RE: [CAD_CAM_EDM_DRO] Positioning

Obsession with precision is the realm of the noob, they eventually buy a
machine and discover not only is it hard to achieve, but unnecessary.





At that point they get side-tracked by either the fun of making stuff, or
building something bigger and/or faster.





Some people never get past that first point.





I've gotten side-tracked by lasers, and no-one talks about precision. They
all cut better than a thou, so any discussions are a bit pointless. Things
like bevels, smoke control, back-flash, auto-focus etc are more interesting.





(Lasers can be a bit too precise. I made some little lidded boxes (MDF) a
while back; the lid went on, and didn't come off. A vacuum (ok, low
pressure) packs a lot of force. Even had finger notches. Cut new ones with
just a whisker of clearance rather than none.)





Besides, good design and technique will beat "precision" most days, and
probably every day in the hobbyist field.





Suppose you need two plates with identical holes bored though them. Do you
obsess with trying to bore the holes one by one precisely as possible, or do
you clamp them together and drill both at once? So they're a thou out,
they're precisely matched and that's more important. Want more? Use the
first as a guide to make the 3rd and 4th. Making engines? Learn how to
lap, and match the piston to the cylinder.





People who think they're working in microns are kidding themselves.


People who think that machine in their shed is capable of microns are
kidding themselves.


People who think you need to work in microns are really kidding themselves.





Ah well, we all need a hobby. Fantasising counts, I guess.





Tony








From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com]
Sent: Wednesday, 4 June 2014 7:48 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: RE: [CAD_CAM_EDM_DRO] Positioning








You know, I think all of this needs a dose of reality. Most people building
DYI CNC machines don't put enough strength and mass into the base to warrant
any positioning closer than +/-.0005 and most should be in the range of
+/-.001.


Without a strong, rigid and massive base on which the machine is built, the
machine will deflect more than the scales will vary.


High speed and heavy cuts will move the Z axis more than that.


So, if you think about it, to get to anything less that +/-.001, you need to
make massive, stable equipment. Be sure nothing deflects. The temperature
in your shop doesn't vary much and your fixturing doesn't allow movement of
the part.


After all that, worrying about using glass scales that are good to +/-.005,
+/-.001 or +/-.0005 seems to be moot.


Seems to me that people are worrying about the wrong thing. Most pictures
of DYI CNC machinery have weak frames and weak axis connection points.I
haven't seen any that featured press fit cross keys to maintain axis
orientation and position nor have I seen any that had massive steel frame
work with ground and scraped pads for mounting surfaces. None of the
discussions about frames have even mentioned stress relieving or how to
mange to square the frames except with a tape rule (+/-.015 at best). And
no where have I seen an discussion about how to level that frame except with
a carpenters four foot level.no precision level or layer system.


The position of the carriage being +/-.001 or .0005. LAUGH OUT LOUD. There
are other issues that need to be dealt with first.


R. Wink




















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