Darryl Keil Last Activity 2025-09-09 11:09 AM
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Dave

 
Subject : Pressing Woes
Posted : 2002-03-09 5:28 PM
Post #29772
I've been making 15x22 panels of 1/2" MDF with a cherry sunburst (radial) pattern on one side and a plain maple back. PVA glue.I've been rolling on the glue, placing 1/8" tileboard both sides, placing a stack of 2 in the bag, and turning on the pump (draws down OK without using closure strips), glue up 2 more, repeat until I have 8 panels in the bag. Seal the bag and wait about an hour.Couple of problems:1) When the bag draws down around the stack, it pushes it sideways and misaligns the veneer with the panel. tried masking tape but little help. The tileboard is cupped because it's only coated on one side. This makes it hard to align everything in the first place. Should I replace the tileboard with something else, rough up it's surface so it's not so slippery? Other suggestions?2) I cut the parts for the sunburst at the local print shop on their guillotine. I use 3-hole white tape buried in the glue,(these are not expensive items). The last batch of 32 sat in the shop about 2 weeks before they were glued up. About 25% of the joints are not tight in the center. Some have pretty good gaps(1/16 or so). First time this hase happened, they looked good going in. Any ideas?3) Can I spray PVA glue? Can I spray it thru the same gun I use for lacquer? Can I leave the glue in the pot and gun, or do I have to clean up right away?There's more but my finger's starting to cramp up.ThanksDave



 
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Darryl Keil

 
Subject : Pressing Woes
Posted : 2002-03-11 8:15 AM
Post #29778 - In reply to #29772
Dear Dave,I only have problems with panels shifting if there is more than one stack in the bag which causes one stack to be pulled towards the other. I solve this by putting one stack almost touching the other.As far as the gaps in your sunburst, I have a few suggestion. First, I would not use three hole veneer tape for a sunburst, it is not strong enough for a complicated pattern and I do not see how you can properly pull the points together without overlaping the veneer tape which you cant do with three hole tape that is on the glue side. Three hole tape is really meant to be used on the glue side of strait flat architectural panels, not on involved panels like sunburst matching. Second, always lay up your panel soon after taping it. Humidity changes and such can easily effect the joints. Last, on any radial matched veneer I dont recommend a white or yellow glue, something more rigid would hold the joints better. Use a urea resin glue.SincerelyDarryl Keil: I've been making 15x22 panels of 1/2" MDF with a cherry sunburst : (radial) pattern on one side and a plain maple back. PVA glue.: I've been rolling on the glue, placing 1/8" tileboard both sides, : placing a stack of 2 in the bag, and turning on the pump (draws down : OK without using closure strips), glue up 2 more, repeat until I have : 8 panels in the bag. Seal the bag and wait about an hour.: Couple of problems:: 1) When the bag draws down around the stack, it pushes it sideways : and misaligns the veneer with the panel. tried masking tape but : little help. The tileboard is cupped because it's only coated on one : side. This makes it hard to align everything in the first place. : Should I replace the tileboard with something else, rough up it's : surface so it's not so slippery? Other suggestions?: 2) I cut the parts for the sunburst at the local print shop on their : guillotine. I use 3-hole white tape buried in the glue,(these are not : expensive items). The last batch of 32 sat in the shop about 2 weeks : before they were glued up. About 25% of the joints are not tight in : the center. Some have pretty good gaps(1/16 or so). First time this : hase happened, they looked good going in. Any ideas?: 3) Can I spray PVA glue? Can I spray it thru the same gun I use for : lacquer? Can I leave the glue in the pot and gun, or do I have to : clean up right away?: There's more but my finger's starting to cramp up.: Thanks: Dave




 
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Dave B

 
Subject : Pressing Woes
Posted : 2002-03-12 9:41 PM
Post #29791 - In reply to #29778
Thankyou Darryl and Bryce for your excellent advice.I have a question about your handheld veneer stitcher Darryl. Would it be better than the 3-hole tape for the sunburst? How fragile is the joint compared to 3-hole? I've been taping 1/2 of the sunburst, then trimming the 1/2 sheets in the guillotine again, and then taping the two halves together, and finally removing the masking tape. All this handling results in some tearing of the joints, usually near the points. Would I experience the same problem with the stitcher? I really appreciate the forum and the time you take to answer our questions.Dave




 
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Bryce

 
Subject : Pressing Woes
Posted : 2002-03-11 1:13 PM
Post #29780 - In reply to #29778
Dave,Awareness and knowledge of the protocol regarding the relative humidity (RH) in your shop and the moisture content (EMC)of your veneer should be monitored closely since apparently you are producing a professionally produced product. I suggest that you do further research in the literature on this subject.Regarding the subject of taping veneer -- you could use masking tape for better pull strength. I've used tape lots over the years but you have to be very careful how you remove it, and you cannot use masking tape with the hot press (although there are exceptions that I won't go into at this time). If you use the right tape (usually a cheap painter's tape) you will not find any significant(if at all) transfer of sticky residue on your face side. If there is any transfer it would be slight and your're going to sand the face anyway.Secondly, if you have not experienced a cupping problem with your completed panels I am surprised. You may be asking for trouble since you have created an unbalanced panel by using maple backers and not the same species as your face veneer.Thirdly, I can't refute Daryl's experience with using urea formaldehyde resin but urea adhesives are not "gap filling" adhesives.Ureas rely on intimate contact between face and substrate to adhere properly. I suspect that with your accumulation of small "pressing gaps" that do inevitably result when assessing your process you are unable to apply correct / consistent pressure to your veneer that is critical when using urea. Failure here could result in bubbles/delam that unfortunately would not raise their ugly heads until your products have been in the field for awhile. TRANSLATION: Returns/ Warranty Adjustments/Refunds/etc. Therefore it's my opinion to perfect your system with a thermoplastic adhesive (urea is a thermoset) since thermoplastics are generally more forgiving. But use a good quality thermoplastic.Lastly, as far as spraying PVA. I haven't done it but from my experience I would expect your lacquer tip would only spit out blobs of PVA due to incomplete atomization (regardless whether you have siphon feed or HVLP). You could try it but may have to purchase new nozzle. If you purchase new nozzle choose the next smallest inside diameter, yes the next smallest. Smaller i.d.'s are used to properly atomize heavier viscosities. Best bet would be to check with the best techie at one of the more popular industrial finishing suppliers in your area. I don't see any probs with leaving glue in the gun unless it is a catalyzed adhesive. Last question for you though is whether you want to cross-contaminate your spray equipment with glue residue. It is almost certain that you'll never get it 100% cleaned out and then later will be using it to spray lacquer. How about a 2d cheap gun? Through experimentation and critical thinking you"ll find a method that works best for you. Good luck. Bryce.
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