I vacuumed 2 cherry tops the other day and both came out with wrinkling in the veneer. I am wondering what possible reasons would cause this. It was raw veneer glued with cold press glue and clamped in a flat bed vacuum press. There was plenty of pressure and I didn't have problems with other veneer layups, only this cherry. Suggestions?

I would guess too much glue.

Did you have a platen on top of the veneer that is rigid enough so it lays completely flat as the bag squeezes down on it? If there were too much glue, this would help to push it out the sides. Another thing, if the veneer itself is not flat and you are not using a platen, the bag itself will not necessarily push all the unevenness out.

To add to what Howard said, Wrinkling is caused by insufficient top pressure. Any give in your top platen will allow the veneer to wrinkle up. Any uneveness in the thickness of the veneer will allow the low spots to wrinkle. For my silly little layups I use sheet cork to take care of this problem. For a 4 by 8 sheet i'll bet there is a rubber membrane used in industry.

Because I'm using a flat press I am using the bottom platen to press down against the table. This works fine and never have had this problem before...only this cherry. I was doing a border veneer around the perimeter and the ends had the grain running perpendicular to the field. I am suspecting that may have not let it expand so I'm relaying up the top without the border and will let you know if that is the culprit. Here is a picture of the small top. The larger one was the worst.

View higher quality, full size image (640 X 480)

Because I'm using a flat press I am using the bottom platen to press down against the table. This works fine and never have had this problem before...only this cherry. I was doing a border veneer around the perimeter and the ends had the grain running perpendicular to the field. I am suspecting that may have not let it expand so I'm relaying up the top without the border and will let you know if that is the culprit. Here is a picture of the small top. The larger one was the worst.

View higher quality, full size image (640 X 480)

It is unclear from your pick where the wrinkling is. I press stuff with the veneer going in all sorts of directions and have never had a problem. Is the wrinkling in the vicinity of the black and white border? If so then these veneers are thicker leaving the cherry room to wrinkle. It doesn't take much. I guess it could be too much glue like Max says but it would have to be way too much. When I use to much glue it just bleeds thru.

Ironically the wrinkling happened inside of the border on both sides. It went in about 4' and length of about 10". Because I had laid it up with the border all as one I thought maybe the veneer going across the end might have kept the piece from expanding under the pressure. There was no bleed thru and I didn't spread the glue any more than normal. Anyway I started over again with a new sheet and didn't do the border, which i will do in a second step and this time no problem.

What's the substrate? Was it dry? Is that frame around the outside solid wood, or veneer? What thickness of veneer? Was the glue fresh?

Thanks to all who responded. I think I've located the problem. I used a solid wood edge which I rabbeted into a particleboard panel. The top, including the stringing was all done in veneer which overlaid the hardwood edge. Only a 1/4" of hardwood came to the top due to the rabbet. I think what happened was the stringing was a few thousandths thicker than the surrounding veneer and thus the pressure from the vacuum was not getting through to the field. This I determined because I had a lot of loose spots on the outside edge as well. I'm making a new top now and have already laid the field which came out fine...no wrinkles. I'm going to do the edge the same as before but in a separate pressing. Also I'm going to put felt between the platen and the veneer for the differentiation between the stringing and the veneer. I made the stringing by making a hardwood sandwich and then cutting thin strips from it. I used a micrometer on the veneer and the stringing and the stringing was about .003" thicker than the veneer. Just barely enough to feel, but apparently enough to cause problems when pressed all at once. I'm working on it today and will let you know how it turns out. No such thing as failure...only experiments to identify what doesn't work!!!

Dan,
Why don't you just plane the banding down to the same thickness as the veneer?

I did try to plane the border down to the same thickness but it blew apart in the planer when I tried. I even tried to run it through the wide belt sander but the sander would not adjust that close. What I did was set up a fence setup on the tablesaw which got me down to .003-.004 of the thickness of the veneer. I laid it up and then used a card scraper to level the stringing down to the veneer level. Not really too hard. I still think the problem was that the stringing being slightly proud of the veneer surface did not allow the pressure of the vacuum to be enough on either side of the stringing. Anyway I'm working on it now and will let you know how it goes.

I use a Veritas inlay scraper to plane down banding,but a block plane will work. Tape 2 strips of the veneer you are using parallel to each other,then the border piece in the middle,the outer pcs.of veneer will act as your depth stop to give you the same thickness. I think it will be worth the few minutes it will take to shave it down.

Ok, I laid up the veneer field in one pressing. No problem with wrinkling. I did the border in a second pressing and used felt between the platen and veneer to help with the thickness difference problem. It seemed to work very well as everything pressed up nicely. I took the stringing down with a card scraper which didn't seem to take too long. I will let you know how it turns out after stain and finishing.

I have had the same trouble with both cherry and mahogany veneers. Although my lay-ups were not as complicated as yours I came to believe the solution was to spray the outside surface with distilled water (lightly) just before it went into the bag so that the veneer didn't ripple from the moisture it picked up from the glue side before I was able to get the pressure on. My results have been flat ever since because it buys me that little extra time by keeping the veneer balanced.