Re: What is the weak link in machine precision - Knee Mills

I think I am starting to understand.

tom.


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "metlmunchr"
<metlmunchr@y...> wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "zipdrive2k"
> <zipdrive2k@y...> wrote:
> Enco has a mill they state the specs are
> > 0.00078/ft. error for squarness and parallelism.
>
> Our friend Ballendo has often mentioned the overstatement of
> accuracies by sellers of low end machine tools. With this in mind

I

> dug out the original verification documents for one of my

machines.

> The limit for parallelism is .00078/ft, while the limit for
> purpendicularity (squareness) is .00118/ft. Notice this squareness
> tolerance is 50% greater than what Enco states. The actual
> measurements for my machine all fell within the stated limits.

Some

> were substantially less than the allowance, while others barely

made

> it under the wire. It's possibly worth noting that these numbers
> are from factory tests on a machine that sold for slightly over a
> quarter million dollars. Do you think it's possible Ballendo has a
> valid point regarding overstatement of accuracy? or does Enco have
> some secret no one else knows when it comes to machine
> construction? My offhand guess would be some of the better
> Taiwanese knee mills will equal Bridgeport's geometry numbers (I
> dont know what BP's specs are), but a further guess would be that
> most of the Chinese iron will fail to equal BP's numbers by a

factor

> of 2 or more. If the upper limit was indeed .00078/ft, then the
> average machine could be expected to have the geometric accuracy of
> a Moore Jig Borer. I kinda doubt that's the case.
>
> Cliff