Re: DRO usage on mills
- From: Don Foreman <dforeman@xxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 07 Mar 2007 23:32:56 -0600
On 7 Mar 2007 20:30:58 -0800, "woodworker88" <woodworker88@xxxxxxxxx>
wrote:
On Mar 7, 6:13 pm, Wayne <wayne1NOS...@xxxxxxxxxxxx> wrote:
I believe I am ready to take the plunge and replace
my mill/drill with a real milling machine. Later add
a drill press (or sooner if I can find good used),
hence my previous post on drill presses.
I don't have space to keep the mill/drill as a drilling
only machine. Little brother has his eye on it anyway.
So now for the really stupid question. I have the
option of getting a DRO with the mill. I've never
used one, so I don't know what they are like. This
is the first research I've done on them. They almost
seem like they can be used as a manual CNC.
I'd also guess that if you are just drilling a hole
you wouldn't have to worry about backlash as the
measurements aren't taken off the leadscrews.
So is a DRO worth it or is it just a fancy gizmo
that really isn't necessary?
Wayne D.
Trust me, it's worth it. Without one, particularly on a really old or
poorly maintained machine, it's a lot harder to make accurate parts.
Plus, there are other factors other than backlash that can ruin
measurements off the dials. I have a 3-axis (knee) Newall on my
machine, and after it was installed, I realized that tightening the
knee lock often moved the measurement 50 thou or more. Now I can get
really accurate measurements in all sorts of setups.
In terms of specific features, pay a few extra bucks for a good one
with bolt hole circles, datums, and other features. It'll save hours
in messing around with the machinists handbook, trying to figure out
the x-y coordinates for some weird pattern. My DRO also has a line
feature, which is like a bolt circle except it is a number of evenly
spaced holes on a line, and you can set the line at an angle to the
travel. It also has a arc interpolation, which allows you to rough
out an arc to 5 thou or so. Not CNC, but if you need to have an arc
on the corner of a part to clear another moving part (a situation I've
run into several times), it's pretty useful.
On two versus three axis, buy a 3 axis knee model. That will probably
be the most useful setup for 99% of the work the average user does.
As far as models go, I really like the Newall because of its useful,
intuitive interface and non-contact scales. Unlike the other models,
the Newall uses induction to measure against a stainless steel tube
filled with ball bearings. That means that the read head (the sensor
part) is completely sealed and doesn't need to mechanically contact
the fixed scale. It slides around the outside of the tube like a
linear bearing, but there is not sensor that physically contacts the
scale, which drastically improves reliability.
Hope this information is useful,
ww88
Most DRO's are non-contact, using optical scales with intrinsic
resolution of typically 50 microinches though the DRO may only resolve
to half a thou.
I find 2-axis quite sufficient, don't lust for a Z axis. Z excursions
are typically rather small compared to X and Y, so a DI works just
fine and I rather prefer it for some reason. YMMV.
.
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