Veneer Splicing Woes

Here's a long, informative discussion of veneer splicers and veneer splicing technique. January 29, 2009

We recently started using a Diehl veneer splicer and we are having varying results. Has anyone experienced a downgrade in glue quality over 24 hours time after splicing? Some pieces go together brilliantly and later on crack right on the glue line. Weíve tried several different application methods and I know that definitely plays into the joint quality. Is there a foolproof glue application method that anyone knows of? Iíve heard that some people use a finish spray system but i don't know if we do enough to warrant that. Even if we did we would need to get extraordinary clamping strength on the stack to prevent the glue from traveling to the top and bottom of the flitches. That is another problem we've been having, dried glue on the heating platens is a nightmare. Is there a solvent that I might not know of? Weíve tried everything we have in the shop and it comes down to slow scraping with a piece of wood which takes forever.

Forum Responses
(Veneer Forum)
From contributor J:
What type of glue are you using? How are you applying it? We sell Acmos 1124B release agent for UF glue.

From contributor C:
Spray it. We have been doing this for 15 years. You can hold the pack tight using a scrap of MDF by hand. If you are brushing it, you may have too much in some areas which is no good, you need to use as little as you can to do the job.

Spraying is no big deal. We buy cheap import guns or use guns from or finish department that are too worn for quality finishing. It's like spraying water. I'm surprised you use a Diehl, which is a tricky machine, yet cannot justify spraying. Be careful with release agents as they can mess up your pressing and or finishing.

From contributor F:
Degradation of glue joints over elapsed time from cutting (24 hours) can happen when gluing many species of wood. I don't see a mention of wood species in the question and that might be helpful. Temperatures, moisture and glue type could affect results as well.

From contributor D:
Welcome to the world of veneer splicing. Your first problem is your splicer, putting it mildly, it's a piece of junk. You've probably acquired it and are using it for none other than the price you got it at. I've been doing veneer work for nearly twenty years and have used several different splicers, from Kuper stitchers to Diel splicers . For the past eight years I have been using a Kuper F/L Innovation splicer with great success. However it is quite expensive and unless youíre doing very large veneer runs (100-200+ books a day) is not cost effective.

With that being said lets address your other problems. Letís talk about your glue, because you didn't mention the brand you are using., I will use the brand I use for an example and to explain what I have found to be a successful veneer splicing process. I use a product that is made by Borden, yes that Borden, the folks that make ice cream, called DS-200/DS201. The 200 is white for lighter veneers and the 201 is for darker veneers. The mix is 2 parts glue to 1 part water by weight. When mixed correctly, the consistency should be about the consistency of a thinned out cake batter. Now, when you apply the glue to the edge of your veneer pack, the rule here is the thinner the better. There are several ways to apply the glue - spray, brush, and etc. Kuper even sells a machine that does this but itís pretty pricey.

I have used all of the above and have had success with all. Because you are limited to either spraying or brushing, may I suggest the brush method. The main reason being you can better control the spread. For clamping the veneer together you can either build a small clamp or what I do is make a solid wood block 4" x 4" square by 10-12" long. When the glue builds up on the block you can either sand it off or run it through the saw or do whatever you like to do to get it cleaned up. I think you get the idea here.

Now the glue spread should be as thin as possible, but not so thin to where it will fail. It's the same concept as gluing solid wood together. Apply a thin coat to both surfaces rather than a lot of glue to one surface for a much superior glue line. O.K, now that we have our veneer glued up, the next step is to fan the veneer out so the book doesn't stick together and tear your edges apart. The dry time for the glue is anywhere from 15-30 minutes based on the humidity in the area.

You will know itís ready when you can touch the edge and it's not sticky. One thing I forgot to mention is check your veneer moisture. Iíve found that 9-11% is the best range for most veneers. Working time for the glue is roughly 6-8 hours. You could probably stretch it to 10 if you have an a/c controlled environment. Anything after that, the glue is pretty much useless. Tust me I've tried to glue up books of veneer the night before and leave them in an a/c'd room and had no success.

Now letís talk about our good old friend Mr. Diehl. First letís talk about heat range. A good range I have found is between 325-340 degrees Fahrenheit. Feed speed is anywhere from 30-40 mpm, meters per minute. The glue build up on your heater bars can be eliminated by applying metal polish to the bars. Just apply it the way you normally would when polishing metal. Spread it across both bars in a thin, even, coat. Let it dry and then buff it with a clean dry cloth. Use a good quality metal polish. Veneering can be quite difficult at times but it's also not rocket science. What I have suggested here are some basic guidelines I have found throughout the years of trial and error that work for me. There are many different ways to do this. Give it a try and tweak it here and there to suit your needs.

From contributor O:
I have been in many veneer shops over the last 20 years. In defense of Deihl splicers, I have seen 30 year old machines perform brilliantly and have seen some produce awful glue joints. I have seen Kuper Innovation machines work flawlessly and I have seen clients who own Kuper Innovations that have become so frustrated with bad glue joints that they turn off the glue pot and use the machine as a reactivating splicer ( similar to a Deihl).

Quality glue joints with any splicer really come down to proper operation and maintenance of the equipment and of course a good quality cut on the veneer to start with by using a veneer saw or guillotine.

On another note for anyone out there who is interested in veneer splicing, Kuper is not the only machine that can apply adhesive to veneer edges and seam them in one pass with high quality results

The Fisher+Ruckle Omnimaster Plus manufactured in Swtzerland, sold and serviced by Joos USA Inc, as well as the Furniertechnik LZM-LA manufactured in Germany, sold and serviced by Veneer Systems Inc. should also be highly considered when looking for a longitudinal veneer splicer that applies glue and seams veneer in one pass. All four brands should perform properly if you know how to use them, and know how to maintain them.

From the original questioner:
We were definitely putting too much glue on the veneer. With spraying I can control the amount of glue much easier. Weíre splicing black walnut, white oak, and maple using national casein splyset. We were going pretty slow; 6 mpm with low temp; 225-250 deg F. The stuff looked great coming out but now we're battling the degrade. The veneers will just snap right on the glue line once dry. We cranked the temp and speed after I read the responses but we seem to get the same result. The last thing I ran was at 350 F at about 30 mpm. Also, I donít think this machine likes going that fast. At first we found that the black walnut worked better than anything, but now it seems that they all fail with an equal amount of disappointment. Also the veneers we're running are about 1.5 - 2 mm. thicker than normal but everyone we talked to about the machine didn't seem to think that would be a problem.

I feel I've learned a good bit but my results are not really improving. Would variation in the temperature mess us up that bad? Could it be that the machine isn't grabbing the veneer hard enough to press it together sufficiently? Is there a splicing wizard that I can invite to the shop?

From contributor C:
Make sure your upper heat bar is as low as you can get it, should leave a bit of a mark on the veneer joint. The quality of your edge is important. Where is your shop?

From contributor J:
I would recommend trying some different splicer glues.

From contributor J:
The main reason white or yellow glue is not used is they are not strong enough for all veneers. Also when you put spliced sheets on the press platens the glue will re-soften and the joints will be open after pressing. Urea glues are a thermoset adhesive and once they are set they cannot be reactivated by heat. It sounds to me like you may be mixing the glue to thin and the chemical bond is not able to form.

From contributor C:
That wasn't an offer. Just wondered if you were close to a few people that I know who service these machines. You're not. Be careful not to use too much glue, that will make a breakable joint. Check your heat bars for temp, make sure they are at target temp (thermostats are dicey). Like most of us, you will end up becoming an expert by default. Certainly try some other glues. If you mix your own, weight the proportions accurately. If your glue is correct, go back and set the heat bars per Diehl and work from there.