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The difference between machining accuracy and positioning accuracy

Med

Plastic
Joined
Jan 19, 2018
Dear all,

Some of vertical milling center suppliers write the acuuracy in thier machin’s catalog as positioning accuracy while other write as machining accuracy!

My inquiry is that is there any difference between machining accuracy and positioning accuracy? Or they are same?
 
Dear all,

Some of vertical milling center suppliers write the acuuracy in thier machin’s catalog as positioning accuracy while other write as machining accuracy!

My inquiry is that is there any difference between machining accuracy and positioning accuracy? Or they are same?

Nice if they were the same. Seldom are. Stuff moves when stressed. Cutting is stressful.

Lightly built machine can only hope to hold spec with many, many LIGHT cuts. Which may not be what a given alloy or tooling is comfortable with.

Very HEAVILY built machine can hold spec with heaver cuts, fewer of them, also do light cuts.

You'll need a Helluva lot more info than that to match any given MC to a particular production environment and goal set.

Can't easily or economically do even that if you do not KNOW what you'll be expecting of it. "Overkill" or deep reserves are nice, but surely are not "free".
 
Anything that comes out of marketing carries likelihood of inflated specs if not downright lies. You don't have to go any further than consumer grade shop vac HP specs to find a criminally egregious example.

Machine tools are more responsibly rated but you still have to have you BS detector in good working order when making a purchase decision.

To me, "positioning accuracy" is the quantfiable result of an axis move as measured by suitable instrumentation. The move is within he tolerance band or it isn't so results are easy to evaluate.

"Machining accuracy" can be a cloudier concept because the "positioning accuracy" is overlaid by tool and part deflection, thermal expansion, etc each attribute in he equation carrying its own load of uncertainty. However, if a prospective machine could machine a series of consistent parts I'd be inclined to accept its value in a production setting provided it competed favorably with comparable machines is its niche.

I'd be inclined to go easy on the employment of cuctter comps etc in demonstrations focusing more on part to part consistency, ease of programming, tool changes, and maintenance plus a ready supply of repair parts, quick field service, and customer support - all essentials in post-purchase customer satisfaction. These after-market customer support features often make or break the success of integrating a new and complex machine tool in a working production shop.

I recall a stout looking machine tool manufactured in the late '80's by a fading giant of a US manufacturers. It featured many novel seeming innovations but they were poorly executed the tool changer was particularly troublesome in that it mis-presented tools, dropped tooling, the post processor was glitchy, and important stuff plain broke.

The company failed soon after leaving Uncle Sam with a white elephant the successor company was reluctant to support. The specs on this machine were excellent and were met at factory acceptance and one installation run-off. Trouble is, it was unreliable in many important particulars. A good idea poorly implemented in tragic ways. A $180,000 pity.
 
Yes and no.
There is a whole marketing game played here.
Add dynamic and static positioning, so confusing.
I have been in the position of telling the market people that is not quite true. They do not care and advertises specs I know damn well will not happen.
Yet they have to play against competitors also doing the same.
Much lying or perhaps just showing your end brighter goes on here.

End position accuracy (like drilling holes) and tool path accuracy on a contour are just different.
Bob
 








 
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