What is meant by (adjective) precision?

[Geswearf]

What is meant by the various levels of 'precision' when used by PM as a descriptor? For example, they offer high precision and ultra precision keyless chucks, precision and ultra precision collets, a regular precision, a high precision, and an ultra precision vise. I understand that a Kurt is a high quality vise, and probably better than a Homge (ultra precision version), and I assume the former one's fit, finish, and accuracy of machining the various parts are probably somewhat better than the latter (I've gleaned this assumption from what I've read here in posts by different people). Absent recognizable name brands with reputations behind the brand, I'm at a loss understanding the differences between those levels of precision, especially since PM tosses those words around to describe a number of items.

I'm asking this here because I'm more likely to get honest answers - I would not expect anyone at PM to tell me that the various words are basically horsehockey but that the more expensive chucks are "better" than the cheaper ones. (I'm ignoring the differences in gripping capacities - the fact that one chuck is a 5/8" capacity chuck and another only 1/2" cannot be explained by one having a descriptor in front of the word precision.)

I suppose I could just bypass their offerings and buy name brands....

 

[davidpbest]

Here is my take. It's mostly marketing fluff designed to differentiate one of their products from another or the competition. There is no "absolute" in these comparisons. Obviously "ultra precision" is intended to confer that it's the best "they" offer - not that it's the best possible. They are trying to distinguish between the relative quality and precision of things that originate in Asia. In addition, they are subtly trying to create some FUD (fear, uncertainty, doubt) in the minds of the potential buyer as part of an up-sell motivation. Everyone does this - "good", "better", "best" - so I don't regard this as inappropriate, but it is worthy of introspection and due diligence. I have interacted with the owner of PM for over 2 decades and regard him as honest and a man of his word. So IMO this is not slick ad copy you're reading, but his frustrated attempt to differentiate various alternative products within his product line specifically, and relative to other suppliers.

 

[benmychree]

I think you "got"it, geaswearf ---

 

[RJSakowski]

In terms of the marksman, precision is being able to cover the bullet holes with a dime while accuracy is being able to hit what you're aiming at
Now, how a marketing person uses those terms is an entirely different matter.

 

[silence dogood]

People many times confuse precision with tolerance. When I helped my carpenter friend on rough construction on building a house, being within a 1/4 of an inch or +/- 1/8" was fantastic. When we built furniture, it was down to less than 1/16" inch. Machine work you will be going down to a thousand. Many plans should state the tolerance of let's say +/- .002". You aim for the middle. You are still good even if you are slightly as long as you are within tolerance. Hopefully, the machine that you have has the precision to better that tolerance. One caveat, a lot of precision depends on your skill level.

 

[markba633csi]

There's also tolerance stacking which is a whole nuther bag of worms
Precision is thrown around so much now it's almost meaningless- like the terms "organic" or "designer"

 

[RJSakowski]

Tolerance is what you want and accuracy is what you get. Precision is what makes accuracy possible but not guaranteed.

A steel rule may be accurate to .001" but it isn't a precision instrument. A 1" 2" micrometer is a precision instrument but if it isn't calibrated properly, it isn't an accurate instrument.

 

[heli_av8tor]

So going back to the context of the OP I surmise that the various adjectives don't mean much unless backed up by numbers, i.e. the tolerances of the offerings. (?)

 

[7milesup]

So going back to the context of the OP I surmise that the various adjectives don't mean much unless backed up by numbers, i.e. the tolerances of the offerings. (?)

Read @davidpbest's post #2. He sums it up eloquently.

Looking at the descriptions of the vises for example, the 6" "Ground Milling Vise" has a flatness of .002". The "High Precision" 6" vise has a .0006" flatness. Interestingly enough, the 6" "Homge Ultra Precision" has a flatness of .001"; however, apparently, the "Ultra Precision" vises come with a certificate of parallelism and squareness.
I own both a PM 5" High Precision vise and a Kurt D688. The difference in quality is very noticeable, but then again, so is the price. Interestingly enough, I could not find comparable specs on the Kurt website. However, Kurt replaced the D688 vise with the DX6 vise, and in their literature, they guarantee the body height between the two with an accuracy of plus or minus .0005".

 

[G-ManBart]

Absent recognizable name brands with reputations behind the brand, I'm at a loss understanding the differences between those levels of precision, especially since PM tosses those words around to describe a number of items.

I don't think there was any intent to have the descriptors mean anything specific, but rather to compare between levels of quality for products of the same type. So you've got regular, precision and ultra precision....good, better, best. They could have just as easily gone with silver, gold and platinum and accomplished the same thing, but it wouldn't have much of a machinist's flair.

I'm guessing, but I think that sort of naming convention will help customers quickly understand why an Ultra Precision 13x40 lathe costs the same as a Precision 14x40 lathe. Barring that, people might ask why the smaller machine costs as much as the bigger machine. No need to dig into the specs...it's right in the name sort of scenario.