Darryl Keil Last Activity 2025-09-09 11:09 AM
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Brent Longtin

Posts: 37

Joined: 2007-10-09
Location: Natick, MA

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Subject : Curved veneering
Posted : 2009-10-03 3:15 PM
Post #35720
I'm about to veneer a hemispherical table apron 3.5" wide and 31" in diameter. It's the Chippendale table from the Marquetry Course book by Metcalf & Apps. The book says drape a layer of breather fabric across the veneer to aid evacuation. Would something like and old towel work? Or should it be thinner?


 
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ckurak

Posts: 107

Joined: 2006-10-28
Location: Florida

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Subject : RE: Curved veneering
Posted : 2009-10-03 4:07 PM
Post #35721 - In reply to #35720
Brent,

I don't have the book you mentioned, but I am guessing that they mean something like "EvacuNet" which VacuPress conveniently sells.

http://vacupress.com/accessories.htm


 
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Don Stephan

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

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Subject : RE: Curved veneering
Posted : 2009-10-04 6:28 PM
Post #35722 - In reply to #35720
I agree with the suggestion to use Evacunet. Keep in mind you don't want the net directly on the veneer. I'd suggest a dry run when you get all together as it can be a challenge to get everything together, keep in lined up, and get the vacuum. Certainly not impossible, just several steps while the glue is curing (and perhaps dripping/squeezing out onto various surfaces).


 
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Brent Longtin

Posts: 37

Joined: 2007-10-09
Location: Natick, MA

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Subject : RE: Curved veneering
Posted : 2009-10-04 7:10 PM
Post #35723 - In reply to #35722
Good points. I ordered up some evacunet. Maybe there's an issue of the evacunet covering telegraphing its pattern onto the presing. Just gotta try this I guess.


 
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ckurak

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Location: Florida

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Subject : RE: Curved veneering
Posted : 2009-10-05 6:04 AM
Post #35724 - In reply to #35723
Brent,

You are correct.

If you place the evacunet directly next to the veneer (you do NOT want to do this) its pattern can telegraph onto the veneer. The evacunet does not have a smooth surface like a caul does. But the evacunet is great for evacuating the air between the glue-up and the bag, and it can also protect the bag from sharp corners on the caul.


 
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Don Stephan

Posts: 825

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

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Subject : RE: Curved veneering
Posted : 2009-10-05 6:24 PM
Post #35725 - In reply to #35723
Brent:
The only purpose of the Evacunet is to create a channel for air inside the bag to reach the vacuum port and hose.
With a typical flat pressing, the grooves in the platen serve this purpose.
If one is pressing a very shallow curved form, such as a 24" long drawer front that is 1" thick at the ends and 2" thick in the center, this could be placed in the middle of even a 4' x 4' grooved platen and there should be enough excess bag around the edges for a good vacuum over the entire drawer front. (I'm guessing a 4' x 4' bag is actually about 50" x 50", leaving a bit of surplus around the platen.)
But let's pretend you're wanting to press veneer onto a half cylinder, 12" diameter and 32" long, well braced internally. Slide this onto a 4' x 4' platen in a 4' x 4' bag, or even onto a 4' x 8' platen in a 4' x 8' bag, and there isn't enough "bag" to conform to the entire curved surface. Place say a 24" x 34" grooved platen into the middle of a 4' x 4' bag, put the cylinder in the middle of the platen, and there is enough "bag" to conform to the entire curved surface without stressing the edges of the bag. But now there is not a pathway for air in the bag to reach the vacuum port. Around the smaller platen the top and bottom surfaces of the bag will press together and air around the cylinder will not be able to reach the vacuum port. place even a 6" wide piece of Evacunet in the bag that reaches from the back edge of the vacuum port a couple inches under the platen, and an air pathway is established.
When using a smaller platen and a curved surface, when a vacuum is formed the bag forms large wrinkles. These wrinkles will want to run all the way to the edges of the bag. Please be aware, if you are using a vinyl bag, that each wrinkle, even if small, has the potential to tear asunder the vinyl at the sealed edges. By turning off the vacuum every so often, sneak up on the final vacuum and work the wrinkles out so that they don't reach the sealed edges. If using a poly bag, this may not be an issue.
Hope I explained this okay, it's what I learned from Yoda Darryl.
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