Hi!
Martin Kopplow has developed really nice technique. He prints directly on kevlar. Check out his tailfeathers on the link below (you must join the SALglider group in Yahoo to see them).
Arne
---------- Forwarded message ---------- Date: Fri, 2 Jul 2004 21:25:07 +0200 From: martin kopplow <[EMAIL PROTECTED]> Reply-To: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: RE: [SALglider] Printing on Kevlar with an inkjet pinter
Ok, I've uploaded two pictures to the SALglider photo section at
<http://photos.groups.yahoo.com/group/salglider/lst?.dir=/Martin+Kopplows+Pictur es/Printing+on+Kevlar+and+tail+bagging&.src=gr&.order=&.view=t&.done=http%3a//br iefcase.yahoo.com/>
Printing on fabric has advantages over printing on tissue when the size of the print is relatively large or even covers the whole part. It saves weight. It does not add a layer to the layup, forming no stress raisers at it's edges. It also makes the building process a bit easier if used appropriately. For a small print, such as a logo, I'd go the tissue way, though.
First Picture ("Layout, print and result"): You can see a finished vert. full flying stab and a printed sheet of Kevlar or glass in front of the computer with the original layout on screen.
Second picture ("Bagging printed glass on balsa") You can see my vacbagging setup for a set of glassed balsa tailfeathers with cambered airfoil. The material under the part is somewhat flexible to allow the bagged part to sink in a little.
Procedure: I first make the layout using my computer. This has the artwork in it plus all the marks for positioning and trimming. Leave a little space around the parts and at the edges of the print area. Then I roll out as much Kevlar or glass as needed on my cutting bench, stroke/blow away all wrinkles. I spray a sheet of usual 80g/m^2 copy paper (the size my printer takes, in my case it is A4) very thin with 3M repositionable photo mount and let dry a minute or so. I then put the paper buttered side down on the fabric at 45°, stroke it on. I trim the fabric exactly to the size of the sheet by either using a roller cutter and steel ruler (glass) or the Kevlar scissors.
After preparing as many sheets as required, I go to my printer, put one in the paper feeder at a time and print on them in draft/economy mode. This ensures there is no excess ink soaking the fabric and blurring the image. Image resolution is limited to less than 30dpi or so by the distance between threads in the cloth, so there's no use in printing high resolution anyway. The first time I tried, I used a strip of tape to secure the sheet's LE when feeding into the printer, but that proved to be unnecessary, at least with my printer. It is - however - not recommended to try this with 90° cloth orientation: Threads (almost) parallel to the paper's edges will most probably get lose and tangle up the printer tractor. Cut the fabric somewhat smaller when 90° is required, so there's plain paper at the edges.
After printing, it is a good idea to let the ink dry a few minutes, then I stick tape (non elastic, but sticky) on the fabric all around the edges and press on tightly. The tape overlaps at the corners, that's important. If I print more than one part on a sheet, I also put a tape in between the parts. Now I cut the parts apart (fabric still on the paper) right in the middle of the tape.
I prepare my bagging rig, resin and tools, and only now I peel off the paper. Grab the paper with one hand, the tape with the other and slowly pull apart. Because of every cloth part being framed by the tape, it will not get irreversibly distorted during the process, even if this may look like it at first glance. I leave the tape on and put the fabric on the bench and blow on them: Just like magic, they will return to their original shape, use no fingers, just take a deep breath and blow on top of it. Then I wet it with epoxy and roll it dry, with the tape still on. Now I put the lower side fabric on a piece of overhead film (print looks mirrored now), put the core on top (can see exactly where, because of the printed reference marks) with the tape still on and place a piece of wetted out carbon roving around the edges of the core (thin one at TE). Now I put the top skin cut on another overhead film, put it on the core, adjust referring to the printed marks, put a sheet of prepared plastic film over everything, seal around the edges with acrylic and switch on the vac rig at max. It's getting noisy now in the shop, so I rather get into the kitchen and have a beer.
After cured, I trim off excess fabric and the tape, sand the edges and so on. The result is in photo #1.
Now I'm looking for a large format printer, that will feed Kevlar right off the roll :-) or at least allow printing the size of a wing panel. I could make nice wing paintjobs that way, or I could even print on the outmost layer of my Kevlar fuselages. I could take a digital photo and print it on, or I could scan a painted design, copy the pattern of my carpet or the sofa upholstery :o) there are tons of possibilities ...
Have fun!
Martin
Disclaimer: This is a scratchbuilder's idea, shared with fellow modellers. If some commercial model manufacturer adapts it and makes money on it without sharing his own techniques, may the lightning strike him.
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