View Full Version : anybody worked from mylar patterns?
Dale R. Hamilton
02-04-2005, 10:38 AM
I've had some boat plans redrawn from paper to full size on a CAD disc. My plan was to send this out to somebody with a shopbot or CNC router who would cut my plywood panels for me. But, this has proven to be too expensive a proposition. After all, I can use a jig saw. So now I want to fall back on next cheaper alternative. I've heard that patterns can be cut from mylar. Can these then be used to trace patterns on plywood? How do the work? Who does this kind of work? How much cost involved? Many thanks for comments.
02-04-2005, 10:53 AM
The maine advantage of mylar is dimensional stability, disadvantage is extra cost. What I did was plot on paper, then glue the paper to plywood, then bandsaw to the lines. If your sections won't fit on a standard sized plot, then several plots can be matched up side by side. Keep the paper plots protected from moisture until glued. Use spray adhesive on the plywood then apply the paper, use waxed paper to protect the plots until you get them positioned. Practice placement with junk paper before glueing the plots. ;)
02-04-2005, 11:54 AM
My experience was with a 50 ft catamaran. Sections (that were Interior bulkheads) were plotted on several E size sheets that were then taped together. Lay out on the plywood, pin prick the lines to transfer, and then draw with a batten. The whole boat was within 1/8 inch in 50ft. Not too shabby! A nice flat full-size surface is a necessity.
02-04-2005, 04:38 PM
I've used Mylar for patterns for the panels of radial-cut sails that I wanted to be able to duplicate. You just lay it on the new fabric (or plywood I suppose, in the case of boat parts) and run a pencil around the edge while holding the edge down so that it doesn't curl as the pencil goes past. Worked fine, though the stuff is pricy, especially for a one-shot deal.
[ 02-04-2005, 04:38 PM: Message edited by: Todd Bradshaw ]
02-04-2005, 10:26 PM
Lay on the full size paper pattern, prick every couple of inches or so along the lines, remove paper, connect pricks and cut. How far off is that gonna be, a couple of hundredths. Why bother with mylar?
02-05-2005, 12:50 AM
I think that he benefit of mylar over paper is mostly that it is stable. When you build the second boat next summer, it won't be 1/4" beamier.
What are you building ? Dale
02-05-2005, 07:45 AM
Error and misery have surrounded all my efforts at lofting with the aid of the copy center. I used mylar, vellum and bond and every time an amplified error creeps in and grows.
Ultimately, painting a couple of pieces of plywood white and drawing the boat on them is FAR more accurate, is just as quick as running around to the copy place, and is essentially free.
Additionally, if you loft it yourself working from lines and offsets, you learn each piece, curve and rate of change in the body of the boat before you begin to build it--which to me is invaluable experience to have going in to a project. I've always said about furniture, boats, houses and so on that if you can draw it, you can build it.
02-05-2005, 10:02 AM
Originally posted by JimConlin:
I think that he benefit of mylar over paper is mostly that it is stable. When you build the second boat next summer, it won't be 1/4" beamier.Yeah, that is my point ezakally. How much does paper really move? Are we talking a 20' boat or a 150' ship. My guess in paper moves more on the order of my 0.02" than your 0.25".
02-05-2005, 10:08 AM
I'm with Billy Bones here. Lofting isn't much of a chore, and can certainly be beneficial in terms making "builder's adjustments" (is the sheer eye-sweet, etc.). No doubt, the CAD drawings are a great reference, but I don't think the jump to patterns is necessarily required or beneficial in the building of a boat. One caveat, I've not built anything that I would deem large, so if that's where you're at, my experience may not apply.
02-05-2005, 11:08 AM
If you glue the paper on plywood and cut to the lines, another boat won't be beamier or whatever unless the plywood changes. Also if you don't keep the plywood, the CAD file will never change, just replot. I got a HP pen D size plotter used, old, but still good for $150. Worth having no trips to the copy center, make plots whenever I need them, paper is cheap.
02-05-2005, 03:27 PM
I have worked with mylar plots up to five metres long.The older ones were excellent because the plotters of that generation used sprocket drive on the perforated edges of the roll and suffered no slippage.The more recent inkjet plotters seem to suffer from slippage,which may be the result of trying to move a comparitively weighty piece of film.The result is that the accuracy of the length plotted needs checking.I have found it useful to have a grid of dashed lines on hundred millimetre spacing plotted both along and across the plot area in order to have a means of checking.I suspect that the logical next step would be to have your parts cut on a CNC router and there are threads in other sections of the forum relating to this.It ought to help to be able to produce parts with no human intervention between designer and intended part.The problem is that the extra efficiency would almost certainly take away some of the fun.
Dale R. Hamilton
02-07-2005, 10:57 AM
I'm building Ray Sargeants 15' sport runabout. Its a plywood stitch & glue job that will be strip planked in mahogany veneer. The last price I got for CNC router cutting of my plywood parts was $45.00 per sheet- and since I needed 18 sheets cut, I felt this was a little too steep.
02-09-2005, 11:20 AM
I find lofting rather tedious. Some find it fun, God bless 'em. But then shaving and brushing one's teeth are tedious too.
Loft it on painted plywood. Luan is cheaper than parts that don't fit.
Unless you're manufacturing multiples of the thing, the hi-tech stuff is a waste of resources, time, and money.
The cad file/plotter road makes more sense if you're building in steel or aluminum.
02-10-2005, 03:11 PM
In the aircraft biz, we use a very heavy mylar called a PCM (photo contact master). It is printed on special plotters in a controled environment. There are 10 inch grids plotted out to insure the dimensions are correct.
This is done to get accuracy of within +/- 0.030 in. Do you need +/- 0.030 in? If not, plot out on paper, use the 10.0 inch grid, and glue the plot to your plywood with contact cement. If you don't want to glue, use a pounce wheel (http://www.leevalley.com/wood/page.aspx?c=2&p=32817&cat=1,250,43298,43305) to mark out your pattern.
02-10-2005, 07:34 PM
Loft the durn boat. Then use mylar laid over the lofting to trace the shape of whatever part you need to produce. Poke holes. Rub chalk or paint or whatever through the holes. Connect the dots. Works for me.
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