Leveling a Machine

[enauman]

I have always leveled my machines when I installed them. Can any of you guys tell me the reason to level a knee mill accurately? Is the accuracy affected if a mill is installed one arc sec as opposed to one arc minute? Is it vibration? Center of gravity? Or is it a preoccupation with accuracy.

Thanks,
Ed

[Larry83301]

I've used knee mills that have been way out of level, up to 6" out side to side. Didn't make any difference. I have even seen them used onboard ship, rocking back and forth. Knee mills are different than CNCs in that respect. Just make sure that the head is square with the table and you will be alright.

[enauman]

Thanks for the reply. I should have mentioned that the machine is a CNC. It is an Acra with a centroid M400S control and inverter drive motor. If that makes a difference.

[Geof]

The only reason for leveling a machine is to make sure it is straight and not twisted. Many machines are large enough that if all the feet are not supporting their share of the machine weight the entire casting will twist or sag; 'level' is just a convenient reference point.

On a knee mill the base is small and it is more or less shaped like a cube, the table is sort of separate from the base because it is on the 'knee' that runs up and down the Z ways.

It is very unlikely that the base on a knee mill would twist even if it was only supported on opposite corners, but even if the base did distort this is not going to be transmitted to the X and Y ways and I think having the base distort enough only from its own weight so that the Z ways were affected does not seem possible.

So don't worry about level, but do worry about getting more or less even support at all four corners otherwise your machine will rock when it is running.

EDIT: typo

[enauman]

Geof: Thanks for the reply. I've got it down to about .0015" per foot and all corners are supported. Based on your reply, that should be good enough. I just used shims with read head anchors but no leveling feet, so it's a hassle to get it any closer. It is doable, but a hassle.

Again,

thanks... Ed

[Geof]

...... I just used shims with read head anchors but no leveling feet, so it's a hassle to get it any closer. It is doable, but a hassle.

Again,

thanks... Ed

I cheated one time: Four steel plates, some very thick epoxy paste, put a little mound of epoxy where the four corners of the machine will be, carefuly put a steel plate on top of the epoxy, very carefully lower the machine onto the steel plates, leave untouched until epoxy cures.

The machine was a Herbert 9C-30 weighing many thousands of ponds, this worked like a charm.