On 06/25/2017 06:51 PM, andy pugh wrote:
On 25 June 2017 at 15:21, dave <dengv...@charter.net> wrote:
I suspect that this is a thermal problem
Whereas I consider the idea that it is a _Computer_ thermal problem almost
inconceivable.
Yes, for a CPU to foul up ONLY the counting of one axis in
ONE direction seems implausible. I'm guessing possibly a
weak encoder that is losing counts when hot. I'd also check
the power supply to the encoder as close to the encoder as
it is available.
I did have a problem with my mill some years ago. I did a
couple things wrong on one job and didn't notice the hole
spacing was off until the parts were used. One error was I
didn't spot the holes, I just drilled them with jobber's
length drills, so all bets on accuracy would be off,
anyway. But, the holes were too widely spaced. Hmmm, many
errors in the machine would cause the holes to be too CLOSE
together. Then, I noticed the spindle speed display was
fluctuating. I started to investigate. On my PPMC system,
the encoder board powers the encoders through the encoder
connector.
I saw that the encoders had about 4.0 V where it should have
been 5.0 +/- 5% or so. The main DC connector to the PPMC
motherboard was making a poor contact, and the whole PPMC
system was running on about 4.1 V! Amazing that it even
worked at all, as that was WAY outside the VCC spec for all
the chips. Once I wiggled the connector, everything
returned to normal.
So, the error was due to one encoder losing counts, so the
machine moved farther than it should have. It was pretty
repeatable, so the error did not accumulate.
Jon
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