Best way to hold aluminum plate down when cutting all the way thru the pattern

[Plugger]

Hi,

I'm building a cnc router to cut shapes out of aluminum plate up to 1/2 inch thick. If I clamp the plate to my sacrificial mdf and use the cnc router to cut out a pattern that makes a complete circle, I presume I need to leave .005" all the way around the bottom to hold the part in place. I guess I could also make the program leave a few small attachment points to hold the part.

Also, will the parts peel away and clean up with an exacto or deburring tool if I leave .005".

Has anybody come up with other ways?

Thanks!!

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[metalworkz]

Hello,
Yes you can leave the thin layer of material(onion skin,foil) to hold the circular blank in place. Some software also will produce bridges or tabs and you can place them along the profile to hold the part while the rest of the profile will cut through the bottom of the blank.
The foil that is left from using this method usually breaks off fairly clean and easily, and in some cases needs very little finishing.

[Fastest1]

Sometimes what I do is put the plate that you are going to cut on parallel blocks so there is clearance underneath. Cut almost all the way thru, then flip it and surface the entire part. It will fall thru when clear and leave no tooling marks and wont bind either.

[luvbug]

Would a spring-loaded or pneumatic hold-down with rollers, attached to the bottom of the Z axis be too much work for the Z axis?

IMHO, if you're not doing repetitive work (cutting the same parts a lot), a vacuum table is overkill.

Double-sided tape might work in some instances.

Before the machine finishes the final through pass, a cantilever clamp might work. (Long arm sticking out from the side of the table to the center of the part.)

Just tossing some ideas out.

[-Chris-]

we use an easy release contact adhesive all the time it cleans off after cutting with a little acetone we also use some strips of scrap mdf and simply screw it down on all four sides of part into mdf table top and cut through entire part usually about .015 below bottom of part.
-Chris-