Patternmakers

[Klox]

Are there any Patternmakers browsing this site?
If so, i would to hear from you....

Klox

[castguy2003]

You got one,

[Klox]

Castguy, we've met on the casting forum, hi again!
As i understand these days Patternmakers are hard to come by. I presume that your one of the guys that can still make a pattern by hand for sandcastings....
May i be so bold to ask if your interested in giving us some background on moulds (the making of), feeders, risers etc....?

Thanx

Klox

[castguy2003]

I got my start back in the early 60's working after school and weekends. Started a dual wood/metal apprenticship in 1969. I am what is known as a Master Patternmaker, meaning I can take a concept from drawing through complete tool.
Up until 1988 I worked the "old fashioned" way with chisels and gouges for wood and manual machines for metal. Then my shop got it's first CNC mill. By 1990 most patterns were done to some extent on CNC.
In the late 90's I left the shrinking pattern trade and went into casting and tooling engineering.
Throw your questions at me.

[Klox]

We've got a bit of a quality problem in South Africa when it comes to foundries doing small batches(read sand casting moulds/patterns). (Anoel, NeoMoses i'm not bashing anyone here!). A (potential) client ask me if i could look into casting jail keys. Currently they take wax patterns from a master pattern and then cast by gravity. I assume the shape is a bit complex as i haven't lay eyes on a sample key yet.... Is it going to be better to go the high pressure die cast route or are there some "hurdles" to overcome i don't know of yet? I presume the matl would be steel/ iron.

Thanx

Klox

[castguy2003]

If you already have wax patterns the route to go would be investment (lost wax) casting. The individual wax patterns would be fastended to a wax "tree" which is really the riser and runner system. The resulting assembly is dipped in a ceramic slurry and dried resulting in a ceramic shell. This is the actual mold. The wax is melted out and the ceramic shell is fired to about 1800-2000 deg F then the molten metal is poured into the shell.
Just about any steel brass ort aluminum alloy can be poured. The resulting casting is "near net shape" meaning very little or no machining is required.

[cadcam]

I agree with Castguy that wax investment would be a better thought..

My thought comes As I started in the machining industry as a Wax investment tool maker and even worked as a tool maker for one of the big foundrys out here.

Still help with some of the programming for all kinds of mold shops out here at times.

[Arnie]

Castguy,

I'm a potter who wants to broaden out to metals. Can you give me some pointers for a ceramic slurry recipe? Lets say for wax models. It needs to be virtually no shrinkage, right? I expect you will use a finer mix for an initial coat and then a dry sandy sprinkle? What is that stuff?

[cadcam]

Wel it matters on the metal you want to pour to the shrinkage.
Lets say 6061 would be close to .025 per inch shrinkage.

[Arnie]

Hmmm, 6061. Would that be an aluminium alloy? Do you mean that it shrinks on solidification? Nearly all clay formulations will shrink from wet to dry and again from dry to fired. Are you saying that the dry to fired shrinkage of the ceramic needs to match the solidification shrinkage of the metal?

[Dogsione]

Arnie,

If I may chime in...

The "Ceramic Shell" that is being referred to uses a colloidal silica binder with a fused silica refractory. It's a specialty product that can be a little touchy to work with - usually the binder must be constantly mixed to keep the colloidal silica in suspension. There are some products available, however, where you don't have to keep mixing. Shellspen, I think, is a brand name.

The other investment option is the 'traditional' one using mostly plaster, sand, and Ludo (sometimes spelled "Lutto" - old ground up molds used as a filler). Use the same wax gating system outlined above. These molds will need to be "burned out" in a gas kiln at around 1050 degrees F for a few days.

The finish right after casting can be quite good with a minimum of chasing.

Another option is to use resin bonded sand of which I'm much less familiar.

[Arnie]

Good on ya Dogsione! Shellspen has a website and it looks like I'll find all I need to know there. I was starting to think it was a dark secret.

www.shellspen.com

I have come across the word 'lutto' before, I met someone who was casting glass and he was using an aweful mix of plaster, ceramic fibre and recycled plaster. Yuk! Oh well, it worked.

thankyou