Re: [CAD_CAM_EDM_DRO] Re: Just How Accurate Is CNC?

I'd just like to appologise for the grammer in that post, it's probably some
of my worst yet! :^)

John (Who thinks it's high time the name John was banned for a few years)

----- Original Message -----
From: "John Heritage" <john.heritage@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, November 08, 2004 3:53 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Just How Accurate Is CNC?


>
>> reputedly achieve positioning and repeatability in the neighborhood
>> of 0.0001". As I said earlier, he is estimating only 0.001 on his
>> machine.
>> It appears to me that his modifications were not too successful.
>> Any thoughts or guidance?
>> Regards to all,
>> Another John
>
> I've never heard of Nantong before, but 0.0001" is a fairly tight
> tolerance
> to hold. The 0.001mm tolerance I mentioned is the tolerance claimed by the
> very newest machines. 0.01mm is a fair tolerance to hold on a part,
> 0.001mm
> is really pushing it futher out. You are essentially trying to machine to
> an
> accuracy of a single micron, which is quite something when most
> micrometers
> can only just about manage to read that level of accuracy.
>
> If you must achieve these kind of accuracies, you should be looking at
> machining quite small work areas if you want to do it within any kind of
> normal budget. I believe the machines mentioned above between a quarter
> and
> half a million dollars each - having a work area of a few metres cubed
> usually.
>
> It is much easier to achieve higher tolerances if your work area and
> forces
> involved are smaller.
>
> You should also ask whether or not you even need those tolerances. If
> you're
> building an engine, there is no way you can realistically expect it to
> function to micron accuracies. As soon as it warms up, it will rocket
> right
> passed those kind of accuracies. So in this instance, thermal modelling
> plays a much bigger role than actual machine accuracy at this level.
>
> I would doubt a standard knee mill would ever manage a single micron
> accuracy. I think they're probably quoting the specifications of a single
> part of the mill, like a surface finish on the ways or something similar.
>
> If I wanted to make something with micron accuracy at home I'd probably
> use
> linear stages designed for and a dental drill for the spindle.
>
> What is it you'd like to make?
>
> Best wishes,
> John
>
>
>
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