First a disclaimer: I'm really new to this, but very excited about giving it a shot. I'm also very limited on fundage, and whatever I spend on backyard industrial supplies is coming directly out of my beer making funds...

I'm currently machining a wax part about the size and shape of a distributer cap for your car (Actually going to replace the distributer cap, as it is a housing for a DIY distributerless ignition system), with a wall thickness of .1875" I would like to cast it in aluminum using some sort of investment method (I suppose) (since dummy here didn't bother to design in any draft on the part!), partially for the education of it, since there are probably some urethanes or epoxys out there that would take the heat and abuse this part needs to be able to take, but aluminum would have more bling factor.

First off, I've got a little benchtop CNC, and the detail and complexity of this part is taking FOREVER to complete even in wax. From what I've read hardly anyone casts something exactly right the first time, so I need to be able to make some copies (besides just machining another one) of my wax master. Silicone mold maybe? There are no undercuts on this part, but there is also no draft at all, and its about 2" deep. Any advice or suggestions for making accurate wax copies?

Next, onto the real mold-

Where should I get investment ceramic materials, and what specifically should I be using for an application like this? And then after the wax is coated with investment, should I bury this whole thing in sand too? Is backyard sand OK here (I live on the coast, the backyard is mostly sand anyway), or will I want to find something special?

With these thin walls I was thinking that I would need to somehow forcibly move the molten aluminum to completely fill the cavity with minimum voids... which then got me to thinking about building my own junkyard centripetal casting machine from a busted air compresser motor, a wheel rim, and a 50-gallon drum (to shield me from the flying molten metal)

So then I start to thinking, how fast should this thing spin? I assume I would want to minimze the sprue length (bringing the casting closer to the center of the rim) but maximize the G's (crank up the RPM, maybe with a pully) but keep the whole contraption balanced enough to not fall appart! Short question: how many G's should my casting see?

Hey Sport. First, if you are using wax for the pattern then you won't need the centrifical casting method. The idea is to build up a coating of ceramic material then melt out the wax leaving the entire cavity as the mold, then simply pour in the moulten metal. As for the ceramic slurry, thats what it's called, do a search for backyard foundry and seek a supplier there. Good luck, Sport..

Well you'll either need a vacum or centrifical caster to fill the cavity....pouring would never work for this part. Generally when you pour you're doing a sand casting or it could also be a "lost foam" casting.

The slury is known as investment for "lost wax" casting....there are different types depending on what sort of metal is being cast.

wow. you're going so fast my head is starting to hurt :)

First off, you need to burn out the wax in the cavity BEFORE you pour the metal. The right equipment for this is aptly named a burn out oven. If you google or look around here, you will see stuff on lost foam casting - this you leave in and pour into the mold, but DONT DO THIS WITH WAX!. The burn out process also dries out and warms up the investment so it’s ready to pour. As Viper says you need a centrifuge or vacuum caster ($$$$). The centrifuge is the poor cousin to the vacuum. The investment is porous so under vacuum the metal gets completely drawn into the cavity (with the investment at the right temp!)

If you want to make more than one, you need to make a rubber mold and for that you need stuff like a vulcanizer. Then you split the rubber mold (in itself a skill), remove the master and cast as many wax patterns as you need.

Look to the jewelry supply industry – any one of their catalogues will be packed with lost wax casting supplies and tools.

I agree with Viper... a lot goes into lost wax casting (both $$$ and special equipment) and you might consider alternatives like sand or lost foam, or why not just turn and mill the part (after all, you are going through that process to create the master).

First off, you need to burn out the wax in the cavity BEFORE you pour the metal. The right equipment for this is aptly named a burn out oven. If you google or look around here, you will see stuff on lost foam casting - this you leave in and pour into the mold, but DONT DO THIS WITH WAX!. The burn out process also dries out and warms up the investment so it’s ready to pour. As Viper says you need a centrifuge or vacuum caster ($$$$). The centrifuge is the poor cousin to the vacuum. The investment is porous so under vacuum the metal gets completely drawn into the cavity (with the investment at the right temp!)

Okay, so maybe I don't need to cast this centrifugally- I was looking at some crank case castings Lyle (www.landstromsfoundry.com) did for a motorcycle in plain old sand casting, and look pretty good. My wall thickness = ~.18 after I've sanded machine marks off. When I turned the workpiece upsidedown to machine the back side, it was about .02" off, I'm not sure if this was from a bad zero location or if the workpiece shifted a little :frown: but it looks nice after a little love from some 1200 grit sand paper.


If you want to make more than one, you need to make a rubber mold and for that you need stuff like a vulcanizer. Then you split the rubber mold (in itself a skill), remove the master and cast as many wax patterns as you need.

They make this look so easy on the Freeman supply videos... but I'm starting to think I just need to be careful with my one wax master and make a plaster mold from it.


Look to the jewelry supply industry – any one of their catalogues will be packed with lost wax casting supplies and tools.

I agree with Viper... a lot goes into lost wax casting (both $$$ and special equipment) and you might consider alternatives like sand or lost foam, or why not just turn and mill the part (after all, you are going through that process to create the master).

yea- in the long run you probably have a point there... but I did cut my wax master at over 10"/min with a wood router bit (Prolly shouldn't try that in Al on a Sherline)! I don't even own a real set of high speed milling bits (yet)... I also didn't want to pony up the cash for 2 2"X6"X6" blocks of Aluminum billet when I've got an office full of raw abandoned 6061-t6 extrusions begging to be reincarnated as something useful. (can this stuff be backyard cast well without modification to the alloy, and if no, what should I do to it?) There's probably 100 pounds+ of it just trashing up my office at work alone!

Perhaps I should make a mold very roughly the shape of my finished part in sand, pour AL in, and then machine out the finished part, since I'm thinking I could never 1- melt enough aluminum in the back yard to fill up a complete 2"x6"x6" block of Al and 2- if I did, ever expect it to cool in a roughly crack-free rectangular solid-like shape, simply due to its massive volume....

HOWEVER Currently plan A (still evolving) is to attempt to make a removable 2-part mold from plaster of paris off my 1 wax master cook it to cure the plaster, and pour AL into that. My intended production run is for 1 good part.

One other thing.... I've been reclaiming machinable wax, curing powdercoated stuff, and was planning on melting wax out of an investment castings in a regular old oven in the garage, a refugee from a kitchen remodel. Why not?

It won't get hot enough to burn out all the wax...plus the investment must be hot enough so the metal doesn't chill when it touches the investment...you'll end up with a partial, porous casting.

It won't get hot enough to burn out all the wax...plus the investment must be hot enough so the metal doesn't chill when it touches the investment...you'll end up with a partial, porous casting.

Should I just make a second crucible and cook my mold while I'm melting the Aluminum?

I'm also struggling with the advantages / disadvantages of sand over plaster. it seems that a much smoother, more detailed surface can be achieved with plaster, but is seems like every example of a part I see like what I'm trying to do has been done with a wood master in a sand casting.

with these walls, would a sand casting work, or would the aluminum freeze too quickly.

I don't have a digital camera with me today or I'd send you a pic of the master, but at least here's a pic of the design in Catia:
http://home.comcast.net/~sporqster/housing.JPG
Note, I left out drilling the screw holes in the master as 1- I thought this would be a pain to flow AL around, and 2 they might not line up after the AL part shrinks, so I thought it best to cast it without the mounting holes and drill them in the casting later.

You are right, the most efficient way to make an irregular shape is casting. from solid it is a dodge to be used when other things like aesthetics don’t matter and IF its less time and $$$ than all the hassle of setting up for casting.

I like your attitude, after all the fun is in the making else we’d all just go a buy commercial stuff, but remember lost wax casting is a pretty tried and true process – you are going to have a tough time inexpensively circumventing its major components.

A lot of guys pour AL in their backyards with good results using a wood pattern and sand, or lost foam. I find lost foam a very cool process that side steps a lot of the tough parts of pattern making etc, but if each master is very difficult to make, you might be better of learning the wood pattern/sand cast approach

PS - since creating the wax pattern is the high value work, why not check out what it would cost to have someone with the equipment do the casting? you will get the best finish with lost wax, but the part will still require machining of mating surfaces.

If you're going to use a rubber mold to make duplicates of the part, you will have to
use a specialty mold rubber. The most common mold rubber used in lost wax casting has
a fairly large shrinkage. Even the expensive silicone mold compounds shrink more than 1%. The two part mold compounds which do not require vulcanising would be the best. Last time I bought a 5 pound kit it cost me several hundred dollars landed in Canada. I think I would try milling the part in aluminum if your machine is capable.

To quote Mcgyver: "Look to the jewelry supply industry – any one of their catalogues will be packed with lost wax casting supplies and tools."

He buried this advice halfway down his page, maybe you skimmed over it. Find a local hobby store that caters to people who do silversmithing and other metal jewellery as a hobby. This is widely done in that field and you do not need a fancy centrifuge. I have seen a system that worked on a spring; the mold is mounted at the end of an 18" arm mounted on a vertical axis, 'down' for the mold is on a radial line, there is a small receptacle that the molten metal is poured into (I think the term for this is a tundish) with a port in the outer side connecting to the mould, you cock the arm through two or three turns, pour in the metal, close the lid and pull the trigger. The only tricky bit is shaping the tundish so that when the arm accelerates the molten metal gets funnelled 'down' into the mold instead of spraying everywhere.

How large is the pattern, how thick are the walls. Centrifical or Vacumn casting will give you a denser casting then a sand casting. A sand casting will also have more surface texture.

You should just mill this sucker out of foam and do lost foam, it is sooooo easy compared to the other types of casting. Lost wax is nice but is really only needed for castings that require small accurate detail. Lost foam still gives you plenty of detail, and very good casting tolerances.

check out http://www.buildyouridea.com and look in the CNC section about "Homebrew HBLB bearings". It is excellent information that I've used, and I've been extremely successful with lost foam. It works great and I think it's the easiest way to cast for the hobbyist!

Here's a picture showing the CAD design image, then the foam part (cut by a foam CNC hotwire cutter in the background) and then the AL cast part after a small bit of filing to clean it (It only needed this because I didn't bother prepping my sand or my foam first caused I was in a hurry). The AL part looks exactly like the foam part; if you hold the foam part over it or the other way around it looks exact!

-niko

If you can make a wooden model of the part, then chemically bonded sand would work, I have made moulds from patterns with no draft on them using this method, the surface finish is really controlled be the grain size of the sand ( smaller grain - finer finish ). I almost always use sodium silicate bonded molding sand, it fairly inert to the environment, you end up with sand bonded with silica gel once it is cured by exposing to CO2, and you can pour the casting without having to dry the mold.

Here's some more cool info about lost foam

http://www.sfsa.org/tutorials/eng_block/GMBlock_20.htm

-niko

I am restoring a 1927 Oldsmobile 4 door Landau and need to locate someone to provide replacement parts using the Lost Wax Process. These pieces are basically the interior door hardware (interior door handles, window roller handles control knobs on the dash panels, and the escutcheons that are used to hold the handles and knobs in place.)

I am having a problem locating anyone who does this type custom lost wax process. Most people are doing jewelry and/or sculptures.

I have pieces from the car that are made of pot metal. Need to have them cast in aluminum, stainless steel or brass. Total of 20 - 30 pieces of various shapes needed.

Can anyone using this thread point me in the right direction?

Thanks,
Gene

Sounds like a job for petrobond Sporqster! I cant see the need to invest if it's going to come into conflict with your beermaking!!

I am restoring a 1927 Oldsmobile 4 door Landau and need to locate someone to provide replacement parts using the Lost Wax Process. These pieces are basically the interior door hardware (interior door handles, window roller handles control knobs on the dash panels, and the escutcheons that are used to hold the handles and knobs in place.)

I am having a problem locating anyone who does this type custom lost wax process. Most people are doing jewelry and/or sculptures.

I have pieces from the car that are made of pot metal. Need to have them cast in aluminum, stainless steel or brass. Total of 20 - 30 pieces of various shapes needed.

Can anyone using this thread point me in the right direction?

Thanks,
Gene

Gene,

First ... You don't want stainless steel... The shrink factor is too much probably something like 12%. Plus steel foundries are usually bigger companies that would not consider taking such a small job. Most of your aluminum foundries also pour brass. There should be several small aluminum foundries in your area if you look. Economically, it would probably be worth your while to try to make your own molds off of your parts in plastic. These will not be the molds for the metal but for the wax. Are you sure the best way is lost wax? There might be an easier way ...... I would have to look at the geometry. Is there any flash on the parts / can you see a parting line? It might be easier to go another route. Are there any undercuts on the pieces/ which way do the parts draft?

Thanks for your answer.
Craig, who is also on this forum recommended that I try using a spincasting process that he was doing. I sent the parts to him but he has developed a health problem and won't be able to work on my parts.
I will have the parts back next week.
I am going to attach some pictures of the parts so you can get an idea of what I am needing.
Any help you can provide will be appreciated. We are shooting for having the car ready for the 2007 Oldsmonile National Show in Bowling Green, KY in July.

Off line I can be reached at decrow@tx.rr.com

Gene Crowdis

Richardson, TX

with these walls, would a sand casting work, or would the aluminum freeze too quickly.
I don't have a digital camera with me today or I'd send you a pic of the master, but at least here's a pic of the design in Catia:
http://home.comcast.net/%7Esporqster/housing.JPG
What walls, we can't see it! :)
Where is the pic in Catia please?
I think I must be going blind! :rolleyes:

Well here I am again. Over 10 months later and I still haven't found anyone to produce the parts for the '27 Olds that I am restoring. See my post of November 2006 for samples of the parts that I need to have made.

I talked with a spincasting company in Dallas and made a deal with the owner to get the parts made. Left them with him for 6 months, then he said he took my parts to a machine shop to get them done. Won't talk to me or return my calls about the missing items I left with him. I was able to get most of the parts from the machine shop. Can't imagine how the spincaaster got the idea they could be machined. Machinist was puzzeled also.

Recently found another guy in North Carolina who sais he could and would do the parts. After three weeks of having my parts to look at, he decided that he didn't have the time to devote to making the parts. No problem, he will be sending them back to me tomorrow.

Can it be this hard to make replacement parts using the spincasting process? Surely there are other demands for low quantity, good quality parts that someone is making.

HELP??
Gene
Richardson, Texas

Gene try in the "RFQ" section...There may be someone local to you who would be willing/able to make your parts? Are they mazak? It looks like a job for Brass to me! :cheers:

Kipper,

The original parts were pot metal with nickel plating. Over the years the tight fit parts have frozen and when there is an attempt to free them up they give way.

I will try RFQ to see if there is any interest. Brass, zinc, aluminum will probably work. Needs to be something that I can have plated and maybe do a little machine work on if necessary. These parts won't get a lot of stress or use. Restored '27 Olds are pretty much for show. I tried a company that did stainless steel, but the quality was very poor.

Thanks for the advice.
Gene

Didn't read all the replies.....I have experience in mold making and casting bronze.

This company: www polytek.com....sorry couldn't get hot link to occur...anyway I have used them....they have all sorts of mold making conncoction,,,and a great catalog....they are in PA.

I would recomment making a rubber....silicon or cheaper polyuretheen mold from your original wax....

Silicon is so pliable.....it can do the odd shapes and undercuts....then you can make duplicates of the original and save what work you have done.

I do "ceramic shell" for the casting mold......this is a slurry of colodial silica in layers over the wax......

The ceramic shell is a bit more difficult....you will have to "sprue" and make "air vents" for the wax.....then make the ceramic shell.

then "burn out"......So you need a kiln and furnace....but aluminum melts much lower temp than aluminum....

You might consider checking out local colleges and universities....art schools....some of them have metal casting facilities.

Anyway, check out Polytek....they have a great catalog. That will get you started.

Idea....with the size of your item.....you can make a wax "tree" and cast several or more of them at the same time.

leland


(file:///Users/lelandimler/Desktop/www.polytek.com:.webloc)

It's tough to spincast some of those parts because of the size and mass. You need large, thick molds to spincast the big stuff and you run into problems with distortion and excess heat.

You could cast in bronze and then plate them, especially if you only need a few copies. Contact a sculptural foundry, that'd be a decent way to go. (doubt it'll be cheap however)

If you can get a two-piece, plaster mold made of your master pattern, you can duplicate the wax pattern fairly easily. soak the plaster mold in water, and then pour molten wax into the mold to fill it up. The wax will harden from the outside in, and when it reaches the thickness that you want the shell to be, pour out the remaining wax. If you make a mistake, or ruin the part getting the mold off, you can just remelt the wax and start over. You really should use a dark sculpture wax that you can probably find by searching the internet for sculpture supply dealers- they will also sell the ceramic slurry material that you need to coat the wax.