Re: [CAD_CAM_EDM_DRO] Machine flex; How much is to much?

For the z-axis I replaced the
riser casting with THK LM slides that now allow the mill to have
about 11" of travel.

Good move, many large CNC's like Mazak use this principle.

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?

Ask any machinist how much deflection is acceptable and he will tell you any is too much. Death, taxes and tool deflection are three consants in which you will never defeat. All machines have it and all machine mfrs battle it. Thats why Okuma and Howa refridgerate their spindles to keep them at constant temperature and size. Thats about as good as it gets. .0005 repeatability. Tool Deflection is directly proportionate to the task at hand, diameter, length and most importantly: sharpness of endmill, the type of material, etc. The more material you remove the more deflection you will be dealing with. Good practice with side milling is leave .010 then come back with a new finish mill with a climb mill pass to the target dims. You mention eliptical bores. You need an extremely rigid machine to correct this. What is happening is the Boring head is not balanced and centrifugal force is throwing the cutter (deflecting) out of its intended path. and this force will take the path of least
resistance. Slow the spindle speed until you have reached a path with no egg-shaping at all and that is the speed in which you must not exceed. Again, Bore it to within .010 and the pull the boring bar sharpen it and go back take it to the target bore size. If its very critical leave .010 and send it out for I.D. grind.

protman16 <tbrooking@...> wrote:
Group,

I have just completed converting a mill/drill to cnc. It has a belt
driven spindle with a round column. 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.

Trevor



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