Obviously tensile strength is important. Many new china/taiwan vises in the couple-hundred dollar range are Ductile Iron and around 30,000. I came across the Yost FSV-5 and it's Forged Steel and claims a 90,000 psi tensile strength and it's around $200.
http://www.amazon.com/dp/B00E8ITETS/?tag=atomicindus08-20
Not being a metallurgist - can someone explain such a difference?
Gray cast iron vs Forged steel - Forged is better, but why is this vise so relatively inexpensive?
Does anyone have any experience with this particular Yost vise?
Thanks,
First, please disabuse yourself of any notion that country or origin or cost has anything to do with the quality of a vise. There's only a weak correlation - no guarantee.
Second, understand that metallurgy and metallurgical science improves over time. It does not go backwards. For some reason, there seems to be a lingering sentiment that old=better and that is totally untrue. Old is only better if it's actually better by virtue of its design.
For example, note that even the king of GJ vises, the Wilton bullet vises, only started to be made of cast Ductile Iron in its modern incarnations. Early bullet vises were made in a time before metallurgy and iron production was able to provide the mechanical properties desired.
The reason cast ductile iron is used is because it's the only cast iron that has mechanical properties that are competitive with steels.
The 60,000psi rating of Wilton's Ductile Iron bullet vises is a tensile strength rating. I have never seen any testing data from Wilton showing that their vises actually are tested to 60,000psi tensile strength (no casting coupons, no destructive testing). Therefore, it only logically makes sense that Wilton's tensile strength rating is a reflection of some ASTM standard, which guarantees some minimum tensile strength. If that's the case, the yield strength of the 60ksi tensile vises would normally be consistent with a 40ksi minimum yield strength. This also corresponds to an elongation at fail of 18%, meaning that you'd see some pretty significant and noticeable distortion in the vise before it breaks, as opposed to gray iron vises, which have virtually 0% elongation and so shatter without a warning.
Where manufacturer matters in cast iron items is the quality and consistency of the castings. Let's say that a random manufacturer makes a cast ductile iron item rated to 60ksi tensile strength. We assume, ignorantly, that the properties of the cast ductile iron item is homogeneous, meaning constant through the entire casting. In reality, for many reasons, casting defects can appear inside the various areas of the castings. Differential cooling can cause stress rises in different parts of the castings.
Part of the "quality" aspect in a vise has to do with whether or not a manufacturer can tightly control the casting quality, and therefore improve the homogeneity of the casting. As a consumer, we can only verify this using first-hand reports and reviews.
The reason why manufacturers don't often use cast steel is because steel is difficult to cast. Its thermal expansion properties are higher than cast iron, which means that you have to cast larger and then machine the pieces to specification. This is why you see forged and machined steel vises. It's not because it makes a necessarily superior product - it's because they have to be post-processed to make the product precise enough for use.
However, the advantage of using steel is that, depending on its alloying composition, the material properties can be very high. Much higher than ductile cast iron. For low-carbon mild steels (like JIS S45C), compared to 60ksi ductile iron, you can have 25% improvement in yield strength (40ksi vs 50ksi) at a similar elongation. In general, most steels in that cast/forged range will have around 50ksi yield strength.
I disagree with an earlier post that says that if you took a hammer to the Yost vise dynamic jaw, it would break. It wouldn't break at all. It would take the shock, bend, then snap back. The dynamic jaw wouldn't break until it distorted to the elongation specified by the material at break.
Engineers know this and this is why the Yost FSV vises are thinner and lighter than equivalent cast iron vises. They have less cross sectional area because they need less material to have equivalent properties to cast iron vises. Less material means less cost (raw materials to build and less money to ship.)
And this is critical: Vises are not designed to be indestructible. They are designed to provide certain parameters of operations within a certain envelope. For example, let's say you need a vise that requires a 6" jaw opening. The Yost FSV-5 weighs 27 lbs and can open to 6 inches. The Wilton 1765 (which opens to 6.5 inches) weighs 70 lbs.
Taking the Yost FSV-5 and Wilton 1765 comparison further, note that the FSV-5 has a smaller throat depth of 3.25", while the 1765 has a throat depth of 4". Making the throat depth larger requires reinforcing the jaws because of the torque applied to the vise when clamping.
Assuming that the yield and tensile strengths of the Yost vise are higher than the Wilton by 25%, what the differing weights can tell you is this: The Yost vises have smaller mechanical cross-sections, which means that they will bend for a given force a greater amount than the Wilton vises. The Yost will experience greater deformation when abused than the heavier Ductile Cast Iron vises before breaking catastrophically.
If Yost made a vise that was identical in design to the Wilton bullet vises but made them out of their forged/machined steel, they would be incredible vises, superior in almost every way. But the cost of making those vises would be very, very high.
So what you're getting in the Yost is: Less weight, more working envelope for the weight, and can take somewhat more abuse than a Wilton before shattering. You also get much less stiffness, less clamping force before bending, and more flexibility. If you're clamping with a vise then flexibility isn't what you want.
IMHO, if you're looking for a vise that you're going to hammer on like a madman and abuse without abandon, get the forged steel vises. First, it's not "cheap" at all. $200 is a lot of money. If your idea of working with a vise involves sledgehammers and cheater pipes, then I would go with a steel vise.
