Darryl Keil Last Activity 2025-09-09 11:09 AM
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Don Stephan

Posts: 825

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

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Subject : Veneering a hollow sculpture stand
Posted : 2013-11-17 6:40 PM
Post #37045
wondering if anyone else has vacuum veneered a hollow box. I've done it several times but for some reason the last one had lots of dry corners.

The stand is 18" x 18" x 23" high, 3/4" MDF with all the joints mitered, the four side joints are splined as well.

The stand went together well, everything was extremely straight and square. Scuff sanded everything with 150 grit 4x24 belt on tight fitting MDF, as always.

I veneered one surface at a tim. Couldn't remember if previous times I vacuumed the uppermost or down surface, didn't think it would make any difference, decided to vacuum veneer the down surface.

48" x 30" grooved platen in middle of 4x8 bag. Rolled the usual layer of plastic resin glue on the uppermost surface of the stand, packing taped the veneer in place against the glue. Carefully turned the stand over so the glue and veneer were on a 1/4" x 48" x 30" melamine caul. Tried to lay the stand down evenly rather than on one edge or corner. Slid the stand and caul onto the platen. Vacupress airform bladder in the stand, evacunet from the platen to the vacuum connection.

Realized a good vacuum each of the five pressings, but almost every one had one or two "dry" corners where the veneer wasn't glued down. The glue was evenly rolled over the entire surface, and each time I rolled to the edges and corners so there was a bit extra glue there.

the last day I vacuum glued the top. simiar process only I packing taped a 1/4" mdf caul over the wet glue and veneer (so the surface was vertical) and vacuum veneered. Still had a dry corner or two.

I'm going to have to start over from scratch, strongly considering leaving the wet surface up this time with 1/4" melamine caul over with just 1/8" overlap all around. Also going to use new plastic resin glue.

Has anyone else vacuum veneered a hollow box like this? If so, how did you position the surface with wet glue and veneer - if horizontal, up or down; or vertical? Thanks.


 
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Tom Eaves

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Joined: 2005-05-28
Location: plainfield, il

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Subject : RE: Veneering a hollow sculpture stand
Posted : 2013-11-18 8:09 AM
Post #37046 - In reply to #37045
Don,
Maybe you have too much pressure in the bladder causing the part to bow? If it is only dry corners I would repair instead of replacing. Tom



 
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Darryl Keil

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Joined: 2003-05-22
Location: Maine

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Subject : RE: Veneering a hollow sculpture stand
Posted : 2013-11-18 4:52 PM
Post #37047 - In reply to #37045
Why would you need to start over from scratch if you just had some corners that were unglued? Can't you just repair the corners.

Is the glued surface facedown against the platen or facing upwards?


 
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Don Stephan

Posts: 825

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

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Subject : More
Posted : 2013-11-18 7:45 PM
Post #37048 - In reply to #37047
keep finding unglued corners, Saturday noticed a chip along one bottom edge where the veneer hadn't been tightly glued, so am expecting poor glue bond numerous other presently undiscovered places. And I nearly sanded through another previously undiscovered unglued corner.

The sculpture stand was placed wet glue side down on a caul and the grooved platen. So if there was a slight hollow to the sides the edges may have been glue starved due to the orientation? that's why I'm considering keeping the wet glue side up next time, thinking that a 1/4" melamine caul could easily conform to any slight hollowing or crowning.

The air bladder was inflated until the bladder was about even with the open bottom of the stand, and the fill line remained on a bag nipple to allow the air bladder to match atmospheric air pressure.


 
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Tom Eaves

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Joined: 2005-05-28
Location: plainfield, il

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Subject : RE: More
Posted : 2013-11-20 8:35 AM
Post #37049 - In reply to #37048
Don,
Sound more like a glue issue than a pressing one was the glue that you use old that why you mention you were going to get new glue? Also why not cut your parts out with the 45s then dry fit disassemble and then do one pressing. This would save time and the life of your bag. Tom



 
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Don Stephan

Posts: 825

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

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Subject : RE: More
Posted : 2013-11-20 6:33 PM
Post #37050 - In reply to #37049
the best way I have found to clamp the mitered corners is with Collins clamps, and they leave dimples everywhere that could not be repaired on a veneered surface. I can run Collins clamps up all 4 sides and around the top as I glue and adjust the pressure as needed to get very accurate miters. I would not want to try band clamps and packing tape wouldn't apply enough clamping pressure to pull the miters close. that's why I veneer the assembled stand.


 
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Darryl Keil

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Location: Maine

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Subject : RE: More
Posted : 2013-11-20 8:06 PM
Post #37051 - In reply to #37048
I would definitely veneer face up with a thinner caul, 1/4" sounds good.

I also would be more inclined to veneer the parts beforehand, miter them and simply use the vacuum to glue the column together. I have had great results gluing up columns this way. I do it with no platen in the bag so the pressure is even on all sides. Pulls everything together nice and square. Of course you will still have to veneer the top in the bag but thats only one surface instead of five.

If you do try it this way, one tip. Do not put the inflatable bladder inside the column for the initial glue up as it may interfere with drawing the miters tight. Just run the vacuum much lower so as not to deflect the column. You dont need any where near as much pressure to glue the miter joints as you do for veneering.


 
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Don Stephan

Posts: 825

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

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Subject : RE: Veneering a hollow sculpture stand
Posted : 2013-11-30 10:11 PM
Post #37056 - In reply to #37045
Yesterday I belt sanded off the veneered sides and top of the sculpture stand - I'll spray paint it as an apology for the delayed veneered stand. I found a number of little "craters" throughout where the veneer was not stuck to the MDF substrate. And the glue seemed much thicker in the middle of the MDF pieces than at the edges. A straightedge on two newly assembled stands found that all five MDF pieces on each stand was slightly lower in the middle, Placing the 1/4" MDF caul on the 3/4" grooved platen made an inflexible surface on which the glue and veneer was placed. With the middle of the stand's surface slightly hollowed, the rigid caul pressed the glue extremely thin around the edges and left it thick in the middle. Next time I will leave the freshly glued surface and veneer up, and the 1/4" melamine caul will have some flex, which should make for a more uniformly thick glue layer. Or so I hope.
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