Darryl Keil Last Activity 2025-09-09 11:09 AM
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Pat McFadden

Posts: 3

Joined: 2009-09-14

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Subject : Veneering a Half Cylinder
Posted : 2009-09-14 1:07 PM
Post #35708
I need to veneer a 28"H x 32"W (16" radius) half cylinder. I'm using 10 mil paperbacked walnut burl veneer over a prefab form from Geometric Forms. It's 3/4" poplar ply with MDF face, with half circle 3/4 plywood ribs spaced @ 6" (5 ribs total) and a 3/4" flat plywood back.

2 Questions:

1) If I put this in my 4x8 30mil poly bag, will it stretch the bag to the point that it will be permanently distorted?

2) I neglected to brace the ribs before I assembled the form. Do I need to worry about the form blowing out?

Thanks,
Pat


 
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Earl

Posts: 75

Joined: 2003-12-04
Location: Pensacola FL

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Subject : RE: Veneering a Half Cylinder
Posted : 2009-09-14 1:42 PM
Post #35709 - In reply to #35708
Pat,

First make sure your bag has plenty of slack to go around the form. If you don't, you can use a smaller grooved platen. Second, I'm not fully understanding your form makeup. I make my forms with a 3/8" bending luan face with 3/4" ribs at 2 1/2-3" spacing. If you have enough face thickness, 3/4", 6" spacing may be fine. You might want to put just the form in the press and check it before gluing up the panel. Look for any drooping or distortion between the ribs.

Edit: If you're using a manufactured curved panel you don't need a form to glueup on. The bag itself, no platen, will conform to the curved piece. And if you're using a form the ends must be braced they can and will collapse if not supported.

Earl


 
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Pat McFadden

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Joined: 2009-09-14

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Subject : RE: Veneering a Half Cylinder
Posted : 2009-09-14 2:09 PM
Post #35710 - In reply to #35709
Thanks, Earl.
The "form" in this case is part of the finished piece. It's a half cylinder with a flat back. I plan to do a test, but my guess is that if it's going to fail, it will happen all at once, with little or no warning.
The form is already built with no bracing. The ribs are glued and screwed to the curved half cylinder and the flat back.

Unless the platen is very close to the same size as the piece, the bag would seem to be "tented" away from the ends. Would this not prevent the ends from collapsing? I plan to drill vent holes thru all 5 ribs to provide airflow.


 
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Earl

Posts: 75

Joined: 2003-12-04
Location: Pensacola FL

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Subject : RE: Veneering a Half Cylinder
Posted : 2009-09-14 4:07 PM
Post #35711 - In reply to #35710
If, your ends are secure around the perimeter, glue & nails/screws, they should be OK. I don't like having gaps between the form and my bag. Though, small ones at the bottom of the form where it meets the platen don't give me any problems. Your bag will stretch some, but doesn't affect performance. Mine (poly bag) is quite old and very distorted.

Earl


 
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Don Stephan

Posts: 825

Joined: 2003-07-18
Location: Cincinnati, Ohio

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Subject : RE: Veneering a Half Cylinder
Posted : 2009-09-20 6:36 PM
Post #35712 - In reply to #35711
Pat: You can "lift" the form by placing an additional piece of 3/4" plywood, the same size as the back, against the back. This allows the bag to conform completely to the veneered surface.
You might contact the manufacturer of the form and ask them about vacuum veneering of the form. It is likely they will have some experience and thoughts to share on their product.


 
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Pat McFadden

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Joined: 2009-09-14

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Subject : RE: Veneering a Half Cylinder
Posted : 2009-09-20 7:11 PM
Post #35713 - In reply to #35712
Thanks, Don.
That's essentially what I did, except I doubled it up. It was a success. For the curved face, I used 1/8" masonite for a caul. I used ratchet straps to tighten down the caul, then secured it with clear packing tape, removed the ratchet straps and shoved it into the bag. Came out perfect. No wrinkles, bubbles or lifted egdes.

Thanks to everyone for the advice, including Darryl, who I spoke with on the phone.

Cheers,
Pat
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