Keith Newton who posts here started a thread in another forum about using drafting dots to join veneer. I was sceptical that the technique would work satisfactorily, but thought I’d give it a go. So, this is a cross posting between two boards, but as I’d put the thing together I guessed I wouldn’t waste the effort on one forum, so here goes. The original thread is here, http://www.woodcentral.com/cgi-bin/messages.pl?read=345407&v1=e2vrt43&v2=bench+plane&v4=hand+tool&v5=e2vrt43 .
I expressed some doubts about the suitability of using drafting dots for this task guessing that they might perform much like masking tape. Masking tape has the nasty habit of adhering too well to the wood and on removal tearing out the grain. It is also quite thick and, on soft veneers, I’ve experienced it leaving a depression in the veneer that’s difficult to remove without cutting through to the ground below.<!—-><!—-> <!—->
I decided to give the drafting tape technique a go on a sample board. I used a piece of 12 mm MDF as the ground and used some offcuts of crown cut black cherry Prunus Seritona and quarter sliced European beech Fagus sylvatica veneers for each face.<!—-> <!—->
<!—-> <!—->The rest is a photo essay of the job with comments here and there and a conclusion at the end.<!—-> <!—->
The following four images show the veneers cut with a guillotine and the prepared edges taped together, the cherry with drafting dots and the beech using masking tape. I used <!—-> <!—->PVA<!—-> glue and applied it the ground on both faces to press the veneers in one go. <!—-> <!—->
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The panel is slipped into the veneer press. I used a heated hydraulic press for speed, although I could have used the vacuum bag press. Hide glue and a veneer hammer don’t work well at all with masking tape as the join ‘cramp’ and I doubt that drafting tape would perform any better. Both these methods are slower anyway and I was after speed.<!—-> <!—->
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The veneered panel gets high pressure heat treatment. The panel stays in the press for about 60 seconds: that’s all the time required for applying veneer with platens heated to 60ºC.<!—-> <!—->
The bottom platen lowers to remove the panel. Normally I slip a sheet of plastic, like a cut up black bin bag, between the platens and the panel to prevent sticking. I didn’t have one handy so slapped a bit of paper towel either side, something I wouldn’t normally do as the paper gets imprinted into the veneer’s grain. <!—-> <!—->
The veneer, the ground and the tape is hot when removed from the press, so you’d think tearing off the masking tape, next, or the drafting dot tape in the image after, wouldn’t cause grain tearout. It does in both cases even though I was very careful how I peeled back the tape. I was a little surprised to see the drafting dot removal caused more damage than the masking tape. However, beech is very hard, and the cherry joined with the drafting dots is a lot softer, so perhaps the tearing out of the grain in the cherry isn’t too surprising.<!—-> <!—->
Glue bleed through on the beech veneer.<!—-> <!—->
<!—-> <!—->Some residual adhesive left on the cherry veneer from the drafting dot.
A bit of prep work is needed, so it’s off to the 100 grit abrasive paper on the stroke sander followed by some hand sanding to 150 grit. After that a bit of carelessly brushed on shellac just to seal the grain. <!—-> <!—->
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In these last four images you can see the general colour and the bit of torn out cherry grain shows rather badly.
Conclusions. I believe I was right to be sceptical of the efficacy of drafting dots used as a means to join veneers prior to gluing. They do tear out the grain on removal just as masking tape does, but I suspect it depends to some extent on the wood species. Neither the masking tape nor the drafting dots imprinted themselves into the wood. The masking tape I suspect was defeated by the hardness of the beech veneer beneath it. The drafting dots are thinner, so perhaps their ability to imprint deeply is compromised.
I shan’t be switching over to using drafting dots to join veneers on a regular basis, particularly for woods that can be ‘stringy’ such as European sycamore Acer pseudoplatanus for example or hard maple Acer sacharum. I might use it for some of the harder tighter grained woods such as ebony or possibly some of the rosewoods. Slainte.
Edited 1/12/2008 8:20 am by SgianDubh
Replies
I expressed some doubts about the suitability of using drafting dots for this task guessing that they might perform much like masking tape.
Why not just use paper and hide glue? NO, I do not use veneers that often..
I just loved your 'paper cutter'! I have worked on ones 100 inches and more. Scarry job!
You ended with.. Conclusions. I believe I was right ...[Message truncated]
Old saying I remember is "Let it all hang out"
EDIT:
Let It All Hang Out by The Hombres
http://www.youtube.com/watch?v=bPNeSLoVmCE
By the way.. You are a Modern Master! Or maybe even better...
Edited 1/12/2008 9:27 am by WillGeorge
"just loved your 'paper cutter'! I have worked on ones 100 inches and more. Scarry job!"
Just gotta keep your fingers out of the way, WG, or anything else soft and fleshy that could 'hang out' under that blade, ha, ha. Slainte.Richard Jones Furniture
Hi Richard,
I used masking tape for a while to join veneers, and while I never had a press stout enough to imprint the tape into the wood ( I always use several layers of newsprint between veneer and caul), getting the stuff to release after pressing was a problem. I found that lacquer thinner is a pretty efficient solvent for the adhesive, and brushing a bit of it along the interface as the tape is pulled up (a tedious job, I admit) will eliminate the tape's lifting strings of veneer as it comes away.
All in all, veneer tape (why do they call it that, anyways?) does work much better.
Ray
Ray,
Using your method (of removing masking tape), have you tried misting the tape with some mineral spirits? You don't lose much if you try it on some scrap, but might gain some.
Best wishes,
Metod
Metod,
Mineral spirits didn't work as well (fast) for me as did lacquer thinner.. Nowadays, I just use masking tape for temporary (no clamping) veneer work, or repair work on finished wood veneers, where it won't stick so tightly. Veneer tape for new work under clamps.
Ray
Ray,
Thanks. I never tried lacquer thinner - but will add it to my list of helpful hints.
Best wishes,
Metod
As you say Ray, it's called veneer tape for a good reason. Removing the stuff is easy enough with a water damp rag and a bit of time.
Shifting masking tape can be very tedious, and not always successful even with cellulose (lacquer) thinners. Some reckon a hairdryer helps in softening the tape's adhesive, but again it's my experience that this isn't always successful either. Slainte.Richard Jones Furniture
Interesting, Richard. I got through a few of those messages before my cat jumped up and cleverly closed the Woodcentral window. I couldn't make head nor tails of Keith's original post, what his question or main statement was. I have a question though, simple curiosity.....do any of the specialty masking tapes work any better? -- such as the blue 3M tape (which comes in different strengths) that painters use to avoid damaging wood finishes.
fg, some of the comments seem to be coming down in favour of the less 'sticky' kinds of masking tape, eg, the low tack blue painter's type sold in the US.
However, one of the comments over at WoodCentral suggested the heat from the hydraulic press I used could have the effect of making the adhesive adhere more effectively to the wood grain. I tend to agree with that, but I usually do stick veneer down with heat. Heat and a hydraulic press means you can often press both sides of a panel in one go, and the panel only has to stay in the press for a minute or so. A large batch of panels can be processed in just an hour, or less than a day anyway. Doing the job in cold presses might take a week or more as you wait for the cure.
One of the problems of masking type tapes that I expereience is their tendency to compress the veneer underneath leaving a hollow. I suspect the heat is a big factor in this. Those that don't use heat in things like unheated bag presses or cold cauls might get away with using masking tape, but the downside is longer pressing time.
The common water and powder form of urea formaldehyde glues used in an unheated press require ~3-1/2 hours at about 20º C (roughly 68ºF.) Powder and resin forms cure in about half an hour, but this form has a three month shelf life. In a heated press at roughly 60º C (~140ºF) even the water + powder urea formaldehyde glues are set in less than two minutes. If you don't have heat, this is one reason that some workers might choose PVA over urea formaldehyde type glues, ie, speed, although some commentators say PVA isn't suitable for applying veneer. That's a position I disagree with as I can't recall how many square metres of veneer I've put down with PVA without a problem. I also know mass production furniture factories that I visit on a regular basis that use PVA to attach veneers-- they, and I, wouldn't do it if it didn't work. Slainte.Richard Jones Furniture
Richard
That's a nice press you have there. 140°F and pressure sure is a helluva lot faster than the 4 hours in a vac-bag, with a heated blanket over the top. That's the best that I can do.
I have used the blue painters tape on occasion, and I'll agree that the veneer tape is definately made for a good reason.
Out of curiosity, what is the pressure created by the press?
Nice pictorial.
Jeff
"Out of curiosity, what is the pressure created by the press?"
Jeff, the dial on the machine is set to 130 Bar. I think the conversion factor is to multiply that number by ~14.5 to give pounds per square inch, so if that's correct we're looking at about 1885 pounds/in². Slainte.Richard Jones Furniture
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