kicad-developers team mailing list archive

[Brian Sidebotham <brian.sidebotham@...>]

2009/7/21 Manveru <manveru@...>:
> 2009/7/21 Brian Sidebotham <brian.sidebotham@...>:
>>
>> [Attachment(s) from Brian Sidebotham included below]
>>
>> Hi Guys,
>>
>> Please find attached a jpg highlighting the problem, and a quick patch
>> to resolve the issue.
>>
>> The problem is that when working with a metric mm grid, the
>> coordinates vary between .002 mm. This leads to several whole units
>> being displayed as .001 below their actual value. This means your
>> brain has to work overtime trying to work out what position you're
>> actually pointing to. See the JPG where the values are 48.999 x 18.999
>>
>> The patch resolves the problem by round to two decimal places for
>> metric, resulting in the display being 49.00 x 19.00 for the above
>> error. This is much easier on the brain!
>>
>> This was bought up by some users recently on the kicad-users list,
>> titled Hard Metric.
>
> First thought I have reading above was "wait a second, mm dimensions
> in most datasheets are up to 3 digits of fractional part". But I've
> just looked into couple datasheets of SMD elements and - surprise -
> they use dimensions up to 2 fractional digits. So two seems to be
> enough.
>
> --
> Manveru
> jabber: manveru@...
>     gg: 1624001
>   http://www.manveru.pl

Hi Manveru,

Some datasheets may well give mm dimensions to 3 decimal places, but
generally only where the part has been design in unified system as
opposed to a part designed in the metric system.

In the metric system, there should be no reason to go below 0.01mm.

Also note, that this is simply the displayed value, if you type in a
pad dimension in mm accurate to 0.001mm, the pad will be placed in
exactly the same position as before.

I must admit, I generally only use metric when placing fixings and
connectors relevant to the mechanical design as I design the
mechanical components in metric so it makes my life easier. SMT
components get placed on a unified grid.

I remember some musings on the list about increasing the internal
resolution of KiCAD, but I don't think there has been any discussion
about that for a while.

Best Regards,

Brian.