Making molds and casting parts.

[Mark42]

One part of my Niagara that is missing the the original MFG company logo that was on each side near the transom. I was fortunate enough to have the owner of the MFGBOATS.COM website mail me an original logo so that I can make a mold and produce a copy for myself.<br /><br />I see that there are molding and casting compounds on the market. Usually latex molding and urathane casting mixes. I was wondering if anyone here had used these products to reproduce pieces of their boats and how well the urathane casting materials hold up to the rough boating environments.<br /><br />One option I had thought of was to cast the piece using regular epoxy resin, but was afraid that it might be too brittle. The logo is about 9" x 2 1/2" x 3/16".<br /><br />As always, any and all suggestions or experiences are greatly appreciated.<br /><br />Thanks,<br /><br />Mark.<br /><br />Updated to correct logo size.

 

[bayman]

Re: Making molds and casting parts.

If you do end up using epoxy resin you might just want to use a fiberglass or other filler. Done correctly epoxy can be really tough.

 

[petrolhead]

Re: Making molds and casting parts.

Cast epoxy is really tough and picks up delicate detail well, I use it all the time at work, use a slow cure to allow any bubbles to rise to the surface. <br />Best for moulds is RTV silicone rubber, no release agent needed, and you can even cast low melt alloys in it if you want to.

 

[18rabbit]

Re: Making molds and casting parts.

Mark – I’m interested in what you are doing. Have you looked at the mold making stuff at Tap Plastics or their website? They usually have how-to instructions…might get you started. If you don’t mind, please take pix of your project and post them here. I’d like to see how you do this…and you’ve already proven you know how to do the pix and posting thing. <br /><br />Whenever I have done any epoxy and/or glass work and I have any epoxy left over I put it into anything handy to mold it…just to see what it’s like. Regular old epoxy is tough as nails when fully cured, more so with micro-fibers, even sharp corners that I would have thought should chip doesn’t. I was surprised at how well epoxy with micro-fibers and silica can hold a sharp, knife-edge. So much for metal detectors and airport security…

 

[Mark42]

Re: Making molds and casting parts.

I did some web shopping and found TAP Plastics and others offer molding and casting stuff. Looks like it would cost about $50 plus shipping for the basic materials I need. Will take pics and post them. <br /><br />The other night I was cleaning up and found a tube of silicone caulk that I forgot to seal up and it started to harden in the tube. So I covered the logo with a little olive oil, cut open the tube and spread the remaining silicone over it. Has been sitting a couple of days, and tonight I'll check to see if it fully hardened. It was just one of those "spur of the minute" things. <br /><br />Thanks for the input on your epoxy experiments. I haven't worked with the fillers. What is the hardend product like? Glass smooth or porus looking? <br /><br />Stuff like that is always fun to do and gives you ideas for future projects. <br /><br />Will keep you posted on this one. <br /><br />Mark

 

[BillP]

Re: Making molds and casting parts.

Mark42,<br />At one time I worked with rubber molds and water based urethane casting resin to make repro antiques. The resin base was powder and then mixed with water to make it pourable. It didn't appear strong enough for marine use.<br /><br />I'd probably use regular slow cure epoxy resin to make the insignias. Epoxy is durable enough to do it. Most big hobby stores would have a pourable casting resin to do it too. Otherwise I might scan the insignia and have a metal shop cut them out with a cnc machine on the desired material. By the way, there is an old MFG like yours for sale here in Fl as a project...$200. Projectboats.net or something like that. Actually, it is bigger with a flat windshield but same looking hull.

 

[Mark42]

Re: Making molds and casting parts.

I picked up a quart can of Bondo brand fiberglass resin at Home Depot and was experimenting with it. I have some powdered aluminum, so I mixed up about an oz of resin and mixed in 1/2 teaspoon of powder aluminum and let harden. It did not come out as nice as I thought. Looks kind of grey where it touched the mold, but the top side is very aluminum looking. Wish it was the other way around.<br /><br />The Bondo resin is listed for boat repair, tubs, jacuzzi, and all around home fixes. It lists a 2 hour cure time. After 24 hours, the little brick I made 1 x 2 x 1/2 inch is hard, but slightly flexable. If I press an indentation with my fingernail, it will come out within 5 minutes. Is this the way fiberglass resin usually hardens? I know its not epoxy, its listed as "monomer" something-or-other resin. <br /><br />I remember fiberglass resin hardening more brittle than this when I used it for auto body repairs years ago. Think the aluminum has affected it?<br /><br />I will be ordering some molding compound soon to make a better mold than the one from silicone caulk. The silicone caulk mold came out ok, with the problem of some air bubbles ruining it. I think it's too thick to fill all the nick and crannies from the tube, even though I spread it around with a spreader.<br /><br />Mark

 

[petrolhead]

Re: Making molds and casting parts.

If you're only making a single casting you can probably do this on the cheap, using wax to make the mould. Just melt some ordinary candle wax and brush it onto the pattern, having treated the pattern with a spray of silicone wax first, continue to build up coats of wax, after the first couple you can just drip it on.<br />When it's reasonably thick and cooled pull the pattern out and pour the epoxy resin in.<br />I've done it this way a few times, silicone is fairly expensive and takes time to cure, wax is quick and cheap but doesn't last long, good for one or two though.

 

[BillP]

Re: Making molds and casting parts.

Regular plaster of paris works fine for small one off molds. Cellophane food wrap can be used for a simple parting agent if you don't mind wrinkles or sanding the part smooth. I made bowls this way.<br /><br />Don't use regular wax for a parting agent if both mold and part are fiberglass. It MAY stick the parts together...I know, I know, some people may have used regular wax successfully but the odds are against it working 100% of the time. If you decide to chance it don't put on a lot of wax coats...that is when it will stick worst. The boat mfg industry found this out a long time ago and that's why real mold release wax was developed. They also learned not to wax everytime a new part was laid up...excess wax makes the parts stick together. At one time, SeaRay was going approx 30 hulls before rewaxing. Their blem and "sticking to mold" problems went away.

 

[18rabbit]

Re: Making molds and casting parts.

There is that rubbery stuff the dentist uses to make very detailed dental molds. It sets up fast, flexible, but rigid enough to hold the weight of plaster without deforming. If you see your dentist regularly I bet they would give you what you need to make your mold if asked. If you only go to the dentist every 7 or 8 years, maybe not. <br /><br />Years ago I used to use plaster for making extremely detailed molds for casting metal objects. As I recall, to release we put the warm-to-touch plaster in water and it fizzled away.