018, 09:30 PM
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Quote:
Originally Posted by Smoojee View Post
Hi, thid is my first post. Im hoping to get some input regarding an idea i had to lighten plywood cabinet frames for a mobile rv build im doing. I was going to use 3/4 inch plywood for the sides of the cabinet boxes but I was thinking of cutting a lattice into the plywood to maybe lighten it by 25 percent or so. I would cut maybe 6 square holes in the sides of each cabinet which would leave a support lattice or web. Will this significantly weaken then cabinet? It seems like it wouldnt...just curious what others think?
I've seen cabinets built like a hollow core door. The shelves and sides were made with 1/8" door skin with a 1/2"x1/2" pine frame between. Look like a lot of work but were very light.
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post #4 of 13 Old 11-01-2018, 07:51 AM
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Pop in to your local caravan dealer and look at some vans. Carry a tape measure.
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post #5 of 13 Old 11-01-2018, 04:09 PM Thread Starter
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Thanks for responses. I just sketched a rough idea of what i was thinking in case my description wasnt clear. I would be removing approximately 1/4 or maybe 1/5 of panel wood but I dont see why this would significantly weaken cabinets because a rather strong internal frame woukd still exist...kind of like a steel skeleton within a skyscraper....or maybe there is another way to build light but strong cabinets?
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post #6 of 13 Old 11-01-2018, 09:03 PM
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Just finished building out some cabinets with my youngest son for his van project. It's a 2016 Ram ProMaster, he and his wife, and 3 dogs are going to live in it. Certainly way out of what I would consider, but it is thier jouney.

We used 1/2" Plywood for all of it, worked great. No way we would have used 3/4".

Last edited by shoot summ; 11-01-2018 at 09:06 PM.
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post #7 of 13 Old 11-01-2018, 11:23 PM
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Great way for the critters to get your food

Quote:
Originally Posted by Smoojee View Post
Thanks for responses. I just sketched a rough idea of what i was thinking in case my description wasnt clear. I would be removing approximately 1/4 or maybe 1/5 of panel wood but I dont see why this would significantly weaken cabinets because a rather strong internal frame woukd still exist...kind of like a steel skeleton within a skyscraper....or maybe there is another way to build light but strong cabinets?
You were given several suggestions:
Use thinner material than 3/4", like 1/2" or even 3/8"
Use a hollow core process with thin skins.
Use a thin material and fold the corners by scoring.
Use a light weight material with thin skins, like Celotex.
Screwing the sides together creates the equivalent of a thicker material

Why pay for more expensive material, then go to a lot of trouble to remove 1/2 of it leaving a way for mice or other vermin to get at your food? That don't make much sense to me.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #8 of 13 Old 11-02-2018, 06:27 AM
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Copy the aircraft manufacturers. Go to a suitable scrap yard and get some lightweight panels.
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post #9 of 13 Old 11-02-2018, 09:39 AM
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If you are set on 3/4" and want low weight consider making your own panels out of 2 sheets of 1/4" with 1/4" strips along the edges, and spaced at some interval across the panel.

A lot of work, or you could mill 3/4" sheets down as you suggest, still a lot of work, or you could use 1/2" and be done with it, easy peasy...
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post #10 of 13 Old 11-02-2018, 10:15 AM
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Quote:
Originally Posted by Steve Neul View Post
I've seen cabinets built like a hollow core door. The shelves and sides were made with 1/8" door skin with a 1/2"x1/2" pine frame between. Look like a lot of work but were very light.
My travel trailer has cabinets with doors built like Steve mentioned - sorta like torsion box style. Trailer has been well cared for but is about 24 years old and the cabinets show issues.
Brian

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post #11 of 13 Old 11-02-2018, 04:13 PM
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From a table online, no indication what the ply is, but an example.

1/4" sheet weight - 22lbs
1/2" sheet weight - 40.6lbs
3/4" sheet weight - 60.8lbs

To achieve the same weight as 1/2" with 3/4" you are going to have to remove 1/3rd of the sheet in some fashion. So out of 32 sq ft for a sheet you will have to remove 10.6 sq ft, that's a bunch, envision a 2'x5' hole in the middle of a 4'x8' sheet.
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post #12 of 13 Old 12-12-2018, 12:22 AM
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I use 1/2" insulating sheathing glued between two sheets of 1/8" hardboard.
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post #13 of 13 Old 12-12-2018, 04:28 PM
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From my experience most beginners tend to over-build when working on RV's, every pound you add in weight increases your stopping distance and your fuel consumption.

Take a look at how the pros do it, design it so each part helps support the next so that a minimium of material is used, they are being smart, not cheap. Any two parts perpendicular to each other become rigid, 1x2 frames with a 1/8" skin panels are as solid as 3/4" ply.

Do a bit of research, lots of information out there and all kinds of people willing to help guide you along that have been many miles down the road.

Wise men speak because they have something to say; fools because they have to say something -Plato

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