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Boat Forum / Building / October 2006Looking For Ideas To Make A Plug For Female Mold
I'm interested in making a plug, than a female mold with parting plane and flange to make several canoes for our club. My plan is to lay out the strongback, attache the stantions, cover the stantions with flexible foam strips (like a strip built canoe), cover the foam with spackle and sand, wax with releasing agent wax, and lay up the fiberglass mold cloth. I read in a book how it is possible to make a plug with spackle dried and sanded. My questions are what would be a good foam sheet thin enough and flexible enough to strip over the stantions. Secondly is is spackle a sufficient finishing material, and finally when making the parting plane and flange do I have to account for shrinkage. I haven't decided if to make the parting plane travel the length or width of the canoe. One canoe manufacture goes length wise while another goes across the width. A flange is neccessary for my mold because the canoe will have tumblehome (cuts in at the sides) and will not lift out of a conventional female mold. Any thoughts would be really appreciated. I've read everything I can get my hands on with no luck. Oh yeah one final question, is there a realease agent tape I lay in the female mold to cover the seam on the parting plane. Spackling past has absolutely no sear strength. If your plug flexes at all it will crack. Also remember that any imperfection in the plug will be reproduced in the final product. I would think about something other than foam for the base. Possibly narrow 1/4" plywood strips. Sand as fair as possible, cover with 2oz scrim cloth and skim coat it with a thin coat of fairing putty. Sand it very fair to about 240 grit and spray a couple of coats of Duratec surface primer. Wet sand with some 600 grit. Now split the plug down the keel line and mount your moldboard. You want that parting angle as sharp as possible. Polish the daylights out of it starting with rubbing compound and ending with McGuire's machine polish. Once you can see your face in it when it is dry, wash it down well and let it dry over night. Spray a very light mist coat of PVA followed by several light coats. PVA is very thin so try to avoid runs by making several light passes rather than one or two heavy coats. Let it dry for several hours before spraying the first gel coat layer of the mould. I would strongly recommend a tooling grade gel coat rather than the normal stuff. On the hull lay-up I wouldn't worry to much about the part line if it is tight. You will get a little gel coat seeping into it. Just sand off the flash and polish out the gel coat.  SignatureGlenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com > I'm interested in making a plug, than a female mold with parting plane > and flange to make several canoes for our club. My plan is to lay out [quoted text clipped - 16 lines] > final question, is there a realease agent tape I lay in the female mold > to cover the seam on the parting plane. > Spackling past has absolutely no sear strength. If your plug flexes at all > it will crack. Also remember that any imperfection in the plug will be > reproduced in the final product. Agreed, spackling (and all the other types of quick-n-easy putty) make terrible molds. They have no strength and they dimple or chip easily... when they don't just fall apart in chunks. > I would think about something other than foam for the base. Possibly narrow > 1/4" plywood strips. Sand as fair as possible, cover with 2oz scrim cloth > and skim coat it with a thin coat of fairing putty. Why not heavier scrim & thickened resin for fairing? If you mix it up to the approximate consistancy of peanut butter, it builds fast and can be sanded relatively easily. > .... Polish > the daylights out of it starting with rubbing compound and ending with > McGuire's machine polish. Once you can see your face in it when it is dry, > wash it down well and let it dry over night. Spray a very light mist coat > of PVA followed by several light coats. PVA is very thin so try to avoid > runs by making several light passes rather than one or two heavy coats. Another option for seperating mold from molded part is .5 mil PVC sheeting. Comes in handy rolls at Home Depot, cheap as heck. Takes 5 minutes or less, leaves a gorgeous smooth finish *if* you didn't get any wrinkles. It can be stretched over a 3D curve but you have to be careful. Heavier stuff is better for flat pieces. In fact I have been using a crude form of "pre-preg" by laying out my laminate on a big sheet of this stuff (sold as painter's drop cloth), wetting it out, then laying another sheet over top & rollering it thoroughly, then carefully peeling & applying it. I have used peel ply doing it, but found that any piece with much contour is better off to be rollered in place on it's final shape, then have the peel ply put down. The peel ply tend to make the laminate want to fold or wrinkle instead of lay down smoothly. > On the hull lay-up I wouldn't worry to much about the part line if it is > tight. You will get a little gel coat seeping into it. Just sand off the > flash and polish out the gel coat. Yeah it's depressing how much time goes into finish work, even when you make stuff from a mirror-bright mold. But it cheers one up every time the finished gets a compliment. Fresh Breezes- Doug King > Spackling past has absolutely no sear strength. If your plug flexes at all > it will crack. Also remember that any imperfection in the plug will be [quoted text clipped - 18 lines] > tight. You will get a little gel coat seeping into it. Just sand off the > flash and polish out the gel coat. Forget plaster. It will crack and will take forever to dry. Wood strips are the traditional way to make a male plug. Plaster isn't good. You don't have to use plywood, thin battens will work too. I don't think you need to cover the wood with a layer of glass for a canoe plug. But you will need a resin based fairing compound - something with microballons. Sand this with no less than 80 grit, then switch to a high build sandable primer. Yes, shrinkage is an issue for polyester layups. Allow about 1% for lack of a more detailed explanation. Evan Gatehouse >I'm interested in making a plug, than a female mold with parting plane >and flange to make several canoes for our club. My plan is to lay out [quoted text clipped - 16 lines] >final question, is there a realease agent tape I lay in the female mold >to cover the seam on the parting plane. If you have a canoe that you like the lines of you could use it for your plug by pulling off the gunwhales. bracing it on the inside and polishing it smooth >>I'm interested in making a plug, than a female mold with parting plane >>and flange to make several canoes for our club. My plan is to lay out [quoted text clipped - 20 lines] >your plug by pulling off the gunwhales. bracing it on the inside and >polishing it smooth I saw someone do this. They used a factory canoe for a male mold and split the bow of the new canoe with a knife then drew it off like a banana skin. Then they taped it back together and surfaced it. You can use clear packing tape for a release tape. There's a blue paste wax you can smear on it if you want. (it might be called Part All), Happy paddling. >>If you have a canoe that you like the lines of you could use it for >>your plug by pulling off the gunwhales. bracing it on the inside and [quoted text clipped - 6 lines] > paste wax you can smear on it if you want. (it might be called Part > All), Happy paddling. A group of us did this many years ago. But we braced the mold and built in the parting line before we laid up the glass for the mold. Worked just fine. However, when we molded our first canoe, it bonded to the mold. The combination of a fresh epoxy mold and the release wax we used didn't work. Had to build a second mold. We were lucky we didn't bond the mold to the original canoe. |
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