Hello again everyone! Is this a familiar view for anyone? You have a lamp (or a stove) missing its pump knob. As I had lanterns of the same type I desided to make a mold from an existing pumpknob, and then make a new pumpknob using casting resin. The silicone I used for makeing the mold is named silicoval NVE and is a 2-component silicone that is ready after about 4 to 6 hours of hardening. Before I mixed the silicone, I carefully brushed some vaseline (specially made for this silicone) on the pumpknob that I intended to make the mold out of so that the pumpknob wouldn't stick to the silicone when it had hardened. Then I poured the silicone over the pumpknob into a small can and waited for 5 hours until it was hard and could remove everything from the can. I cut up the mold into two pieces (could have made the mold in separate parts also but I wanted to test this way first) and removed the pumpknob inside. Now I had to make the threads into a brass tube,so that the pumpknob wouldn't brake when screwed on the pump rod. And I then cut the brasstube into the right size and put a screw with the same thread into it (so I can get the brasstube out of the mold later and to get the brasstube at the right place in the mold also). With a file I trimmed both ends on the threaded brass tube. ...and welded a square brass plate at the lower end of the tube so that the tube wont spin or come out of the ready made pumpknob. Here is the "baseplate" welded (with Castolin 157) When this was done, I had to cover the inside of the mold with a special fluid and let it dry for 20 minutes. This fluid will prevent the ready made pumpknob from sticking to the mold. During waiting for the fluid to dry, I mixed the casting resin with the hardener. ...and then tinted to the right colour, (the original pumpknob was probably black on this one, but I couldn't get any black tinting colour so I took a red opaque colour instead as that one reminds me of the colours they use on Optimus lamps cleaning needle wheel and I might need that colour someday) After the resine was ready coloured and mixed, I poured the fluid into the mold. The resine that was left over I poured in a separate tray in order to check on that one when the resine was hard enough to remove from the mold.I pressed in the brasstube with the threads ... and waited for one whole day (24 hours)until I opened up the mold and removed the ready made pumpknob. I noticed that there was some air bubbles in the resine on this one, so I decided to make another one the next day, but with the left over resine I filled the small holes in the first one, so that one will also be usable Hope this gave some ideas to others who are missing either the pumpknob or the wheel for the cleaning needle on a lamp or a stove.
Hi Anders, nice tutorial. Would like to find out what equivalent fluids would be available here in the US. As for the air bubbles, I would suggest the next time after pouring, use sort of a vibrator to shake out the bubbles if the hardening time is long. Just thought of that when my dad taught me working on pouring concrete for building pillars. Ron
Thank You Ron! I actually started to make a second pumpknob after I noticed the airbubbles, but I havent removed it from the mold yet. But I did a small change to the mold and made a second air hole in order to get the air out, and after pouring the fluid into the mold I tapped the bottom of the mold for a long time, with a knife, in order to make airbubbles come out of the mold. I could actually see a couple of airbubbles come out also so I am a bit excited about what the result will be. As I said, the mold could have been made in a different way, and the next time I will make a mold, I will not split it in half with a knife as I did on this one, but make the mold into two separate phases so I first make the bottom of the mold, then the top of the mold, because then I can deside where the mold will be split. Now it is possible to see on the new pumpknob, the place where the mold was separated, as there is a thin line. Nothing big, but I learned that the second way woud be better and will try that the next time. I can try to find the information about the fluids I used (well the Silicoval NVE was viewed in one of the pictures) when I get home, and if I find anything useful I will write it down here so you can search for similar products. The material I bought was rather expensive, all in all more than 70€ and that only includes 2 dl of casting resin so if I make only these 2 pumpknobs they will have a price of 35€ each
The second pumpknob was almost perfect, only one airbubble close to the brasstube. I checked the resin bottles. On the resin it simply says cold glaze resin and in the paper I got with it, it says epoxy resin. On the hardener it says cold glaze hardener. The maker is Creartec and it is made in Germany, but I stumbled over several different makes on the Internet when I was searching for the right materials, so there are probably a lot of different names on these to choose from.
That particular silicone needs to be vacuum evacuated to get the air bubbles out. I use a brand called Alumilite Quick-Set RTV (sets at room temp) its thin enough that the air bubbles don't form. They also offer a 2-part resin that you can dye different colors (red, black, etc.)
The problem was actually not in the silicone as much as in the epoxy resin. But when stiring slowly and not making bubbles when mixing with the harder, and then, my secret weapon, putting the whole thing in the ultrasonic cleaner in some water, the bubbles comes out pretty nice
True, but the feeling of succeeding in making something new is better than the feeling of buying something . And if you have a part that you will not find anywhere, and it is possible to make a new copy of it, then I don't see any reason to not make the copy.
I do have a suggestion: put some sort of knurling on the outside of the brass tube so there is more grip for the resin so it is less likely to pull out...
Thank You mcdugal2 for the suggestion. I was thinking about the knurlings and tried to make it both with a pair of pliers and a wrench, but I couldnt make the type I wanted, so I ended up with making the square plate at the bottom end of the brass tube. As this also is bigger than the rest of the tube, the tube will not come out, and as it is square it will not turn around either so I think it does the job.
Made a new controlling wheel for an Optimus also. The material is a lot more glossy than the original, but still, better than no wheel The one to the right is the copy if someone didn't notice.
Thats some dedication, I would just stick any old knob on, but thats me, Have you seen these for holding the threads http://www.bighead.co.uk/ Keep up the good work
What I do to eliminate the chances of air bubbles forming is to "paint" the inside of the mold with a good coat of your resin (or whatever you happen to be using) and while the resin on the mold is still wet pour your remaining resin into the mold. I can (almost) guarantee no bubbles.
