[HaroldSAJS]

I am machining a piece 0of 6061 T6 aluminum. The work piece is .3125" thick. I am holding the material on it's edges. After I attempt to machine the face of the work piece down to 7mm (.2755"), I am faced with a problem that the thickness of the material varies and is out of specification in areas.

I am attributing this problem to bowing of the work pieces when it is placed and tighten in the vise.

Does anyone have any ideas about how to hold the work piece so that this problem does not occur?

The part has eight through holes, four of which are tapped.

[txcncman]

Did you indicate the face of your material to verify flatness to begin with?

Most thin material will "stress relieve" during machining. There are several techniques that can be employed to compensate for this.

[DMF_TomB]

I am machining a piece 0of 6061 T6 aluminum. The work piece is .3125" thick. I am holding the material on it's edges. After I attempt to machine the face of the work piece down to 7mm (.2755"), I am faced with a problem that the thickness of the material varies and is out of specification in areas.

I am attributing this problem to bowing of the work pieces when it is placed and tighten in the vise.

Does anyone have any ideas about how to hold the work piece so that this problem does not occur?

The part has eight through holes, four of which are tapped.

use a fixture plate. basically clamp thin part to thicker part. thin parts over 2" and especially over 4" bow easily in a mill vise. picture attached shows part held with clamps. i have also used double sided tape to hold sheetmetal to a piece of laminated 3/4" plywood. the smooth surface plywood is used for signs and concrete forms. because the plywood is smooth like formica double sided tape sticks better to it. often the part clamp area is milled off later. the extra tabs are just for holding the part. I have made sheet metal parts as big as 1 foot by 2 foot using a little tape, plywood, and clamps

[keebler303]

A couple thoughts:
Don't tighten it so tight and take lighter cuts. Use a torque wrench for repeatability.
Use a fixture and bolt down the part using the through holes.
Use a vacuum chuck.

Matt

[txcncman]

Are you trying to achieve parallelism or flatness or both?