1/4 " underlayment ply radius

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1/4 " underlayment ply radius

Postby QueticoBill » Tue Jul 18, 2017 7:37 pm

So searching here failing me again, will I be able to bend ultraply or similar to 30" radius? 27"? 24"? APA says 1/4" bends to 24" dry but I'm skeptical. Outer veneer grain parallel with axis.

Thanks. I will buy a sheet and try it but wondered if there is a chance.
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Re: 1/4 " underlayment ply radius

Postby tony.latham » Tue Jul 18, 2017 9:46 pm

QueticoBill wrote:So searching here failing me again, will I be able to bend ultraply or similar to 30" radius? 27"? 24"? APA says 1/4" bends to 24" dry but I'm skeptical. Outer veneer grain parallel with axis.

Thanks. I will buy a sheet and try it but wondered if there is a chance.


I just stuck my head in the shop and tried bending a 36" x 30" piece. I don't think it's possible.

Two layers of 1/8" Baltic birch would be easy. Doing it and avoiding a void would be the challenge.


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Re: 1/4 " underlayment ply radius

Postby aggie79 » Wed Jul 19, 2017 7:40 am

I'm with Tony. Bending two sheets of 1/8" is a lot easier than then bending one sheet of 1/4" plywood.

If you want to try bending the 1/4", you may want to try doing so the way Jerry did for his Retro-Kamper build:
http://www.tnttt.com/viewtopic.php?p=612443#p612443

As you can see, Jerry starting the bends using ratchet straps:

Image

I believe he "crept up" on the radius he needed.

Here is a picture of his installed "pre-bent" plywood:

Image[/quote]

To me, the question is why do you need 1/4"? If you use spars, 1/8" is sufficiently strong.
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Re: 1/4 " underlayment ply radius

Postby tony.latham » Wed Jul 19, 2017 8:02 am

To me, the question is why do you need 1/4"? If you use spars, 1/8" is sufficiently strong.


I strongly agree, especially if it is backed by hard foam.

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Re: 1/4 " underlayment ply radius

Postby greygoos » Wed Jul 19, 2017 8:22 am

QueticoBill wrote:So searching here failing me again, will I be able to bend ultraply or similar to 30" radius? 27"? 24"? APA says 1/4" bends to 24" dry but I'm skeptical. Outer veneer grain parallel with axis.

Thanks. I will buy a sheet and try it but wondered if there is a chance.

Use material that bend easily. I am finishing up a project where I used FRP from Home depot to make the radius. Yes it is 2 times the cost of plywood and there is added weight but I was done in under an hour, no waterproofing, sanding, filling, etc. I then skinned in aluminum.
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Re: 1/4 " underlayment ply radius

Postby QueticoBill » Wed Jul 19, 2017 3:01 pm

Thank you all. I'll get the 1/4 inch for floor and walls and play with it. I plan sparless roof so will see if glue and 1/8 makes sense for the one section that is tight radius, and still use 1/4 for the rest. That would only be 2 extra pc. I wish there was some engineering data for 1/8 but non published I can find.
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Re: 1/4 " underlayment ply radius

Postby aggie79 » Wed Jul 19, 2017 8:15 pm

QueticoBill wrote:I wish there was some engineering data for 1/8 but non published I can find.


Search for "3mm Baltic or Russian Birch":

https://www.wolstenholme.com/pdf/Baltic%20Birch%20Plywood%20Specifications.pdf
https://forestplywood.com/infographics/guide-to-baltic-birch-plywood/
http://packardforestproducts.com/products/plywood/imported-plywood/russian-birch/

BTW, the lower section of my hatch has a 12" radius. It was no problem bending the 1/8" / 3mm Russian Birch plywood at that radius.

Image

The lower front corner of my teardrop has a 6" radius. I skinned that in 1/8" ply also, but that tight of a radius took some persuasion and colorful language. :?
Last edited by aggie79 on Thu Jul 20, 2017 9:08 am, edited 1 time in total.
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Re: 1/4 " underlayment ply radius

Postby QueticoBill » Thu Jul 20, 2017 7:04 am

Thank you. I did mean engineering values like allowable tension and compression values and modulus of elasticity, not the physical characteristics.

Nice work!
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