On 1/7/2015 5:19 AM, Rick wrote: > They are the carbon contact type, and I have tried the repair paint from > "Circuit Works, model # CW2605" and it seems to rub off after a while, > and I did some serious cleaning with q-tips and isopropyl alcohol on the > pads to get any oil and dirt off. Yesterday I tried another brand, MG > Chemical, model# 8339, and it seem to be a little better product, so now > I will need to get some into a machine to see how it works. > > I was just wondering if there was anybody that supplied or could even do > a short run of some replacement buttons.
There are electrically conductive silicones. Could be possibilities there. Use the conductive stuff just on the contact pads. Conductive silicone could be put into holes in a mold to form the contact pads then non-conductive silicone could be put into the mold to form the rest of the button. Make the mold on your CNC machine, design it to use a really large syringe to inject the silicone for the main part of the button. To not have bubbles, without having an injection molding machine set up for silicone, you can use a pressure pot. There are ones already configured for this but it's much cheaper to buy a 2-1/2 gallon one from Harbor Freight, unscrew the pickup tube from the lid and put a second pressure gauge in the paint outlet. First step, mix and put conductive silicone in the contact pad holes, put the mold in the tank and pump it up to 40~60 PSI. Let sit a day. Second step, remove from the tanks, assemble the mold then mix the non-conductive silicone, fill up the syringe and inject into the mold until it comes out the vents. You want the mold to have plenty of sprue and long vents to avoid air pushing in and ruining the casting when it's in the pressure tank. No, I don't want to take on the job of making reproduction buttons for this, but I'll share what I've learned in the past 14 years making RTV and hot vulcanized silicone molds and resin and metal casting in them. In the 90's I did a bunch of fiberglass molds and before that I grew up around plaster mold making and ceramic casting. Molding & Casting, it's what I do. :) (Along with fixing up machine tools, auto mechanics, carpentry, wiring, plumbing, painting and much more...) There are three main types of RTV silicone. Condensation cure, which cures by evaporation of a part of the mix. Most of these use acetic acid (smells like vinegar) and are *never* to be used on anything electrical because some of the acid remains and will cause corrosion, so will the evaporating acid. Another type uses alcohol, probably the stuff made for aquariums. Tin cure. This type shrinks some when curing and has a somewhat limited shelf life after curing. It's slightly less expensive than platinum cure and its curing is not inhibited by contact with other types of silicone. Platinum cure is the most expensive but most varieties have pretty close to zero shrinkage. It also has an indefinite shelf life after curing. Aside from price, its down side is curing is inhibited by contact with condensation cure and tin cure silicones and anything with sulfur in it such as polysulfide rubber and anything with latex, which includes most masking tapes and rubber bands. --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com ------------------------------------------------------------------------------ Dive into the World of Parallel Programming! The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
