Hi, I'm new here and I am looking into make a bike part called a hood. This is a sleeve that goes over a brake shifter this part for a particular shifter is no longer produced. I've researched this and I think I need either a 3 or 4 part mold. I'll attempt to attach a picture. Based on what I have learned i am pretty sure I need to create the inner mold 1st. I'm just not sure the best way. Like do I just submerge the part and the cut around it for the inner part? The part is about 3 1/2 x 2 1/2 x 1 1/2 inches wide and is hollow along the length. The rubber is about 2.5mm thick in most places and is fairly soft. Any suggestions are really appreciated.
You can probably get away with just a two piece mold. I would glue down the wide piece to the bottom of the mold box and fill it up to around halfway up to the narrow end. Be sure to add "registry keys" in the top, if you wait until the top of bottom half is mostly gelled up but still moveable you can just push whatever you use as the keys in the top without needing to worry about how to suspend them. Once the bottom is cured, remove the registry keys and be sure to spray or brush on a release agent over the entire surface of the bottom half (and especially inside the empty areas made by the keys) before pouring the second half. Any spot that doesn't have release agent on it will let the silicone bond with itself and you'll need to cut it loose. Also you'll need to be sure to put a pour hole in the top too so plan where you want that to go. I hope this helps.
Hey there. I have managed to make several copies! Still practicing since I cannot seem to get them 100 percent perfect. I have left air bubbles or got to aggressive and overfilled and I think forced air into the top of the mold. Gonna get it eventually.
What are you using as the casting material? If it's a quick curing resin type, you might want to try something with a longer open time and use a toothpick or any long thin item to encourage the bubbles to rise away from the bottom. Vibration such as tapping the mold helps too. I'd mix up two smaller batches, pour the first one in the bottom of the mold, use a toothpick to run around the bottom area a little, then mix up the rest of the casting material and pour it in. And depending on what your casting material is, you should be able to "recycle" it to use as a filler for a larger cast or use "drips" off a fresh pour to fill in some of the bubbles - I can't count how many times I've fixed my castings with drips.
Hi there, I am still working on this and still having issues with small bubbles near the single vent hole. I am going to attach pictcres. I included a picture of what this is for just for reference. The OEM is a soft grippy type rubber its a TPE. These are no longer made and are hard to find. The replacements I am making are a polyurethane 50 hardness. The ones I have been able to make while not perfect work well. The molds are made of silicone and are pretty firm. My issue is I wind up in most cases small bubble/air holes near the edge of the (hood) near where the single vent hole is. I have tried pushing extra product thru, which just ends up wasting material, I also have tried tapping the mold on the table or floor. The way the hood is oriented in the mold is horizontal with the lowest part at the bottom. The fill hole are at the top and are on the actual bottom of the hood when its installed. I use a medium working polyurethane that gives me about 15 to 17 minutes working time. I have been filling the molds tilting them at 45 degrees which puts the single vent hole at the highest point. I have tried partly filling and then letting the process settle a bit for a minute or so going back and forth between both molds left and right. just frustrating that I cannot seem to figure out this puzzle. I am thinking that this is a somewhat complex mold to be working with since I am a newbie. Any help or suggestions would very greatly appreciated. just for info I build the molds using foam core board, hot glue and clay. I suspended the hoods in the middle using super glue to two acrylic rods with the air vent a small point hold at the very base of the hood. I attached pics of the results and the molds. please help. :-( I'll reply again with a couple more pics.
Another thing you can try is using a syringe to "inject" the casting material to get it in there better - it might help and it might not but it's worth a try. You could also cut out some of the area around the vent hole and make it more "funnel" shaped, sometimes a funnel shape will help prevent some of the air from getting into the mold from the pour since you pour the casting material down the side of the funnel.
Another thing to try is an "open top" mold where you don't use a pour vent. The tops of the castings are level anyway so you might could just leave off the top of those as you don't fill past the tops anyway.
Also for some bubbles that caused voids on some of my castings, I've used "drips" to fill them in. What I call drips are just pretty much droplets that I use the tip of a toothpick to drip into the holes to fill the holes with. I've mixed up tiny amounts to make the drips and they've come out looking fine.
Hi there, From the start I have been using these squeeze bottles normally used for doing tie-dye they have a narrow tip on the end that you can cut to size. I got those at Hobby Lobby. That has seemed to work well for me. I did appear to have some success vibrating the molds. I used my dough nut compressor that was near by and kicked it on and sat the mold on it while injecting the urethane with the squeeze bottle. Not sure at this point if that was by chance or a solution. I'll need to try some more.
Definitely let us know how it works out, I'm to the point that I want to see them come out exactly right for you. And the compressor is a great idea, I'm one of those people who will use a tool for something that you normally wouldn't think of using it for - I made a mini electric mold mixer (for mixing 180g at a time) using a milk frother head and an electric screwdriver. Works great for me and saves my poor hands from cramping.
I have finally broke down and ordered a degassing kit. I am going to try to degas the urethane before I inject it to the mold and the I will degas the mold right about when its full. I then try injecting the last bit of material. dunno what else to try. I know there are cyclist who want these badly. I sold 19 sets that I had even though they were not perfect. I was able to touch up many of them that had small holes. That was a fantastic idea! everyone that has gotten thinks they are great and close to the EOMs. Thanks Benny