Re: [CAD_CAM_EDM_DRO] Re: PIC based DRO
Posted by
Ian Wright
on 2000-03-16 16:31:19 UTC
Hi,
One thing which those wanting high accuracy in a DRO should not overlook is
the effect of temperature on the work being machined or the machine itself.
I had the opportunity a while back to get first-hand knowledge of the
methods used by James Chesterman & Co. in the production of high accuracy
scales and measuring equipment and I was surprised at first to find that
they didn't use any form of environmental control of temperature in their
premises. The reason for this, I was told, was that the graduating machines
and standard scales were all made of metals having the same coefficient of
expansion (iron and steel) and so, once they had been tested and verified as
absolutely correct at the 20 deg C standard temperature, it didn't matter
what temperature they were used at in the workshop as the raw materials
would have expanded or contracted by the same amount and so would also be
correct at 20 when finished. For this reason glass scales were avoided
except as negatives for photoetching the cheaper range of scales. So, from
this, it would seem that steel DRO encoder strip would be the best choice
and that it should be intimately fixed to the machine if possible, with wire
'rope' on a rotary encoder being the next best. Comments?
Ian
--
Ian W. Wright
Sheffield UK
One thing which those wanting high accuracy in a DRO should not overlook is
the effect of temperature on the work being machined or the machine itself.
I had the opportunity a while back to get first-hand knowledge of the
methods used by James Chesterman & Co. in the production of high accuracy
scales and measuring equipment and I was surprised at first to find that
they didn't use any form of environmental control of temperature in their
premises. The reason for this, I was told, was that the graduating machines
and standard scales were all made of metals having the same coefficient of
expansion (iron and steel) and so, once they had been tested and verified as
absolutely correct at the 20 deg C standard temperature, it didn't matter
what temperature they were used at in the workshop as the raw materials
would have expanded or contracted by the same amount and so would also be
correct at 20 when finished. For this reason glass scales were avoided
except as negatives for photoetching the cheaper range of scales. So, from
this, it would seem that steel DRO encoder strip would be the best choice
and that it should be intimately fixed to the machine if possible, with wire
'rope' on a rotary encoder being the next best. Comments?
Ian
--
Ian W. Wright
Sheffield UK
----- Original Message -----
From: James Eckman <fugu@...>
> If you really need the accuracy vs. needing repeatability, you might
> need the more expensive glass doodads