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Casting with rubber molds
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jstewartdunn
Could you use a silicon rubber mold to cast a wax part instead of using
resin? You would then use the wax part to produce a lost wax part in brass. J J Stewart Dunn Windham, NH
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On Dec 15, 2005, at 8:50 AM, jstewartdunn wrote:
Could you use a silicon rubber mold to cast a wax part instead of usingIndeed you could, although it does seem more complicated that just casting it in resin <G>. In addition, many RTV rubber molds can be used with low melting temp metal alloys to cast parts in metal. My general impresession has been that for ease and accuracy of reproduction, it is hard to beat resin. BTW, my favorite casting resin is Railroad Resin, from Trainstuff http://www.trainstuffllc.com/public_html/tips%20&%20clinics/Resin% 20Clinic/railroad%20resin.htm Regards Bruce Bruce F. Smith Auburn, AL http://www.vetmed.auburn.edu/~smithbf/ "Beer is proof that God loves us and wants us to be happy" - Benjamin Franklin __ / \ __<+--+>________________\__/___ ________________________________ |- ______/ O O \_______ -| | __ __ __ __ __ __ __ __ | | / 4999 PENNSYLVANIA 4999 \ | ||__||__||__||__||__||__||__||__|| |/_____________________________\|_|________________________________| | O--O \0 0 0 0/ O--O | 0-0-0 0-0-0
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Gary Mittner
I agree with Bruce on Railroad Resin by Trainstuff. I have used it in G
scale for parts for the B6sb I did as well as making full copies of the PRR Scale Test cars in G scale. I think their website is http://www.trainstuffllc.com If not, do a google search.......Gary Come visit my PRR Pages: http://www.angelfire.com/film/prrpics/PRR-Pages.html
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Ken Hough <k4sb@...>
Of first concern is shrink. If you make a silicone mold (there are nearly
50 different compounds) you need a no or low shrink mold compound. Second, lost wax shrinks about 7%. All metal shrinks when cooling. Some resins do not shrink at all. I use Alumilite. Why? Because I always have after I experimented.It is very low shrink. I sold a resin O scale PCC car 20 yrs ago. I made the master exact size. Using Alumilite silicone and their resin my castings had just a 1-2% shrink. No one noticed. Neither did I. NOW however there are many others worth a look. Look for linear shrinkage. Ken Could you use a silicon rubber mold to cast a wax part instead of using resin? You would then use the wax part to produce a lost wax part in brass. J J Stewart Dunn Windham, NH SPONSORED LINKS Ken Hough Photographic Repair Service Specializing in the Complete restoration of Deardorff View Cameras Est 1982 www.deardorffcameras.0catch.com 219 462 0281
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J W Box
Ken:
My firm has been using silicone rubber molds to make wax patterns for investment castings for years. We have a small in-house casting foundry that casts aerospace alloys exclusively - exclusively, that is, except for my brass engine parts that I sneak in periodically. Rubber mold techniques were pioneered by the jewelry making industry decades ago. Choose an RTV compound that has zero (< 0.1%) shrinkage. I like an old Dow-Corning silastic compound called Silastic E, but it is getting hard to find and there are many others that work fine. If you control wax injection temperatures, metal melt temperatures and mold temperatures closely, you can make castings with an overall shrinkage of less than 2% from pattern to part. That's a lot of "ifs", but any caster with his process under control can do this. If you really want to get into this, buy the book Centrifugal or Lost Wax Jewelry Casting for Schools, Tradesmen, Craftsmen by Murray Bovin. It's an old book that concentrates on the casting part of the process, not mold making, but the concepts are all there. I bought it over 25 years ago when I wanted to make parts for Bob Smith of Central Locomotive Works in my garage. I never did make parts for Bob, but I used the experience to cast several million small parts for the medical and aerospace industry. There's new technology on the immediate horizon that may change pattern making. Rapid prototyping machines (rp) now exist that can take a 3D computer model and make the pattern. Once you have drawn a part, you can simply scale it in software and make the pattern in any scale. I showed a bunch of PRR parts in my preferred scale of 1/32 at my table at Cocoa Beach Prototype Modelers show last January. No one seemed interested, go figure. I have some photos at: www.galtran.com/PRR_L2_Construction_Information/pennsylvania_railroad_l2s_cl ass_3.htm Bill Box
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Judd Barton <NNNPRRJRB@...>
Group
toggle quoted messageShow quoted text
A small operation that is using the rapid prototyping machines is Mark4design <www.mark4design.com>. He is presently working on a PRR X23 in N scale his company and a few other projects for other firms. He is open for ideas in for other projects. Judd Barton J W Box wrote:
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Ken Hough <k4sb@...>
You did not say your company did lost wax! I built a centrifugal caster 20
years ago. I used a 24 in dia feed pot for a farm as the base. Been there and still at times do it. My newest project is the wire support arms for the cantenary on our clubs layout. I need hundreds of them.. What's with Dows Silastic E anyway? I used it for molds too and it is tough to get. I contacted Dow last year and was told I could not get an account and they would not tell me of a distributor. For really flexible delicate molds I Castaldo Econosil Mold Rubber. I have a friend who bought a 3 axis laser RP machine. I've done some neat "one offs" on it. Thanks for the book hint. Ken Ken: My firm has been using silicone rubber molds to make wax patterns for investment castings for years. We have a small in-house casting foundry that casts aerospace alloys exclusively - exclusively, that is, except for my brass engine parts that I sneak in periodically. Rubber mold techniques were pioneered by the jewelry making industry decades ago. Choose an RTV compound that has zero (< 0.1%) shrinkage. I like an old Dow-Corning silastic compound called Silastic E, but it is getting hard to find and there are many others that work fine. If you control wax injection temperatures, metal melt temperatures and mold temperatures closely, you can make castings with an overall shrinkage of less than 2% from pattern to part. That's a lot of "ifs", but any caster with his process under control can do this. If you really want to get into this, buy the book Centrifugal or Lost Wax Jewelry Casting for Schools, Tradesmen, Craftsmen by Murray Bovin. It's an old book that concentrates on the casting part of the process, not mold making, but the concepts are all there. I bought it over 25 years ago when I wanted to make parts for Bob Smith of Central Locomotive Works in my garage. I never did make parts for Bob, but I used the experience to cast several million small parts for the medical and aerospace industry. There's new technology on the immediate horizon that may change pattern making. Rapid prototyping machines (rp) now exist that can take a 3D computer model and make the pattern. Once you have drawn a part, you can simply scale it in software and make the pattern in any scale. I showed a bunch of PRR parts in my preferred scale of 1/32 at my table at Cocoa Beach Prototype Modelers show last January. No one seemed interested, go figure. I have some photos at: www.galtran.com/PRR_L2_Construction_Information/pennsylvania_railroad_l2s_c l ass_3.htm Bill Box SPONSORED LINKS Ken Hough Photographic Repair Service Specializing in the Complete restoration of Deardorff View Cameras Est 1982 www.deardorffcameras.0catch.com 219 462 0281
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