Colt parts...sintered vs. investment cast

[JNewell]

Been reading my new copy of Kuhnhausen's book on the Mk III and Mk V Colt actions and he mentions that some of the internal parts (which had been machined in the earlier D, I and other revolvers) were made from sintered metal in the Mk III and then investment cast in the Mk V.

I'm familiar with investment casting. How does sintered metal fabrication differ? What are the relative advantages/disadvantages of one versus the other? (Dfariswheel, are you out there for this one???)

 

[Highland Ranger]

Basically heating up metal powder and mushing it together . . . .

My recollection is weaker parts, but the article below indicates possible advantages.

http://en.wikipedia.org/wiki/Sintered

Bottom line is if some engineer does his job right, the part will be made sucessfully using the cheapest process posible to deliver the desired wear, strength and other attributes.

 

[numbertwentynine]

modern sintering or powder metalurgy is capable of making very complex parts from very hard metals. I would say it is far better than casting when talking about cast iron or any of the super alloys, steel is probably about the same. when i say modern I would probably say in the last 15 or so years. i don't know about the stuff from way back.

 

[dfariswheel]

Sintered steel was an early version of today's MIM (Metal Injection Molding).

Powdered steel is injected into a mold, the mold is heated until the steel melts and fills the mold.
The mold is opened, and a basically finished part is revealed often needing nothing more than case hardening.

The advantages were lower priced guns, and even revolvers could be "machine fitted".

In the old Colt's each and every part was made over-sized, and a Master fitter assembled the revolver by stoning and filing the part to an exact fit.

With Colt's revolutionary system, the assembler selected a part from a bin and test fitted it. If it didn't fit, another part was tried.

The advantages were a gun that cost significantly less since there was a huge saving in human labor.

This meant a $400 King Cobra versus a $1000 Python.

When Colt did a slight redesign of the Mark III and brought out the Mark V, the sintered steel hammer and trigger were changed to cast steel.
Colt decided cast steel was a better option for hammers and triggers, but other parts were still sintered parts.

The design of the Mark III with it's machine fitted, sintered parts revolutionized the gun industry, and virtually every DA revolver made since uses Colt's system, and an almost exact copy of Colt's transfer bar action.

The only real downside to this is if repairs are needed. Since the parts are case hardened with a super thin, near glass hard surface, cutting, re-fitting, and even most polishing of parts is impossible.

Repairs are done the same way the gun was first assembled: A new part is test fitted, and if it doesn't fit, another is pulled from the bin.
The problem is, most gunsmiths don't HAVE a bin full of parts to allow selecting another.
This often leads to local gunsmiths trying to "get it to work" by stoning parts.
Since this breaks through the thin case coating, soft metal is exposed, and the part soon wears and stops working properly, often dangerously.

This is why the traditional "get it to work" gunsmithing techniques of heating and bending, stretching, and stoning can't be used on modern guns like the later Colt's, the S&W's, the Ruger's, Dan Wesson's, and Taurus's.

The up side is, you can buy a $500 gun instead of a $1200 gun.

 

[JNewell]

Sintered steel was an early version of today's MIM (Metal Injection Molding).

Powdered steel is injected into a mold, the mold is heated until the steel melts and fills the mold.

Thanks, that was pretty much what I remembered...

When Colt did a slight redesign of the Mark III and brought out the Mark V, the sintered steel hammer and trigger were changed to cast steel.
Colt decided cast steel was a better option for hammers and triggers, but other parts were still sintered parts.

Do you know what attributes of the parts made investment casting a better choice?

 

[Highland Ranger]

Precise casting method that also requires less machining than traditional cast parts. Difference would be the surface hardness issue . . . . ?

 

[fletcher]

I wouldn't think surface hardness would be too much different. For the same metal, the surface hardness will be primarily a function of the thermal history of the part during casting.

Note that sintering does not take place above the melting point, but below. It operates by diffusion, driven by reaching a lower surface energy. Typical casting does require melting the metal. Sintering is capable of obtaining a higher quality part. But, it does boil down to:

Bottom line is if some engineer does his job right, the part will be made sucessfully using the cheapest process posible to deliver the desired wear, strength and other attributes.

 

[dfariswheel]

The apparent reason for the change from the Marks III's sintered steel to the Mark V and later guns cast steel hammer and trigger was a few cases of broken parts.

There were a few Mark III triggers that broke through the frame pin hole, and cases of the hammer stop "nose" chipping or breaking.

 

[EddieCoyle]

Powdered steel is injected into a mold, the mold is heated until the steel melts and fills the mold.
The mold is opened, and a basically finished part is revealed often needing nothing more than case hardening.

Close, but not quite accurate. Cold powdered metal (along with a small amount of binder) is compressed under 10's or 100's of tons of pressure in a powdered metal press. The resulting "green" part is checked (usually by weighing it) then heated in a sintering furnace to burn out all of the binder and fuse the powdered metal together. The resulting near net-shape part may have secondary forging or machining operations done to it after sintering.

These parts can be made very strong - many gears are made this way, as well as connecting rods for high-performance engines.

 

[Standing Wolf]

This meant a $400 King Cobra versus a $1000 Python.

I think it originally meant a $350 Trooper Mark III versus a $450 Python. I'd guess the price differential rose with time.

 

[Dienekes]

I once had a Mk III trigger snap in two just dry firing it.

Not much of a confidence builder.