I need veneering help!!! QUICK!!!

[Guy Germaine]

This morning, I tried my hand at veneering for the first time. I just took it out of the clamps and cauls and it's blistered ALL OVER!

Here's what I did:
I cut my MDF a bit oversized and put glue on the veneer and the MDF. I then turned it over and did the same thing on the other side. Then, I set the "package" on a flat workbench (solid core door), put a piece of MDF as a caul on top, and then 5 2X4's on edge with a chitload of clamp pressure on both ends. What did I do wrong? Is there any way to savlage this, or am I out $60 worth of veneer?

[Cecil Arnold]

Were your 2x4s cut square or did you trim them to apply pressure from the center out? If they were square and straight then when you applied pressure on the ends you only helped them bow in the center. If you used yellow glue (you shouldn't have) you can use an iron to heat the glue and get it to stick. Really need more information. What kind of glue, how large was the piece, shape of calls?

[Charlie Plesums]

if you used yellow or white glue, I would immediately soak it in water. The glue will gradually soften, and you can clean out the veneer, dry it slowly, and start over. The sooner you start, the easier it will soften.

[Guy Germaine]

I am using Titebond Cold Press glue. Here is how I had it glued up:
http://www.fototime.com/80EEC7B50242DB1/standard.jpg

[Mark Rios]

Well it's obvious.......you used the wrong colored clamps on the left side.


:D :D :D :D :D

[joseph j shields]

Guy,

"it's blistered ALL OVER!"... do you mean bubbles??

I did some veneering (before I got a pump&bag) and had a couple of bubbles. I used an iron and pressed them down. It seems to be work.

If you plan on doing more veneering, I would suggest getting a pump & bag. I got mine at joe woodworker and have been very pleased. I have never had any problems since...

-jj

[Matt Meiser]

Is that a huge sheet of veneer lying on the bench with a smaller piece being glued to it? I've always seen it done with a piece about the size of the veneer. Also, was it warm enough in your shop? I turned up the temperature to about 70 during my veneer glue up.

[Frank Chaffee]

Guy,
If it is not too late take Charlie Plesums’ advice to salvage your veneer.

Then listen to Cecil Arnold. Clamping cauls are most often sawn to a light bow so that clamping force on their ends flattens them and distributes pressure evenly across the part.

From your pic in post #4 we can see that the right end of the cauls is cantilevered quite a distance beyond the edge of the clamp blocks (sheets?).

Centering the piece on the table and curving the cauls may help.

But look at Matt’s cool system that he just built too.

Frank

[Steve Wargo]

I use a dry hot iron to fix bubbles. It happens. SOmetimes I even get them in the press. This is often in my case a result of too little glue, in which case I use an exacto to slice the veneer and pump in a little more glur then spot clamp it with some wax paper between the caul and the veneer. If you used plenty of glue the hot iron method should work fine. I've even ironed lifted spots as long as a week after glue up. Hope this helps.IMHO there is no way that you're getting adequate pressure with a quick clamp. You'd be better off using C-Clamps than the quick clamps. You probably coupld have used an extra couple cauls as well. Good luck.

[Barry O'Mahony]

I usually do veneering this way and am successful. Some items worth mentioning:

--did you use a roller to squeeze out any possible bubbles between the core and the veneer? If bubbles are present, pressure alone won't get rid of them.

--the Quick Clamp in the forground is an obvious problem. I doubt they can excert more than 100 lbs of force, versus 1000 lbs for something like a K-body. In fact, all the clamps look a little on the light-weight side for this application. Remember each clamp is responsible for supplying the clamping force on a surface equal to half the length of the caul x the caul-to-caul spacing distance.

--With only a single sheet of MDF on the top, it looks like you could have used more cauls. Force only transfers through the MDF sheet at a 45 degree angle at most, so ideally, the caul-to-caul spacing shouldn't be much more than the thickness of the top MDF sheet.

[Guy Germaine]

Well...Regarding the first top with all the bubbles, it's history! http://www.freeyabb.com/phpbb/images/smiles/icon_sad.gif
I tried everything, and it was just too bad. As for the other top, I glued the bottom veneer on by itself and let it set. I only put glue on the substrate, and not the veneer. It came out fine. Once that was done, I turned it over and spread glue on the substrate and let it sit for about 45 minutes. I then positioned the veneer on the substrate and taped it down and used an iron, starting in the center and working my out to all 4 sides. It took about 15 minutes to get it all "ironed" out, but it worked great. No bubbles, or wrinkles anywhere. Now, I need to make a trip over to Woodcraft and get some more veneer. http://www.freeyabb.com/phpbb/images/smiles/icon_rolleyes.gif

I think this will be my last veneering project until I can get a vacuum press. http://www.freeyabb.com/phpbb/images/smiles/icon_biggrin.gif

[Tim Sproul]

The clamps on the right side are the problem. The clamps need to be on the veneer...not off the edge like your picture shows. Clamping the way you did will lead to problems because wood flexes. Those 2x4's are trying to arch with the crown up. If you clamp the right so the clamp heads are on the plattens, no problems. I've done the clamp press several times with PVA based adhesives. No need to roller the veneer to the substrate. The other odd thing you mentioned was waiting 45 minutes between applying the adhesive to the substrate and applying the veneer to the adhesive. I apply adhesive to the substrate, apply the backer veneer, flip and apply more adhesive, show veneer and then right into the press it all goes. I don't think you want the adhesive to become tacky (I'm supposing that's why you waited 45 minutes). If the adhesive is tacky, the plattens have a difficult time doing their job of pressing everything together. My understanding is that you want to press both sides at the same time. Part of the cause of warping with a single sided veneer is the adhesive, especially with water-based. The moisture affects one side more than the other and then the adhesive cures with the moisture differential, adding non-uniform stress in the substrate as the veneered panel equalizes moisture content. The moisture content differential is uniform/symmetric if you veneer both sides at the same time. The other factor is that most adhesives (I think contact cement is one of the few that is exempt from this) change size as they cure. This adds more stress...which if you do one side at a time is unbalanced. Stress in the veneer panel isn't bad, it is only bad when it isn't balanced/symmetric, just like with solid wood.

For clamp-press veneering, you want the plattens (the sheets that sandwhich the veneer and substrate) to be 3/4 inch rather than thin stuff. The thickness is needed to more evenly distribute the clamping force. For vacuum bag pressing, the plattens can be thinner since the bag applies pressure very uniformly. I haven't had issues using 3/4 plattens. I made mine like Joe Woodworker's website suggests. I also recommend you get the wooden roller or the rubber roller for rolling seams (bookmatching, quartering etc) and the glue roller(s) too. Not the unibond glue roller but the 4 inch or the 6 inch rubber foam glue rollers.

I got the Vacu-Press Compact 100. It works well. You can get it direct from vacu-press or from Rockler.