Darryl Keil Last Activity 2024-10-10 3:42 PM
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Jack Anderson

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Joined: 2003-08-16
Location: Sauk City, Wisconsin

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Subject : How long in the vacuum press?
Posted : 2008-03-18 8:06 PM
Post #34442
I was recently advised that one should never leave a veneered panel in the vacuum press overnight (or essentially approaching 6-8 hours or more). What guidance does this forum have on how long a panel should (and shouldn't) be left in the bag under vacuum? Thanks.


 
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Brian Gray

Posts: 339

Joined: 2004-01-21
Location: Sandusky, OH

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Subject : RE: How long in the vacuum press?
Posted : 2008-03-18 9:22 PM
Post #34443 - In reply to #34442
I can't think of any reason why it would hurt something to be in a bag for an extended period of time.

I'm not intending to be blunt, but the person who advised you to never keep something in the bag for longer than 6-8 hours is simply wrong.

Unibond should cure overnight, epoxy should cure from 4 hours to 12 hours, depending on your brand, activator, etc. Take a look at the recommended curing time for your adhesive, and feel free to add a couple of hours, just in case. Especially if the adhesive is effected by heat (most are).

I honestly can't think of a single reason or instance where your wouldn't want a piece to be in the bag for an extended period.


 
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Darryl Keil

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Joined: 2003-05-22
Location: Maine

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Subject : RE: How long in the vacuum press?
Posted : 2008-03-18 9:57 PM
Post #34444 - In reply to #34442
Jack,

I have never found that to be true at all. In fact I have repeatedly experience that panels stay flatter if I leave them in overnight. You can obviously take them out sooner but there is no problem with leaving them in longer.

With yellow glue, I would say a minimum of 1 hour press time, with 2 hours ideal. With catalytic glues such as epoxy, urea resin and polyurethane the press times are variable depending on mixing ratios, temperature and moisture so its impossible to give specific times. If you're not in a hurry leaving a panel in the press overnight is the safest bet.

By the way, what was the reason for not leaving a panel in overnight?

Darryl


 
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Jack Anderson

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Joined: 2003-08-16
Location: Sauk City, Wisconsin

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Subject : RE: How long in the vacuum press?
Posted : 2008-03-19 7:29 AM
Post #34445 - In reply to #34444
First, thanks for your responses, guys. I appreciate the opportunity to tap into so much experience.

Darryl, no reason was given, the only thing offered was that it's "generally a bad idea to press a veneer longer than 2 hours (for standard veneer glue)." That was contrary to what I had learned (and practiced on a limited basis).

Thanks again,
Jack


 
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Dave Shaw

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Joined: 2005-11-06
Location: Arizona

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Subject : RE: How long in the vacuum press?
Posted : 2008-03-19 5:15 PM
Post #34446 - In reply to #34442
I did leave a panel overnight and a good part of the next day one time. It was very warm in my shop 90+ for most of that time. I believe I used a water based glue (not smart). The upshot of that was little black mold spots all over the ropey cherry veneer. The panel was usable but I learned not to do that again. Other than that one experience I've not had any problems leaving the panels in the press overnight.

Dave


 
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Barry Daniels

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Joined: 2008-12-15
Location: Houston, TX

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Subject : RE: How long in the vacuum press?
Posted : 2008-12-23 1:36 PM
Post #35145 - In reply to #34446
Mold can't grow that quickly. It was probably staining due to tannin.


 
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Don Stephan

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

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Subject : RE: How long in the vacuum press?
Posted : 2008-12-23 2:43 PM
Post #35146 - In reply to #35145
I'll second the feeling that the black spots were probably tannin reactions. Last week I pressed some inlaid cherry gift trays, with the outer field quarter sawn cherry. In a couple corners there were a few black spots under the veneer tape. In the future I'm going to try to remember to use only distilled water for my veneer tape dispenser, and to moisten the tape after pressing. If memory serves, oak, walnut and cherry are most susceptible to this tannin staining - iron particles in the water react with tannin in the wood producing the black stains. The same principle is an old-time method of staining sometimes called "iron bugg" and described in detail in Jeff Jewitt's "Taunton's Complete Illustrated Guide to Finishing."


 
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Brent Longtin

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

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Subject : RE: How long in the vacuum press?
Posted : 2008-12-31 9:15 AM
Post #35158 - In reply to #34442
I used to press for up to four hours, sometimes more, using Titebond veneer glue. Then I read somewhere that long press times could lead to mold discoloring the veneer, or deprive the glue of oxygen coming through the veneer that it needs to cure properly. So I now press for about two hours. No problems.


 
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jerry

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Joined: 2007-02-22

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Subject : RE: How long in the vacuum press?
Posted : 2008-12-31 10:29 AM
Post #35159 - In reply to #35158
using unibond i run the press for 2- 2.5 hours and then remove the piece - have had no problems. i do wrap the work with an electric blanket set to high while pressing.

jerry


 
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cpa

Posts: 4

Joined: 2009-01-15
Location: Bay Area, CA

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Subject : RE: How long in the vacuum press?
Posted : 2009-01-15 2:57 PM
Post #35206 - In reply to #34442
How long in the press depends upon the glue you are using. The glue I use says to press for 45-60 minutes and then pull it out to cure. I've heard that leaving it in the press for too long can interfere with proper curing.

Besides, I don't want my press pumping up and down all night long so I love the short clamp time.

So far so good.
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