I’m looking forward to doing some casting work towards the end of winter. The main goal for now are some EBT Vulcan truck side frames. The part would be roughly 3.75" x 1.125" X .75" I plan to spin cast these, using the lost wax technique. My big question I was hoping some of you experienced casters could shrink (pun intended) is about shrinkage. With a brass part of that size, will I have to make the waxes and mold oversize to combat shrinkage as it cools, or will the extra supply of molten brass in the crucible be drawn it to compensate for it?
so you want the spin on casting. Didn’t the one guy say 3% shrinkage?
Metal shrinks as it cools.
Wax shrinks as it cools.
Rubber molds (vulcanized) shrink as they cool.
Both metal and wax have to be in the liquid state to move,
thus both shrink, the more steps you add, the less you get!
I have all the tools to cast, but nobody wants to pay for castings.
The 3% David remembers was the allowance for printed masters/models. I shared my research trying to drum up bidness.
I can’t tell you the amount of shrinkage the brass or what metal you are using, my experience was in gold and silver…
John
John Caughey said:
Metal shrinks as it cools.
Wax shrinks as it cools.
Rubber molds (vulcanized) shrink as they cool.
Both metal and wax have to be in the liquid state to move,
thus both shrink, the more steps you add, the less you get!
I have all the tools to cast, but nobody wants to pay for castings.
The 3% David remembers was the allowance for printed masters/models. I shared my research trying to drum up bidness.
I can’t tell you the amount of shrinkage the brass or what metal you are using, my experience was in gold and silver…
John
ps; casting temp affects the outcome too.
OOPS hit quote, meant to edit…
Long time ago, in a scale far from G, Precision Scale Co. used to do custom casting. I was inquiring about doing some fairly large (for ‘O’ scale) castings and was told that the masters needed to be 8% oversize, and 10% if there was going to be post process machining.
That being said the casting process has changed considerably over the years since then (somewhere near 40 or so). Back then it was real wax for the lost wax part, dental plaster for the refractory and vulcanized rubber molds. Today the non vulcanized molds hold up near as well as the older vulcanized ones, the waxes tend to be more of a resin from a 3D printer, and the refractory is a ceramic slurry that holds detail even better than the dental plaster.
If I can find it, I purchased a book on setting up a ‘garage’ casting business. It was an interesting read then, and I am sure most of it is still pertinent today.
Bob C.
Been wondering how to put a bronze or brass cap on the stack of the 1 1/2 inch live steamer. Haven’t found anyone to ask, yet.
Why don’t you ask John? He keep saying he wants to get into casting.
I’d machine threads into it and screw it on, or hard silver solder. Silver bearing solder may be too low temp. I don’t know live steamer parameters well enough to advise.
John
Thanks for the advice guys. 10% is the number I’ve always heard as well. So I guess that going to be my starting point for the fist master. Of course there will be some post process machining, for the axle holes (more likely bearing holes) and possibly in the bolster slide area. I just talked to a fellow at the NNGC in Maine who was using Precision Scale Co. for some casting and he was very pleased as well as the cost seeming reasonable. I’ve thought of out sourcing the casting but it’s something Ive always wanted to do. Maybe more in the vain of larger sand casting for 2.5" scale, but I suppose it’s good to start small, even though there is very little in common with those two processes.
Ric, Can you post a picture of what you’d like to attach and where? John’s suggestions sound very appropriate, but it’s had to make the proper decision without seeing it. If you guys want to pull that big RV up in front of our house the next time you are rambling through the area, it sounds like a job we could turn out in about an hour in the shop.
A big RV, up the cowpath you call a road? I would like to see that. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)
All things are possible. Some take guts or gonads, some take mind altering substances, some just take stupidity and blind luck. I’m still a work in progress and prior results should only be called experiences. Some experiences leave permanent scars or reminders. 
My thoughts of the brass at the top of the stack is no different than some of the Bachmann Annies or many other engines. Maybe it is screw fitted or maybe just tight tolerance press fitting or just sits there. Never explored the thoughts, before.
Ric Golding said:
All things are possible. Some take guts or gonads, some take mind altering substances, some just take stupidity and blind luck. I’m still a work in progress and prior results should only be called experiences. Some experiences leave permanent scars or reminders.
My thoughts of the brass at the top of the stack is no different than some of the Bachmann Annies or many other engines. Maybe it is screw fitted or maybe just tight tolerance press fitting or just sits there. Never explored the thoughts, before.
I like to think that in my case its skill, instead of blind luck. But that is simply the delusion I prefer to operate with. As for permanent reminders, I have several of those. Somedays, its difficult to just get out of bed and stand up like a person.
Ric Golding said:
Been wondering how to put a bronze or brass cap on the stack of the 1 1/2 inch live steamer. Haven’t found anyone to ask, yet.
See my post today on turning wheels in the Arrowhead Water Car thread. We can turn a nice brass or bronze ring for the stack, Easy to mount and make. Just send me a print of what you need.