Re: Machine flex; How much is to much?

Jon,

I normally do rough cuts then go back and finish with one or more
passes at about 0.010 or less for most jobs. Maybe I should provide
an example; 1/2" endmill, 0.200 depth of cut, cutting aluminum. Not
sure of speeds and feeds, but I would say they would be slower then
ideal.

Trevor

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> protman16 wrote:
>
> >Group,
> >
> >I have just completed converting a mill/drill to cnc. It has a
belt
> >driven spindle with a round column. For the z-axis I replaced the
> >riser casting with THK LM slides that now allow the mill to have
> >about 11" of travel. There are a couple of reasons why I did this.
> >First is that 5" travel is too short most jobs that I run, second
is
> >that when boring using the quill there is too much flex resulting
in
> >elliptical holes (same applies for side milling).
> >Currently I have not measured the amount deflection but I will
> >attempt to very soon.
> >My question is to the group what amount of cutter/spindle
deflection
> >is acceptable on this type of mill that still provides reasonable
> >accuracy and good repeatability?
> >
> >
> >
> It depends on what you are doing. If you are roughing out cavities
in
> stainless steel, or making precision bores for engine cylinders,
then
> .001" at 50 - 100 Lbs load might be totally unacceptable. This is
the
> level of stiffness for a Bridgeport Series-I head with the double-
swivel
> joint. That is why the BOSS and some other CNC models did not have
> the swivel there, as they needed more stiffness. The Bridgeport
quill
> is one of the stiffest things on that machine, it is a MASSIVE piece
> of steel, precision lapped to a very tight fit in the head casting.
> The cheap Chinese machines are made to much looser fits.
>
> Without telling us what you are doing, asking for stiffness is
almost
> meaningless. 0.00001" deflection would send a coordinate measuring
> machine to the trash bin. .005" would be excellent for a wood
router.
>
> I was playing with my mini-mill that I use mostly for testing and
> demos, and find it is VERY flimsy. I can see the vise vibrating
about
> .01" during light cuts in aluminum with a 1/4" end mill. I can
also see
> the table "weave" as I crank the X axis handle. The gibs are
obviously
> loose, but the table feels stiff when cranking it. (I have made
the mods
> such that the handles can still be used for manual machining.)
>
> Jon